Standard Handbook of Chains: Chains for Power Transmission and Material Handling (Mechanical Engineering (Marcell Dekker): A Series of Textbooks and Reference Books)

DK4023_half 7/22/05 3:36 PM Page 1 Standard Handbook of Chains Chains for Power Transmission and Material Handling Sec...

Author: American Chain Association

277 downloads 1766 Views 20MB Size Report

This content was uploaded by our users and we assume good faith they have the permission to share this book. If you own the copyright to this book and it is wrongfully on our website, we offer a simple DMCA procedure to remove your content from our site. Start by pressing the button below!
Report copyright / DMCA form

DOWNLOAD PDF

DK4023_half 7/22/05 3:36 PM Page 1

Standard Handbook of Chains Chains for Power Transmission and Material Handling Second Edition

© 2006 by American Chain Association

DK4023_series.qxd

8/15/05

8:52 AM

Page 1

MECHANICAL ENGINEERING A Series of Textbooks and Reference Books Founding Editor L. L. Faulkner Columbus Division, Battelle Memorial Institute and Department of Mechanical Engineering The Ohio State University Columbus, Ohio

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31.

Spring Designer’s Handbook, Harold Carlson Computer-Aided Graphics and Design, Daniel L. Ryan Lubrication Fundamentals, J. George Wills Solar Engineering for Domestic Buildings, William A. Himmelman Applied Engineering Mechanics: Statics and Dynamics, G. Boothroyd and C. Poli Centrifugal Pump Clinic, Igor J. Karassik Computer-Aided Kinetics for Machine Design, Daniel L. Ryan Plastics Products Design Handbook, Part A: Materials and Components; Part B: Processes and Design for Processes, edited by Edward Miller Turbomachinery: Basic Theory and Applications, Earl Logan, Jr. Vibrations of Shells and Plates, Werner Soedel Flat and Corrugated Diaphragm Design Handbook, Mario Di Giovanni Practical Stress Analysis in Engineering Design, Alexander Blake An Introduction to the Design and Behavior of Bolted Joints, John H. Bickford Optimal Engineering Design: Principles and Applications, James N. Siddall Spring Manufacturing Handbook, Harold Carlson Industrial Noise Control: Fundamentals and Applications, edited by Lewis H. Bell Gears and Their Vibration: A Basic Approach to Understanding Gear Noise, J. Derek Smith Chains for Power Transmission and Material Handling: Design and Applications Handbook, American Chain Association Corrosion and Corrosion Protection Handbook, edited by Philip A. Schweitzer Gear Drive Systems: Design and Application, Peter Lynwander Controlling In-Plant Airborne Contaminants: Systems Design and Calculations, John D. Constance CAD/CAM Systems Planning and Implementation, Charles S. Knox Probabilistic Engineering Design: Principles and Applications, James N. Siddall Traction Drives: Selection and Application, Frederick W. Heilich III and Eugene E. Shube Finite Element Methods: An Introduction, Ronald L. Huston and Chris E. Passerello Mechanical Fastening of Plastics: An Engineering Handbook, Brayton Lincoln, Kenneth J. Gomes, and James F. Braden Lubrication in Practice: Second Edition, edited by W. S. Robertson Principles of Automated Drafting, Daniel L. Ryan Practical Seal Design, edited by Leonard J. Martini Engineering Documentation for CAD/CAM Applications, Charles S. Knox Design Dimensioning with Computer Graphics Applications, Jerome C. Lange


DK4023_title 8/15/05 9:00 AM Page 1

Standard Handbook of Chains Chains for Power Transmission and Material Handling Second Edition

CHA

N

A

S

ER I CA N

IN

AM

American Chain Association

S O C I A T I O

Boca Raton London New York

A CRC title, part of the Taylor & Francis imprint, a member of the Taylor & Francis Group, the academic division of T&F Informa plc.


DK4023_Discl.fm Page 1 Thursday, July 7, 2005 11:09 AM

Published in 2006 by CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2006 by American Chain Association CRC Press is an imprint of Taylor & Francis Group No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number-10: 1-57444-647-9 (Hardcover) International Standard Book Number-13: 978-1-57444-647-0 (Hardcover) Library of Congress Card Number 2005043944 This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Standard handbook of chains : for power transmission and material handling / American Chain Association.--2nd ed. p. cm. ISBN 1-57444-647-9 1. Chain drive--Handbooks, manuals, etc. 2. Chain conveyors--Handbooks, manuals, etc. I. American Chain Association. TJ1051.S77 2005 621.8'59--dc22

2005043944

Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com Taylor & Francis Group is the Academic Division of T&F Informa plc.


and the CRC Press Web site at http://www.crcpress.com

DK4023_C000.fm Page v Wednesday, October 12, 2005 10:55 AM

Foreword The predecessor organization of today’s American Chain Association (ACA) was formed in the 1930s. While the routine function of collecting and correlating marketing data for distribution was important, their primary purpose was continued development of the American chain industry and its customers. This objective “to develop and promote standards of sound manufacturing and engineering practice, and through well-guided research, to foster improvements in the quality and utility of the industry’s products” was spelled out in the first pages of one of its early publications. This credo, as promulgated by the then Association of Roller and Silent Chain Manufacturers (ARSCM) soon led to a series of projects to build and operate chain test equipment in the laboratory. From those projects were developed the horsepower curves covering all basic sizes of standard roller drive chains. These were included in a hardbound chain design manual, published by ARSCM in 1955, and entitled Design Manual, Roller and Silent Chain Drives. That edition and its softbound successors, published in 1968 and 1975, have seen nearly 30,000 copies distributed by the association. The association soon expanded to include manufacturers of engineering steel chains and malleable chains, and the association name was changed to the American Sprocket Chain Manufacturers Association (ASCMA) and then to the present American Chain Association (ACA). Laboratory projects were extended to engineering steel drive chains and horsepower ratings were developed for those chains. These tables and other data developed by the association were adopted by the then American Standards Association. This latter organization also went through name changes and is known today as the American National Standards Institute (ANSI). The standards and tables developed by the ACA are revised and updated periodically and resubmitted to ANSI for adoption. The inclusion of other types of chain in the ACA program and the development of horsepower curves for engineering steel drive chains also entailed considerable standardization of sizes. It also led to the publication, in 1971, of another manual, Engineering Steel Chains, ACA Applications Handbook; a slightly revised version appeared in 1973. The roller and silent chain manual and engineering steel chain manual, published as separate handbooks, contain some duplicate information. The text of the combined manual was formed by an editorial blending of the various sections of the two original manuals, plus some additional material not appearing in those publications. Publication of the combined manual also represents a continuation of the objectives of the ACA to enhance the quality and utility of its products. The manual presents the information developed by the ACA and all its member companies. The authorship of the first combined manual in 1982 was a combined effort of the technical committee and other representatives of the member organizations of the ACA over a period of 25 years. The second edition is the fruit of an additional 20 years of research, testing, and analysis by the member companies of the ACA. New power ratings were developed for roller and silent chains. A new chapter on flat-top conveyor chains was developed and written. And new expanded information on installation, lubrication, and maintenance was included. Customary inch-pound units are used throughout the handbook. That is because all of the American National Standard chains and sprockets were originally designed using customary inchpounds units. All calculations should be done using customary units. When all calculations are finished, the final results can be converted to SI units using the publication, SI-1, ASME Orientation and Guide for Use of SI (Metric) Units. The ACA member organizations participating in the revised combined manual may be found on the ACA Web site: www.americanchainassn.org.


DK4023_C000.fm Page vii Wednesday, October 12, 2005 10:55 AM

Preface The first edition of this handbook was a landmark publication. It served the chain industry very well for more than 20 years. It guided many engineers and technologists through their first chain drive or conveyor selection. But the first edition was beginning to show its age. It was growing out of date in several ways. It definitely was time for a major revision. All of the existing chapters were rewritten so they would be easier to read and understand. The new chapters were written with the same goal in mind. Many copies of this book will go to people who need to absorb the information quickly and put it to use at once. Chapter 3 was completely reorganized and extensively revised to include new information on chain design considerations. Much research has been done and data released since 1982. Quite a lot of it is published here for the first time. Chapter 5 has new increased power ratings for roller chains. It also has new information on selecting drives with a life of other than 15,000 hours. Chapter 7 has new increased power ratings for silent chains. All of the chapters on selecting chain drives were reorganized to make the selection steps similar. Chapters 9 and 10 were reorganized to make the selection steps similar for all chain conveyors. Chapter 12, on selecting flat-top chain conveyors, is all new. There was nothing on flat-top chains in the first edition. This is a major addition. The former chapter 12 has been divided into three separate chapters. Now, chapter 13 deals with chain lubrication, chapter 14 deals with installation, and chapter 15 deals with chain inspection and maintenance. Much thought and effort was put into this second edition. A major effort was made to make it as user friendly as possible. The goal was to make this handbook easily usable for maintenance and distribution personnel, as well as college students and professional engineers. Personally I am very honored that the ACA selected me to do the actual writing of the second edition of this handbook. But I owe a huge thanks to all of the past and present members of the ACA Technical Committee. The ACA Technical Committee, supported by the member companies of the ACA, originally developed all of the information for this handbook. We think the effort was worth it. We hope that you will too. John L. Wright Indianapolis, Indiana


DK4023_C000.fm Page ix Wednesday, October 12, 2005 10:55 AM

About the Author John Wright worked for Diamond Chain Co. for 32 years. He worked in several different positions in both product engineering and applications engineering. John was General Product Manager when he retired from Diamond Chain in 1996. At that time he was responsible for all of the technical information and assistance that Diamond Chain provided to customers and users. After retiring from Diamond Chain, John started his own technical consulting business. John now works with users on chain drive and conveyor problems. He trains plant engineering and maintenance personnel on selecting and caring for chain drives and conveyors. He also does some technical writing. Before writing the revision for Chains for Power Transmission and Material Handling, John wrote several magazine articles and contributed a chapter on chain drives to a mechanical engineering handbook. From 1996 to 2004, John was chairman of the ACA Technical Committee and the ASME B29 Standards Committee for Chains, Attachments, and Sprockets for Power Transmission and Conveying. At the same time, John was the ANSI delegate to the ISO for Chains and Sprockets for Power Transmission and Conveyors. While he was chairman of these committees, John led the effort to redevelop and revise several important chain standards. He also worked very hard to bring many ANSI standards into harmony with their related ISO standards.


DK4023_C000.fm Page xi Wednesday, October 12, 2005 10:55 AM

Contents Chapter 1

A Brief History of the Development of Chain ............................................................1

Early Developments ...........................................................................................................................1 Cog Chain ..........................................................................................................................................1 Cast Detachable Chain.......................................................................................................................1 Cast Pintle Chain ...............................................................................................................................2 Precision Roller Chain .......................................................................................................................4 Engineering Steel Chain ....................................................................................................................9 Silent Chain......................................................................................................................................10 Flat-Top Chain .................................................................................................................................12 Terminology .....................................................................................................................................13 Chapter 2

A Chain Overview: Uses and Advantages.................................................................17

General .............................................................................................................................................17 Types of Chain .................................................................................................................................17 Scope of Chains Covered.................................................................................................................17 Styles and Forms of Chains.............................................................................................................17 Straight and Offset Link Chains ......................................................................................................18 Chains with and without Rollers .....................................................................................................19 Uses of Chain...................................................................................................................................20 Standard Chains and Their Uses .....................................................................................................20 The Advantages of Chains in Applications .....................................................................................38 Advantages of Roller Chains in Drives...........................................................................................38 Advantages of Silent Chain Drives .................................................................................................39 Advantages of Engineering Steel Chain for Drives ........................................................................39 Advantages of Chains on Conveyors and Bucket Elevators ...........................................................39 Advantages of Using Chain in Elevator Materials Handling .........................................................40 Chapter 3

Chain Design Considerations, Construction, and Components.................................41

Basic Chain Functions .....................................................................................................................41 General Chain Design Considerations.............................................................................................41 Roller Chain Design Considerations ...............................................................................................50 Leaf Chain Design Considerations ..................................................................................................60 Silent Chain Design Considerations ................................................................................................66 Engineering Steel Chain Design Considerations ............................................................................71 Flat-Top Chain Design Considerations............................................................................................79 Conclusion........................................................................................................................................84 Chapter 4

Sprockets.....................................................................................................................85

Types of Sprockets...........................................................................................................................85 Sprocket Tooth Forms....................................................................................................................100 Sprocket Wheel Design..................................................................................................................106


DK4023_C000.fm Page xii Wednesday, October 12, 2005 10:55 AM

Silent Chain Sprocket Teeth ..........................................................................................................109 Engineering Steel Chain Sprocket Teeth.......................................................................................112 Flat-Top Chain Sprocket Teeth ......................................................................................................117 Sprocket Hubs, Keys and Keyways, Setscrews, and Shafting Selection......................................120 Chapter 5

Roller Chain Drives..................................................................................................129

Typical Applications.......................................................................................................................129 Scope ..............................................................................................................................................129 General Roller Chain Drive Selection Guidelines ........................................................................129 Roller Chain Drive Selection Procedure .......................................................................................138 Sample Roller Chain Drive Selection............................................................................................167 Equations for Horsepower Ratings................................................................................................168 Vibration.........................................................................................................................................171 Acknowledgment............................................................................................................................175 Chapter 6

Engineering Steel Chain Drives ...............................................................................177

Typical Applications.......................................................................................................................177 Scope ..............................................................................................................................................177 General Engineering Steel Chain Drive Selection Guidelines .....................................................177 Engineering Steel Chain Drive Selection Procedure.....................................................................183 Sample Engineering Steel Chain Drive Selection.........................................................................188 Basis of Horsepower Ratings ........................................................................................................193 Alternate Selection Method ...........................................................................................................198 Chapter 7

Silent Chain Drives ..................................................................................................201

General Guidelines for Silent Chain Drive Selection ...................................................................201 Silent Chain Drive Selection Procedure ........................................................................................208 Sample Silent Chain Drive Selection ............................................................................................217 Derivation of Silent Chain Power Ratings ....................................................................................218 Chapter 8

Tension Linkage Chains ...........................................................................................219

Roller Chains as Tension Linkages ...............................................................................................219 Tension Linkages Using Leaf Chain .............................................................................................220 Dimensions and Arrangements of Leaf Chain ..............................................................................220 Tension Linkages Using Engineering Steel Chains ......................................................................223 Characteristics of Engineering Steel Chain Tension Linkages .....................................................225 Draw Bench Applications ..............................................................................................................228 Tension Linkage Chains for Dam and Lock Gates.......................................................................229 Other Applications .........................................................................................................................230 Catenary Tension and Chain Sag...................................................................................................231 Chapter 9

Engineering Steel Chain Conveyors ........................................................................233

Types of Engineering Steel Chain Conveyors...............................................................................233 Engineering Steel Chain Conveyor Selection Guidelines.............................................................249 Engineering Steel Conveyor Chain Selection Procedure ..............................................................256


DK4023_C000.fm Page xiii Wednesday, October 12, 2005 10:55 AM

Chapter 10 Roller Chain Conveyors ...........................................................................................267 Types of Roller Chain Conveyors..................................................................................................267 Roller Chain Conveyor Selection Guidelines................................................................................267 Multiple-Strand Conveyers ............................................................................................................275 Roller Conveyor Chain Selection Procedure.................................................................................279 Precision Indexing..........................................................................................................................277 Environment ...................................................................................................................................279 Sample Roller Chain Conveyor Selection .....................................................................................288 Chapter 11 Chains for Bucket Elevators.....................................................................................293 Elevators Using Engineering Steel Chains....................................................................................293 Take-Ups ........................................................................................................................................303 Design and Selection of Chain and Bucket Elevators ..................................................................304 Selection Steps ...............................................................................................................................307 Elevator Chain Selection Example ................................................................................................312 Roller Chain Equipped Bucket Elevators......................................................................................314 Pivoted Bucket or Pan Conveyors .................................................................................................314 Operation Practices ........................................................................................................................315 Chapter 12 Flat-Top Chain Conveyors........................................................................................319 Flat-Top Chain Conveyor Selection Guidelines ............................................................................319 Flat-Top Conveyor Chain Selection Procedure .............................................................................329 Sample Flat-Top Chain Conveyor Selection .................................................................................339 Selection Software .........................................................................................................................341 Chapter 13 Chain Lubrication.....................................................................................................343 Purpose of Lubrication...................................................................................................................343 Lubricant Characteristics ...............................................................................................................343 Lubrication of Drive Chains ..........................................................................................................345 Lubrication Types for Chain Drives ..............................................................................................345 Chain Casings ................................................................................................................................347 Temperature Increase in a Chain Casing.......................................................................................350 Lubrication of Exposed Drive Chains ...........................................................................................351 Lubrication of Conveyor, Bucket Elevator, and Tension Linkage Chains....................................351 High-Temperature Lubrication.......................................................................................................355 Conclusion......................................................................................................................................358 Chapter 14 Chain Installation......................................................................................................359 Safety Precautions..........................................................................................................................359 Chain Guarding ..............................................................................................................................359 Installation Steps ............................................................................................................................359 Conclusion......................................................................................................................................374 Chapter 15 Chain Inspection and Maintenance ..........................................................................375 Safety Precautions..........................................................................................................................375 Inspection Program ........................................................................................................................375


DK4023_C000.fm Page xiv Wednesday, October 12, 2005 10:55 AM

Inspection and Maintenance of Chain Drives ...............................................................................376 Inspection and Maintenance of Chain Conveyors and Bucket Elevators .....................................383 Inspection and Maintenance of Tension Linkage Chains .............................................................385 Replacing and Repairing Chains ...................................................................................................386 Protecting Idle Chains and Sprockets............................................................................................386 Conclusion......................................................................................................................................386


DK4023_C001.fm Page 1 Wednesday, August 17, 2005 8:57 AM

Brief History of the 1 ADevelopment of Chain EARLY DEVELOPMENTS Chains have been used for centuries to drive machines and move materials on conveyors and up elevators. In 225 B.C., Philo described a chain-driven water lift, as shown in Figure 1-1. This was really a form of bucket elevator. Leonardo da Vinci sketched the chain designs shown in Figure 1-2 in the 1500s. Some of those designs are remarkably similar to modern bar link, leaf, and silent chains. Figure 1-3 shows Ramelli’s waterwheel-driven pump from the 16th century, which used a chain to drive the pump. There are probably many other examples of chains used in drives and conveyors before the 19th century. But modern chain development really began in the 1800s.

COG CHAIN Cog chain was developed in the early 1800s to transmit power or motion between the shafts of treadmills to water elevators, weaving looms, and harvesting machinery. This chain, shown in Figure 1-4, consisted of rectangular cast links connected by looped and riveted iron bands. It became known as cog chain because the links contacted the sprocket tooth, or “cog,” as it was then called. This chain was used to mechanize farm implements, but it broke easily and was difficult to repair in the field.

CAST DETACHABLE CHAIN Cast detachable chain (Figure 1-5) was introduced in 1873 and overcame many of the problems of cog chain. This chain was made of simple identical cast links that were easily coupled and uncoupled by hand. It greatly improved the performance of power takeoffs from cleated bull wheels in contact with the ground under horse-drawn farm implements. Thus, agricultural equipment was soon mechanized and the use of chain for drives rapidly spread to other major industries. This basic detachable chain design is one of the early chain concepts that have come down to us today almost unchanged. Malleable iron and fabricated steel detachable chain is still in use today and is still made by some manufacturers. By the late 1800s manufacturers developed cast attachment links and installed them at intervals in basic chains. Figure 1-6 shows a cast detachable attachment link. Users could bolt malleable iron buckets to these attachment links and, when used vertically, it became a bucket elevator for loose bulk materials. By the 1890s, manufacturers made and sold bucket elevators like the one shown in Figure 1-7 as a standard machine. An apron conveyor was made by bolting slats or flights rather than buckets to the cast attachments to convey bulk materials horizontally or up mild inclines. Drag conveyors were made by using different types of attachments and scraper flights in a trough to convey bulk materials up steep inclines as well as horizontally. Figure 1-8 shows an early version of a drag conveyor from a manufacturer’s catalog. The modern cast and fabricated steel descendants of the detachable chains discussed previously are outside the scope of this book.

1



2

Standard Handbook of Chains

FIGURE 1-1 Philo’s chain driven water lift.

FIGURE 1-2 Leonardo da Vinci’s sketches of chain.

CAST PINTLE CHAIN The next important development after cast detachable chain was the cast pintle chain, shown in Figure 1-9. Pintle chain is the direct ancestor of both standard roller and engineering steel chains. It has a “closed-barrel” design, heavier link sections, and steel pins or pintles. Pintle chain evolved from cast detachable chain to withstand heavier loads, higher speeds, and more severe operating conditions in both drives and conveyors. The original pintle chain design was soon modified to meet special needs. For example, “shoes” were added to provide greater resistance to sliding wear, as illustrated by the links shown in Figure 1-10. This design is still widely used today. Short-pitch pintle chains were used for both drives and conveyors. However, new chains with a longer pitch were soon developed for conveyors. Not only did the longer pitches give these chains



A Brief History of the Development of Chain

3

FIGURE 1-3 Ramelli’s waterwheel-driven pump.

FIGURE 1-4 An early cog chain.

better economics because of fewer joints, they also provided more space for attachment wings or more complex designs, such as in Figure 1-11. Soon, exposed hardened steel bushings were installed in the barrels of the cast links to provide increased resistance to wear. Links of this type, shown in Figure 1-12, worked quite well in abrasive materials and became the standard bucket elevator chain used during the first third of the 20th century. Next, it was found that rollers revolving on the link barrels greatly reduced the power needs on long conveyors by eliminating the sliding friction of the links on conveyor ways or tracks. The



4


FIGURE 1-5 Cast detachable chain.

FIGURE 1-6 A cast detachable attachment link.

links were split through the chain centerline perpendicular to the axes of the pins to accommodate the rollers. This design is shown in Figure 1-13. By the early 1900s, the cast pintle chain had become an efficient and dependable product for power transmission, conveying, and elevating. Cast chains are not discussed further in this book, but they are historically important because they are the ancestors of both roller and engineering steel chains.

PRECISION ROLLER CHAIN A few years after cast detachable chain was introduced, a chain made of all steel parts was introduced for driving bicycles. A patent for roller chain was issued in 1880. That was the beginning of the roller chain industry. Figure 1-14 shows a length of standard roller chain. Figure 1-15 shows a cutaway view of the component parts of a roller chain as it engages a sprocket. There was little development of roller chain for the first decade or so, but much more development was done in the 1890s. By the early 1900s, roller chains drove the wheels of safety bicycles (Figure 1-16), as well as automobiles, trucks, and the propellers of the Wright Brothers’ airplane that flew at Kitty Hawk (Figure 1-17).




FIGURE 1-7 An early bucket elevator using cast chain.

FIGURE 1-8 A drag conveyor from the 1890s.

FIGURE 1-9 Cast pintle chain.

FIGURE 1-10 Cast pintle chain with wear shoes.


5


6

FIGURE 1-11 An M-3 attachment link for a cast pintle chain.

FIGURE 1-12 Pintle chain with hardened steel bushings.

FIGURE 1-13 Pintle chain with cast rollers.

FIGURE 1-14 Typical roller chain.





7

FIGURE 1-15 Roller chain construction and operation.

FIGURE 1-16 Chain drive on a safety bicycle (1895).

The chains developed in the late 1800s were a key component in the development of vehicles and other industrial equipment. They met or exceeded the needs of their time in terms of loadcarrying capacity, speed of operation, and wear life. However, development of the machines of which they were a part occurred so quickly that the early designs had to be constantly upgraded. There was a great demand for large amounts of chain for bicycles, and soon for motorcycles, automobiles, and trucks. That sparked organized methods of manufacturing that led to the modern chain industry. Figure 1-18 shows modern chain drives in a machine. Two major factors combined to make the roller chain industry what it is today: automation and standardization. Automation helped manufacturers meet the demand for the large amounts of highquality chain that were used on machines made by other industries. Manufacturing equipment, such as punch presses and automatic screw machines, ran long hours at high speeds to make component



8


FIGURE 1-17 Roller chain drove the propellers on the Wright Brothers’ first airplane.

FIGURE 1-18 Typical roller chain drives in a machine.

parts. Those parts were then fed into automated high-speed assembly machines that produced finished chain. Standard dimensions and capacities ensured that roller chains would fit and operate as the designer planned. Standard dimensions also ensured that links and chain from one manufacturer would fit sprockets and connect to chain from another manufacturer. This permitted many manufacturers of roller chains to participate in the then booming market. The result was that the industry soon became known as the precision roller chain industry. Efforts to standardize, beginning as early as 1913, led to the precision roller chain industry being one of the first in the world to have published standards available to designers and others concerned with roller chains. The basic series of roller chains—precision power transmission roller chains—were the first roller chains to be covered in an American National Standard, ASME B29.1 (then ASA B29a) in 1930. Since then, several varieties of roller chains have been standardized, and they will be covered in subsequent chapters of this book.




9

FIGURE 1-19 Typical engineering steel chains with rollers.

ENGINEERING STEEL CHAIN Engineering steel chains were first developed in the 1880s. They were developed for greater strength, speed, and shock resistance, and for better dimensional control than could be obtained from cast pintle chains. Early engineering steel chains were designed for difficult conveying applications. Just as with roller chains, engineering steel chains were developed as all-steel products fabricated from rolled shapes. One exception was that rollers, particularly flanged rollers, were made of cast iron, and this exception has continued to the present. The early engineering steel chains were taken directly from cast pintle chains. They were designed with the same pitches and similar dimensions as cast chains so that the steel chains would fit identical sprockets. This meant that higher strength steel chains could be substituted for cast chains when necessary without having to change sprockets. Larger sizes of engineering steel chains were soon developed. Pitch, strength, wear life, and carrying capacity were increased to meet the heavy-duty needs of industry. For convenient and practical attachment spacing, many conveyor class engineering steel chains were made with a pitch size an even increment of 1 foot. Typical sizes, as manufactured for many years, are 4-, 6-, 9-, 12-, and 18in. pitches. Many of these designs have identical joint details and are available in three or more of the standard pitches, with a wide range of attachment types available. Most engineering steel chains were developed to operate dependably in the most demanding conditions. Many classes of engineering steel chains are covered by the ASME B29 series of standards, and those standard chains are often available from manufacturers’ stocks. However, an important part of the engineering steel chain market is special chains for unique installations or to meet unusual designs needs. There are many general types of engineering steel chains, and some of those covered in this book are shown in Figure 1-19 to Figure 1-22. Those with steel rollers are perhaps the most widely used on both drives and conveyors. The bushed, rollerless style meets the needs of many conveyor and bucket elevator applications. Welded steel versions of the basic cast chains are now quite popular, and a simple bar-link type is used for slow-moving conveyors and tension linkages. Each of these types is illustrated and described in detail in a subsequent chapter. It is only in the past few decades that certain engineering steel chains have been standardized so that recognized standards could be issued. The first engineering steel chains to be covered by an ANSI standard were heavy-duty offset sidebar power transmission roller chains (ASME B29.10). That was soon followed by standards covering steel bushed rollerless chains (ASME B29.12) and



10


FIGURE 1-20 Bushed rollerless engineering steel chain.

FIGURE 1-21 Welded steel version of pintle chain.

FIGURE 1-22 Bar-link, or block and bar, style engineering steel chains.

heavy-duty roller-type conveyor chains (ASME B29.15). Since then, several varieties of engineering steel chains have been standardized, and these are covered in subsequent chapters of this book.

SILENT CHAIN Early designs of silent chain may be seen in Leonardo da Vinci’s sketches from the 1500s. However, the first notable commercial use of silent chain was not until 1843 in the SS Great Britain. Sir Isambard Kingdom Brunel supervised the building of the Great Britain, and it was a revolutionary ship design in many ways (Figure 1-23). It was the first seagoing iron steamship, the first propellerdriven steamship to cross the Atlantic, and the first vessel driven by inverted-tooth, or silent, chain. Two 1800 HP steam engines drove the ship. The silent chain drive delivered power from the engines to the propeller shaft by way of large wooden-tooth sprockets (Figure 1-24). Propeller speed was a mere 53 rpm, stepped up from an engine output speed of only 18 rpm. The chain was a massive, five-strand assembly that weighed about 7 tons. No record remains of the chain’s pitch, but this first commercially applied silent chain may still be the largest ever constructed.




11

FIGURE 1-23 The SS Great Britain of 1845. It used the first silent chain drive of importance.

FIGURE 1-24 The silent chain drive of the SS Great Britain.

From 1895 to about 1925, the chain industry greatly improved the design of silent chains. Manufacturers in Europe and the United States developed and patented unique chain joints that increased service life and load carrying capacity. From the 1930s on, silent chain was used in a variety of industrial applications, including drives in paper and textile mills, flour and feed mills, printing presses, industrial fans and blowers, pumps, and machine tools. It was also commonly used as a timing chain in early automobile engines. Throughout the 20th century, the industry improved material quality, processing technology, and chain designs to increase the load and speed capacity of silent chain. That led to its being used in many demanding industrial and automotive applications, particularly those requiring a compact, high-speed, quiet drive (Figure 1-25). In recent years there has been renewed interest in the use of silent chain for automobile camshaft timing. Silent chain is also used in the drive train of snow-



12


FIGURE 1-25 Typical silent chain drive.

mobiles and four-wheel-drive recreational vehicles. Outside the power transmission market, silent chain can be found serving as a conveying surface in a variety of material transport applications (Figure 1-26). The chain’s positive, smooth operation, as well as the extensive range of available pitches, widths, and assembly styles, offers distinct advantages to conveyor system designers and operators. Silent chains are made up of stacked rows of flat link plates with gear-type contours designed to engage sprocket teeth in a manner similar to the way a rack engages a gear (Figure 1-27). The links are held together at each chain joint by one or more pins, which also allow the chain to flex. The design of both the link contour and the chain joint directly influences a chain’s useful load carrying capacity, its rate of wear and service life, and its quietness of operation. Sprocket tooth design also influences these characteristics. Accordingly, each of these areas—link, joint, and sprocket design—has been the subject of considerable research in an effort to optimize chain design and performance. While the industry standard (ASME B29.2) defines the key features of silent chains and sprockets most commonly used for industrial power transmission, there exist a large number of unique chain designs that have been developed by different manufacturers for specific applications.

FLAT-TOP CHAIN In the 1920s and 1930s, major improvements were made in the production of food and beverage products. The introduction of high-speed processing, filling, and packaging equipment drove the need for a chain with a flat carrying surface for material handling. The first flat-top chains were produced by simply welding steel plates to roller chain, thus producing a flat surface where products or packages could be carried. The first hinge-type flat-top conveyor chain was introduced in 1935. It was made of a series of flat plates with curled tangs on each side that formed the outer portion of a hinge. Pins were inserted into the holes of the curled tangs to make a continuous flat-topped conveyor chain that could flex in one direction. These first flat-top chains were available in carbon and corrosion-resistant steel (Figure 1-28) and were widely used in the brewing industry to convey glass bottles.




13

FIGURE 1-26 Typical silent chain conveyor.

Continuing developments in the food and beverage industries produced the need for flat-top chains made from materials other than steel. By the 1960s, flat-top chains made from plastic were widely available (Figure 1-29). Straight-running flat-top chains are standardized in ASME B29.17M, Hinge Type Flat Top Conveyor Chains and Sprocket Teeth. A straight conveyor is not always possible, due to flow processes, obstructions in the plant, etc., so side-flexing flat-top conveyor chains were developed. These chains are based on straightrunning designs, but have additional clearance in the joint that permits the chain to traverse curves in one or two directions (Figure 1-30). Side-flexing flat-top chains are not covered by any ANSI standard, but they are an important item in the flat-top product line and will be covered further in this book.

TERMINOLOGY Certain terms and phrases commonly used in discussions of chain are well known and accepted. “Chain pitch,” “pitch diameter,” “link,” and “sprocket” are the most common. These are defined, implicitly at least, in many places in the text. Varying terms are sometimes used in catalogs and other published works for what are functionally similar parts of different types and classes of chains. These differences in terms stem from



14


FIGURE 1-27 Silent chain meshing with sprocket.

FIGURE 1-28 Steel flat-top chain.

the separate, but parallel, development of roller chain and engineering steel chain over a span of more than 100 years. Each group developed its own terms. Their use then spread from the catalogs and advertising of manufacturers to technical papers, ANSI standards, and other published works. For example, the tension members between the joints of roller chain are called link plates, while the functionally similar members of engineering steel chain are usually called sidebars. But in some types of chains used for tension linkage applications, these parts are called blocks and bars.




15

FIGURE 1-29 Plastic flat-top chain.

FIGURE 1-30 Side-flexing flat-top chain.

FIGURE 1-31 Typical link plate for roller chain and sidebar for engineering steel chain.

At first, the differences in terms would seem to add confusion to what appears to the casual observer to be a very complex subject. But actually the variations in terms are quite useful. The different terms are generally applied to components that are functionally similar, but differ widely in shape, finish, and many other ways. Figure 1-31 shows a link plate for a roller chain and a sidebar for engineering steel chain.



16


A link plate in a roller chain is likely to be placed in a drive running in a friendly environment. But that link plate will be subjected to an enormous number of cycles at very high loads. A roller chain often has to be replaced because of wear elongation, and sometimes due to link plate fatigue. On the other hand, a sidebar in an engineering steel chain is likely to be placed in a conveyor running in a wet and dirty environment. The sidebar is subjected to relatively few cycles at high loads, but is subjected to a lot of moisture and dirt. Engineering steel chains more often have to be replaced because of corrosion and abrasive wear. Each part, link plate, or sidebar is processed to give the part the properties best suited to the end use. The holes in link plates are usually put through special processing to improve quality, and link plates are heat treated and finished to increase fatigue strength. The holes in sidebars are somewhat less finely finished, and sidebars are heat treated for corrosion and abrasion resistance. Sidebars are generally left with a rather rough finish. Once understood, the different terms are no longer so confusing. They help the user to quickly recognize important differences in size, shape, finish, and end use.


DK4023_C002.fm Page 17 Thursday, August 18, 2005 6:40 AM

Chain Overview: 2 AUses and Advantages GENERAL This chapter is intended to give the reader an overview of the various standardized types of chain and their uses. Chains may be classified in many different ways. From a theoretical viewpoint, chain is a continuous flexible rack engaging the teeth on a pair of gears. Certainly, a sprocket, being a toothed wheel whose teeth are shaped to mesh with a chain, is a form of gear. From a viewpoint based on its history and development, chain is a mechanical belt running over sprockets that can be used to transmit power or convey materials. Neither of these aspects relate to the practical standpoints of either the producer or the user of the product. To the manufacturer, engineers, and shop people, chain is probably best defined by how it is made and assembled. To the salesperson, it is defined in terms of cost and how it will be used. To the user, the classification is unimportant aside from being an aid to secure the right product for the function needed.

TYPES OF CHAIN In chapter 1, the evolution of the chain industry was outlined from the first cast chains to flat-top chains. This book outlines four major kinds of chain from an industry standpoint: roller chains, silent chains, engineering steel chains, and flat-top chains.

SCOPE OF CHAINS COVERED The chains discussed herein are standard chains assembled from parts fabricated from steel or molded from plastic. Cast link chains are beyond the scope of this book, but cast carrier rollers are found in some conveyor chains. Assembly is usually by means of interference fits or by welding. Pin ends may be staked, spun, or riveted. The basic designs of these chains are predicated on function and long life in service. Joints that constantly flex over sprocket wheels are designed with maximum bearing areas and they often have hardened pins and bushings to resist wear. Chain tension members, such as link plates and sidebars, are often heat treated for toughness and shock resistance as well as to augment yield strength. The unit-link top plates in flat-top chains usually have strengthening ribs beneath the flat tops to provide adequate tensile strength.

STYLES AND FORMS OF CHAINS Regardless of whether chains are roller chains, silent chains, engineering steel chains, or flat-top chains, their styles may be classified as follows: • •

Straight link chains, which have alternate “inside” and “outside” links. These include chains with rollers and chains that are similar to chains with rollers, but are rollerless. Offset link chains, which have all links alike. These include integral link chains, such as bar-link, flat-top, and welded steel chains, where internal rollers cannot be installed. 17



18


FIGURE 2-1 Typical offset and straight link drive chains.

FIGURE 2-2 Roller chain offset section.

These differences in configuration and details are important to both manufacturers and users, not only because of cost, but for other reasons of a technical nature. It is obvious that chains exist in about every possible combination of the styles listed above. All told, however, there is probably a good deal less offset chain furnished than straight link, and more with rollers than without them.

STRAIGHT AND OFFSET LINK CHAINS Figure 2-1 illustrates typical straight and offset link chains. The configuration of the tension members of these chains (in this case, sidebars, as these are engineering steel drive chains) may be the only difference in the construction of the two chains. If pitch and joint details are identical and the sidebar cross sections are identical, so that the only difference is straight or offset link construction, the chains can be operated over the same sprockets and for the same purpose. But they should not be “mixed” by intercoupling links of one into the other unless the manufacturer specifies that this is permissible. The differences in use for a given application stem from the fact that straight link chains consist of inside and outside links and that offset links are all alike. For this reason, strands of straight link chains must be used with an even number of links unless one special offset link (Figure 2-2) is used. On the other hand, offset chain strands can be used with either an odd or even number of links. Straight link chains operate equally well in either direction of travel, but offset chains should operate in a specific direction (referring to closed or open end forward) to obtain the best service. The recommended direction of travel for offset chain strands varies with the application, and manufacturers’ recommendations should be followed. The details of travel direction are discussed in subsequent chapters. Each style has advantages. Straight link chain is easier to manufacture and may give a cost advantage to the user. Attachments are more easily provided in straight link designs, and may cause fewer problems in use. For a given strength, a slightly shorter pitch chain can be provided in straight link chain, since space for an offset need not be provided. Figure 2-1 demonstrates this; although sidebar thickness and cross section are similar, the pitch of the straight link drive chain can be considerably less. In drives, short pitch is reflected in terms of smaller sprockets and quieter operation.



A Chain Overview: Uses and Advantages

19

An advantage of offset chain is that a worn drive strand can be easily shortened by removal of a single link. To shorten a straight link roller chain containing a connecting link, a pair of links (one inside and one outside) is removed and replaced with a single offset link. If the straight link chain does not have a connecting link, a section consisting of five links, two inside and three outside links, must be removed. The central three links are replaced with a two-pitch offset section (as shown in Figure 2-2), and two of the outside links are replaced with two connecting links. Take care in such cases that the replacement offset link has offsets that will clear the ends of the adjacent straight links when the chain flexes. There are some applications, mostly with rollerless chains on conveyors or bucket elevators, where offset chains give excellent wear life when operated open end forward. The user should carefully follow the manufacturers’ recommendations for those applications.

CHAINS WITH AND WITHOUT ROLLERS To a user, the presence or absence of rollers is probably of far greater interest than whether straight or offset links are present in a chain being considered for an application. The major purpose of rollers is to reduce friction, but the rollers in chains have two separate functions, the two functions usually being provided by the same roller. These functions are •

•

To engage the sprocket teeth and thus transfer any sliding action to the internal members of the chain, which are designed for that purpose. This is discussed further in subsequent chapters. To serve as a guide or to support a chain and material carried on it on tracks or ways, as is characteristic of conveyors and some bucket elevators.

Rollers in drive chains, of which roller chain is the prime example, normally are smaller in diameter than the height of the link plates of the chain, as shown in Figure 2-3. Thus, the link plates serve as guides when the chain engages the sprockets, and may also do so when the chain is riding on guides, as in a bucket elevator. Rollers on conveyor chains normally have diameters considerably larger than the widths of their adjacent sidebars, as shown in Figure 2-4. This is done for two reasons. First, and most obvious, the large rollers, called carrier rollers, carry the sidebars well above the conveyor tracks

FIGURE 2-3 Double-pitch roller chain with small rollers.

FIGURE 2-4 Engineering steel chain with large carrier rollers.



20


and thus prevent friction. Second, larger rollers have a definite mechanical advantage over smaller rollers relative to rotational friction, and thus help reduce chain pull. This is discussed more fully in chapter 9. The carrier rollers in most chains are also used to engage the sprockets. However, carrier rollers, equipped with antifriction bearings, are sometimes used as outboard rollers on rollerless chains. Rollerless chain is similar in appearance to chain with rollers, and is used for applications where rollers are not required. Most rollerless chains are engineering steel chains. There are other types of chain that do not have rollers, because rollers would obviously not be appropriate. Examples are bar-link, silent, and flat-top chains, which were shown in Figures 1-22, 1-25, and 1-28. The following sections list the various types of chain, with some details of their construction and intended uses. However, designers should consult the appropriate ASME standards and manufacturers’ catalogs for detailed information, including dimensions, working loads, and similar data.

USES OF CHAIN The major uses of the four types of chain listed above are in drives (power transmission), conveyors, bucket elevators, and tension linkages. Each of these applications is discussed in detail in subsequent chapters. Some standard chains are designed for use in only one of these application. However, some chains are designed so that they can be adapted to more than one use. Roller chains and engineering steel chains are used in all types of applications. Silent chain is essentially for drive applications, although a few conveying applications exist. Flat-top chain is intended only for conveying. Roller chains are usually thought of as being mostly for drives, while engineering steel chains are used for conveyors and bucket elevators, but there are many exceptions. In fact, there are enough exceptions that a chapter in the drives section covers heavy-duty offset sidebar engineering steel chain drives and another chapter in the conveyors section covers roller chain conveyors. Both are the subject of ASME standards. A drive is a means of transmitting power, of which force, motion, and time are components. A tension linkage transmits force and motion, without the time component. In the same vein, both conveyors and bucket elevators handle materials. A conveyor moves materials horizontally or at a slight angle. A bucket elevator moves materials vertically upward or at a slight angle. The overlap in applications is handled in this book by grouping tension linkages with drives, and bucket elevators with conveyors.

STANDARD CHAINS AND THEIR USES AMERICAN NATIONAL STANDARDS The B29 series of the American National Standards, covering chains, attachments, and sprockets for power transmission and conveying, were designated as ANSI B29.xx standards for many years. Recently, however, ANSI and ASME agreed that the standards developed by ASME would be designated simply as ASME standards, and did not need to carry the ANSI prefix. All B29 standards are developed by ASME and approved by ANSI as American National Standards, but now they are designated simply as ASME B29.xx standards.

ROLLER CHAIN As outlined in chapter 1, roller chain is covered by ASME B29.1 and several related standards. Roller chains are manufactured in several types, each designed for a particular use. All roller chains are constructed so that the rollers are evenly spaced throughout the chain. A major advantage of roller chain is that the rollers rotate when contacting the teeth of the sprocket.




21

FIGURE 2-5 Roller chain principal dimensions.

Two types of roller chains are in common use: single strand and multiple strand. In multiple strand, two or more chains are assembled side by side on common pins that maintain the alignment of the rollers in the several strands. Standard roller chains are defined as pitch proportional, which makes them different from other types of chains with rollers. The ASME standards’ nominal dimensions for these chains are approximately proportional to the chain pitch. The pitch of a roller chain is the distance between the centers of adjacent joint members. The three most important roller chain dimensions are pitch, roller diameter, and inside chain width, as indicated in Figure 2-5. These dimensions determine the fit between the chain and the sprockets. Chain width is the nominal distance between the link plates of a roller link, and is approximately five-eighths of the pitch. Note that this is not the overall width of the chain. Roller diameter is the outside diameter of the roller, and is approximately five-eighths of the pitch. For the various standard chain sizes, ASME B29.1 specifies that the pin diameter be approximately 5/16 of the pitch, and the link plate thickness be approximately one-eighth of the pitch. In addition, the limiting dimensions required for interchangeability are given in the standard. General roller chain dimensions, as specified in the standard, are given in Table 2-1. The purpose of the standard, as indicated by the dimensions given in Table 2-1, is to make chains and sprockets interchangeable. That permits the chain of one manufacturer to replace the chain of another. This does not mean that for any given type, all chains are identical; factors not affecting intercoupling or interchangeability on sprockets are left to the manufacturers. Standard Roller Chain Number Designations A standard roller chain number is a shorthand device that provides complete identification of an individual chain. The right-hand digit in the chain designation is 0 for roller chains of standard proportions, 1 for lightweight chain, and 5 for rollerless bushing chain. The numbers to the left of the right-hand figure denote the number of 1/8 -in. segments in the pitch. For example, number 50 indicates a 5/8 -in. pitch chain of basic proportions (see Table 2-1). Number 41 designates a narrow, lightweight, 1/2 -in. pitch chain. Number 35 indicates a 3/8 -in. pitch rollerless bushing chain. And number 100 indicates a chain of basic proportions with 10/8 -in. or 1 1/4 -in. pitch. The letter “H” following the number of the chain denotes a chain of the “heavy” series having all link plates 1/32 -in. thicker than the link plates of a basic chain of corresponding pitch. For example, the number 80H designates a 1-in. pitch chain with link plates that are 5/32 -in. thick instead of 1/8 -in. thick as in standard number 80 chain. A hyphenated suffix number, following the basic chain number, indicates the number of strands in a multiple-strand chain. For example (see Table 2-1), 60-2 designates two strands of a number 60 chain in parallel having common pins, 60-3 designates a triple strand, 60-4 a quadruple strand, and so on. And the number 80H-2 designates two strands of a number 80, heavy series chain.



22


TABLE 2-1 General dimensions of ASME B29.1 roller chain

Types of Roller Chain Roller chains are used for both drive and conveyor applications. There is a separate series of chains for each application area. There are three types of standard power transmission roller chain: • • •

ASME B29.1 standard single strand, shown in Figure 2-6. ASME B29.1 standard multiple strand, shown in Figure 2-7. ASME B29.3 standard double-pitch power transmission roller chain, shown in Figure 2-8.

The most commonly used chain for drives is the single-strand standard series roller chain. The horsepower rating capacities of these chains cover a wide range of drive load requirements. Multiple-strand roller chains are used to provide increased power capacity without the need for increasing the chain pitch or its linear speed. For a given power load, a multiple-strand chain with smaller pitch can be run at a higher speed than single-strand roller chain of larger pitch. In the power transmission field, standard roller chain applications range from fractional horsepower drives to those requiring in excess of 1000 hp. The 1/4 -in. pitch chains, weighing less than 2 oz./ft., have been applied to such intricate machines as microfilm projectors. On the other hand, large-pitch multiple-strand chains, weighing over 50 lb./ft., meet the requirements of such heavyduty service as oil field equipment (Figure 2-9). The double-pitch series of drive chains is similar to the standard series (having the same pin, bushing, and roller diameters), except that the pitch is twice that of the standard chain. This form of double-pitch roller chain normally has figure-eight-shaped link plates.




FIGURE 2-6 Standard single-strand roller chain.

FIGURE 2-7 Standard multiple-strand roller chain.

FIGURE 2-8 Double-pitch power transmission roller chain.

FIGURE 2-9 Roller chain drives in a drawworks.


23


24


Double-pitch power transmission roller chains are particularly applicable to power drives where speeds are slow, loads are moderate, or center distances are long. For such applications, the longer pitch results in a lighter and less expensive chain. The standards also specify connecting links, offset links, and offset sections that are used to connect the free ends of roller chain. There are four standard types of conveyor roller chain: • • • •

ASME B29.1 standard series roller chain, shown with A-1 attachments in Figure 2-10. ASME B29.4 double-pitch conveyor roller chain, with small diameter rollers, shown with A-2 attachments in Figure 2-11. ASME B29.4 double-pitch conveyor roller chain, with large diameter or carrier rollers, shown with A-2 attachments in Figure 2-12. ASME B29.27 hollow-pin roller conveyor chain, in single pitch or double pitch, as shown in Figure 2-13.

The ASME B29.1 standard series of roller chains used for conveyor applications are basically the same as the drive chains, with the addition of attachments. These chains usually have figureeight-shaped link plates, but some manufacturers offer straight-edged link plates on special order. The ASME B29.4 series of double-pitch conveyor roller chains, with either small or large diameter rollers, have the same pin and bushing diameters as the ASME B29.1 standard series chains, but have straight-edged link plates of twice the pitch.

FIGURE 2-10 Standard precision roller chain with bent attachments for conveyor service.

FIGURE 2-11 Double-pitch conveyor roller chain with small rollers and bent attachments for conveyor service.




25

FIGURE 2-12 Double-pitch conveyor roller chain with large carrier rollers and bent attachments for conveyor service.

FIGURE 2-13 Single-pitch hollow-pin chain.

Many standard attachments are available for conveyor roller chains and those are listed in the ASME standards B29.1 and B29.4. Many more special attachments are made for conveyor roller chains and those may be found in manufacturers’ catalogs. Double-pitch conveyor roller chains are often preferred for conveyor service because of lighter weight and lower cost. A further advantage is that the longer pitch provides space for the large diameter carrier-type rollers shown in Figure 2-12. The ASME B29.27 series of conveyor chains come in either single-pitch or double-pitch. The chains with small diameter rollers actually are rollerless chains. The bushings normally have the same diameter as the rollers in B29.1 series chains, and the hollow pins usually have the same diameter as the bushings in B29.1 series chains. The double-pitch hollow-pin chains with large diameter rollers are true roller chains and the rollers have the same outside diameter as the large rollers in B29.4 large roller series chains. Hollow-pin chains are most often used without attachments in cross-rod-type conveyors. Finally, there are three types of roller chain for use in tension linkages: • • •

ASME B29.8 leaf chain. ASME B29.24 roller load chain for overhead hoists. Rollerless lift chain.

The ASME B29.8 leaf chains will be covered more fully in a following section and in the chapter on tension linkages. The B29.24 series of roller load chains have the same dimensions as ASME B29.1 chains of the same pitch, but they are designed specifically for use as load chains in overhead hoists. ASME B29.1 chains should never be used on overhead hoists, and the chain manufacturer should be consulted about applications of ASME B29.24 chains in overhead hoists. Rollerless lift chains are not covered by any American National Standard. They may be either ASME B29.1 or B29.24 chains without rollers. The rollers are omitted because lift chains normally run over sheaves instead of sprockets, and omitting the rollers reduces the cost of the chain.



26


FIGURE 2-14 Leaf chain with cross section showing construction.

Rollerless lift chains are used in applications similar to leaf chains, but where a hardened bushing is needed to combat abrasive wear. The term chain tension linkage is used when the linear motion of the chain is not continuous in one direction. In other words, the chain must move back and forth. Roller chain is often specified where the positive action of a chain is required for certain hoists, marine steering equipment, and similar applications.

LEAF CHAIN Leaf chain, sometimes called “cable chain” or “balance chain,” is used for tension linkage applications. It consists of steel link plates, with contours that are usually the same as the roller link plates in roller chain, laced on pins in a way that permits the chain to flex freely at each joint. All of the link plates have the same contour to permit the chain to be properly supported when running over a sheave. A typical section of leaf chain is shown in Figure 2-14, as well as a drawing showing a lacing pattern, as it would be shown in the ASME B29.8 standard, Leaf Chain, Clevises, and Sheaves. Leaf chain lacing patterns are the way that the link plates are interlaced in alternate links. The pattern shown in Figure 2-14 consists of alternate links of three pin links and four articulating links. The three link plates in the pin links function the same as the pin link plates and center plates in a roller chain. The four link plates in the articulating links function the same as roller links in a roller chain, but without any bushings or rollers. The lacing pattern of the chain in Figure 2-14 is called a 3 × 4 lacing. That comes from the fact that the chain has three link plates in each pin link and four link plates in each articulating link. American National Standards leaf chain number designations consist of a BL prefix followed by three or four digits. The last two digits indicate the lacing pattern and the first two indicate the chain pitch in eighths of an inch. For example, a BL-534 leaf chain would be of 5/8 -in. pitch, having three link plates in each pin link and four link plates in each articulating link, just as in the example chain in Figure 2-14.




27

FIGURE 2-15 Typical silent chain.

Leaf chain normally is not used in endless strands, because it has no provision to engage sprockets. Force is usually applied to the ends through clevises or other means of attachment through the chain pins. Typical leaf chain applications are those where a strong, flexible linkage with very little elastic stretch (and a resulting positive action) is required. Changes of direction are usually made over sheaves or rollers. Leaf chain is commonly used on lift trucks and for counterweights on heavy machine tools. It is equally appropriate for similar applications requiring continuous support of a load randomly movable in either direction between limits.

SILENT CHAIN Silent chain, also called “inverted tooth” chain (Figure 2-15), consists of a series of toothed link plates assembled on joint components in a way that allows free flexing between each pitch. The teeth on the link plates mesh with a sprocket, similar to the way a rack meshes with a gear (Figure 2-16). The great majority of silent chain is used in drives. Silent chains are made up of stacked rows of load carrying link plates (Figure 2-17). Increasing the number of rows of links increases the chain width, tensile strength, and load carrying capacity. Using this feature, manufacturers make silent chains ranging from less than an 1 in. wide to more than 20 in. wide, with power capacities ranging from a fraction of a horsepower to more than 2000 hp. Standard Silent Chain The American National Standard, ASME B29.2, Inverted Tooth (Silent) Chain and Sprockets, covers one type of silent chain for drives. The standard lists nine sizes of silent chain with pitches from 0.1875 in. to 2.0 in., and widths from 0.25 in. to 20 in. This standard mainly standardizes the sprocket



28


FIGURE 2-16 Silent chain meshing with sprocket.

FIGURE 2-17 Stacked link plates in silent chain.

tooth form. It requires that a standard silent chain from any manufacturer will run over the standard sprockets from any other manufacturer. It does not standardize joint design or joint dimensions, so silent chains from different manufacturers usually cannot be connected together. Standard Silent Chain Number Designations In the standard, silent chains are designated by a combined letter and number symbol as follows: •

•

For chains of 3/8 -in. pitch and larger, a two-letter symbol, SC (denotes conformance with ANSI standard B29.2), one or two digits indicating the chain pitch in eighths of an inch, and two or three digits indicating the chain width in quarter inches. For example, SC302 designates a silent chain of 3/8-in. pitch and 1/2-in. width; SC1012 designates a silent chain of 1 1/4 -in. pitch and 3-in. width. For 3/16 -in. pitch chains, a two-letter symbol, SC, the digits 03, indicating 3/16 -in. pitch, two digits indicating the total number of links wide, and the approximate width in 1/32




29

of an inch. For example, SC0315 chain is 3/16-in. pitch silent chain, approximately 15/32 in. wide. Link plates of silent chains manufactured to the ANSI B29.2 standard are stamped with a symbol indicating the pitch; for example, SC6, or simply 6, indicates a plate with a 3/4 -in. pitch. Link plates of silent chains not conforming to the ANSI B29.2 standard are generally stamped with a number of the manufacturer’s choice. Standard silent chain is used in a wide variety of industrial drives where a compact, high-speed, smooth, low-noise drive is required. Common uses are on drives in paper and textile mills, flour and feed mills, printing presses, industrial fans and blowers, pumps, and machine tools. Nonstandard Silent Chain There are several classes of silent chain that are not produced by all manufacturers and are not covered by any standard. Nevertheless, these special silent chains meet important needs in the marketplace. The most common nonstandard silent chains are probably the high-performance drive chains. High-performance silent chains are specially designed to carry greater loads and run at higher speeds than standard silent chains. They generally have unique joint designs with rocker-type pins that virtually eliminate chordal action. And they usually require specially designed sprockets. Highperformance silent chains are available in a wide range of sizes with pitches from 0.375 in. to 2.0 in. and in widths of less than 1 in. to more than 20 in. High-performance silent chains are used on very-high-speed drives where exceptional smoothness and quietness are required. These chains are commonly used on drives in the transfer cases of four-wheel-drive vehicles, in the drive trains of snowmobiles, and in industrial equipment where ultimate smoothness is required. Other nonstandard silent chains are duplex, conveyor, and specialty chains. Duplex silent chains (Figure 2-18) have teeth extending on both sides of the pitch line to permit the chain to run on serpentine drives where sprockets engage both sides of the chain.

FIGURE 2-18 Duplex silent chain.



30


FIGURE 2-19 Examples of specialty silent chains.

Conveyor silent chains often use flat-back link plates that provide a smooth conveying surface and may use joint designs that resist fouling. Conveyor silent chain is frequently used to convey hot glassware and other products where ventilation from below the conveyor is desired, or where exceptionally smooth transport is required. A typical silent chain conveyor is pictured in Figure 1-26. Specialty silent chains are made for specific applications where attachments or unusual configurations are needed. Some examples of specialty silent chains are shown in Figure 2-19.

ENGINEERING STEEL CHAIN Engineering steel chains are made of fabricated and machined steel. They are designed for a wide variety of uses and operating conditions. Because of their broad range of uses, there are many types available and many ways to classify them. Engineering steel chains have been in existence for more than a century. But manufacturers identify similar types of engineering steel chains by widely differing terms. The same applies to the component parts of this class of chains. In recent decades, a concerted effort has been made by the American Chain Association to standardize the terminology and limit dimensions for this class of chains. We now have ASME standards for many styles of engineering steel chains. The classifications and terms used in this manual are in accordance with current standards or current practice where standards do not exist. However, the terms used in some manufacturers’ catalogs may not agree completely with this handbook. When a designer encounters terms that are not included in this handbook, he or she should contact the manufacturer that published the catalog. Types of Engineering Steel Chain Generally speaking, the types of engineering steel chains as classified under ANSI standards fall into the following categories or types: •

•

Straight sidebar steel chains • With rollers • Rollerless Offset sidebar steel chains • With rollers




• • •

31

• Rollerless Bar-link chains (often called “block and bar”) Welded steel chains Open-barrel steel pintle chains

Straight Sidebar Chain with Rollers Straight sidebar roller chain is shown in Figure 2-20. These chains have steel bushings and pins and are assembled using interference fits between those parts and the sidebars. Rollers are installed to turn freely on the bushings between the inside sidebars. Most chains of this type have carrier-type rollers, their diameter being considerably larger than the width of the sidebars on each side. ASME standard B29.15 lists a few of the more popular steel roller conveyor chains and attachments. But manufacturers produce many more models of this type of chain and furnish them with a wide variety of attachments. These chains are mainly used in conveyors with flights or slats, although they are also sometimes used in bucket elevators and scraper conveyors. Straight Sidebar Chain without Rollers Straight sidebar rollerless chain is shown in Figure 2-21. These chains also have steel bushings and pins and are assembled using interference fits between those parts and the sidebars, but no rollers are installed over the bushings. ASME standard B29.12 lists 10 of the more popular steel roller conveyor chains, along with a few of the more common attachments. However, manufacturers produce many more models of this type of chain and furnish a wide variety of attachments for them. Steel-bushed rollerless chains are mostly used in bucket elevators, although they are also used in conveyors. Most of these chains are used where they must run in abrasive materials or other difficult-to-handle materials. The chain is usually furnished with attachments that are specified for the particular application. Offset Sidebar Chain with Rollers Offset sidebar roller chain consists of a pair of offset sidebars with a bushing and pin assembled into the sidebars. A roller is installed to turn freely on the bushing between the sidebars. Each link of the chain is identical, as is shown in Figure 2-22. ASME standard B29.10 lists eight models of chain, ranging in pitch from 2.5 in. to 7.0 in. But several manufacturers make many more models. The standard includes only single-strand chain, but multiple-strand chain can be obtained from most manufacturers. Almost all offset sidebar roller chain is used in drives. Only a small amount of this chain, usually with attachments, is used in conveyors.

FIGURE 2-20 Straight sidebar engineering steel conveyor roller chain with flanged rollers and K-2 attachments.



32


FIGURE 2-21 Straight sidebar rollerless chain with attachment lug on outside link.

FIGURE 2-22 Heavy-duty offset sidebar power transmission roller chain.

FIGURE 2-23 Offset sidebar rollerless chain with K-2 attachments.

Offset Sidebar Chain without Rollers Offset sidebar rollerless chain consists of a pair of offset sidebars with a bushing and pin assembled into the sidebars. No roller is installed on the bushings. Figure 2-23 shows an example of this type of chain with attachments. No ASME standard currently covers this type of chain. Offset sidebar rollerless chain is used primarily on conveyors and bucket elevators. Such chains usually slide on ways or between guides. One specialized use is on conveyors, where the load is carried on the ways, with outboard rollers having antifriction bearings; the chain bushings engage the sprocket teeth to drive the conveyor. Bar-Link Chain Bar-link chains are sometimes called block and bar or steel block chains. Figure 2-24 shows a typical example of a bar-link chain. This type of chain usually consists of two outer sidebars, one center bar, and two pins making up a two-link section. Bar-link chain usually does not have bushings, with the center bar flexing directly on the pin. Sprocket contact is with the ends of the center bars. No ASME standard currently exists for bar-link chains. These chains are also made in multilaced construction, as shown in Figure 2-25. Chains with this type of construction are often called leaf chains.




33

FIGURE 2-24 Bar-link chain, often called block and bar chain.

FIGURE 2-25 Multilaced leaf-type bar-link chain.

Bar-link chains are frequently used in tension linkage applications. A design of this type is so commonly used in steel mills for this application that it is known as draw bench chain. Steel barlink chains are also used on slow-moving conveyors, such as steel mill coil conveyors (with outboard rollers), and are made in very large versions to raise and lower river and canal lock and dam gates. Welded Steel Chain Welded steel chains are similar to offset sidebar rollerless chains, except that the barrels (bushings) are welded to the sidebars rather than being held together by tight fits and locking surfaces. Figure 2-26 shows welded steel mill chain and Figure 2-27 shows welded steel drag chain. Nine models of welded steel mill chains are listed in ASME standard B29.16 and nine models of welded steel drag chain are listed in ASME standard B29.18. Welded steel drag chains generally are wider and have a different barrel design than mill chains. Welded steel mill chains are offered with a wide variety of attachments for general conveying service. They are also often used as plain chain for slow-moving conveyor drives. Welded steel drag chains are used for drag conveyors handling bulk materials. Open-Barrel Steel Pintle Chains Open-barrel steel pintle chain is an economical, lightweight conveyor chain. The basic chain consists of one-piece offset formed steel links and pins. The pins are fixed against rotation by mechanical locks or interference fits. A section of the basic chain is illustrated in Figure 2-28. The barrels are open, leaving the pins exposed on one side, with sprocket contact being against either the barrel or the exposed pins. The open barrel provides a ready outlet for foreign material and rust to escape from the pin area and makes seizing unlikely. ASME standard B29.25 lists six models of open-barrel steel pintle chain, along with two commonly used attachments. Open-barrel steel pintle chain is primarily used in agricultural equipment and conveyors running in dirty environments.



34


FIGURE 2-26 Welded steel mill chain link.

FIGURE 2-27 Welded steel drag chain.

Other Engineering Steel Chains Many other types of engineering steel chains exist, although most of them are not the subjects of published standards. Special-purpose chains for handling materials, such as double-flex conveyor chains, welded rooftop and flat-top chains, steel detachable chains, and steel fabricated chains with plastic bushed rollers for use where lubrication is unacceptable, are only a few of the products available. All of these may be found in manufacturers’ catalogs. The types of chain described previously also exist in many special forms. Figure 2-29 shows various specialized types and standard types with attachments that are available. Attachments for Engineering Steel Chain Since engineering steel chains are used in such a wide variety of applications, many different attachments are available. Figure 2-30 illustrates some of the more common attachments available for engineering steel chains for use in conveying and elevating. These attachments are better suited




35

FIGURE 2-28 Open-barrel steel pintle chain.

for straight sidebar chain, but some can be adapted for offset construction. Many other types of attachments are made to meet specific requirements.

FLAT-TOP CHAIN The flat-top chains covered in this handbook are made of simple, two-piece assembled links with a pitch of 11/2 in. Each link consists of a formed steel, or molded plastic, hinged top plate connected to adjacent top plates with a pin, as shown in Figure 1-27 (steel) and Figure 1-28 (plastic). The pins normally are held in place either by interference fits or by knurls. Top plates are commonly available in widths of from 2 1/4 in. to 12 in., depending on the particular type and model of chain. Standard Flat-Top Chain ASME standard B29.17 covers only three basic models of straight-running flat-top chain. A basic steel chain, a normal-duty plastic chain, and a heavy-duty plastic chain. The standard lists limiting dimensions that ensure the chains are interchangeable. The standard requires that the standard chain from one manufacturer will run on the standard sprockets from another manufacturer, and that a standard chain from one manufacturer will interconnect with the standard chain from another manufacturer. The pitch of all the standard chains is 11/2 inches. The standard steel chains may be made of either corrosion-resistant or carbon steel. Top-plate width is not covered by the standard. The designer must consult manufacturers’ catalogs for such information. Standard flat-top chains are exclusively intended for use on conveyors. They are widely used in straight-running flat-top conveyors in the beverage bottling and canning, food processing, and product packaging industries. Standard Flat-Top Chain Number Designations The numbers for standard flat-top chains consist of two digits, a single letter, and two more digits. The first two digits signify the pitch of the chain in 1/16 of an inch. The letter designates the material from which the chain is made: A, austenitic stainless steel link and pin; B, carbon or low alloy steel link and pin; P, plastic link. The last two digits signify the width of the hinge in 1/16 of an inch. The standard number does not cover top plate width. For example, the number 24C26



36


FIGURE 2-29 Other types of engineering steel chains.

designates a carbon steel, straight-running flat-top chain with a pitch of 1 1/2 , inches, and a hinge width of 1 inches. A similar chain made of stainless steel would have the number 24A26. Even though there is a standard number designation, the listed standard chains are also widely known by accepted industry numbers. Many manufacturer’s catalogs designate the standard flattop chains as follows. The number 815 often is used for standard number 24C26 (or 24A26) steel, straight-running flat-top chain. The number 820 often is used for standard number 24P26 plastic, normal-duty, straight-running flat-top chain. The number 821 often is used for standard number 24P86 plastic, heavy-duty, straight-running flat-top chain. Nonstandard Flat-Top Chain There are a great many nonstandard flat-top chains available for just about any special conveying need one can imagine. There are heavy-duty steel flat-top chains to carry larger loads than




37

FIGURE 2-30 Typical chain attachments.

standard chains. There are side-flexing flat-top chains, in both steel and plastic, to convey products around corners without the need for turntables. There are high-friction flat-top chains to carry products up steep inclines. There are gripper chains to carry products vertically. And there are low backline pressure chains for use in conveyors where the product is frequently stopped. There are also flat-top chains that consist of special #40 or #60 base roller chains with top plates that snap onto those chains. Limited space prohibits covering any but the most common flat-top chains in this handbook. The best known, and possibly the most commonly used, of the nonstandard flat-top chains are the side-flexing flat-top chains. Obstructions and nonlinear process flows do not always allow the use of straight-running conveyors. So side-flexing flat-top chains were developed. The side-flexing flat-top chains considered in this book are similar to the standard straightrunning flat-top chains, but they have specially designed joints that permit them to run around a curve. Side-flexing flat-top chains also need a bevel or a tab on either side of the hinge to prevent the chain from lifting while it goes around a turn. A plastic side-flexing flat-top chain with tabs is shown in Figure 1-29.



38


The number 881 is often used to identify steel side-flexing flat-top chain. The number 880 is often used to identify plastic, normal-duty, side-flexing flat-top chain. And the number 882 is often used for plastic, heavy-duty, side-flexing flat-top chain. Side-flexing flat-top chains are widely used in conveyors in the beverage bottling and canning, food processing, and product packaging industries.

THE ADVANTAGES OF CHAINS IN APPLICATIONS Earlier in this chapter, the uses of the chains covered in this book were classified, in theory at least, into those transmitting power or force and those handling materials. Chains were classified as roller, silent, engineering steel, and flat-top. There are excellent reasons why there are many kinds of chains to perform so many varied functions. When we review the functions of the chains covered here, we find that chains have some general advantages over other equipment intended to do the same functions. • • • • • • • •

Chains have controlled flexibility in only one plane. Chains have a positive action over sprockets; no slippage takes place. Chains can carry very heavy loads with little stretch. The efficiency of a chain joint passing around a sprocket approaches 100% because of the large internal mechanical advantages of links in flexure. Chains provide extended wear life because flexure takes place between bearing surfaces with high hardness designed specifically to resist wear. Chains can be operated satisfactorily in adverse environments, such as under high temperatures or where they are subject to moisture or foreign materials. Chains can be manufactured from special steels to resist specific environments. Chains have an unlimited shelf life; they do not deteriorate with age or with sun, oil, or grease.

Now let us consider the advantages of chains from the standpoint of drives. Chains have certain advantages, in addition to those just named, over other types of power transmission equipment.

ADVANTAGES OF ROLLER CHAINS IN DRIVES • • • • • • • • •

Roller chains can bridge relatively large gaps between shafts. Roller chain drives are often simpler, less costly, and more practical than gear drives. Roller chain drives normally are more compact than belt drives, and they can be nearly as compact as gear drives. Roller chains need a smaller arc of contact than belt drives because they do not depend on friction as belts do. Roller chains are easier and less costly to install than gears or belts. Roller chains do not require as precise alignment as gear or belt drives. Roller chain drives permit easier and less costly changes in center distance or speed ratios. Roller chains require less slack side tension and thereby reduce the load on the shaft and bearings. Roller chain elongation due to normal wear is a slow process when the chain is adequately lubricated, and does not affect satisfactory operation of the drive. Therefore, adjustments are needed less frequently in a roller chain drive than in a belt drive.




39

ADVANTAGES OF SILENT CHAIN DRIVES Silent chain has all of the advantages of roller chain listed above, except for one. Silent chain drives require nearly as precise alignment as gear drives to obtain peak performance and service life. In addition, • • • •

Silent chains are less affected by chordal action and joint friction than other chains; silent chains engage sprockets with reduced vibration, noise, and frictional losses. Silent chain can operate at loads and speeds that often exceed the capability of belts and other types of chain. Silent chain drives are quieter and smoother than roller chain drives, and in some cases are quieter than gear drives. Silent chain drives are more compact than gear drives when the shafts must turn in the same direction.

ADVANTAGES OF ENGINEERING STEEL CHAIN FOR DRIVES Engineering steel chain has all of the advantages of roller chain listed above, except that engineering steel chain drives tend to be somewhat noisier than roller chain drives. That is because of the additional clearances built into engineering steel chains and the pitch-line clearance usually provided in sprockets for engineering steel chain drives. However, • • •

Engineering steel chains can span extremely long gaps between shafts. Engineering steel chains can absorb very large shock loads because of their toughness and elasticity. Engineering steel chains can run in very dirty conditions without serious damage. That is because the added clearance built into these chains provides ready egress of dirt and debris.

ADVANTAGES OF CHAINS ON CONVEYORS AND BUCKET ELEVATORS • • • • • • • • •

Chain conveyors often are simpler and less expensive than belt conveyors on short to medium shaft center distances. Chain conveyors will generally operate at much slower speeds than belt conveyors. Chain conveyors are most easily adapted for assembly and processing applications. Chain conveyors permit indexing of parts and packages. Chain conveyors can be designed for storage and holding stations, to permit intermittent movement of materials to processing stations as required. Chain conveyors can be designed to handle more abrasive materials at higher temperatures than belt conveyors. Chain conveyors can be designed to accommodate higher impact and shock loads at loading stations than belt conveyors. Chain conveyors are easier and less costly to alter when requirements change. Chain conveyors elongate slowly due to normal wear, and wear elongation does not affect satisfactory operation, as does stretch in a belt conveyor. Thus, a chain conveyor will generally require fewer adjustments than a belt conveyor.



40


ADVANTAGES OF USING CHAIN IN ELEVATOR MATERIALS HANDLING Chain elevators are especially advantageous because: • • • •

Chain elevators can handle many special types of materials, such as material that is very hot or of large bulk. Chain elevators are not very sensitive to packing of material between elevator buckets and the chain; it can be a much greater problem in a belt-type elevator. Large chain elevators for handling heavy degradable materials can be operated at speeds that are too slow for comparable belt elevators. Initial installation, replacement, and maintenance costs of chain elevators are in many instances less than those for belt elevators.



Design Considerations, 3 Chain Construction, and Components BASIC CHAIN FUNCTIONS For the purposes of this book, chains have four basic functions: • • • •

To To To To

transmit power. convey objects or materials. convert rotary motion to linear motion, or linear motion to rotary motion. synchronize or to time motion.

These seem very simple, and they are, but the details must be handled in a much different way for each class of chain.

GENERAL CHAIN DESIGN CONSIDERATIONS This section reviews the general considerations for the design of roller, silent, engineering steel, and flat-top chains. The considerations differ as the functions of each type of chain differ. The specific design considerations for each class of chain will be covered later. The following discussions are very brief, as a thorough discussion of these factors is beyond the scope of this book. This chapter is only intended to acquaint the reader with the factors that chain designers must consider. It does not try to teach the reader how to design chains.

TENSILE LOAD Nominal Tensile Load The main consideration for all types of chain is the nominal tensile load that is required to perform the basic function. The nominal tensile load generally fluctuates in a regular cycle. For example, the chain tension from the nominal load in a chain drive increases as the chain moves around the driven sprocket. The tension remains basically constant at a high level as the chain runs through the tight strand. Tension then decreases as the chain moves around the driver sprocket. It then remains basically constant at a low level as it runs through the slack strand. This cycle then repeats again and again. Figure 3-1 roughly shows how the tension varies in a chain that is 100 pitches long as it runs around 20-tooth sprockets. This nominal tensile load is the basic load considered in almost all chain ratings. Shock Load Shock loads are caused by the characteristics of the power source and the driven machinery. They occur repeatedly in a regular cycle, usually one or more times in each shaft revolution. They usually must be added to the nominal tensile load. Service factors are used to account for commonly known shock loads in most chain drives and conveyors.

41



42


120

Relative Nominal T ension, %

100

80

60

40

20

0 0

20

40

60

80

100

120

No. of Pitches

FIGURE 3-1 How the tension varies in a chain that is 100 pitches long as it runs around 20-tooth sprockets.

Inertia Load As the term is used here, inertia loads are different from shock loads. Inertia loads are the occasional loads imposed on the chain by unusual, and often unexpected, events. They may come from starting a heavily loaded conveyor or a drive with a large flywheel. Or they may be caused by a sudden momentary jam in the driven machine or conveyor. The drive or conveyor designer should calculate expected starting loads and be sure that they are never more than the yield strength of the chain. Centrifugal Tension In high-speed drives, centrifugal force is generated as the chain travels around the sprockets. Centrifugal force also may be generated by the chain’s travel over a curved path between sprockets. The tensile load from centrifugal force may have to be added to the nominal tension when appropriate. Centrifugal tension is one of the factors that is used in setting chain drive ratings at high speeds. Catenary Tension The weight of that portion of the chain that hangs in a catenary generates additional tensile loads in the chain. The tensile load from the catenary tension must also be added to the nominal tension when appropriate. Catenary tension is usually a minor consideration in drives, but it may be a major consideration in conveyors. Chordal Action As the chain wraps a sprocket, it effectively forms a regular polygon. That causes the chain strand to rise and fall each time a joint engages a sprocket tooth. This motion is called chordal action, and the effect is illustrated in Figure 3-2. Chordal action also causes the chain speed to increase and decrease each time a joint engages a sprocket tooth. Of course, the tension in the chain changes slightly every time the chain speed changes. This varying tensile load from chordal action must be added to the nominal tension along with the other fluctuating tensile loads mentioned above. The



Chain Design Considerations, Construction, and Components

43

FIGURE 3-2 Chordal action.

tension from chordal action is one of the factors that is used in setting chain drive ratings at high speeds. Vibration Chain vibration can cause very large increases in chain tensile loading if the vibration occurs at or near the natural frequency of the chain. The added tension from vibration can sometimes be as large as the nominal tensile load. Here again, any varying tensile load from vibration will be added to the nominal tensile load. The natural frequency of the system should be calculated when necessary, as suggested in later chapters. Then, if a possible problem with vibration is found, the system should be redesigned to avoid the natural frequency.

CHAIN STRENGTH General A chain used in a drive or conveyor may be subjected to some, or all, of the tensile loads that were described earlier. So the chain must have adequate tensile strength properties to withstand the wide range of tensile loads that may be imposed on it. The main strength properties that a chain may need are discussed below. Ultimate Tensile Strength The ultimate tensile strength of a chain is the highest load that the chain can withstand in a single application before breaking. All chains must have a certain minimum ultimate tensile strength to be of any use. Yield strength and fatigue strength are some fraction of the ultimate tensile strength. But neither fatigue nor yield strength is a fixed fraction of ultimate tensile strength. The main value of a specification for minimum ultimate tensile strength is to indicate that all of the parts have been produced and processed correctly, and to ensure that the chain has been assembled properly. The ultimate tensile strength should not be used to select a chain for a drive or a conveyor. The maximum allowable working load of a particular chain is the term that should be used for



44


selecting chains. That term may be based on the fatigue limit or bearing pressures, and those values are usually not a fixed ratio of the ultimate tensile strength. Yield Strength The yield strength of a chain is the maximum load from which the chain will return to its original state (length). For many standard chains, the yield strength is approximately 40% to 60% of the minimum ultimate tensile strength. Loading the chain beyond its yield strength, even once, will permanently elongate the chain. Then the chain will no longer fit the sprocket properly. Loading the chain beyond the yield strength may also weaken the chain by reducing the press fits that hold the chain together. Figure 3-3 shows a typical load elongation diagram for chain. The figure clearly shows that the yield point for the particular chain shown is at 60% of the ultimate tensile strength. That is not true for all chains.

FIGURE 3-3 A typical load elongation diagram.




45

Fatigue Strength The fatigue strength of a chain is the fluctuating load that the chain will withstand for a given number of cycles. A more complete explanation of the fatigue strength of roller chains may be found in the ASME B29.26 standard, Fatigue Testing Power Transmission Roller Chain. A typical graph of chain fatigue strength is shown in Figure 3-4. This is also called an F-N chart. The vertical axis represents the maximum value of the fluctuating load; the horizontal axis represents the number of cycles that the chain will withstand that load before it fails. The graph shows that as the fluctuating load decreases, the number of cycles before failure increases. When considering fatigue strength, one area of great interest is the fatigue strength between 10,000 cycles and 1,000,000 cycles. This is called the finite-life region and loads on chains sometimes do reach into this area. Fatigue Limit The fatigue limit of a chain is defined as the fluctuating load at which the chain will withstand 10,000,000 cycles with only a 0.135% probability of failure. Figure 3-4 shows that the F-N curve begins to “flatten out” after about 1,000,000 cycles, and the curve becomes almost horizontal at 10,000,000 cycles. Because of this, the fatigue limit is the approximate load below which the chain should last an indefinite (extremely long) time without failing. The fatigue limit is more than just a theoretical number. It is the basis for the low-speed part of the American Chain Association (ACA) power ratings for roller, engineering steel, and silent chains. Those ratings are given in chapters 5–7 of this book. Published values for maximum allowable working load are usually equal to the fatigue limit. The fatigue limit of a chain is not directly related to the ultimate tensile strength of that chain. The fatigue limit of a chain cannot be obtained by multiplying the ultimate tensile strength by some factor. The fatigue limit can only be determined by extensive testing.

FIGURE 3-4 A typical graph of chain fatigue strength. This is also called an F-N chart.



46


Some manufacturers state that the maximum allowable working load for their chains is a constant fraction of their published ultimate tensile strength. That does not mean that what was said in the preceding paragraphs is wrong. It just means that those manufacturers state the maximum allowable working load in a different way, and that those manufacturers take care to ensure that their published working loads are maintained.

WEAR General For this section, wear is defined as the removal of material by mechanical action; that action is usually rubbing between two surfaces. Wear can be minimized, but it cannot be eliminated. Joint Wear Joint wear is wear between a pin and its mating surface that causes the chain to get longer. The mating surface may be a bushing, a link plate, or an integral link of the chain (as in block and bar or flat-top chains). It could even be another pin in silent chain. Joint wear probably is the main concern in almost all chain design. That is because chain wear elongation is often the reason a chain has to be replaced. As chain joint wear occurs, the resulting elongation is different for straight sidebar chain than it is for offset sidebar chain. Figure 3-5 illustrates this difference. In straight sidebar chain, the effective pitch (as the sprocket “sees” it) of the bushing stays about the same as the chain wears. All of the wear elongation appears in the pin link. In Figure 3-5, the pitch over the bushing link (A2) is the same as the unworn link (A1). But the pitch over the pin link (B2) is longer than the unworn link (B1). However, for the offset sidebar chain, elongation is uniform from link to link (A3 is longer than A1 and A3 = B3). The pitch across two links (A2 + B2 and A3 + B3) shows that the resultant wear over two joints is the same for either type of chain. Roller and Sprocket Wear Roller and sprocket wear is a dual concern. In most cases, wear of the outside diameter of the roller is a minor concern. The roller turns against the sprocket only briefly, and it presents a slightly different surface each time it contacts the sprocket. But wear of the sprocket tooth, especially on the smaller sprocket, is often a great concern. Wear of the tooth working face alters the way the chain engages the sprocket. Worn sprocket teeth can cause erratic action and large shock loads. Roller and Bushing Wear Wear between the roller and bushing is a concern in conveyor chains that carry the material and roll on a track (Figure 3-6). As this kind of wear progresses, it can wear through the bushing, seriously weakening the chain, and allow the chain to break. If only the bushing breaks, the chain may drop the load on the deck and no longer convey the material. Link Plate and Track Wear Wear between link plates and a track is a very important consideration in conveyor chains that carry the material and slide on a track (Figure 3-7). As this kind of wear progresses, it wears material off the edges of the link plates and weakens the chain. If enough material is worn away, the chain can break and stop the conveyor. It can also damage the material being conveyed or the conveyor itself.




47

FIGURE 3-5 Elongation is different for straight sidebar chain than it is for offset sidebar chain.

In this type of wear, material is also worn off the track. The wear is usually not smooth or uniform. As the track is worn, it can cause surges, undesirable vibration, and momentary jams in the conveyor. Link Plate and Sprocket Wear Link plate and sprocket wear is a consideration in designing silent chains. The link plates engage the sprockets instead of rollers, bushings, or full links. Excessive wear of the mating surfaces of silent chain link plates and sprocket teeth can cause erratic action and increase noise and vibration.



48


FIGURE 3-6 Wear between the roller and bushing.

FIGURE 3-7 Wear between link plates and a track.

Link Plate and Sheave Wear Wear between the link plate contours and the sheaves is a major consideration in designing leaf and lift chains. As a leaf chain or lift chain runs over a sheave, the ends of the link plates rub against the outside diameter of the sheave. That wears material off the link plate edges and weakens the chain. The rubbing action also may harden the link plate edges and make them brittle. This gives the chain very poor resistance to shock loads. Sheave wear is also a concern in designing leaf chains. As the sheave wears, small hollows may be worn in the sheave surface where each joint contacts the sheave. This can cause erratic action if the wear progresses far enough. Chain Joint Galling Joint galling is a serious consideration when chains, mainly roller chains, are used in drives that run at high speeds with high loads. Joint galling occurs when the load or speed exceeds the limits in the power ratings and the lubrication system cannot carry heat away fast enough. Galling is a factor that is included in setting chain ratings at high speeds and/or high loads. Galling is also called scuffing or scoring. Some experts say that galling is a very severe type of wear. Others say that galling is welding, followed by an immediate breaking away of the surfaces. It makes little difference to the chain designer which one is correct. In some cases, it appears that some kind of mechanical action deeply grooves the bearing surfaces. In other cases, it appears that large amounts of heat are generated and severely damage the bearing surfaces. Roller Impact When a sprocket tooth picks up a chain roller, there is an impact, and the magnitude of the impact increases with speed and tension. It also increases with a reduced number of teeth on the sprocket. At some point the roller will break from impact fatigue. The chain designer must ensure that chain rollers have enough impact resistance to meet the ratings for the subject chain.




49

LUBRICATION Required Lubrication Power ratings for drive chains are normally set so that the chain will transmit the rated power only when a specified type and amount of lubrication is provided. The chain must then have the characteristics that will permit it to perform to the ratings. It is very important to properly lubricate a chain drive or conveyor. Chains usually operate in air. So if lubrication is poor or absent, the wear type not only changes from lubricated wear to dry wear, but the humidity and oxygen in the air causes the lubricated wear to change to corrosion wear. Then corrosion combines with wear to cause very rapid chain elongation. Available Lubrication The load and speed ratings for conveyor chains may be set based on available lubrication. In this case, the chain must have the characteristics to give acceptable service with the type of lubrication that is available.

ENVIRONMENT General Most drive chains are designed to operate under clean, well-lubricated conditions. Ideally the drive is enclosed in a casing that retains the lubricant and excludes dirt, water, and other things that might harm the drive. The oil supply may also be cooled to keep the operating temperature from getting too high. Many times the actual operating conditions fall far short of the ideal. That is especially true for conveyor chain that cannot be enclosed. The chain designer must consider conditions that may be hostile to the chain. Abrasive Conditions Conveyor chains often have to work in abrasive conditions. It is not unusual for conveyor chains to be used in such highly abrasive materials as sand, gravel, stone, and slag. It is normal for conveyor chains to be exposed to the normal dirt and contamination that is present when the chain is not enclosed. Many slow-speed drives also are exposed to dirt and contamination when they are not enclosed. Corrosive Conditions Some chain conveyors, and some unenclosed chain drives, must work in corrosive conditions. Chains made from conventional materials are expected to operate in mildly corrosive conditions. The most common corrosive condition is water being splashed on the chain. Other chains must operate in very corrosive conditions. Many such cases may be found in fertilizer, chemical, paper, and food processing plants. Chains that are made to work in these conditions normally are made from special materials, and some design factors may be modified. High or Low Temperatures Most standard chains are designed to operate in a temperature range from 32°F to 150°F. Sometimes chains must work in temperatures between 150°F and 350°F. Chains made from conventional materials usually are acceptable, but special lubricants may be needed. This is also



50


true for chains operating in temperatures between 32°F and -40°F. When the chain must work in temperatures between 350°F and 500°F, extra clearances as well as special lubricants normally are needed. Special materials are often needed in chains that are used in temperatures above 500°F or below -40°F.

ROLLER CHAIN DESIGN CONSIDERATIONS GENERAL Roller chains are used in a wide variety of applications, but most roller chain is used in drives. The shaft speeds of the drives range from less than 50 rpm to nearly 10,000 rpm, and the amount of power transmitted ranges from a fraction of a horsepower to more than 1000 hp. The main design considerations for a roller chain to be used on a drive are the various tensile loads, certain types of wear, roller and bushing impact, and galling.

ROLLER CHAIN PROPORTIONS The major dimensions of standard roller chains are approximately proportional to the chain pitch. These proportions were derived from detailed engineering studies and much experience. These proportions give an excellent balance of properties needed for a roller chain to perform well in a wide variety of applications. The approximate proportions of standard roller chains, conforming to ASME B29.1, are listed below. • • • • • •

Roller width ≈ 5/8 of the pitch. Chain (roller) width ≈ 5/8 of the pitch. Pin diameter ≈ 5/16 of the pitch. Link plate thickness ≈ 1/8 of the pitch. Maximum roller link plate height ≈ 0.95 × pitch. Maximum pin link plate height ≈ 0.82 × pitch.

TENSILE LOADS

AND

REQUIRED STRENGTH

General A roller chain drive or conveyor may be subjected to all of the tensile loads that were listed earlier, thus the roller chain must have several tensile strength properties to withstand the wide range of tensile loads that may be imposed on it. The main strength properties that a roller chain must have are discussed below. Ultimate Tensile Strength Ultimate tensile strength is not a major consideration in designing roller chains. It is only important because yield strength and fatigue strength depend on ultimate tensile strength. Minimum ultimate tensile strength (MUTS) is a requirement in the ASME standards that govern roller chains. A well-made roller chain almost always meets the standard. Yield Strength Yield strength is an important consideration in designing roller chains. For standard roller chains, conforming to ASME B29.1, the yield strength is about 60% of the MUTS. Figure 3-8 is a diagram of how a standard roller chain elongates as a tensile load is applied.




51

FIGURE 3-8 A diagram of how a standard roller chain elongates as a tensile load is applied.

Fatigue Strength Fatigue strength in the finite-life range is a very important consideration in designing roller chains. Loads may sometimes exceed the fatigue limit in some very-high-performance drives. The chain must have adequate fatigue strength to endure these occasional loads if the chain is intended to be used in such high-performance drives. Fatigue Limit The fatigue limit is a critical consideration in designing roller chains. The roller chain must have a fatigue limit high enough to perform to its rating. Figure 3-4 can be simplified into a fatigue rating graph for standard roller chain; such a graph is shown in Figure 3-9. A roller chain manufacturer’s engineers can use graphs similar to this to estimate the fatigue performance of a roller chain. A heavy dashed line is plotted at 60% of MUTS on the graph in Figure 3-9. This represents the yield strength of the chain.



52


FIGURE 3-9 Typical fatigue rating curve for roller chain.

WEAR General Wear is a most important consideration in designing roller chains. Roller chains used in drives are normally most affected by joint wear and roller and sprocket wear. Roller chains used in conveyors are most affected by joint wear and either roller and bushing wear or link plate and track wear. More information that is specific to the wear of roller chains follows. Chain Joint Wear Chain joint wear may be the most important factor to consider when designing a roller chain. As discussed earlier, as the joints wear, roller chains get longer. Sprockets for roller chain are designed to accept up to 3% elongation (1.5% for double-pitch chains) from wear. When the chain elongates beyond that point it no longer fits the sprockets and the system will not operate properly. Figure 4-28b shows how a worn roller chain fits a sprocket. A plot of several roller chain wear tests, all using the specified type of lubrication, is shown in Figure 3-10. Two important concepts can be derived from Figure 3-10. One is that wear per pitch in roller chains progresses in rough proportion to the number of cycles to the 1/3 power. The other is that there is an extremely large natural variation in roller chain wear rates. Many engineers are surprised to see so much variation in wear rates. But the results of these tests agree well with those of wear tests done on many different types of bearings using many different materials. Testing shows that there is a very large amount of variation in all types of wear. Roller and Sprocket Wear As explained earlier, roller wear usually is not a major concern. However, wear of the teeth on a small sprocket may be a very important concern because badly worn sprocket teeth can impose large shock loads on the chain. This is explained in more detail in chapter 15, about chain drive and conveyor maintenance.




53

FIGURE 3-10 A plot of several roller chain wear tests, all using the specified type of lubrication.

Other Types of Wear Roller and bushing wear, and link plate and track wear were discussed earlier. More discussion that is specific to roller chain is not needed. Chain Joint Galling Chain joint galling is a major consideration in designing drive roller chains only if the chains are intended to be used on high-speed, high-performance drives. Roller Impact Roller impact is an important consideration in designing drive roller chains. Other Considerations Lubrication and environmental considerations are not discussed here. They are either specified or excluded in the ratings. However, ACA roller chain manufacturers do make chains that are designed to operate with minimal or no lubrication. They also make chains that are designed to operate in adverse environments.

ROLLER CHAIN CONSTRUCTION

AND

COMPONENTS

Assembled Roller Chain Single-Strand Roller Chain Single-strand roller chain is an assembly of alternating pin links and roller links, as shown in Figure 3-11. The pins are free to articulate in the bushings and the links are arranged in such a way that the rollers can engage the teeth of a sprocket and transmit motion and force. An exploded view of pin links and roller links is shown in Figure 3-12.



54


FIGURE 3-11 Single-strand roller chain is an assembly of alternating pin links and roller links.

FIGURE 3-12 An exploded view of pin links and roller links.




55

Pin Links

The pin links are subassemblies of two pins that are press fitted into the holes of two pin link plates. The press fit between the pin and the pin link plates prevents the pin from rotating. The ends of the pins may be either riveted or cottered on the ends to prevent the pin link plates from being forced off the ends of the pins. The two types of pin links are shown in Figure 3-13. Roller Links

The roller links are subassemblies of two bushings press fitted into the holes of two roller link plates with two rollers installed on the outside of the bushings. The press fits prevent the bushings from rotating in the link plate holes when the chain joint articulates. The rollers are free to turn on the outside of the bushings. An assembled roller link is shown in Figure 3-14. Multiple-Strand Roller Chain Multiple-strand roller chain is simply two or more strands of chain assembled side by side on common pins. A typical double-strand roller chain is shown in Figure 3-15. The roller links in multiple-strand roller chain are identical to those in single strand. Of course, the pin links have longer pins to accommodate the multiple strands in the chain.

FIGURE 3-13 The two types of pin links.

FIGURE 3-14 An assembled roller link.



56


FIGURE 3-15 A typical double-strand roller chain.

The link plates between strands of multiple-strand roller chain are called center plates. They often appear to be identical to the pin link plates, but they almost always are a slip fit on the pins. In a few cases, the center plates are press fitted onto the pins. Multiple-strand chains with press fit center plates generally have higher fatigue strengths than chains with slip fit center plates. But chains with press fit center plates must be furnished to a specified length by the manufacturer. The press fit center plates are almost impossible to disassemble in the field. Double-Pitch Roller Chain Standard double-pitch roller chain uses the same pins and bushings as standard single-pitch roller chain, but the pitch of the link plates is twice that of single-pitch chain. The link plates for doublepitch power transmission chain have a figure-eight shape. This is so they can clear the hub of small sprockets. The rollers for these chains are the same as those for standard single-pitch chains. Doublepitch power transmission chain is shown in Figure 2-9. The link plates for double-pitch conveyor chains have straight edges, providing a continuous surface on which the chain may slide in a conveyor. The rollers for the small-roller series are the same size as for standard single-pitch chains. The rollers for the large-roller series are about twice the diameter of those for the small-roller series. The diameter of the large rollers is larger than the link plate height so that the chain can roll on them when used in a conveyor. Double-pitch conveyor chains are shown in Figures 2-11 through 2-13. Connecting Links and Offset Links Connecting Links If the chain length is an even number of pitches, a connecting link may be used to connect the two ends of the chain together on the drive or conveyor. The partially assembled connecting link consists of two connecting pins press fitted and riveted in one link plate. The holes in the cover plate are either a slip fit or a light press fit on the ends of the connecting pins. The cover plate is then secured in place by cotter pins or a spring clip. The two most common types of connecting links are shown in Figure 3-16. The cover plate may be retained with something other than a cotter pin or spring clip. Figure 3-17 shows a number of different retaining devices. Offset Links If the chain length is an odd number of pitches, an offset link may be used at one end of the chain. Then a connecting link may be used to connect the two ends of the chain together and make the chain endless. An offset link is a combined pin link and roller link (Figure 3-18). It consists of two offset link plates, one bushing with a roller assembled at one end, and one pin at the other end. The pin is slip fit in the offset link plates. It has a head on one end and a flat on the other to prevent rotation, and it is held in place by a cotter pin. Offset links generally do not meet the ACA power ratings for standard roller chains. The offset bend, the slip fit pin, and the D-shaped hole in one offset link plate greatly reduce the capacity of an offset link.




57

FIGURE 3-16 The two most common types of connecting links for roller chain.

FIGURE 3-17 Different retaining devices.

Offset Sections An offset section is an assembly of a standard roller link and an offset link that is connected by a riveted pin (Figure 3-19). The pin is press fit into the offset link plates. This provides much greater operating strength than a single-pitch offset link. Because the pin is press fit in the offset link plates, two standard connecting links must be used to connect the offset section to the chain and make it endless.



58


FIGURE 3-18 An offset link is a combined pin link and roller link.

FIGURE 3-19 An offset section is an assembly of a standard roller link and an offset link that is connected by a riveted pin.

FIGURE 3-20 A section view of a loaded roller chain.

ROLLER CHAIN PARTS General Figure 3-20 is a section view of a loaded roller chain. The figure shows how the parts in the chain react when a load is put on the chain. The bending of the pins and pin link plates is exaggerated to emphasize the effects of loading. Some parts must perform two or more functions at the same time, and some of those functions may conflict with each other. For example, some parts must have high surface hardness to resist wear, but they must also have high ductility to withstand considerable bending. The chain designer




59

is faced with a great challenge in deciding how to best serve all of the requirements. A discussion of the functions and design of individual roller chain parts follows. Rollers The load from transmitting power or conveying materials is first transferred from the working faces of the sprocket to the outside of the chain rollers, or vice versa. There also may be a large impact force when the sprocket teeth pick up rollers from the tight span of the chain. Rollers must be strong enough to withstand these large forces without distorting or breaking, and rollers must be hard enough to resist wear from engaging the sprocket teeth. In addition to being strong and hard enough, rollers must be ductile enough to absorb large impact forces without cracking or breaking. Large-diameter conveyor rollers are not subjected to large impact forces because conveyor chains run at much slower speeds than drive chains. Thus large-diameter conveyor rollers may be somewhat harder, with less impact resistance, than small-diameter rollers for drive chains. Bushings All of the operating forces are next transferred from the inside of the rollers to the outside of the bushings. Any impact forces that were not absorbed by the rollers are transferred to the bushings. The bushings then transfer those forces to the roller link plates and pins. Bushings must have enough strength and rigidity to transfer the force applied near the middle of the bushings (from the roller) to the roller link plates that are assembled onto each end of the bushings. The bushings are assembled into the holes of the roller link plate with a press fit. Thus the bushings must have enough strength to withstand the press fit stresses without cracking. Bushings transfer the operating forces to the pins, and they have to do this while the pins are turning inside the bushings. Bushings need to have high surface hardness to resist wear when the joint flexes, but bushings must not be so hard that they are brittle. Pins The operating forces are next transferred from the inside of the bushings to the pins. The pins then transfer those forces to the pin link plates, and they must do so while the pins are turning in the bushings. Pins act as both beams and bearings in a chain. Pins need enough strength to transfer the forces to the pin link plates without deforming or breaking. Pins also need high surface hardness to resist wear when the joint flexes. But they also must have enough ductility that they can withstand considerable bending without cracking or breaking. Finally, the pin ends must be ductile enough that they do not crack or spall when the pin ends are staked, spun, or riveted. Pin Link Plates Tensile forces are applied to the pin link plates by pins that are assembled through holes in the pin link plates. The holes in the link plates are significant stress risers. Pin link plates are primarily tension members. They also are subjected to substantial bending and stress forces around the holes. Pin link plates must have enough strength to withstand the tensile forces without deforming or breaking, and they must have enough ductility to withstand substantial bending and to resist fatigue. The holes must be made with special processing to resist fatigue.



60


Roller Link Plates Tensile forces are applied to the roller link plates by bushings that are assembled into the holes in the roller link plates. The holes in the roller link plates are significant stress risers, and the stress concentration is even more severe because the bushing is not assembled all the way through the link plate. Roller link plates are primarily tension members, but they are also subjected to bending and stress forces around the holes. Roller link plates must have enough strength to withstand the tensile forces without deforming or breaking, and they must have enough ductility to withstand some bending and to resist fatigue. The holes must be made with much special processing to resist fatigue. Other Roller Chain Parts A discussion of other roller chain parts, such as offset link plates, cotters, and spring clips is beyond the scope of this book.

LEAF CHAIN DESIGN CONSIDERATIONS GENERAL Leaf chains are used almost exclusively for lifting and counterbalancing. Tensions are very high, but speeds are slow. Loads may be less than 1000 lb. to more than 100,000 lb, but the chains work intermittently and speeds are seldom more than about 50 ft./min. The main considerations in designing leaf chains are tensile loads, joint wear, and link plate and sheave wear.

LEAF CHAIN PROPORTIONS The major dimensions of standard leaf chains are proportional to the chain pitch. Those proportions were derived from engineering studies and experience. The standard proportions give a good balance of properties needed for a leaf chain to lift large loads while giving acceptable wear life. The approximate proportions of the standard “BL” series of leaf chains, conforming to ASME B29.8, are maximum link plate height is 0.95 × pitch, and pin diameter is approximately 3/ × pitch. Link plate thickness is approximately equal to that of standard roller chain of the 8 next larger pitch. Until 1977, there was a lighter “AL” series of leaf chains listed in the standard, but they were dropped from the standard in 1977 because of declining use. The “AL” series of leaf chains will not be discussed here.

TENSILE LOADS

AND

REQUIRED STRENGTH

General The most common use for leaf chain is probably on lift trucks. A leaf chain used on a lift truck is normally under a substantial static load from the trucks lifting carriage. In addition, the chain must withstand the nominal working load from carrying the material. It must absorb shock loads from moving material over uneven surfaces, and it must withstand inertia loads from picking up the material to be moved. A graph of the tension in a typical leaf chain used on a lift truck might look something like the graph in Figure 3-21. The strength properties of a typical leaf chain are discussed below.




61

FIGURE 3-21 A graph of the tension in a typical leaf chain used on a lift truck.

Ultimate Tensile Strength Just as with roller chains, leaf chains must have a certain minimum ultimate tensile strength. That is because yield strength and fatigue strength are generally related to tensile strength. However, ultimate tensile strength should not be used for selecting leaf chains because it can mislead the user into overloading the chain. For example, the MUTS of a leaf chain with 4 × 4 lacing is about 30% higher than the MUTS of a leaf chain with 3 × 4 lacing. But the fatigue strength of leaf chains is related to the number of articulating link plates in the lacing. Leaf chains with 3 × 4 lacing have the same number of articulating link plates in each link as leaf chains with 4 × 4 lacing. So the fatigue strength of a leaf chain with 3 × 4 lacing is about the same as the fatigue strength of a chain with 4 × 4 lacing. Yield Strength Yield strength is a major consideration in designing leaf chains. Leaf chains must often lift very large loads, and the leaf chain needs to have a high enough yield strength that it will not permanently stretch when it lifts these large loads. Fatigue Strength Fatigue strength is also a major consideration in designing leaf chains. Leaf chains move at low speeds and accrue load cycles very slowly. Many leaf chains work in the finite-life range (between 10,000 and 1,000,000 cycles), so good fatigue strength in the finite-life range is very important. Fatigue Limit The fatigue limit is moderately important in designing leaf chains, mainly because fatigue strength in the finite-life range is related to the fatigue limit (see Figure 3-4). It is also because leaf chains accrue load cycles very slowly.



62


WEAR General Wear is a very important consideration in designing leaf chains. Leaf chains are mostly subjected to joint wear and link plate/sheave wear. Both of these types of wear reduce the strength of a leaf chain. A discussion of how these types of wear affect leaf chain follows. Joint Wear Joint wear is a very important consideration in designing leaf chain. When a leaf chain runs over sheaves, the joints articulate and material is worn off the outside diameter of the pins and the inside diameter of the holes in the articulating link plates. As that material is worn away, the chain not only gets longer, but the load-carrying sections of the pins and articulating link plates gets smaller. Link Plate and Sheave Wear For the reasons stated before, link plate wear, from running over sheaves, is a very important consideration in designing leaf chains. Sheave wear is normally not a major consideration in designing leaf chains.

LUBRICATION The lubrication that a leaf chain receives, or does not receive, is a serious concern in the design of leaf chains. Some leaf chains will receive little or no lubrication in service, and the designer must consider this.

ENVIRONMENT The environment in which a leaf chain works is a serious concern in the design of leaf chains. Most leaf chains are not protected in any way from the surrounding environment. Many leaf chains work outdoors in all kinds of weather.

LEAF CHAIN CONSTRUCTION

AND

COMPONENTS

Assembled Leaf Chain Leaf chain is an assembly of alternating sets of pin links and articulating links on pins that are free to articulate in the holes of the articulating links. A drawing of a typical leaf chain with 4 × 4 lacing is shown in Figure 3-22. The pin link plates normally are press fitted onto the ends of the pins in the chain. The center link plates are usually slip fitted on the pins. Figure 3-23 shows the components of a typical leaf chain. Leaf chains are intended to run over sheaves, so there is no provision for them to engage a sprocket. Clevis Pins A clevis pin is used to connect the end of a leaf chain to an outside clevis, as shown in Figure 3-24. The outside clevis gets its name because the outer tangs of the clevis fit outside of the articulating link plates of the chain. Connecting Links A connecting link is used to connect the end of a leaf chain to an inside clevis, as shown in Figure 3-25. The inside clevis gets its name because the outer tangs of the clevis fit inside of the chain.




63

FIGURE 3-22 Typical leaf chain with 4 × 4 lacing.

FIGURE 3-23 The components of a typical leaf chain.

The connecting link consists of two connecting pins press fitted into one pin link plate, the required number of center link plates, and a cover plate. Either cotters or a spring clip may be used to hold the cover plate in place. The cover plate should be an interference fit on the pins to give the connecting link about the same strength as the pin links in the chain. Clevises Space does not permit a discussion of clevises here. Some information on the design of clevises is contained in the ASME B29.8 standard, or the user can obtain more information on the design of clevises from the leaf chain manufacturer.

LEAF CHAIN PARTS General Leaf chain is a rather simple lacing of pins and link plates, as shown in Figure 8-8. Operating forces are transmitted from the clevis pin or connecting link to the articulating link plates. The articulating link plates then transfer those forces to the next pin, which transfers the forces to the pin link plates and center plates. And then the sequence repeats. Here again, some parts must perform two or more functions at the same time. For example, the articulating link plates need high hardness to resist wear, but they also need good ductility to withstand large shock loads. The designer must decide how to best serve these conflicting requirements. Pins The tension forces on a leaf chain subject the pins to mostly shear with some bending, and they do so while the pins turn in the articulating link plates. The pins act as both beams and bearings in a leaf chain. The pins need enough strength and ductility to transfer the load from the articulating link plates to the pin link plates and center plates without deforming or breaking.



64


FIGURE 3-24 Clevis pin connecting leaf chain to outside clevis.

The pins also need high enough surface hardness to resist wear when the joint articulates under heavy loads. Pin Link Plates The pin link plates in a leaf chain are mostly tension members, but they are also subjected to some bending. The holes in the pin link plates are significant stress risers that produce high stress concentrations around the holes. The pin link plates must be strong enough to withstand the tensile forces without deforming or breaking, and they must have enough ductility to withstand some bending and resist fatigue. The holes must be made with some special processing to resist fatigue. Center Link Plates The center link plates in a leaf chain are almost totally tension members. They are subjected to very little bending. The holes in the center link plates are significant stress risers that produce high stress concentrations around the holes. The center link plates must be strong enough to withstand




65

FIGURE 3-25 Connecting link connection leaf chain to inside clevis.

the tensile forces without deforming or breaking, and they must have enough ductility to resist fatigue. The holes must be made with some special processing to resist fatigue. Articulating Link Plates The articulating link plates in a leaf chain are almost totally tension members. They are subjected to very little bending. The holes in the articulating link plates are significant stress risers that produce high stress concentrations around the holes. In addition, the articulating link plates must transmit very high tensile forces while a pin turns in the holes of the link plate. The articulating link plates may be the most critical parts in a leaf chain. They must be strong enough to withstand the tensile forces without deforming or breaking, and they must have enough ductility to resist fatigue. The holes must be made with much special processing to resist fatigue.



66


Finally, the articulating link plates must be hard enough to resist wear when the pin turns in the holes under high loads.

SILENT CHAIN DESIGN CONSIDERATIONS GENERAL A few silent chains are used in conveyors, but most silent chains are used in high-speed drives. Shaft speeds of silent chain drives generally range from about 100 rpm to more than 10,000 rpm. The amount of power transmitted may be as little as a fraction of 1 hp or it may be more than 2,000 hp. The main design considerations for a silent chain to be used on a drive are the various tensile loads, joint wear, and link plate and sprocket wear. A consideration for silent chains with singlepin joints may be galling. Silent chain manufacturers have developed several joint designs to reduce chordal action and joint wear. These different designs can be classified into two broad categories. They may be single-pin or two-pin joints. Silent chains with two-pin joints are much more popular for power transmission. Silent chains with single-pin joints are more common for conveying and will be covered here briefly. Silent chains with two-pin joints will and be discussed more extensively.

SILENT CHAIN PROPORTIONS The size of the pins and the thickness of the link plates are roughly proportional to the pitch of silent chain, but these dimensions are not standardized as they are for roller chain.

TENSILE LOADS

AND

REQUIRED STRENGTH

General A silent chain with single-pin joints may be subjected to all of the tensile loads that were described earlier, but a silent chain with two-pin joints practically eliminates chordal action. A silent chain with two-pin joints usually runs very smoothly. It is not affected much by tensile loads from chordal action or the types of vibration that are related to chordal action. Silent chains must have certain tensile strength properties to withstand the wide range of tensile loads that may be imposed on them. The main strength properties that a silent chain must have are discussed below. Ultimate Tensile Strength Ultimate tensile strength is not a major consideration in the design of silent chains. Ultimate tensile strength is not to be used for selecting silent chains. There is no requirement for MUTS in ASME B29.2, and while silent chain manufacturers may have internal specifications for MUTS, they generally do not publish such values for their chains. Yield Strength Yield strength is not a major consideration in designing silent chains. Yield strength prevents the chain from permanently elongating when extremely heavy loads are applied to the chain. However, extremely heavy loads occur more often in low-speed drives, and silent chains are normally intended for high-speed drives.




67

Fatigue Strength Fatigue strength in the finite-life range is a moderately important consideration in designing silent chains. Loads occasionally exceed the fatigue limit in some very-high-performance drives. The chain must have adequate fatigue strength to endure these occasional loads only if the chain is to be used in such high-performance drives. Fatigue Limit The fatigue limit is a most important consideration in designing silent chains. The lower-speed part of the power ratings for silent chains is based on a minimum fatigue limit.

WEAR General Wear is a most important consideration in designing silent chains, just as it is in other types of chain. The two major concerns in designing silent chain are joint wear, and link plate and sprocket wear. Joint Wear Joint wear is a major consideration in designing silent chains. As the chain runs over the sprockets, the joints flex. Material is worn off the joint components and the chain gets longer. The chain then rides farther out on the sprocket teeth. This can increase noise and reduce efficiency. Link Plate and Sprocket Wear For the reasons stated earlier, link plate and sprocket wear are important considerations in designing silent chains.

OTHER CONSIDERATIONS Lubrication and environmental considerations are not discussed here. Silent chain drives generally run at higher speeds than other types of chain drives. Oil bath or oil stream lubrication is usually specified in the power ratings. These types of lubrication require a casing, which shields the drive from most contaminants. Normally there is also some impact between the link plates and sprocket teeth when the chain engages the sprocket. These impact forces are generally small and they are accounted for in the power ratings.

SILENT CHAIN CONSTRUCTION

AND

COMPONENTS

Assembled Silent Chain Silent chain consists of three main components. There are rows of tooth-shaped driving links that engage the sprocket teeth. These links are assembled on joint components that hold the rows of driving links together and allow the chain to flex when it runs over the sprockets. There may be guide links that maintain tracking on the sprockets. The guide links may be assembled on the sides or in the middle of the chain. Typical silent chains with side guides and center guides are shown in Figure 3-26 and Figure 3-27. Driving links can be added to each row, which increases the chain’s width and capacity. Joint designs can be classified into two broad categories: single-pin and two-pin. The singlepin joint usually uses a round or oval pin. The round pins may articulate in hardened bushings,



68


FIGURE 3-26 Typical silent chain with side guides.

FIGURE 3-27 Typical silent chain with center guide.

FIGURE 3-28 Silent chain with single-pin joints.

FIGURE 3-29 A typical silent chain with two-pin joints.

while the oval pins may rock directly on the surfaces of the holes in the driving link plates. A silent chain with single-pin joints is shown in Figure 3-28. Chains with single-pin joints generally are simple to connect and resist joint fouling well. The two-pin joint normally uses two pins with convex surfaces. Those surfaces roll against one another as the joint engages the sprocket. A typical silent chain with two-pin joints is shown in Figure 3-29. Two-pin joints greatly reduce friction and wear by eliminating sliding. Two-pin joints also practically eliminate the effects of chordal action. The curved surfaces of the pins act as cams, increasing and then decreasing the pitch slightly as each link engages a sprocket tooth. That pitch change is designed to counteract the speed variation from chordal action.




69

Connecting Links and Offset Links Connecting Links For a chain with single-pin joints, the connecting link may consist simply of a pin that is headed on one end and drilled to accept a cotter or roll pin on the other end. Washers may be furnished for one or both ends of the pin. For chain with two-pin joints, the connecting link normally consists of one short pin and one long pin. The long pin is headed on one end and drilled to accept a cotter or roll pin on the other end. The short pin may be held in place by side links or by washers that are furnished for the ends of the long pin. Such a connecting link is shown in Figure 3-30. Offset Sections An offset link for a silent chain is shown in Figure 3-31. It is a factory assembly of three or more pitches in length with the middle pitch (row) being offset by link plates. The offset link plates are half the thickness of the normal driving link plates and have an offset bend that lets them connect to the ends of a chain with an odd number of pitches.

FIGURE 3-30 Connecting link for silent chain with two-pin joints.

FIGURE 3-31 An offset link for a silent chain.



70


SILENT CHAIN PARTS General Only parts for silent chains with two-pin joints will be discussed here. Contact an ACA silent chain manufacturer for information on parts for silent chains with single-pin joints or for connecting and offset links. Driving Link Plates Tensile forces are transferred from the sprocket teeth to the joints through the driving link plates (Figure 3-32). The holes and the crotch in the link plates are significant stress risers. The driving link plates are primarily tensile members in silent chain. They are not subjected to much bending. Driving link plates must have sufficient strength to withstand the tensile forces without deforming or breaking, and they must have enough ductility to resist fatigue. The holes and the crotch area often must be designed for and be made with special processing to resist fatigue. In addition, they need to have enough wear resistance to withstand any sliding that occurs between the link plate edges and sprocket teeth. Joint Components: Pins The joint components—pins in a two-pin joint—transfer the tension forces from one row of driving link plates to the next (Figure 3-33), and they must do so while the joint is flexing and the pins are rolling on one another. The pins in silent chain are subjected almost entirely to shear and bearing (Hertz) stresses. They are not subjected to much bending because of the way that the link plates are laced on the joints.

FIGURE 3-32 Tensile forces are transferred from the sprocket teeth to the joints through the driving link plates.

FIGURE 3-33 The joint components transfer the tension forces from one row of driving link plates to the next.




71

The pins in a silent chain with two-pin joints need great strength to withstand the high shear stresses without deforming or breaking, and they need high hardness to withstand the very high bearing stresses between the pins. The pins need a moderate amount of ductility to absorb the small amount of bending and to have sufficient fatigue resistance.

ENGINEERING STEEL CHAIN DESIGN CONSIDERATIONS GENERAL Many different types of engineering steel chains are used in a wide variety of applications. Most engineering steel chains are used in conveyors, bucket elevators, and tension linkages. Only a few are used in drives. Space does not permit a discussion of all the different types of engineering steel chains mentioned in chapter 2. Only straight sidebar chains, with and without rollers, for conveyors and bucket elevators, and offset sidebar chains for drives will be discussed. Welded steel chains and block and bar chains are beyond the scope of this chapter. The straight sidebar conveyor chains discussed here are steel bushed rollerless chains and steel roller conveyor chains. The main design considerations for these chains are most tensile loads, several types of wear, lubrication, and environment. The main design considerations for an engineering steel chain to be used on a drive are very similar to those for a roller chain. These include the various tensile loads, certain types of wear, roller and bushing impact, and galling.

ENGINEERING STEEL CHAIN PROPORTIONS

AND

CLEARANCES

The dimensions of offset sidebar drive chains are generally proportional to the pitch. For example, roller diameters are approximately one-half the pitch and pin diameters are approximately oneforth of the pitch. Other dimensions are only very roughly proportional to the pitch. In contrast, the dimensions of engineering steel conveyor chains are not proportional to the pitch. Engineering steel chains generally have much larger clearances between moving parts than roller chains of the same size. The clearances between the pins and bushings, the bushings and rollers, and the inner and outer links are proportionally much larger. The larger clearances are provided so that dirt and debris can pass freely out of the bearing areas. The debris is, thus, not as likely to clog the joints of the chain, causing them to bind or seize.

TENSILE LOADS

AND

REQUIRED STRENGTH

General An engineering steel chain in a conveyor or drive may be subjected to all of the tensile loads that were described earlier. However, the tensile loads from centrifugal force, chordal action, and vibration are not very likely to be a major factor. Thus, engineering steel chain must have certain tensile strength properties to withstand the wide range of tensile loads that may be imposed on it. The major strength properties that an engineering steel chain must have are discussed below. Ultimate Tensile Strength Ultimate tensile strength is not a major consideration in designing engineering steel chains. That is because yield strength and fatigue strength are only generally related to ultimate tensile strength. MUTS is a requirement in most of the ASME standards that govern engineering steel chains, and a well-made chain usually has no difficulty meeting the standard that applies.



72


Yield Strength Yield strength is an important consideration in designing engineering steel chains. For many engineering steel chains, the yield strength is about 40% to 60% of the MUTS. Fatigue Strength Fatigue strength in the finite-life range is a very important consideration in designing engineering steel chains. Loads sometimes exceed the fatigue limit in some heavily loaded conveyors and drives. Fatigue Limit The fatigue limit usually is not a critical consideration in designing engineering steel chains. This is because most engineering steel chains accrue cycles very slowly and these chains are expected to wear out before fatigue can cause the chains to fail.

WEAR General Wear is probably the most important consideration in designing an engineering steel chain. Joint wear, roller and bushing wear, and sidebar and track wear are the greatest concerns for conveyor chains. Joint wear and roller and sprocket wear are the major concerns for drive chains. Chain Joint Wear Chain joint wear may be the most important factor to consider when designing an engineering steel chain. As the chain runs over the sprockets, the joints articulate and material is worn off the outside diameter of the pins and the inside diameter of the bushings, and as this material is worn away, the chain gets longer. Sprockets for engineering steel chain are designed to accept chain elongation from wear of 3% to 6%. When the chain elongates beyond this point, it no longer fits the sprockets and the system will not operate properly. Figure 3-34 illustrates sprockets with new and worn chain. As was noted earlier, offset sidebar chains wear differently than straight sidebar chains. Offset sidebar chains must be installed to run in a particular direction to obtain better wear life. This will be covered in the chapter on chain installation.

FIGURE 3-34 Sprockets with new and worn chain.




73

Roller and Sprocket Wear As was discussed earlier, roller wear in drive chains usually is not a major concern, but roller wear in conveyor chains may be a serious concern. Wear of the teeth on a small sprocket can impose large shock loads on the chain. Roller and Bushing Wear As was discussed earlier, roller and bushing wear is a very important consideration in designing engineering steel roller conveyor chains. Sidebar and Track Wear As was discussed earlier, sidebar and track wear is a very important consideration in designing engineering steel roller conveyor chains.

LUBRICATION Lubrication, or a lack of it, is a major concern in designing engineering steel conveyor chains. Many engineering steel conveyor chains must work with little or no lubrication, and thus material selection is very important. Lubrication is a concern in designing offset sidebar drive chains. The minimum types of lubrication are shown in the power rating tables, but designers must know that the recommended type of lubrication may not always be used.

ENVIRONMENT Environment is a major concern in designing engineering steel conveyor chains. Standard conveyor chains must work in mildly corrosive conditions. Some conveyor chains must also work in highly abrasive conditions. Highly abrasive conditions are typically found in mining and grain handling. Extreme temperatures are usually not a major concern in designing standard engineering steel chains. Only design considerations for standard engineering steel chains were covered earlier. Engineering steel chain manufacturers also make many special chains to work in very hostile conditions.

ENGINEERING STEEL CHAIN CONSTRUCTION

AND

COMPONENTS

Steel Roller Conveyor Chain Steel roller conveyor chain is an assembly of alternating pin links and roller links. The pins are free to articulate in the bushings and the links are arranged in a way that permits the rollers to engage the teeth of a sprocket and transmit motion and force. The components of such a chain are shown in Figure 3-35. The diameter of the rollers is greater than the sidebar height. The chain rides on these rollers while it carries the material on a conveyor. Steel Bushed Rollerless Chain Steel bushed rollerless chain is the same as steel roller conveyor chain except it does not have rollers.



74


FIGURE 3-35 The components of steel roller conveyor chain.

FIGURE 3-36 Offset sidebar drive chain components.

Offset Sidebar Drive Chain Offset sidebar drive chain is a series of identical offset links. The pins are free to articulate in the bushings and the rollers are free to turn on the bushings. The rollers are uniformly spaced so they can engage the teeth on a sprocket and transmit motion and force. The components of such a chain are shown in Figure 3-36. The diameter of the rollers in this type of chain is less than the sidebar height.




75

Pin Links Pin links are subassemblies of two pins fitted into the holes of two outer sidebars. The pins are held in the sidebars by a head or fastener on one end and by riveting, staking, or another fastener on the other end. The pins are prevented from rotating in the sidebars by press fits or a mechanical locking feature. Bush Links Bush links are subassemblies of two bushings fitted into the holes of two inner sidebars. The bushings usually are held in the sidebars by press fits. The bushings are prevented from rotating in the sidebars either by the press fits or a mechanical locking feature. Rollers that are free to turn on the bushings are assembled on the bushings for roller conveyor chains. Offset Links Offset links are subassemblies of two offset bent sidebars with a bushing press fitted into the narrow end and a pin press fitted into the wider end. The pin is held in the sidebars by a head or fastener on one end and by riveting, staking, or another fastener on the other end. The pin and bushing are prevented from rotating in the sidebars either by the press fits or a mechanical locking feature. A roller that is free to turn on the bushing is assembled on the bushing. Connecting Links Connecting links for chains with straight sidebars may consist of an outer sidebar with two pins fitted in it with another outer sidebar furnished to complete the link. The sidebar is retained on the pins by a cotter pin or some other retaining device. Also, because engineering steel chains often have a very long pitch, two connecting pins and two regular outer sidebars may be furnished. These pins and sidebars are identical to those normally assembled into the chain. In other words, every pin link in the chain can be a connecting link. For offset sidebar chains, a connecting pin with a retaining device is normally furnished, and the connecting pin may be identical to the pins in the chain.

ENGINEERING STEEL CHAIN PARTS General The major stresses on the components of an engineering steel chain are shown in Figure 3-37. The figure shows how the parts in the chain react when a load is put on the chain. The bending of the pins and sidebars is exaggerated to emphasize the effects of loading. Some parts must perform two or more functions at the same time and some of these functions conflict with each other. For example, pins must have high surface hardness to resist wear, but they must also have high ductility to withstand bending. The chain designer is faced with a great challenge in deciding how to best fulfill all of the chains requirements. A discussion of the functions and design of individual roller chain parts follows. Rollers In an engineering steel chain with rollers, the load from transmitting power or conveying materials is first transferred from the working faces of the sprocket to the outside of the chain rollers, or vice versa. In drives, there also may be an impact force when the sprocket teeth pick up rollers from the tight span of the chain. Rollers must be strong enough to withstand these forces without distorting or breaking, and rollers must be hard enough to resist wear from engaging the sprocket teeth. Conveyor rollers are



76


FIGURE 3-37 Diagram of stress in engineering steel chain.

FIGURE 3-38 Typical rollers for engineering steel chain.

not subjected to high impact forces because conveyor chains run at much slower speeds than drive chains. Thus, conveyor rollers can be somewhat harder, with less impact resistance, than the rollers for drive chains. Typical rollers for engineering steel chains are shown in Figure 3-38. Large steel roller conveyor chains that are used on bucket elevators or in other extremely abrasive applications may be equipped with pressure-lubricating fittings on the rollers or pins (Figure 3-39). Bushings In a rollerless chain, the load from transmitting power or conveying materials is first transferred from the working faces of the sprocket to the outside of the chain bushings, or vice versa. In a chain with rollers, the operating forces are transferred from the inside of the rollers to the outside of the bushings. The bushings must then transfer those forces to the roller link plates and the pins. Bushings must have enough strength and rigidity to transfer the force applied near the middle of the bushings to the inner sidebars that are assembled onto each end of the bushings. Most




77

FIGURE 3-39 Pressure lubrication fittings for conveyor chain rollers.

FIGURE 3-40 Typical bushings for engineering steel chains.

bushings are assembled into the holes of the inner sidebars with a press fit. The bushings also must have enough strength to withstand the press fit stresses without cracking. Bushings transfer the operating forces to the pin, and they have to do so while the pins are turning inside the bushings. Bushings need to have high surface hardness to resist wear when the joint flexes, but bushings must not be so hard that they are brittle. Typical bushings for engineering steel chains are shown in Figure 3-40. Pins The operating forces are transferred from the inside of the bushings to the pins. The pins must then transfer these forces to the outer sidebars, and they must do so while the pins are turning in the bushings. Pins act as both beams and bearings in a chain. Pins need enough strength to transfer the forces to the outer sidebars without deforming or breaking. Pins also need high surface hardness to resist wear when the joint flexes. They also must have enough ductility that they can withstand considerable bending without cracking or breaking. Finally, the pin ends must be ductile enough that they do not crack or spall when the pin ends are staked, spun, or riveted. Typical pins for engineering steel chains are shown in Figure 3-41. Outer Sidebars Tensile forces are applied to the outer sidebars by pins that are assembled through holes in the sidebars. The holes in the sidebars are significant stress risers. The outer sidebars are primarily tension members, and they also are subjected to substantial bending and stress concentrations around the holes. The outer sidebars must have enough strength to withstand the tensile forces



78


FIGURE 3-41 Typical pins for engineering steel chains.

FIGURE 3-42 Typical straight and offset sidebars.

without deforming or breaking, and they must have enough ductility to withstand substantial bending and to resist fatigue. Inner Sidebars Tensile forces are applied to the inner sidebars by bushings that are assembled into the holes in those sidebars. The holes in the inner sidebars are significant stress risers. The stress concentration is even more severe because the bushing is not assembled all the way through the link plate. The inner sidebars are primarily tension members, but they are also subjected to bending and stress concentrations around the holes. The inner sidebars must have enough strength to withstand the tensile forces without deforming or breaking, and they must have enough ductility to withstand some bending and to resist fatigue. Offset Sidebars Offset sidebars must function as both inner and outer sidebars. Offset sidebars are subjected to the same tension forces as both inner and outer sidebars. Offset sidebars must have all of the strength, ductility, and fatigue resistance of both the inner and outer sidebars. In addition, offset sidebars are subjected to large bending stresses at the offset bends. Offset sidebars need great rigidity to prevent tension forces from “straightening” the bends and causing the chain joints to bind. Offset sidebars also need very good fatigue resistance to prevent cracks from developing at the inner radii of the bends. Typical straight and offset sidebars are shown in Figure 3-42.




79

FLAT-TOP CHAIN DESIGN CONSIDERATIONS GENERAL Flat-top chains are used almost exclusively on conveyors. In practice, the flat-top chains covered here are basically special types of slat conveyors. Flat-top chain conveyor speeds are generally less than 300 ft./min and the maximum chain pull is usually much less than 1000 lb. The major design considerations for flat-top chains to be used in conveyors are several of the tensile loads, several types of wear, lubrication, and environment.

SCOPE

OF

CHAINS CONSIDERED

Only unit-link flat-top chains with a 11/2 -in. pitch will be considered here. Only a few basic straightrunning and side-flexing chains will be covered and only chains made for carbon steel, stainless steel, acetal, and low-friction acetal are included.

TENSILE LOADS

AND

REQUIRED STRENGTH

General The tensile loads of greatest concern are the nominal tensile loads, shock loads, and inertia loads. The main strength properties that a flat-top chain must have are discussed below. Ultimate Tensile Strength Ultimate tensile strength is not a major consideration in the design of flat-top chains. Yield Strength For the reasons stated earlier, yield strength is an important consideration in designing flat-top chains. Other Strength Characteristics Fatigue strength and fatigue limit are not major concerns in designing flat-top chains.

WEAR General Wear may be the most important consideration in designing flat-top chains. Joint wear and top plate and track wear are certainly the greatest concerns. Top plate and sprocket wear are also of some concern. Joint Wear Joint wear is a very important consideration in designing flat-top chains. As the chain runs over sprockets, the joints articulate and material is worn off the outside diameter of the pins and the inside diameter of the top plates, and as this material is worn away the chain gets longer. The sprockets for flat-top chains are not designed to accept much wear elongation. Thus, when the chain elongates even a moderate amount, it will no longer fit the sprocket and the conveyor will not function properly.



80


Top Plate and Track Wear Wear between the top plates of the chain and the track, or wear strips, that they ride on is a major concern in designing flat-top chains. As straight-running chains operate, material is worn off the top plates and wear strips, and the top plates get thinner and weaker. As this type of wear progresses, the chain may start to malfunction or it may break. As side-flexing chains operate, material is worn off the bevels or tabs of the top plates and the curved sections of track. As this type of wear progresses, the bevels or tabs may break off, allowing the chain to jump out of the track. Top Plate and Sprocket Wear Top plate and sprocket wear is not a major concern in designing flat-top chains because the chain spends only a small part of the cycle articulating on the sprocket teeth.

LUBRICATION Lubrication, or lack of it, is a major concern in designing flat-top conveyor chains. Many flat-top chains must work with little or no lubrication. When the chain must operate with no lubrication, selecting materials for the top plates and tracks is extremely important.

ENVIRONMENT Environment is a major consideration in designing flat-top chains. Many flat-top chains must operate in very abrasive or corrosive conditions and some flat-top chains must operate in very low or very high temperatures. Material selection is critical in designing a chain that will work well in these conditions.

FLAT-TOP CHAIN CONSTRUCTION

AND

COMPONENTS

Straight-Running Steel Flat-Top Chain Straight-running steel flat-top chain consists of a series of steel top plates with hinge-like barrels curled on each side. Pins are inserted through the barrels to make a joint. Pins are retained by press fits or heading in the barrels of one top plate and are free to articulate in the barrels of the next link. Thus a continuous length of flat-top chain is formed. The joints in straight-running chain permit flexing in only one plane. The barrels mesh with the teeth of a sprocket to drive the conveyor. Figure 3-43 shows an exploded view of straight-running, steel flat-top chain. Side-Flexing Steel Flat-Top Chain Side-flexing steel flat-top chain is similar to the straight-running type with one major difference. The barrels in which the pins are free to turn are specially formed to permit the joint to flex sideways. Thus, the chain can flex in two planes. The amount of side flexing is limited so that the chain retains enough strength and bearing area to work well as a conveyor. As a side-flexing chain is pulled around a curve, it is often pulled up and out of the track. Thus, side-flexing flat-top chains have bevels or tabs to hold them down in the tracks as they round a curve. Figure 3-44 shows a side-flexing steel flat-top chain with tabs.




81

FIGURE 3-43 Typical straight-running steel flat-top chain construction.

Straight-Running Plastic Flat-Top Chain Straight-running plastic flat-top chain is similar to straight-running steel flat-top chain except the top plates are molded plastic. Figure 3-45 shows an exploded view of a straight-running, plastic flat-top chain. Side-Flexing Plastic Flat-Top Chain Side-flexing plastic flat-top chain is similar to side-flexing steel flat-top chain except the top plates are molded plastic. Figure 3-46 shows an exploded view of a side-flexing, plastic flat-top chain.

CONNECTORS In most cases, the connector for flat-top chains is just a connecting pin. The connecting pin is usually either knurled or enlarged on one end to retain the pin in one barrel of the top plate. Sometimes the pin is just a straight pin and relies on a press fit in one end barrel to retain it.

FLAT-TOP CHAIN PARTS Top Plates General The top plates have three functions in flat-top chain. The barrels on each side of the top plate mesh with the sprocket teeth and drive the conveyor. The top plates are the primary tension members in



82


FIGURE 3-44 Side-flexing steel flat-top chain with tabs.

the chain and they must transfer all tensile loads from one link to the next. The top plates also serve as slats, as in a slat conveyor, and carry the conveyed material. Steel Top Plates Steel top plates may be made from either carbon steel or stainless steel. Of course, top plates made from stainless steel must have adequate corrosion resistance to operate well in corrosive environments. The barrels of the top plates must be curled very accurately. One reason is to ensure that the outside diameter meshes with the sprocket teeth correctly. Another reason is to ensure that the inside diameter presents a large bearing area to the pin. If the top plate is for side-flexing chain, the inside diameter must be carefully contoured to give good bearing area while providing the needed turning radius. The top plates must have enough strength to withstand the expected tensile forces without deforming. Top plates need high surface hardness to resist wear in the barrels when the pin turns in the barrels under load. They also need high surface hardness to resist wear on the carrying surface when the product slides on it, but they must not be so hard that are brittle and crack under repeated loading.




83

FIGURE 3-45 Typical straight-running plastic flat-top chain construction.

FIGURE 3-46 Side-flexing plastic flat-top chain.

Plastic Top Plates Plastic top plates are made from several different types of thermoplastics. Many are molded from acetal or low-friction acetal. Low-friction acetal is a blend of acetal with another plastic with a very low coefficient of friction. The plastic used must have good corrosion resistance and the plastic must also have good wear resistance in conditions where there is little or no lubrication. The barrels of the top plates must be molded very accurately, for the same reasons that the barrels of steel top plates must be curled very accurately.



84


Plastic top plates must have enough strength to withstand the expected tensile forces without deforming or cracking. Plastic top plates need good wear resistance to combat wear in the barrels when the pins turn in the barrels under load, and they need good wear resistance to combat wear on the carrying surface when the product slides on it. Plastics generally have good wear resistance rather than high hardness. Pins Pins transfer the tensile loads from the barrels of one top plate to the barrels of the next top plate, and they must do so while the pins are turning in the barrels. The pins in flat-top chains act as both beams and bearings. Pins need high surface hardness to resist wear when the joints flex and they need high strength to carry the conveyed loads. The pins in stainless steel and plastic flat-top chains are usually made from stainless steel to provide the needed corrosion resistance.

CONCLUSION The reader can easily see that a chain designer must know a great deal about how a chain will be used and the conditions in which it will be used. He or she must then translate those requirements into specifications for parts and assembled chain. The considerations and principles presented here are only the most basic of those that a chain designer must deal with. Many issues, several of which are in direct conflict with each other, must be resolved to design and produce a chain that will do what the user wants and expects. The member companies of the ACA have done much research; both in the laboratory and in the field, so they can design and build better chains for a wide variety of uses. These companies have also studied lubrication and operating conditions so they can give better advice to users. The member companies of the ACA continue to do research into both chain and manufacturing technologies. They do so to provide better performing and more economical chains to serve the ever-increasing needs of chain users.


DK4023_C004.fm Page 85 Wednesday, October 12, 2005 11:20 AM

4 Sprockets The performance of a conveyor or drive depends on sprocket-chain interaction. Choosing the right sprocket is as important as choosing the right chain. Thus the designs of chains and sprockets must be compatible. Standard sprockets are classified as either semiprecision (cast tooth or flame-cut tooth) or precision (machine-cut tooth). Today sprocket teeth can be cast or flame cut almost as accurately as they can be machine cut. The difference between precision and semiprecision really involves much more than just how accurately the teeth can be cut. The types of sprockets chosen are a function of the type of chain and the requirements of the application. Generally only precision sprockets are used with roller and silent chains. Accurately cut teeth are necessary for roller or silent chain to perform well in moderate- to high-speed drives. On the other hand, accurately cut teeth are not nearly as necessary for a slow-moving, long-pitch conveyor chain. The path and speed of roller or silent chain links around the drive sprocket differ in many ways from those of long-pitch conveyor chain. The tooth geometry of machine-cut sprockets for roller or silent drive chain usually differs in many ways from that of cast or flamecut sprockets for a slow-moving, long-pitch conveyor chain. The form and finish of the sprocket teeth are different and so are the functions of the respective installations. In each case, the design and degree of precision and finish of the portions of the sprocket that interact with the chain must be matched to the chain. For this reason, sprockets normally should be obtained from the manufacturer of the chain unless chains and sprockets are manufactured to a tight and accepted standard such as ASME B29.1. Wear causes the chain to elongate and alters the form of the sprocket teeth. Thus, worn sprockets should always be replaced when a new chain is installed (or vice versa).

TYPES OF SPROCKETS GENERAL Sprockets are made in various ways and from many materials. Manufacturing methods and materials are chosen to produce a tooth form with the precision and surface finish that is needed. Added processing, such as heat treatment, is done to give the load-carrying capacity, rotating speed capability, and service life that the sprockets must have. The two basic types of sprockets—precision and semiprecision—are mainly classified by the way they contact and operate with the chain. The two types may be subdivided by materials and manufacturing methods. Other factors include economics and the degree of accuracy required by the chains with which the sprockets are paired. Sprockets for roller chain and silent chain are normally made from steel or cast iron with machine-cut teeth. The working surfaces of the teeth are usually highly finished. Sprockets for engineering steel chains are generally made from steel or cast iron and the teeth are often flamecut or cast. Sprockets for flat-top chain may be made from steel, cast iron, or plastic. The teeth are usually machine-cut on steel and cast iron sprockets and molded on plastic sprockets. These are generalities, and exceptions are not hard to find. That is especially true with engineering steel

85



86


FIGURE 4-1 Roller chain sprockets, types A, B, and C.

chains. However, regardless of how the sprocket teeth are formed, the most important thing is that the chain and sprockets are designed to operate together. Sprockets with machine-cut teeth are smoother and quieter in operation. They are commonly used in moderate- to high-speed drives. Sprockets with cast or flame-cut teeth are less costly, and they give adequate life when used on slow-speed drives and conveyors. The various kinds of sprockets that are furnished by manufacturers are reviewed in the following sections.

SPROCKETS

FOR

ROLLER CHAIN

Sprockets for Single-Strand Precision Chain The ASME B29.1 standard defines the dimensions, tolerances, and tooth form for standard roller chain sprockets. These will be discussed in the design section later in this chapter. Four sprocket types are included in ASME B29.1 standard: • • • •

Type A is a plain plate sprocket without hub. Type B has the hub on one side only. Type C has the hub on both sides. Type D has a detachable hub.

Types A, B, and C are shown in Figure 4-1; type D is shown in Figure 4-2. Another design of a demountable hub-type sprocket is shown in Figure 4-3. It is a combination of a tapered split bushing with a tapered bore sprocket. The design provides for a positive grip fit to the shaft and a choice of finished bore sizes within a single sprocket selection. These sprockets are made in both the B and C sprocket styles. Between the hub and the rim, a sprocket may be one of several forms, according to the size. Smaller sprockets are usually solid, except for the shaft bore, since their weight is not excessive. Medium sizes are usually cast with webbed forms and have cored holes between the hub and the rim to reduce their weight (Figure 4-4). Larger sprockets are usually cast and made in the form of



Sprockets

87

FIGURE 4-2 Roller chain sprocket, type D.

FIGURE 4-3 Taper lock bushing and sprocket.

spoked wheels to obtain the minimum possible weight (Figure 4-5). Where the sprocket must be mounted between bearings, split forms (Figure 4-6 and Figure 4-7) are used to permit installation and removal without disturbing the shaft. Some type D sprockets consist of a solid hub and a split plate (Figure 4-2). Other type D sprockets are made with both the hub and the plate split (Figure 4-7). In the manufacture of any split sprocket, care must be taken to prevent any variation of the pitch at the split line. Figure 4-7 shows special dowels on the split for this purpose. Shear pin and slip clutch sprockets are designed to prevent damage to the drive or to other equipment caused by overloading or stalling. A shear pin sprocket consists of a hub that is keyed to the shaft and a sprocket that is free to rotate either on the shaft or on the hub when the shear pin breaks (Figure 4-8). The pin is designed to shear under a specified load. The shear pin is designed to transmit up to a predetermined amount of torque and to shear when it is overloaded. When the pin shears, the sprocket is free to rotate either on the shaft or on the hub that is keyed to the shaft. The shear pin is made of a material with known shearing strength, and its failure point



88


FIGURE 4-4 Typical webbed sprocket, type C.

FIGURE 4-5 Typical spoked sprocket, type C.

can be established with reasonable accuracy by machining it with a groove of a calculated diameter at the shear plane. The assembly can be returned to working condition by inserting a new shear pin. Sprockets for Multiple-Strand Roller Chain Sprockets for multiple-strand roller chain are made as integral wheels with correct spacing for the strands and alignment of teeth. Typical sprockets for multiple-strand roller chain are shown in Figure 4-9.



Sprockets

89

FIGURE 4-6 Typical split sprocket, type C.

FIGURE 4-7 Typical roller chain split sprocket with split demountable hub.

Sprockets for Double-Pitch Roller Chain There are two forms of sprockets for double-pitch roller chain. One is designated as single-cut (Figure 4-10) and the other as double-cut (Figure 4-11). Note the difference in tooth form. The term effective teeth indicates the number of teeth that engage with the chain during one revolution of the sprocket. The number of effective teeth on a single-cut sprocket is equal to the number of actual teeth, while the number of effective teeth for a double-cut sprocket is one-half the number of actual teeth. For a sprocket with an odd number of teeth, the number of effective teeth is fractional. For example, with 25 actual teeth, there are 121/2 effective teeth. The advantage of an odd number of actual teeth is that each tooth will engage the chain only on every other revolution, thus practically doubling the life of the sprocket. With an even number of actual teeth, the same effect can be obtained by



90


FIGURE 4-8 Shear pin hub sprocket.

FIGURE 4-9 Typical sprockets for multiple-strand roller chain.

periodically advancing the chain by one tooth on the sprocket. Note that a double-cut sprocket cannot be made for conveyor series chain with carrier-type rollers, as insufficient space exists between the rollers for the “extra” teeth. Sprockets for double-pitch chain have larger pitch diameters and bottom diameters than sprockets for the corresponding base chain. However, when the sprocket has more than 35 teeth, the differences may be neglected.



Sprockets

FIGURE 4-10 Single-cut sprocket for double-pitch roller chain.

FIGURE 4-11 Double-cut sprocket for double-pitch roller chain.


91


92


MANUFACTURING SPROCKETS

FOR

ROLLER CHAIN

Smaller sprockets are generally cut from steel bar and are finished all over. The size of sprockets cut from bar stock is limited by the maximum diameter of the commercially available stock. When sprockets are made from steel, the body of the sprocket can be heat treated to make it more shock resistant and the tooth surfaces can be hardened to resist wear. Where corrosion exposure is great, stainless steel or bronze may be used. Formica, nylon, and various plastic materials may also be used. Sprockets are sometimes made from forgings or forged bars. The extent of finishing depends on the particular specifications that apply. Many sprockets are made by welding a steel hub to a steel plate. This process produces a onepiece sprocket of desired proportions and one that can be heat treated. For large roller chain sprockets, cast iron is commonly used. Cast roller chain sprockets have cut teeth, and the rim, hub, face, and bore are machined. Cast iron is often used in the large sprockets of drives with large speed ratios. Cast iron is acceptable in this case because the teeth of the larger sprocket are subjected to fewer chain engagements in a given period. For severe service, cast steel or steel plate is preferred.

SPROCKETS

FOR

SILENT CHAIN

The tooth forms for silent chain sprockets are covered by the ASME B29.2 standard and will be discussed later in the design section of this chapter. Sprockets for silent chain are manufactured using the same processes, materials, and hub configurations as roller chain sprockets, but their tooth forms are visibly different. As illustrated by the sprockets shown in Figure 4-12, the teeth on silent chain sprockets closely resemble the teeth of a gear. While they are visually similar to gears, silent chain sprockets are made with specially designed tooling that is different from that used to produce gears. Also, silent chain sprocket tooth forms and key sprocket dimensions do vary between different styles of silent chain. Standard silent chains use a standard sprocket tooth form described by ASME B29.2. There also are nonstandard silent chains, such as high-performance, duplex, and reversible silent chains. Those nonstandard chains often require special sprockets that may be unique to a specific manufacturer. It is critical that chains and sprockets are fully compatible, so it is good practice to consult a chain’s manufacturer for detailed sprocket specifications. A typical sprocket for duplex silent

FIGURE 4-12 Sprockets for standard silent chain.



Sprockets

93

FIGURE 4-13 Sprocket for duplex silent chain.

FIGURE 4-14 Sprocket for reversible silent chain.

chain is shown in Figure 4-13, and a typical sprocket for reversible silent chain is shown in Figure 4-14.

SPROCKETS

FOR

ENGINEERING STEEL CHAIN

Sprockets for engineering steel chains are made of various metals, in various forms, and in shapes to suit the requirements of the particular application. Standard sprockets are available for most applications. Just as there are engineering steel chains that are offered in many versions and styles not included in ASME standards, so too are there many such sprockets. Most of these are very similar to standard sprockets, and many are made to work with standard chains where a standard sprocket will not meet the needs of the application. This section mainly considers sprockets for standard chains or chains that vary only slightly from standards. Listings of special sprockets must be taken from manufacturers’ catalogs.

MATERIALS USED

IN

SPROCKET MANUFACTURE

Sprockets for engineering steel chains are usually made of the following materials:



94


FIGURE 4-15 Typical cast iron arm center sprocket.

• •

•

•

Cast iron: often the most economical and selected for moderate conditions. Chill iron: these sprockets have the teeth cast in a chill. The chill results in rapid cooling of the tooth surface upon casting, which results in a smooth hard tooth that can resist ordinary abrasion with a depth of hardness between 1/16 and in., depending on the sprocket size. Cast or fabricated steel: cast steel sprockets have cast teeth, whereas fabricated steel sprockets have flame-cut teeth. Both are designed to sustain heavy torque and shock loads. For the most demanding work in highly abrasive conditions, the teeth are flame or induction hardened. Stainless steel: used where sprockets are exposed to corrosion.

Special materials such as iron and steel alloys, bronze, and aluminum can be used to satisfy special requirements. Cast Iron Sprocket Types Arm centers (Figure 4-15) are used on cast sprockets whenever possible to reduce their weight and cost. This also makes them easier to handle. The same effect can be obtained with fabricated steel sprockets by flame-cutting holes in the plate. This is shown in Figure 4-16. Solid centers (Figure 4-17) are for sprockets that are too small to accommodate arms. They are also used when allowable chain pull exceeds the strength of arm sprockets or when hub diameters are very large. Split sprockets (Figure 4-18) are sometimes used when the sprocket must be mounted between bearings. This type of sprocket can be installed and removed without disturbing the shaft and other parts of the machine. Segmented removable rims (Figure 4-19) are bolted to the sprocket center. These sprockets are designed to be installed and replaced without removing the chain, hubs, bearings, or shafts.



Sprockets

95

FIGURE 4-16 Fabricated steel sprocket with lightening holes.

FIGURE 4-17 Typical cast iron solid or plate center sprocket.

Traction Wheels Traction wheels (Figure 4-20) are sometimes used on the head shaft of single-strand bucket elevators when the unit has frequent obstructions or very large overloads. Traction wheels, however, must be used with care. The friction between the chain and head wheel must be sufficient to transmit



96


FIGURE 4-18 Typical split cast iron spoked sprocket.

FIGURE 4-19 Sprocket with chilled iron segmental removable rims.

the power required to drive the unit under normal load. Consult an engineering steel chain manufacturer for advice on conditions where traction wheels may be used. If slipping occurs, heat and sparks may be generated. Accordingly, it is important that traction wheels not be used where sparks could result in an explosion. Special-Purpose Sprockets for Engineering Steel Chain Figure 4-21 shows a group of special sprockets that are used only for specific purposes. These are usually made from cast iron, often with chilled wearing surfaces.



Sprockets

97

FIGURE 4-20 Typical traction wheel with chilled iron segmental rims.

FIGURE 4-21 Types of cast iron sprockets for engineering steel chains.

A cast iron shear pin hub sprocket is shown on the left side of Figure 4-21. It operates exactly like the similar roller chain sprocket shown in Figure 4-8. These are often used in conveyor drive service. The two center wheels shown in Figure 4-21 are used on drag conveyors with welded steel drag chain. Both wheels are drive units. The extensions on the wide flange or drum sprocket prevent spillage when discharging the conveyor over the head shaft (see chapter 9). The sprocket at the right has flanged rims to support the chain by contact with the sidebars, extending the service life of both the chain and sprocket. This type usually is used on sanitary conveyors. These chilled iron wheels are often furnished in a “hunting tooth” design. Their function is similar to the double-cut roller chain sprockets shown in Figure 4-10. In this type of design, the sprocket tooth pitch is slightly larger than half the pitch of the chain, the sprocket being cast with an odd number of teeth. The links only engage every other tooth at a given instant. This means that each tooth on the sprocket will engage the chain only on every other revolution, thus nearly doubling the sprocket life. (This concept was first used in wooden gearing in the early 19th century.) Another type of special-purpose sprocket is shown in Figure 9-34. This is a compensating sprocket. It is used to drive the head shaft in conveyors that use long-pitch engineering steel chains.



98


FIGURE 4-22 Steel fabricated, cut-tooth sprocket for offset sidebar drive chain.

Sprockets for Engineering Steel Offset Sidebar Drive Chain Sprockets for engineering steel offset sidebar drive chain are usually made of cast steel or are flame cut from steel plate. The hubs and other parts are usually fabricated. The standard tooth form is defined in ASME B29.10. Figure 4-22 shows the sprockets for a double-strand special version of a 6-in.-pitch drive chain that conforms to the ASME B29.10 standard. These sprockets use the American National Standards (ANS) tooth form and were machine cut to ensure alignment of the double-strand chain under heavy loads. These sprockets were made from alloy steel and were heat treated. Sprockets for offset sidebar chains do not always have machine-cut teeth. Many offset sidebar drive sprockets have cast or flame-cut teeth. There is a wide range of tooth designs. Consult the chain manufacturer for advice on using sprockets that do not have machine-cut teeth per ASME B29.10. Sprockets for Other Types of Engineering Steel Chain From the discussions here, one can see that a wide range of sprocket styles are available for most types of engineering steel chain. The tooth form and dimensions must properly match the chain type and dimensions. Other than that, it might seem that the chains of this class can be operated on any type of wheel, but that is not the case. Certain wheel styles will not work with certain chains in some applications. For example, a roller chain will not work on a traction wheel. Normally a certain style of sprocket is almost always used for a given type of chain. All other sprocket styles are used only in special cases. Table 4-1 tabulates the styles of sprockets that are most often used with the types of engineering steel chain described in this book. The tabulation is not a recommendation of what should be used. Rather, it is a general guide to what is normally used. As with most generalities, there are exceptions. In the key to the usages, round and square symbols are used. The round symbols indicate that the sprocket type is fairly routinely used with the chain noted. Those standard wheels will often be listed in the manufacturers’ catalogs. Here, “normally” and “often used” usually denote



Sprockets

TABLE 4-1 Styles of sprockets used with standard chains


99


100


FIGURE 4-23 Style of sprockets for flat-top chain.

differences in cost, and sometimes in quality. The square symbols indicate that use of a particular wheel with the chain indicated is either infrequent or inappropriate. The major reason for “infrequent” use is generally cost. But the main reason for “inappropriate” use is usually a technical factor. Any installation that uses a chain-sprocket match indicated by the square symbols should only be done after consulting with the manufacturer of the chain involved.

SPROCKETS

FOR

FLAT-TOP CHAIN

The tooth form for flat-top chain sprockets is covered by ASME B29.17 and will be discussed later in the design section of this chapter. This section considers sprockets only for standard flat-top chains described in this book. The only flat-top chains covered in this book are unit link chains with 11/2 -in. pitch. Thus the number of styles of sprockets discussed here is very limited. Three widely used sprocket styles for flat-top chain are shown in Figure 4-23. The sprocket in Figure 4-23a is a block body sprocket. The block body style is usually offered for smaller numbers (13 to 21) of teeth. They may be made of cast iron, steel, or stainless steel and normally have machine-cut teeth. The sprocket in Figure 4-23b is a cast iron arm center sprocket. The arm center style of sprocket is generally offered for larger numbers of teeth (19 to 41), and they also normally have machinecut teeth. The sprocket in Figure 4-23c is a thermoplastic split sprocket. These sprockets are usually offered with a medium number of teeth (21 to 29) and the teeth are generally molded. The advantage of these sprockets is that they can be installed or removed without disturbing the shafts or bearings. Molded thermoplastic sprockets can be obtained in either split or solid form. They are most often used in wet or mildly corrosive environments.

SPROCKET TOOTH FORMS DESIGN CONSIDERATIONS The major function of a sprocket is to transmit torque. So, the main considerations in designing a sprocket tooth form are as follows. • •

The sprocket teeth must transfer the tension load to the chain or absorb the tension load from the chain. The sprocket should engage the chain as smoothly and consistently as possible, whether the sprocket is a driver or driven sprocket or an idler.



Sprockets

• • •

101

The sprocket should distribute the tension so that each tooth in engagement carries a share of the load. The sprocket must accommodate a reasonable amount of wear, either in the form of pitch elongation of the chain or tooth and bottom (or root) diameter wear of the sprocket. The design must be suitable for the conditions in which it is expected to operate, including the possibility of foreign materials being forced between the chain and the sprocket teeth.

There are many similarities between the teeth of sprockets for roller chain, silent chain, the various engineering steel chains, and flat-top chains, and yet there are important design and conceptual differences. There are also basic differences in the terminology of design factors and even in the way the teeth are expected to interface with their chains. The major differences probably arise from the intended function of each type of sprocket tooth. For example, the sprockets for roller chain absorb pitch elongation from wear in one way, but the sprockets for engineering steel conveyor chain absorb that same pitch elongation in a very different way. On roller chain sprockets, elongation is absorbed by the rollers riding farther out on the working face of the sprocket tooth as the links pass around the sprockets. A trace of the path would be vaguely parabolic. The link would move in, seat briefly on the sprocket bottom diameter, and then move out again. The teeth for engineering steel chain sprockets usually include pitch line clearance, a factor not used on roller chain sprockets. Pitch line clearance provides a short segment of the sprocket bottom diameter in the gaps between the teeth. With pitch line clearance, the roller of an engineering steel conveyor chain can move a small distance along the bottom diameter of the sprocket; this absorbs the pitch elongation from wear. Other chains and their sprockets may be designed in other ways to absorb wear elongation in different ways. Chain-sprocket interaction is very complex in theory. It can be even more so when the effects of wear and elastic deformation of the chain and sprocket under load are considered. A discussion of these effects is beyond the scope of this book. This book must limit the scope to the tooth forms and dimensions as specified by ASME B29 standards and accepted practice. The following sections discuss basic tooth designs for roller chain, silent chain, engineering steel chain, and flat-top chain.

ROLLER CHAIN SPROCKET TEETH Definitions Pitch diameter: The diameter of the pitch circle through the chain roller centers as the chain wraps the sprocket. But chain pitch is measured on a straight line between center of adjacent rollers, so the chain pitch lines form a series of chords of the pitch circle. Bottom diameter: The diameter of a circle that is tangent to the curve (called the seating curve) at the bottom of the tooth gap. Caliper diameter: For a sprocket with an even number of teeth, the caliper diameter is the same as the bottom diameter. For a sprocket with an odd number of teeth, the caliper diameter is the distance from the bottom of one tooth gap to the bottom of the nearest opposite tooth gap. The latter is not really a diameter. So some call it a caliper dimension. Outside diameter: The diameter over the tips of the sprocket teeth. Tooth form: The outline of the working surfaces of the tooth that transfer forces to or absorb forces from the rollers (or bushings) of the chain. Tooth profile: The outline of the tooth section that is projected on a plane through the sprocket axis and the center of the tooth.



102


Groove diameter: The diameter of the grooves in a multiple-strand sprocket. The maximum groove diameter is the largest groove diameter that will clear the roller link plates in the chain. Hub diameter: The outside diameter of the hub extension of a sprocket. The maximum hub diameter is the same as the groove diameter. Hub length: The distance between the end surfaces of the hub. It also is called the length through bore. Bore: The sprocket bore is the inside diameter of the hole centered on the axis of the sprocket. The maximum bore diameter is limited by the maximum allowable stress in the hub and is considered later in this chapter.

ROLLER CHAIN SPROCKET DIAMETER Figure 4-24 shows the important diameters of roller chain sprockets and the equations for computing them. The first three terms are given dimensions. The first and third terms, P and Dr, are standard dimensions and can be obtained from Table 2-6. The second term, N, must be supplied by the sprocket designer. Tolerances on critical limiting dimensions are given in ASME B29.1 or can be obtained from the sprocket manufacturer. The pitch diameter probably is the most important diameter of the sprocket, but it cannot be measured directly. Thus manufacturers usually control the bottom diameter, or caliper diameter, in production. The tolerance on bottom diameter is always negative, to avoid chain binding. Measuring the caliper diameter over two concave surfaces is difficult. Measuring the caliper dimension over gauge pins is easier and more accurate. A gauge pin is put in the two tooth gaps and the distance over the gauge pins is measured. The gauge pin diameter is equal to the maximum roller diameter of the chain. Figure 4-25 illustrates measuring the caliper dimension over gauge

FIGURE 4-24 ANS roller chain sprocket diameters.



Sprockets

103

FIGURE 4-25 Caliper diameter over gauge pins.

pins. The diameter of one gauge pin must be subtracted from the measured value to obtain the bottom or caliper diameter.

ROLLER CHAIN SPROCKET TOOTH FORM Figure 4-26 shows the standard tooth form for roller chain sprockets. The figure also shows the equations needed to compute all of the dimensions needed to draw and make the tooth form. Just as for sprocket diameters, the first and third terms, P and Dr, are standard dimensions and can be obtained from Table 2-1. The second term, N, must be supplied by the sprocket designer. Tolerances on critical limiting dimensions are given in ASME B29.1 or may be obtained from the sprocket manufacturer. The standard tooth form is generated from the path of the chain roller as it moves from the chain pitch line of the tight strand into the pitch circle of the sprocket. One can lay out the tooth form by following the terms and equations in Figure 4-26. Note that radius R of the seating curve and radius F of the topping curve include the necessary clearance allowances between the sprocket and the engaging rollers. The tooth form shown in Figure 4-26 is a theoretical tooth form for the specific number of teeth. It is designed so that the chain rollers ride out toward the tips of the sprocket teeth as the chain wears and elongates. Figure 4-27a shows a new roller chain on a new sprocket. Figure 4-27b shows a worn roller chain on a new (or unworn) sprocket. These drawings illustrate how the chain rollers ride further out on the sprocket teeth as the chain elongates from wear. There are many ways to produce sprocket teeth, and the actual tooth form may not exactly match the theoretical tooth form because of that. When standard space cutters or milling cutters are used, the actual tooth form matches the theoretical tooth form only at 56 teeth. When hobs or shapers are used, the actual tooth comes very close to the theoretical tooth form for all numbers of teeth, but the actual tooth form matches the theoretical only when the cutting tool is based on a specific number of whole teeth. Cast, powder metal, or molded plastic teeth may vary from the theoretical tooth form in various ways depending on how the pattern, die, or mold is made.



104

FIGURE 4-26 ANS roller chain tooth form.

FIGURE 4-27 New and worn roller chain on new sprocket.




Sprockets

105

Many years of experience shows that all of the actual tooth forms mentioned above give acceptable service. The main thing is that the seating curve, bottom diameter, flange width, and chordal pitch engage the chain rollers without wedging or binding.

ROLLER CHAIN SPROCKET TOOTH LOADING The standard tooth form is designed to distribute a portion of the tension force to all of the teeth engaged with chain rollers. Figure 4-28 is a force diagram that shows how the tension force is distributed. The force bearing on each tooth may be found using the following equations: P1 = t1

sin α sin α = t0 sin φ sin α + φ

(

⎡ sin α sin α Pn = tn = t0 ⎢ sin φ ⎢⎣ sin α + φ

(

)

⎤ ⎥ ⎥⎦

n −1

)

⎡ sin α ⎤ ⎢ sin α + φ ⎥ . ⎣ ⎦

(4.1)

(4.2)

It can be shown that the tension load is distributed to the teeth of a typical 15-tooth sprocket, such as that shown in Figure 4-27, as follows. About 31% of the load is taken by the first tooth,

FIGURE 4-28 Forces on roller chain sprocket teeth.



106


FIGURE 4-29 Standard roller chain tooth profiles.

22% by the second, 16% by the third, 12% by the forth, 8% by the fifth, 6% by the sixth, and 4% by the seventh. That accounts for 99% of the total chain tension. There is no load on the eighth tooth because the slack strand tension takes up the remaining 1% of total chain tension. This analysis is purely theoretical, but testing and experience verify that actual tooth loading is reasonably close to the theoretical. The force diagram in Figure 4-28 may also be used to compute the tension in each link and the ejection force imposed on each roller engaging the sprocket, but that is beyond the scope of this book. For more information, see the book Mechanics of the Roller Chain Drive by R. C. Binder (Prentice Hall, 1956).

ROLLER CHAIN SPROCKET TOOTH PROFILES The sprocket tooth profiles on a roller chain sprocket must engage the chain without any wedging or binding. That is especially important with multiple-strand roller chain. Figure 4-29 shows the tooth profiles for standard single- and multiple-strand chain. Figure 4-29 also shows the equations for calculating all of the important dimensions of the standard tooth profile. Tolerances on critical limiting dimensions are given in ASME B29.1 or may be obtained from the sprocket manufacturer.

SPROCKET WHEEL DESIGN BAR STEEL SPROCKET WHEELS For typical bar steel sprocket wheel proportions, refer to Figure 4-30. The hub wall thickness, H, for such sprockets is a function of the pitch diameter, PD, and the bore diameter, D, as follows: H=Z+


D + 0.01PD , 6

(4.3)


Sprockets

107

FIGURE 4-30 Roller chain bar steel sprocket wheel dimensions.

where Z Z Z Z Z

is a constant that depends on PD (for PD up to 2 in., = 0.125 in.; PD 2 in. to 4 in., = 0.187 in.; PD 4 in. to 6 in., = 0.25 in.; PD larger than 6 in., = 0. 375 in.);

Normal hub length, L is: L = 3.3H,

(4.4)

HD = D + 2H,

(4.5)

with a minimum of 2.6 H. Hub diameter HD, is:

with a maximum allowable value given by the equation for maximum hub diameter (MHD) in Figure 4-26.

SINGLE-STRAND CAST SPROCKET WHEELS Typical cast sprocket wheel sections are shown in Figure 4-31, where P is the chain pitch and W is the nominal chain width, with other dimensions as shown. Acceptable dimensions are approximately as follows: H = 0.375 +


D + 0.01PD 6

(4.6)

L = 4H, for semisteel castings

(4.7)

C = 0.5P

(4.8)

C' = 0.9P

(4.9)

E = 0.625P + 0.93W

(4.10)

F = 0.156 + 0.25P

(4.11)


108


FIGURE 4-31 Single-strand roller chain cast sprocket wheel dimensions.

TABLE 4-2 Web thickness of single-strand cast roller chain sprocket wheels as a function of chain pitch P /8 1/ 2 5/ 8 3/ 4 1 1 1/4 3

T 0.312 0.375 0.406 0.437 0.500 0.562

P 1 1/2 1 3/4 2 2 1/4 2 1/2 3

T 0.625 0.750 0.875 1.000 1.125 1.250

G = 2T

(4.12)

R = 0.04P.

(4.13)

The web thickness, T, is a function of the chain pitch, as given in Table 4-2.

MULTIPLE-STRAND CAST SPROCKET WHEELS For typical proportions of multiple-strand cast sprockets, refer to Figure 4-32. The various proportions are the same as those given for single-strand cast sprocket wheels except as follows: R = 0.5T

(4.14)

LM for quadruple strands = E.

(4.15)

Values for T are given as a function of chain pitch P in Table 4-3.



Sprockets

109

FIGURE 4-32 Multiple-strand roller chain cast sprocket wheel dimensions.

TABLE 4-3 Web thickness of multiple-strand cast roller chain sprocket wheels as a function of chain pitch P /8 1/ 2 5/ 8 3/ 4 1 1 1/4

T

3

T 0.375 0.406 0.437 0.500 0.562 0.625

P 1 1/2 1 3/4 2 2 1/4 2 1/2 3

T 0.750 0.875 1.000 1.125 1.250 1.500

SPOKED SPROCKET WHEELS The design of spoked (see Figure 4-5) sprocket wheels is usually based on the following assumptions: • • • •

The maximum torque load acting on a sprocket is the chain tensile strength times the sprocket pitch radius. The torque load is equally divided between the arms by the rim. Each arm acts as a cantilever beam. The arms are generally elliptical in cross section, with the major axis twice the minor axis.

SILENT CHAIN SPROCKET TEETH SILENT CHAIN SPROCKET DIAMETER Figure 4-33 shows the important diameters of silent chain sprockets and the equations for computing them. The first two terms are given dimensions. The first term, P, is a standard dimension and can be obtained from ASME B29.2. The second term, N, must be supplied by the sprocket designer. Tolerances on critical limiting dimensions are given in ASME B29.2 or may be obtained from the sprocket manufacturer. The pitch diameter probably is the most important diameter of the sprocket. Unfortunately, one cannot measure it directly, so manufacturers usually closely control the diameter in production.



110


FIGURE 4-33 ANS silent chain sprocket diameters.

SILENT CHAIN SPROCKET TOOTH FORM Figure 4-34 shows the layout of a standard tooth form, expressed in terms of the pitch and number of teeth. It can be seen from the figure that the angle between the left and right face of a given tooth (60º720º/N) decreases as the number of teeth is reduced. For a 12-tooth sprocket, the angle becomes zero and the tooth faces are parallel. Thus 12 is the minimum number of teeth that can be produced in a standard sprocket. In practice, sprockets this small are seldom used; better results are obtained with 17 or more teeth.

SILENT CHAIN SPROCKET TOOTH PROFILES Figure 4-35 shows standard sprocket face profiles for center guide, two-center guide, and sideguide sprockets. The dimensions for each profile depend on the pitch and are defined in the ASME B29.2 standard. Selected profile dimensions are shown in Table 4-4. The standard also defines which guide types are used for various chain pitches and widths. These are listed in Table 4-5.



Sprockets

FIGURE 4-34 Layout of standard sprocket tooth form for silent chain.

FIGURE 4-35 Standard sprocket tooth profiles for silent chains.


111


112


TABLE 4-4 Standard dimensions for silent chain sprocket profiles Dimensions Chain Pitch (in.) 3/ 8 1/ 2 5/ 8 3/ 4 1 1 1/4 11/2 2

A

R ± 0.0003 .200 .200 .250 .360 .360 .360 .360 .360

.133 .133 .177 .274 .274 .274 .274 .274

C ± 0.005 .100 .100 .125 .180 .180 .180 .180 .218

Da ± 0.010 1.000 1.000 2.000 4.000 4.000 4.000 4.000 4.000

W ± 0.010 –0.000 .410 .410 ... ... ... ... ... ...

a For double guides only

TABLE 4-5 Standard chain guide types for various silent chain widths Chain Pitch (in.) 3

/8 1/ 2 5/ 8 3/ 4 1 1 1/4 11/2 2

Range of Chain Widths (in.) Side Guides 1/ 2 1/ 2 . . . . . .

. . . . . .

Center Guides 3/ to 2 1/ 4 2 3/ to 3 1/ 4 2 1 to 4 1 to 6 2 to 6 2 1/2 to 7 3 to 7 4 to 7

Double Guide 3 to 6 4 to 8 5 to 10 7 to12 7 to 16 8 to 20 8 to 24 8 to 30

ENGINEERING STEEL CHAIN SPROCKET TEETH ENGINEERING STEEL DRIVE CHAIN SPROCKET TOOTH FORM General The sprocket tooth form for engineering steel drive chains is specified in the ASME B29.10 standard. A drawing of the tooth form and the equations for computing the main dimensions are shown in Figure 4-36. It differs from the tooth form for roller chain in that the pitch line clearance and bottom diameter are slightly smaller than the theoretical root diameter. These differences permit the use of a less precisely made tooth form for engineering steel drive chains than the machinecut tooth form for roller chains. Engineering steel chain drives are often operated in locations where mud, dirt, ore, rock dust, etc. get into the chain. These drives are often exposed to the weather. Pitch line clearance and the undercut bottom diameter both help provide proper chain-sprocket action under such adverse conditions.



Sprockets

113

FIGURE 4-36 Standard tooth form for engineering steel offset sidebar drive chain.

The first five terms are given dimensions. All except Nt are obtained from the ASME B29.10 standard. The remaining dimensions that define the tooth form will be discussed in the following paragraphs. Pocket Radius The main purpose of the pocket radius is to reduce the stress concentration between the working face and the bottom diameter. The pocket radius should intersect the working face below the point where the loaded roller makes contact with the tooth. The maximum pocket radius can be equal to the roller radius, but it is better to have a pocket radius smaller than the roller radius. Pitch Line Clearance Pitch line clearance provides at least three benefits. It reduces the possibility of material being trapped in a tooth pocket; it accommodates minor manufacturing inaccuracies; and it reduces the possibility of certain malfunctions. Pitch line clearance reduces the effective pressure angle; however, pitch line clearance of 10% of the chain pitch reduces the pressure angle by only 1 or 2 degrees. Pitch line clearance also reduces the tooth thickness, and too much pitch line clearance can seriously weaken the tooth. Pressure Angle The ability of the sprocket to transmit torque largely depends on the tooth pressure angle. Note that there is no equation for pressure angle given in Figure 4-36. Values for pressure angles are given in ASME B29.10. Generally each tooth in contact on a sprocket should share the load. Therefore, sprockets with few teeth should have small pressure angles, and sprockets with many teeth should have much



114


larger pressure angles. As the pressure angle increases, the tooth force decreases, causing an increase in link tension. Working Face The working face normally is straight, or nearly straight. It may be any shape as long as the pressure angle is maintained within one or two degrees. The face must be long enough to accept the desired amount of chain elongation, but it must not be so long that it interferes with the roller as the chain flexes into and out of the tooth pocket. As a roller swings out of the tooth pocket, it moves away from the working face until the link centerline is normal to the working face. The roller then converges toward the working face plane. The roller path is shown in Figure 4-37. The working face does not normally extend beyond the point of maximum divergence of the roller flex path, but the working face may be longer if the roller flex does not interfere with the tooth. Topping Radius The main purpose of the topping radius is to guide the roller into the tooth gap should a malfunction take place. Generally the topping curve should diverge from the roller flex path.

ENGINEERING STEEL DRIVE CHAIN SPROCKET DIAMETER Figure 4-36 also shows the important diameters of engineering steel drive chain sprockets and the equations for computing them. It is important that the bottom diameter not be larger than the root diameter. The difference is called undersize compensation. It is provided mainly to accept the possible buildup of material in the tooth pockets. It also allows for some production variation. The tolerance on bottom diameter is always negative to avoid chain binding. Note that no equation is given to compute the outside diameter. The outside diameter of an engineering steel sprocket is determined by the factors that are used in the layout of the tooth form. It is accepted “as is.”

FIGURE 4-37 Path of a roller during operation.



Sprockets

115

FIGURE 4-38 Forces on a sprocket tooth as chain tension is applied.

ENGINEERING STEEL DRIVE CHAIN SPROCKET TOOTH PROFILE The final two items in Figure 4-36 define the tooth profile for engineering steel drive chain sprockets. The important thing here is to provide enough side slope—clearance between the tooth and the sidebars—that the chain does not bind or “hang up” on the sprocket tooth.

FORCES

ON THE

SPROCKET TEETH

CHAIN LINKS

AND IN THE

Force is transmitted in an engineering steel chain and sprocket drive through contact between the chain barrel, or roller, and the working face of the tooth. These forces are shown in Figure 4-38. The tooth face is at an angle to the pitch line of the chain. Therefore, when chain tension, T, is applied, two forces result. One is the tooth force, Tt, which is normal to the working face. The other is the roller ejection force, Tr, which is parallel to the tooth face. The tension in the link that goes to the next tooth pocket must counteract the roller ejection force, but that link tension is not exactly opposite to the roller ejection force. The link tension must be greater than the roller ejection force. A component of the link tension must be equal and opposite to the roller ejection force. Then another component must be opposite to the tooth force to keep the system in equilibrium. That second component reduces the tooth force. Friction, which tends to reduce the roller ejection force and the link tension, is not considered here. The tooth and link forces can be determined from Equation 4.16 and Equation 4.17:

Tt = T

TL = T


(

sin 360 / N

(

)

)

sin 360 / N + sin θ

sin θ sin 360 / N + sin θ

(

)

(4.16)

(4.17)


116


where N is the number of teeth, T is the chain tension (in pounds), TL is the link tension (in pounds), Tt is the tooth force (in pounds), T1 is the component of chain tension (in pounds), T2 is the component of chain tension (in pounds), and is the pressure angle. The force diagram shown in Figure 4-38 is repeated at each tooth in contact with the chain. Each tooth absorbs the same percentage of the remaining tension. Link tension at any tooth is the unabsorbed chain tension at that tooth. Although link tension decreases as the link progresses around the sprocket, this tension theoretically never reaches zero. Neglecting friction, the percentage of chain tension not absorbed by the teeth can be found using Equation 4.18: n

⎡ ⎤ sin θ ⎥ , Tu = 100 ⎢ ⎢⎣ sin 360 / N + sin θ ⎥⎦

(

)

(4.18)

where Tu is the unabsorbed chain tension (in percent) and n is the number of the tooth (i.e., the nth tooth).

HOW

THE

SPROCKET ACCOMMODATES BACKLASH

AND

CHAIN WEAR

Pitch line clearance can create backlash between the chain rollers and sprocket teeth. The effect of backlash can be relieved by making the bottom diameter smaller than the root diameter. The difference in diameters must be enough that the roller entering the sprocket from the tight strand is on one side of the tooth pocket, while the roller entering from the slack strand is on the opposite side of the pocket. The position of the chain during backlash is shown in Figure 4-39. Under load, roller ejection force pushes the roller center out to the pitch diameter. As the chain wears, the pitch increases and the roller moves outward on the sprocket teeth until it finds the greater pitch diameter that fits the elongated pitch of the chain. This can be seen in Figure 4-40. Most of the chain tension is absorbed by the sprocket teeth between points B and A. This is so whether the chain is new or worn. Slack strand tension is absorbed between points C and A. At point A, the unabsorbed tight strand tension and unabsorbed slack strand tension is equal. Thus point A is called the balance point. When the system is functioning properly, the working face is the only tooth surface contacting the roller, except at the balance point.

TYPICAL TOOTH FORMS

FOR

ENGINEERING STEEL CHAIN SPROCKETS

Typical tooth forms for different types of engineering steel chains are shown in Figure 4-41. One can see notable differences between sprockets made for drive chains, conveyor chains, and bar-link chains. Actually, although the tooth profiles shown in Figure 4-41 are termed typical, sprocket tooth forms used for engineering steel chains can have quite a large variety of shapes and forms. For example, some of the sprockets for long-pitch conveyor chains have a superficial resemblance to the bar-link chain sprockets of Figure 4-41, but have pockets for the chain rollers at the corners, the flats being to clear the chain through-rod bushings in the center of the links.



Sprockets

117

FIGURE 4-39 Position of chain during backlash.

FIGURE 4-40 Sprockets with worn chain.

Sprockets for engineering steel chain should be purchased with the chain. The buyer should rely on the experience of the manufacturer to furnish the sprocket tooth design that is right for each application.

FLAT-TOP CHAIN SPROCKET TEETH FLAT-TOP CHAIN SPROCKET TOOTH FORMS Type A Tooth Form A drawing of the type A tooth form for standard flat-top chain is shown in Figure 4-42. Equations for computing the important dimensions are also shown in Figure 4-42. The tooth form is simply a pair of pocket radii connected at the bottom diameter by pitch line clearance. The height of the tooth must be cut off near the pitch diameter to clear the bottom surface of the top plates in the chain.



118


FIGURE 4-41 Typical tooth forms for engineering steel chain sprockets.

Type B Tooth Form A drawing of the type B tooth form for standard flat-top chains is shown in Figure 4-43. Equations for computing the important dimensions are also shown in Figure 4-43. This tooth form resembles the tooth form for engineering steel chains in that it has a pressure angle, a working face, and pitch line clearance. Here again, the height of the tooth must be cut off near the pitch diameter to clear the bottom surface of the top plates in the chain.

FLAT-TOP CHAIN SPROCKET DIAMETER Important diameters for standard flat-top chain sprockets are also shown in Figure 4-42 and Figure 4-43. In most cases, the barrels of the chain engage every other tooth on the sprocket, so the number of effective teeth is one-half the number of actual teeth on the sprocket. The number of effective teeth must be used to compute the correct pitch diameter. The maximum outside diameter is larger than the pitch diameter only for sprockets with 19 actual (or 9 1/2 effective) teeth or more. That is one of the reasons why a sprocket in a flat-top chain conveyor should have at least 19 actual (or 9 1/2 effective) teeth.

FLAT-TOP CHAIN SPROCKET TOOTH PROFILES The tooth profiles for standard flat-top chains numbered 24C26 (815) and 24P86 (821) are shown in Figure 4-44. Note that the face width of the sprockets for 24P86 chains is much wider than for 24C26 or 24P26 chains. The dimensions of the groove required for 24P26 chains are shown in Figure 4-45. The groove is required to accommodate the strengthening rib on the underside of 24P26 (820) chain.



Sprockets

119

FIGURE 4-42 Standard flat-top chain tooth form, type A.

SPROCKETS

FOR

SIDE-FLEXING FLAT-TOP CHAIN

Side-flexing flat-top chains, and their sprockets, are not included in the ASME B29.17 standard. Thus, there are no standard dimensions to ensure that chain from one manufacturer will fit the sprockets of any other manufacturer. Always consult the chain manufacturer about sprockets for nonstandard side-flexing chain, and always consult the chain manufacturer about sprockets for any nonstandard flat-top chain.

SPROCKET PITCH DIAMETER One equation can be used to figure the pitch diameter of most any chain sprocket. When each link in the chain has the same nominal pitch, the centers of each tooth space represent a regular polygon. One may then figure the pitch diameter using Equation 4.19. PD = P


1 180 sin N

(4.19)


120


FIGURE 4-43 Standard flat-top chain tooth form, type B.

FIGURE 4-44 Standard flat-top chain sprocket tooth profiles.

Values of pitch diameter for a unity pitch chain, for numbers of teeth from 4 through 100, are shown in Table 4-6. Multiply the value in the table by the actual chain pitch to obtain the pitch diameter of sprockets for a chain with any pitch other than one.

SPROCKET HUBS, KEYS AND KEYWAYS, SETSCREWS, AND SHAFTING SELECTION GENERAL Selecting the sprocket of a chain drive often requires the smallest chain and sprocket that is permitted by the shaft and sprocket hub sizes. The hub size must be large enough to include a standard keyway and setscrew, yet it must be small enough to clear chain link plates or sidebars. Table 4-7 shows the



Sprockets

121

FIGURE 4-45 Standard flat-top sprocket groove.

TABLE 4-6 Pitch diameters of sprockets as a function of chain pitch and number of teeth

maximum bore and hub sizes of roller chain sprockets with 11 to 25 teeth. For applications where single-strand roller chain is not adequate, multiple-strand chain can be used.

KEYS, KEYWAYS,

AND

SETSCREWS

To secure sprockets to the shafts, both keys and setscrews should be used. The selection of sizes is usually based on industry standards, where keys are matched to shafting sizes for strength. Table 4-8 and Table 4-9 list recommended sizes of setscrews and keys of various types for standard shafting sizes. The key is used to prevent rotation of the sprocket on the shaft. Keys should be carefully fitted in the shaft and sprocket keyways to eliminate backlash, especially under fluctuating loads. A setscrew should be located over a flat key to prevent longitudinal movement.



122


TABLE 4-7 Maximum bore and hub diameters of roller chain sprockets (with standard keyway)

TABLE 4-8 Standard setscrew dimensions Sprocket Bore & Shaft Diameter D Inches 1/ — 9/ 2 16 5/ — 7/ 8 8 15/ — 1 1/ 4 16 15/16 — 1 3/8 17/16 — 1 3/4 113/16 — 2 1/4 25/16 — 2 3/4 27/8 — 3 1/4 33/8 — 3 3/4 37/8 — 4 1/2 4 3/4 — 5 1/2 5 3/4 — 7 3/8 7 1/2 — 97/8 10 — 12 1/2


Size of Setscrew Used with Parallel Key Inches 1/ 4 1/ 4 3/ 8 3/ 8 3/ 8 1/ 2 5/ 8 5/ 8 3/ 4 3/ 4 7/ 8 1 1 1/4 1 1/4


Sprockets

123

TABLE 4-9 Standard keys and keyways

In addition, setscrews may be used to prevent axial displacement of the sprocket on the shaft. For such use, setscrews are usually located 90° or 180° from the keyway. The hub thickness must be sufficient to provide a setscrew thread engagement at least equal to the screw diameter.

SELECTION

OF

SHAFTS

The shaft sizes for larger sprockets are usually selected before selecting the proper hub size. This is so whether it is for a drive or a conveyor. The data and examples given in this section are based on sprockets for engineering steel chain, but they apply equally well to shaft selection for roller chain or silent chain drives. Shafts are subject to two forces, a bending moment and a torsional moment. The bending moment is the force that tends to bend the shaft and the torsional moment is the force that tends to twist the shaft. The first step in shaft selection is to calculate these moments. In order to calculate them, we must first know the chain tension, the bearing locations, plus any other forces acting on the shaft. The chain tension must take into account not only the forces involved to do work but, as in an elevator, must consider the weight of the chain, attachments, buckets, and any take-up weights. The bending moment can be calculated using the standard bending moment equation for the given condition. The torsional moment equals the net chain tension times one-half the pitch diameter of the sprocket. The charts and engineering data in the following discussion on the strength of shafting are based on ASME standards.



124


TABLE 4-10 Service factors for shaft selection Service Factor Stationary Shaft

Rotating Shaft

For Bending 1.0

For Torsion 1.0

Suddenly Applied Loads

1.5 to 2.0

1.5 to 2.0

Gradually Applied or Steady Loads

1.5

1.0

Suddenly Applied Loads Minior Shocks only

1.5 to 2.0

1.0 to 1.5

Suddenlly Applied Loads Heavy Shocks

2.0 to 2.5

1.5 to 2.5

Nature of Loading Gradually Applied Loads

FIGURE 4-46 Selection chart for shafts from 1 3/16 to 2 11/16 in diameter.

For ordinary conditions of service, the selection of a shaft may be made using the service factors in Table 4-10 and the shaft selection charts in Figure 4-46 to Figure 4-48. These shafting selection charts are based on 6000 lb./in.2 maximum permissible shear stress for commercial steel shafting with allowance for standard keyways. When a shaft is not weakened by keyways, the size obtained from the chart should be multiplied by 0.91 to obtain the proper diameter. When a material justifying a shear stress other than 6000 lb./in.2 is used, the correct shaft diameter



Sprockets

125

FIGURE 4-47 Selection chart for shafts from 2 15/16 to 5 7/16 in diameter.

FIGURE 4-48 Selection chart for shafts from 515/16 to 12 in diameter.

can be determined by multiplying the shaft diameter obtained from the charts by one of the factors in Table 4-11. The following method of shaft selection is general and applies to all cases of shaft design. The only limitation is that a selection made in this way does not consider the rigidity or the deflection of the shaft, which may be the controlling factor.



126


FIGURE 4-49 Chart for selecting hub classes for sprockets used with engineering steel chains.

TABLE 4-11 Shear stress and strength factors for shaft selection Shearing Stress LBS per sq in. 6,000 8,000 10,000


Factor With Keyway Without Keyway 1.00 .91 .91 .83 .84 .77

Ultimate Strength of Steel Used 55,000 75,000 95,000


Sprockets

127

Example A conveyor has a head shaft that is subjected to 15,200 in.-lb. torsion and 10,200 in.-lb. bending. The shaft is to be of commercial steel. The nature of the loading requires service factors of 1.5 for bending and 1.0 for torsion. To find the proper shaft size, proceed as follows. In Figure 4-46, the torsional moment may be found on the vertical scale for the service factor of 1.0. Draw a line horizontally to the right from the 15,200 point on the scale. At the bottom of the chart the bending moment is given on the horizontal scale. Find the 10,200 point on this scale. Run a line diagonally and to the right until it intersects the 1.5 service factor line, then project a vertical line upward until it intersects the horizontal line you drew first. From the last point of intersection, we find that the nearest standard shaft size is 211/16, so this is the proper size. To the right on this same chart, the horsepower ratings are given per 100 rpm based on the formula: HP =

TS , 63025

(4.20)

where T is torque (in⋅pounds) and S is speed (in rpm). The horsepower is directly proportional to the speed of the shaft (in rpm).

HUB

AND

KEY SIZE

From the working load of the chain and the pitch diameter of the sprocket, the class of hub required can be taken from the hub class chart in Figure 4-49. Assume, for example, a working load of 1500 lb. and a pitch diameter of 20 in. The horizontal and vertical lines intersect at H, which is the required hub class. Now turn to the upper section of Table 4-12. Draw one line down from H and draw another line out from bore size 211/16 in. This assumes the shaft size determined in the preceding example. The lines intersect at 51/4 in., and that is the minimum diameter of the hub. At the same time, the top row of the table shows a maximum allowable torque of 17,000 in.-lb. (15,200 was the actual torque in our example). The bottom row of the table shows a hub length of 3 1/2 in. Finally, the second and third columns of the table show a key size of in. and a setscrew size of in. The righthand column shows that for a sprocket rotating on the shaft (such as a foot sprocket on a conveyor), a smaller hub is permissible—one 4 1/4 in. in diameter. The same holds for a hub setscrewed to the shaft. The bands of figures in Table 4-12 represent a balance between chain and shaft sizes. When the hub class and bore intersect in the blank space below and to the left of the band, it means that the chain and sprocket will not transmit the full torque value of the shaft. When the intersection is above and to the right of the band, the chain and sprocket are stronger than the shaft; the shaft may fail, or the designer has selected a heftier (and more expensive) chain than is needed. Thus the charts can also be used as a design check on the size of the shaft. When the hub class and bore size intersect outside the band, however, the reason may be that the assembly, although correctly designed, has unusual features. For instance, a sprocket installed at one end of a long shaft might sustain a high bending moment in proportion to the torsional moment, and the shaft selected for it would be unusually large compared with the working load. This means that the bore size would be large, the hub class (which is computed by using the working load) would be small, and the lines would intersect below and to the left of the band. In such a case, calculate the hub dimensions this way, as shown in Table 4-12. When the lines intersect above the band, use the first hub diameter left of the point of intersection. When they intersect below the band, use the first hub diameter to the right of the point of intersection. In both cases, the correct hub length is in the same column as the hub diameter.



128


TABLE 4-12 Hub selection table for engineering steel chain sprockets

The performance of the entire conveyor or drive installation depends largely on sprocket-chain interaction. So choosing the right sprocket is as important as choosing the right chain. The sprocket and chain designs must be compatible, and for this reason, sprockets normally should be obtained from the manufacturer of the chain.



5 Roller Chain Drives TYPICAL APPLICATIONS Roller chain drives perform efficiently and economically in a wide range of applications. Roller chain drives are commonly used in drives in industrial conveyors and processing equipment, in construction and agricultural equipment, on bicycles and motorcycles, in oil well drilling rigs, and in large stationary engines. Some typical drives using single-strand and multiple-strand roller chains are shown in Figure 5-1.

SCOPE This chapter covers selecting roller chain drives with only one driver and one driven sprocket using American National Standards (ANS) roller chains conforming to ASME B29.1, “Precision Power Transmission Roller Chains, Attachments, and Sprockets.” Table 2-6 lists general dimensions of chains covered in ASME B29.1. Many manufacturers also make double-pitch drive chain covered in ASME B29.3. Although not covered by any ASME standard, many manufacturers also make high-strength, sealed joint, and corrosion-resistant chains that run on standard ASME B29.1 sprockets. Double-pitch and nonstandard drive chains are beyond the scope of this chapter, so the designer should consult an ACA roller chain manufacturer for help in selecting drives using chains not covered by ASME B29.1. The following guidelines and procedures are intended to help a drive designer manually select a suitable roller chain drive as quickly and efficiently as possible. Some manufacturers offer roller chain drive selection software. These programs eliminate much of the work in selecting a roller chain drive, but be sure to read and follow all of the cautions and restrictions that come with such software.

GENERAL ROLLER CHAIN DRIVE SELECTION GUIDELINES SELECTION OPTIONS Several different chain and sprocket combinations usually can be found for a particular application. It is good practice to make two or three alternative selections and then make a final selection based on cost, space, and weight constraints, required life, or other important factors. The chain normally should be the weakest component in a chain drive because the chain usually is the least costly component to replace. Be careful not to select a chain and sprocket combination with too much capacity. The more expensive bearings and shafting may then become the weakest components in the drive.

CHAIN PITCH The smallest pitch, single-strand chain that will transmit the required power at the specified speed usually is the best selection. Higher speed generally requires a smaller pitch chain.

129



130


FIGURE 5-1 Typical drives with single- and multiple-strand roller chains. R-r

R

r

FIGURE 5-2 Chain rise and fall as it engages a sprocket.

NUMBER

OF

SPROCKET TEETH

Small Sprocket The small sprocket must be large enough to accept the specified shaft diameter and keyway. Table 47 gives maximum recommended bore and hub diameters for roller chain sprockets with up to 25 teeth. A sprocket is essentially a polygon, and the chain strand rises and falls as each roller engages a sprocket tooth, as shown in Figure 5-2. This oscillation is called chordal action and causes cyclic chain velocity variation and roller impact on each sprocket tooth. Velocity fluctuation from chordal action decreases as the number of teeth on the sprocket increases, as shown in Figure 5-3. Therefore, a small sprocket should have more teeth as the speed increases. A suggested minimum number of teeth on a small sprocket for a given chain pitch and shaft speed may be obtained from Table 5-1. The small sprocket, or any sprocket with fewer than 25 teeth, should have an odd number of teeth. In a roller chain, the pin link elongates with wear, but the roller link does not. Pin links and roller links engage the sprocket teeth differently as the chain wears. A given tooth on a sprocket with an even number of teeth engages the same type of link on every revolution and the wear on alternate teeth is noticeably different. However, a given tooth on a sprocket with an odd number of teeth engages a pin link on one revolution and a roller link on the next revolution and the wear on all of the teeth will be more nearly equal.



131

Roller Chain Drives

14%

12%

Velocity Variation, %

10%

8%

6%

4%

2%

0% 5

10

15

20

25

30

Number of Teeth on Sprocket

FIGURE 5-3 Velocity variation from chordal action.

The small sprocket in a roller chain drive should have at least 11 teeth. The chain and sprocket with fewer than 11 teeth has more power capacity than the cold rolled shafting that will fit into the sprocket. That combination can cause the more costly shafting to fail before the chain. The largest sprockets practical should be chosen for a low speed ratio (1:1 to 2:1) drive that has the chain slack span on top. This will reduce the possibility of contact between the chain strands as the chain wears. Large Sprocket The number of teeth on the large sprocket limits the maximum allowable chain wear elongation. The chain elongates with wear and when chain elongation, over the arc of engagement, nears onehalf pitch, the chain can jump teeth and damage the chain or sprocket. The ACA recommends that maximum permissible chain wear elongation be no more than 3%. The maximum elongation, in percent, that a large sprocket will accept is 200/(number of teeth on the large sprocket). So a sprocket with 67 teeth is the largest that can utilize the maximum allowable chain wear elongation of 3%. The large sprocket normally should have 120 teeth or less because it is difficult, and expensive, to manufacture sprockets with more than 120 teeth.

HARDENED SPROCKET TEETH Tooth loads and engagement frequency increase with fewer teeth on the sprocket. Sprocket teeth should be hardened when the number of teeth is 25 or less and the sprocket is used in: • • • •

heavily loaded drives abrasive conditions high-speed drives drives that require extremely long life

CHAIN WRAP

ON

SMALL SPROCKET

The chain should wrap at least 120 degrees, or three teeth, on the small sprocket. The wrap may be as little as 90 degrees only if excellent chain adjustment is maintained. The chain can jump



132


TABLE 5-1 Suggested minimum number of teeth on a small sprocket Small sprocket speed 10,000 8,000 6,500 5,000

Chain pitch

27 25 25 23

26 25

27

4,000 3,500 3,000 2,500

22 22 21 21

24 24 23 22

25 25 24 23

27 26 25 24

27 26 25

27

2,000 1,760 1,600 1,400

20 19 19 18

21 21 20 20

22 22 22 21

23 23 22 22

24 24 23 23

25 25 24 24

27 26 25 25

26 26

26

1,200 1,000 900 800

18 17 17 17

19 19 18 18

20 20 19 19

21 21 20 20

22 21 21 20

23 22 22 22

24 23 23 22

25 24 24 23

26 25 24 24

26 25 25 24

26 26 25

27 26 25

26

700 600 500 400

16 16 15 15

18 17 16 16

18 18 17 17

19 19 18 17

20 19 19 18

21 20 20 19

22 21 21 20

23 22 21 20

23 23 22 21

24 23 22 22

24 24 23 22

25 24 23 22

26 25 24 23

300 200 100 90

14 13 11 11

15 14 12 12

16 15 13 13

16 15 13 13

17 16 14 14

18 17 15 14

19 17 15 15

19 18 16 15

20 18 16 16

20 19 17 16

21 19 17 17

21 20 17 17

22 20 18 18

80 70 60 50

11 11

12 11 11 11

12 12 12 11

13 13 12 12

13 13 13 12

14 14 13 13

15 14 14 13

15 15 14 14

16 15 15 14

16 16 15 15

16 16 15 15

17 16 16 15

17 17 16 16

11

11 11

12 11

12 12 11

13 12 11

13 13 12

14 13 12 11

14 13 12 11

14 14 13 11

15 14 13 11

15 14 13 12

0.250

40 30 20 10

0.375 0.500 0.625 0.750 1.00 1.25 1.50 1.75 2.00 2.25 2.50 3.00

teeth and damage the chain or sprocket if chain adjustment is not closely maintained with a wrap of less than 120 degrees. The wrap on the small sprocket will always be 120 degrees or more when the drive ratio is 3:1 or less.

DRIVE RATIO The drive ratio is the speed of the faster shaft divided by the speed of the slower shaft. The drive ratio normally should not be more than 7:1 in a single-stage drive (Figure 5-4a), but may be as



Roller Chain Drives

133

FIGURE 5-4 7:1 ratio drive layouts.

FIGURE 5-5 Minimum center distance.

large as 10:1 with careful design and very good maintenance. A two-stage drive usually is better (Figure 5-4b) when the drive ratio is more than 7:1. Check high-ratio drives carefully to ensure there is adequate wrap on the small sprocket.

CHAIN LENGTH Chain length must always be an integral number of pitches. Design the drive to use an even number of pitches whenever possible. An offset link is required in a chain with an odd number of pitches. Avoid using offset links because they reduce chain capacity 30% or more and are expensive.

CENTER DISTANCE Minimum Center Distance To avoid tooth interference, the minimum center distance is one-half the sum of the outside diameters of the two sprockets (Figure 5-5). To ensure adequate wrap on the small sprocket, the ACA suggests a minimum center distance of the sum of the outside diameter of the large sprocket plus one-half the outside diameter of the small sprocket.



134


FIGURE 5-6 Preferred center distance.

Practical Center Distances It is good practice to set the center distance at 30 to 50 times the chain pitch (Figure 5-6). The longest practical center distance is about 80 times the chain pitch because chain sag and catenary tension become very large. It may be desirable to set the center distance to as little as 20 times the chain pitch for a pulsating drive or a drive with fewer than 17 teeth on the small sprocket. Adjustable Centers Chain drive designers should provide adjustable centers, commonly a moveable motor mount, whenever possible. The range of adjustment should be equal to at least 1∫ pitches of chain. Fixed Center Distance Sometimes adjustable centers or idlers cannot be provided. Then the designer must calculate and specify an exact center distance. The designer should make a conservative selection (overchain the drive somewhat) and specify type B or type C lubrication to minimize wear.

CHAIN WEAR

AND

SAG

As explained in chapter 3, chain elongates as it wears. Wear elongation is limited to a maximum of about 3% for standard and heavy series chain drives. However, wear elongation may be limited to only 1% in drives where timing or smooth operation is critical. In addition, using sprockets with more than 67 teeth gradually reduces the allowed wear percentage for all teeth more than 67. Elongation appears as sag in the slack span, as shown in Figure 5-7. The designer must provide sufficient clearance to prevent the chain from contacting the bottom of the chain case or other parts of the machine. Information on the design of chain cases can be found in chapter 13.

IDLER SPROCKETS When adjustable centers cannot be provided, an idler sprocket may be used to maintain correct static chain tension (Figure 5-8 and Figure 5-9). An idler sprocket should have at least as many teeth as the small sprocket, and should engage the slack span of the chain. An idler sprocket engaging the taut strand will reduce the chain’s service life because there will be more articulations under load. The chain should engage at least three teeth on the idler sprocket. Where two consecutive sprockets mesh with opposite sides of the chain, leave at least three free pitches of chain between the points of engagement.



Roller Chain Drives

FIGURE 5-7 Chain sag with wear elongation.

FIGURE 5-8 Idler sprocket application on horizontal drives.

FIGURE 5-9 Idler sprocket application on vertical drives.


135


136


FIGURE 5-10 Preferred drive arrangements.

MULTIPLE-STRAND CHAIN Where the transmitted power or speed is too high, or the space is too small, for a single-strand chain with sufficient capacity, the designer may need to select multiple-strand chain. Multiplestrand chain can transmit more power at higher speeds than larger single-strand chain with equal or greater load capacity.

DRIVE ARRANGEMENTS Drive arrangements that represent good practice are shown in Figure 5-10. Consult an ACA roller chain manufacturer about other drive arrangements.

MULTIPLE-SPEED DRIVES When a drive operates over a range of speeds and loads, the designer must ensure that the selected chain and sprockets have adequate capacity at the most severe operating condition. Those conditions are often, but not always, the highest and lowest operating speeds.

MULTIPLE DRIVEN SPROCKETS Roller chain drives with multiple driven sprockets are fairly common (Figure 5-11). The drive designer should consult an ACA roller chain manufacturer for advice on drives with multiple driven sprockets. This is because each manufacturer uses different service factors for multiple driven sprockets.



Roller Chain Drives

137

FIGURE 5-11 Multiple sprocket drive.

FIGURE 5-12 Rack drive.

No equations are given to calculate the required chain length on drives with multiple driven sprockets. The chain length usually is found by a large-scale layout or multiple geometric calculations. Software is available to select roller chain drives with multiple driven sprockets. That software is very useful and convenient, but the methods and equations are proprietary to the particular developer.

RACK DRIVES An unusual use of roller chain to drive several sprockets simultaneously is the rack drive, illustrated in Figure 5-12. In a rack drive, the pinions are arranged with their tooth contact surfaces in a straight line, and a straight run of roller chain acts as a rack. The pinions usually have a cycloidal tooth form to enable proper single-tooth engagement with the chain and a guide shoe may be used at each sprocket to keep the chain rollers engaged with the sprockets. Consult an ACA roller chain manufacturer for assistance with designing a rack drive.



138


ROLLER CHAIN DRIVE SELECTION PROCEDURE STEP 1: OBTAIN NECESSARY INFORMATION Obtain the following listed information before selecting a roller chain drive. Make every effort to obtain all of the needed information. • • • • • • • • •

Type of power source. Type of driven equipment. Power required, or input power. Size and speed of the driver shaft. Size and speed of the driven shaft. Shaft center distance and drive arrangement. Available center distance adjustment, if any. Space restrictions. Available lubrication.

In addition, the designer should determine if there are any unusual drive conditions, such as • • • • • •

Adverse environment (corrosive, wet, dirty, etc.). Frequent stops and starts. High starting or inertial loads. Temperatures greater than 150˚F or less than 0˚F. Large cyclic load variations in each revolution. Multiple driven shafts.

If any of the listed or other unusual drive conditions are found, contact an ACA roller chain manufacturer for assistance. Many chain manufacturers offer self-lubricating, sealed joint, corrosion-resistant, plated, coated, or other specialty chains designed to operate in particular hostile environments.

STEP 2: DETERMINE

THE

SERVICE FACTOR

The nominal required power, or input power, is usually given. Peak power may be much larger, depending on the type of power source and driven equipment. Drive designers use a service factor to account for the difference between nominal and peak power. Service factors to estimate the difference between nominal and peak loads induced by combinations of different types of power sources and driven equipment are shown in Table 5-2. The load characteristics of various types of driven equipment are shown in Table 5-3.

STEP 3: CALCULATE DESIGN POWER Calculate the design power by multiplying the nominal required power, or input power, by the service factor obtained from Table 5-2.

STEP 4: SELECT

A

PRELIMINARY CHAIN SIZE

Enter the chain selection charts, Figure 5-13 and Figure 5-14, with the design horsepower and the speed of the small sprocket (faster shaft). The area in which the two lines intersect indicates the pitch size (chain number) of the preliminary chain selection.



139

Roller Chain Drives

TABLE 5-2 Service factors for roller chain drives Type of Input Power Type of Driven Load Smooth Modreate Shock Heavy Shock

Internal Combustion Engine with Hydraulic Drive 1.0 1.2 1.4

Electric Motor or Turbine 1.0 1.3 1.5

Internal Combustion Engine with Mechanical Drive 1.2 1.4 1.7

TABLE 5-3 Load classifications Smooth load Agitators – Pure liquid Blowers – Centrifugal Bucket elevators – Uniformly loaded or fed Conveyors – Uniformly loaded or fed Feeders – Rotary table Generators Machine tools – Drills, grinders, lathes Pumps – Centrifugal Screens – Rotary, uniformly fed

Moderate shock load Beaters Bucket elevators – NOT uniformly loaded or fed Clay working machinery – Pug mills Compressors – Centrifugal Reciprocating, 3+ cylinders Conveyors – Heavy duty, NOT uniformly loaded Cranes and hoists – Medium duty, skip hoists (travel and trolley motion) Dredges – Cable, reel, and conveyor drives Feeders – Apron, screw, rotary vane Food processing machinery – Slicers, mixers, grinders Kilns and dryers Machine tools – Boring mills, milling machines, hobs, shapers Mills – Ball, pebble, and tube Paper processing machinery – Pulp grinders Pumps – Reciprocating, 3+ cylinders Textile machinery – Calendars, mangles, nappers Woodworking machinery

Heavy shock load Boat propellers Clay working machinery – Brick presses Briquetting machines Compressors – Reciprocating, 1 or 2 cylinders Conveyors – Reciprocating and shaker Cranes and hoists – Heavy-duty, logging, and rotary drilling Crushers Dredges – Cutter head, jig, and screen drives Feeders – Reciprocating, shaker Machine tools – Punch presses, shears, plate planers, cold formers Mills – Draw benches, hammer, rolling, wire drawing Paper processing machinery – Calendars, mixers, sheeters Pumps – 1 or 2 cylinders Printing presses Textile machinery – Carding machinery

If the power, or speed, is more than the rating for single-strand chain, multiple-strand chain may be needed. Multiply the rated power, or divide the design power, by the multiple-strand factor from Table 5-4 and select a multiple-strand chain from Figure 5-13 or Figure 5-14. This chapter has factors for selecting multiple-strand chains only of up to four strands. However, many ACA roller chain manufacturers offer wider multiple-strand chains. Consult an ACA roller chain manufacturer for assistance with selecting five-strand or wider multiple-strand chains. Note that an optimum selection is where the drive operates near the peak of the rating curve. That is where one can use the maximum capacity of the chain.



140


1000.0 1000 700

240 200 180 160 140

400

200

120

100 100.0

100

70

Single-Strand Design Horsepower

80 40 60 50

20

40 10 10.0 35

7 41

4

25

2

1 1.0 0.7 0.4

0.2

0.1 10

100

1000

10000

Rotational speed of small (25-tooth) sprocket, r/min

FIGURE 5-13 Chain selection chart: standard series.

STEP 5: SELECT

THE

SMALL SPROCKET

AND

SPECIFIC CHAIN SIZE

Select the Small Sprocket If the preliminary selection is single-strand chain, enter the rating table (Table 5-5 through Table 5-28) with the faster shaft speed for the selected chain. Follow that column down until the design power is reached or exceeded. The number of teeth on the small sprocket can be read from the leftmost column of the table. Check this selection against Table 4-7 to ensure that it will accommodate the specified shaft size. Also, check this selection against Table 5-4 to ensure that the number of teeth on the sprocket is appropriate for the shaft speed (within two or three teeth). Repeat this procedure for heavy series chain of the same pitch. If the preliminary selection is multiplestrand chain, or if you want to consider multiple-strand chain, divide the design power by the multiple-strand factor from Table 5-4 before entering the rating table. Select a Specific Chain Size It is suggested that the drive designer select a small sprocket and chain from at least the next smaller and next larger pitch sizes. The designer may then select the chain that best meets the user’s particular requirements.



141

Roller Chain Drives

FIGURE 5-14 Chain selection chart: heavy series.

TABLE 5-4 Multiple-strand factors Number of Strands 2 3 4

STEP 6: SELECT

THE

Multiple-Strand Factor 1.7 2.5 3.3

LARGE SPROCKET

Calculate the number of teeth on the large sprocket by multiplying the number of teeth on the small sprocket by the desired drive ratio (faster shaft speed/slower shaft speed). Round the result to the nearest integral number of teeth. Check the sprocket sizes and center distance to be sure the drive will fit within any space restrictions. If it does not fit, return to the previous step and consider multiple-strand chain. If the drive ratio is critical, one can adjust the number of teeth on the small and large sprockets to obtain an exact, or more nearly exact, drive ratio. If the drive ratio is not critical, one can adjust the number of teeth on the small and large sprockets to permit the use of stock sprockets with an acceptable speed ratio.



142


TABLE 5-5 Center Distance Factors L-n N-n 13 12 11 10 9 8 7 6 5 4.8 4.6 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 2.9 2.8

KCD 0.24991 0.24990 0.24988 0.24986 0.24983 0.24978 0.24970 0.24958 0.24937 0.24931 0.24925 0.24917 0.24907 0.24896 0.24883 0.24868 0.24849 0.24825 0.24795 0.24778 0.24758

STEP 7: CALCULATE

THE

L-n N-n 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 1.95 1.90 1.85 1.80 1.75 1.70 1.68 1.66 1.64 1.62 1.60 1.58 1.56

KCD 0.24735 0.24708 0.24678 0.24643 0.24602 0.24552 0.24493 0.24421 0.24380 0.24333 0.24281 0.24222 0.24156 0.24081 0.24048 0.24013 0.23977 0.23938 0.23897 0.23854 0.23807

L-n N-n 1.54 1.52 1.50 1.48 1.46 1.44 1.42 1.40 1.39 1.38 1.37 1.36 1.35 1.34 1.33 1.32 1.31 1.30 1.29 1.28 1.27

KCD 0.23758 0.23705 0.23648 0.23588 0.23524 0.23455 0.23381 0.23301 0.23259 0.23215 0.23170 0.23123 0.23073 0.23022 0.22968 0.22912 0.22854 0.22793 0.22729 0.22662 0.22593

L-n N-n 1.26 1.25 1.24 1.23 1.22 1.21 1.20 1.19 1.18 1.17 1.16 1.15 1.14 1.13 1.12 1.11 1.10 1.09 1.08 1.07 1.06

KCD 0.22520 0.22443 0.22361 0.22275 0.22185 0.22090 0.21990 0.21884 0.21771 0.21652 0.21526 0.21390 0.21245 0.21090 0.20923 0.20744 0.20549 0.20336 0.20104 0.19848 0.19564

CHAIN LENGTH

Chain length is a function of the center distance and the number of teeth on each of the sprockets. Chain length must be an integral number of pitches, and preferably an even number of pitches to avoid using an offset link. Sometimes an exact chain length cannot be calculated because the required length of the chain changes as it engages each sprocket tooth. However, a nearly exact chain length can be calculated using Equation 5.1, which is derived from the data in Figure 5-15. Note that the chain length calculated by Equation 5.1 and Equation 5.2 is in pitches. That calculated chain length must be multiplied by the chain pitch to convert it to inches (or millimeters): ⎡ ⎤ N+n α L = 2 ⎢C cos α + + N − n ⎥ pitches, 4 360 ⎣ ⎦

(

)

(5.1)

where C is the desired center distance (in pitches), L is the chain length (in pitches), N is the number of teeth on the large sprocket, and n is the number of teeth on the small sprocket. Equation 5.1 can be simplified to Equation 5.2. That gives a good approximation of the required chain length and is adequate when the center distance is adjustable by at least plus or minus onehalf pitch:


143



Roller Chain Drives

TABLE 5-6 Horsepower ratings for single-strand no. 25 chain




144


145



Roller Chain Drives





146


147



Roller Chain Drives





148


149



Roller Chain Drives

TABLE 5-12 Horsepower ratings for single-strand no. 60H chain




150


151



Roller Chain Drives





152


153



Roller Chain Drives





154


155



Roller Chain Drives





156


157



Roller Chain Drives





158


159



Roller Chain Drives





160


161



Roller Chain Drives





162


163



Roller Chain Drives





164


165



Roller Chain Drives

TABLE 5-28 Horsepower ratings for no. 240H chain


166


FIGURE 5-15 Chain length calculation.

pitches.

STEP 8: CALCULATE

THE

(5.2)

FINAL CENTER DISTANCE

The calculated chain length is often fractional. If so, the designer must select a whole, preferably even number of pitches, and determine the center distance from that. The most convenient way to determine center distance is by the use of center distance tables, or personal computer programs, provided by some ACA roller chain manufacturers. An approximate center distance, in pitches, can be calculated using Equation 5.3. Equation 5.3 was derived by rearranging Equation 5.2, and is acceptable when the center distance is adjustable by at least plus or minus one-half pitch. Note that the center distance calculated by Equation 5.3 and Equation 5.4 is in pitches. That calculated center distance must be multiplied by the chain pitch to convert it to inches (or millimeters):

pitches.

(5.3)

A more exact center distance C can be calculated using Equation 5.4 from the data in Figure 5-16:

pitches.

(5.4)

The trigonometric functions in Equation 5.4 have been combined into a single factor, KCD, for selected values of the term

. Values for the factor KCD are tabulated in Table 5-5. Using the

factor KCD, a nearly exact center distance C’ can be calculated using Equation 5.4a: pitches.


(5.4a)


167

Roller Chain Drives

The center distance obtained from a table, or computer program, or calculated from Equation 5.4 or Equation 5.4a must be multiplied by the chain pitch to obtain the center distance in inches (or millimeters). The center distance obtained from a table, or computer program, or calculated from Equation 5.4a are maximums. Any tolerance applied must be negative only. If a positive tolerance is applied, it may damage the chain or other components of the drive.

STEP 9: SELECT

THE

TYPE

OF

LUBRICATION

The designer should select the type of lubrication recommended in the power rating tables. More detailed information on roller chain drive lubrication can be found in chapter 13.

SAMPLE ROLLER CHAIN DRIVE SELECTION STEP 1: OBTAIN NECESSARY INFORMATION The power source is an electric motor. The driven equipment is a two-cylinder pump. Input power is 40 hp. The driver shaft turns at 900 rpm and is 2.375 in. in diameter. We want to turn the driven shaft at 300 rpm and it is 3 in. in diameter. The desired center distance is 40 in. and the shafts and centers are both horizontal. The center distance adjustment can be 2 in. or more if needed. Lubrication will be what is recommended by the ratings. There are no space restrictions or unusual drive conditions.

STEP 2: DETERMINE

THE

SERVICE FACTOR

The service factor, from Table 5-2, is 1.5.

STEP 3: CALCULATE

THE

DESIGN POWER

Input power is 40 hp and the service factor is 1.5. Thus the design power is 40 hp × 1.5 = 60 hp.

STEP 4: SELECT

A


Entering Figure 5-13 with a design power of 60 hp and a speed of 900 rpm yields a preliminary selection of ANS no. 80 chain (on a 25T sprocket). Entering Figure 5-14 with a design power of 60 hp and a speed of 900 rpm yields a preliminary selection of ANS no. 80H chain (on a 25T sprocket). However, since no. 80 chain is adequate, there is no need for no. 80H. The preliminary selection is no. 80 chain.

STEP 5A: SELECT

THE

SMALL SPROCKET

Entering Table 5-13, the rating table for no. 80 chain, at 900 rpm shows that no. 80 chain on a 21tooth sprocket has adequate capacity. The no. 80, 21-tooth sprocket will accept the 2.375-in. diameter shaft (Table 4-7) and is very close to the suggested minimum of 22 teeth for no. 80 chain at 900 rpm. Examining Table 5-15 and Table 5-11, the rating tables for no. 100 and no. 60 chain, shows that a no. 100 chain on a 19-tooth sprocket or a no. 60-2 chain on a 28-tooth sprocket would also be adequate. Both of these sprockets will accept a 2.375-in. diameter shaft.

STEP 5B: SELECT

A

SPECIFIC CHAIN SIZE

The suggested minimum number of teeth for no. 100 chain at 900 rpm is 23. The no. 100 chain on a 19-tooth sprocket might run too rough. A no. 60-2 chain on a 28-tooth sprocket would be



168


considerably more expensive than a no. 80 chain on a 21-tooth sprocket. The best selection appears to be a no. 80 chain on a 21-tooth sprocket.

STEP 6: SELECT

THE

LARGE SPROCKET

The speed ratio is 900/300 = 3.0. Thus the large sprocket should have 3.0 ∞ 21 teeth = 63 teeth. This is a nonstock sprocket for most manufacturers. The nearest size stock sprocket is a 65-tooth sprocket. The 65-tooth sprocket gives an output speed of 291 rpm, or 3% less than the desired speed. If maintaining the output shaft speed is critical, the added expense of a made-to-order 63tooth sprocket might be justified. In this example we will assume that a 3% speed difference is acceptable and select the stock 65-tooth sprocket.

STEP 7: CALCULATE

THE

CHAIN LENGTH

Now we can calculate the chain length using Equation 5.2: L = 2 ( 40 ) +

65 + 21 ( 65 − 21) + = 80 + 43 + 1.23 = 124.23 . 2 4 π 2 ( 40 ) 2

We round the chain length down to 124 pitches to obtain an even number of pitches and avoid using an offset link.

STEP 8: CALCULATE

THE


We now calculate the final center distance using Equation 5.3: C=

124 − 43 + 78.54 = 39.9 ± 0.5 pitches. 4

Next, we calculate a more nearly exact center distance using Equation 5.4a: L−n = 2.34 , N −n and from Table 5-28, KCD = 0.24618 (interpolated between 2.3 and 2.4): C′ = 0.24618(2(124)–65–21) = 0.24618(162) = 39.88 pitches (and inches).

STEP 9: SELECT

THE

TYPE

OF

LUBRICATION

The type of lubrication, indicated in Table 5-13, is type B, “Oil Bath or Slinger Disc Type Lubrication.” A chain case is required for type B lubrication. Information on the design of chain cases can be found in chapter 13.

EQUATIONS FOR HORSEPOWER RATINGS GENERAL Extensive research by ACA members has produced reliable power ratings for ANS roller chain drives conforming to the ASME B29.1 standard. The power capacity of roller chain drives operating



169

Roller Chain Drives

FIGURE 5-16 Sample roller chain power rating chart.

within standard conditions is limited by link plate fatigue strength, roller and bushing impact fatigue, galling between the pin and bushing, the type of lubrication. The standard conditions are • • • • • •

Chain length of 100 pitches. Service factor of one. A well-aligned two-sprocket drive on parallel horizontal shafts. Use of the recommended type of lubrication. A nonhostile environment. An expected service life of approximately 15,000 hours.

A sample graph of the horsepower ratings for no. 60 chain is shown in Figure 5-16.

LINK PLATE FATIGUE STRENGTH Equation 5.5 defines the power rating of ANS roller chains, limited by link plate fatigue strength: HPL = K L nR 0.96 p ( 3.0− 0.07 p ) , where HPL is the horsepower rating limited by link plate fatigue strength; KL is 0.0044 for all standard series chains except no. 41, 0.0044(TH/TS)0.5 for heavy series chains, and 0.00242 for no. 41 chain; n is the number of teeth on the small sprocket; p is the chain pitch (in inches); R is the speed of the small sprocket (in rpm); TH is the link plate thickness for heavy series chains; and TS is the link plate thickness for standard series chains.


(5.5)


170


ROLLER

AND

BUSHING IMPACT

Standard Conditions Equation 5.6 defines the power rating of ANS chains limited by roller and bushing impact fatigue at the standard conditions of 15,000 hours of life and 100 pitches of chain length: HPR =

K R n1.5 p 0.8 , R1.5

(5.6)

where HPR is the horsepower rating limited by roller and bushing impact fatigue; KR is 17,000 for all standard and heavy series chains except no. 25, no. 35, and no. 41, 29,000 for no. 25 and no. 35 chains, and 3400 for no. 41 chain. Adjustment for Life and Chain Length The power rating at a chain length and life other than 100 pitches and 15,000 hours may be obtained by multiplying Equation 5.6 by the following factors: For chain length other than 100 pitches, multiply Equation 5.6 by the factor ⎛ ChainLength, pitches ⎞ K Length = ⎜ ⎟⎠ ⎝ 100

0.4

.

For life other than 15,000 hours, multiply Equation 5.6 by the factor ⎛ ⎞ 15000 K Life = ⎜ ⎝ DesiredLife, hours ⎟⎠

0.4

.

These factors may be combined to yield ⎛ ChainLength, pitches ⎞ K Combined = 7.42 ⎜ ⎝ DesiredLife, hours ⎟⎠

0.4

.

Galling between Pins and Bushings Equation 5.7 defines the power rating of ANS chains limited by galling between the pins and bushings: ⎡ R 3n 3 p 5 (2 + 0.03226 n ) ⎤ HPG = K G np 2 − ⎢ ⎥, 3.96 ⋅ 1012 ⎣ ⎦ where


(5.7)


171

Roller Chain Drives

HPG is the horsepower rating limited by galling between the pins and bushings; KG is 6.452 for all standard series chains except no. 41, 5.807 for heavy series chains, and for no. 41 chain, use the same speed limits as for no. 40 chain.

TYPE

OF

LUBRICATION

Equation 5.7, with a different constant KG, also defines the power rating of ANS chains limited by the type of lubrication. Oil Bath or Slinger Disc Lubrication For oil bath or slinger disc lubrication, KG equals 3.226 for all standard series chains except no. 41, 2.903 for heavy series chains, and for no. 41 chain, use the same speed limits as for no. 40 chain. Manual or Drip Lubrication For manual or drip lubrication, KG equals 0.3226 for all standard series chains except no. 41, 0.2903 for heavy series chains, and for no. 41 chain, use the same speed limits as for no. 40 chain.

ADJUSTMENT

FOR

CHAIN LENGTH

The galling and lubrication limits are greater for longer chains than for shorter chains. If the selected chain length, L, is much longer or shorter than 100 pitches, Equation 5.7 can be modified to account for the different chain length. The modified equation is shown in Equation 5.8: ⎡ R 3n 3 p 5 ((2 + 0.03226 n ) / L ) ⎤ HPG = K G np 2 L − ⎢ ⎥. 3.96 ⋅ 1012 ⎣ ⎦

(5.8)

One normally needs to account for chain length only if the chain is operating at the galling (or lubrication) limit and the chain length is more than 10 pitches different from 100 pitches.

HORSEPOWER RATING TABLES

FOR

ANS CHAINS

The horsepower rating tables for ANS standard and heavy series roller chains at the standard conditions listed above are shown in Table 5-5 through Table 5-28.

VIBRATION GENERAL It is well known that a roller chain can vibrate noticeably when the frequency of an exciting source is close to one of the natural frequencies of the chain. Under certain conditions, the vibration may be so severe that it can damage or destroy the chain or the drive. Some factors of the drive are fixed, such as shaft speed, the amount of power transmitted, the load characteristics of the driven machine, and any space limitations. Other factors may be controlled



172


by the drive designer, such as the pitch, the number of strands of chain, the number of teeth on the sprockets, and the type of input power. When the designer knows the fixed characteristics of the drive and the factors that can be controlled, he or she can use the following explanations and equations to determine if a proposed drive might have a serious vibration problem. Then the designer can select a chain and sprockets that will minimize the chances of destructive vibration. The information given here is very basic and brief. If chain vibration is suspected or found, contact an ACA roller chain manufacturer for assistance.

SOURCES

OF

EXCITEMENT

Large Cyclic Loads Many roller chain drives have large cyclic loads or impulses. These cyclic loads may occur once, or a few times, per revolution and they may come from either the driven machine or input power source. The magnitude of the impulse depends on how much the peak load exceeds the mean load, how much the peak power pulse exceeds the mean input power, the inertia of the driving and driven machines, and the stiffness of the drive. The frequency of the impulses is the sprocket speed, in revolutions per second, divided by the number of impulses per revolution. Machines that cause one impulse per revolution are punch presses, shears, one-cylinder pumps or compressors, and one-cylinder engines. Machines that cause a few impulses per revolution are duplex and triplex pumps or compressors, two-, three-, and four-cylinder internal combustion engines, and other reciprocating or cam-actuated machines. The effects of large cyclic loads often can be reduced by putting a fluid coupling or some other type of cushioning device in the drive. Chordal Action As was shown earlier in this chapter, chordal action produces at least two possible sources of vibration. Each time a chain roller engages a sprocket tooth, chordal action makes the chain span both rise and fall laterally, and increase and decrease in speed. The procedure for calculating the force caused by chordal action is beyond the scope of this book. However, it is known that the force increases very rapidly with speed and somewhat less rapidly with the chain pitch. The frequency of the impulses caused by chordal action is the tooth contact frequency, or the sprocket speed, in revolutions per second, times the number of teeth on the sprocket. The effects of the impulses caused by chordal action can be reduced by selecting a smaller chain pitch or a sprocket with more teeth. Multiple-strand chain may be needed when a smaller pitch chain or a sprocket with more teeth is used. Roller-Tooth Impact When the chain roller engages a sprocket tooth, there is an impact caused by chordal action. The maximum force during this impact depends on the chain pitch, the sprocket speed, the effective stiffness of the roller against the sprocket tooth, and the effective mass of the part of the chain involved in the impact. The effective stiffness and mass are very difficult to determine. They are affected by sprocket and roller materials, the amount and quality of lubrication, and possibly other factors. However, it is known that roller-tooth impact forces increase with chain pitch and sprocket speed. The frequency of roller-tooth impact is the tooth contact frequency and its harmonics. Roller-tooth vibration, and the impacts that incite it, are the source of most of the noise in a roller chain drive. The amplitude of roller-tooth vibration increases approximately with the square of sprocket speed, so it is very important in high-speed drives. This is one of the reasons why the power capacity of a roller chain decreases so rapidly at high speeds (see Equation 5.6). The effects of roller-tooth impact forces can be reduced by selecting a smaller chain pitch or a sprocket with more teeth. Multiple-strand chain may be needed when a smaller pitch chain is used.



173

Roller Chain Drives

TYPES

OF

VIBRATION

AND

NATURAL FREQUENCIES

Lateral Vibration In lateral vibration, the chain vibrates up and down (in a horizontal drive) about the chain’s axis like a plucked string. It is the most visible, and may be the most common, type of chain vibration. The natural frequency of lateral vibration in a chain is given by Equation 5.9: fL =

n 2l

gT Hz, W

(5.9)

where fL is the natural frequency of lateral vibration in the chain (in Hz), n is an integer representing the harmonic of the vibration, l is the length of the taut span of the chain (in ft), g is a gravitational constant (32.17 ft/sec2), T is the tension applied to the chain (in lb), and W is the unit weight of the chain (in lb/ft). The natural frequency for lateral vibration is usually quite low. The excitation from chordal action is probably too small at such slow speeds to cause noticeable vibration. However, the excitation from a large cyclic load may be enough to cause damaging vibration at resonance. The frequency of the exciting force should be at least 1.4 times the natural frequency to avoid resonance and damaging vibration. The very low tension in the slack span normally gives a natural frequency that is too low to cause a vibration problem. A spring-loaded idler in the slack span may increase the tension and natural frequency enough for it to cause a destructive vibration, either at the resonant frequency or at one of the harmonics of that frequency. The drive designer should always check the resonant frequency of the slack span when considering or using a spring-loaded idler in the slack span. Axial, or Spring-Type, Vibration In axial vibration, the chain acts like a spring connected between two rotors. This type of vibration is not readily seen, but at resonance it may be identified by increased noise. The natural frequency of axial vibration in a chain is given by Equation 5.10: fA =

1 2π

(

k J1R22 + J 2 R12 lJ1J 2

)

Hz,

(5.10)

where fA is the natural frequency of axial vibration in chain (in Hz), J1 is the rotating inertia related to the input sprocket (in lbm·ft2/g), J2 is the rotating inertia related to output sprocket (in lbm·ft2/g), R1 is the pitch radius of the input sprocket (in ft), R2 is the pitch radius of the output sprocket (in ft), g is the gravitational constant (32.17 ft/sec2), k is the unit stiffness of the chain (in lbf), and k is approximately 1,000,000p2 lbf for ANS chains, where p is the chain pitch (in inches).



174


Here again, the natural frequency for axial vibration is usually quite low and the force from chordal action at such slow speeds is probably too small to cause noticeable vibration. However, the impulse from a large cyclic load may be enough to cause damaging vibration at resonance. The frequency of the exciting force should be at least 1.4 times the natural frequency to avoid resonance and damaging vibration. Wave-Type Vibration In wave-type vibration, the chain vibrates axially like an elastic bar that is excited at its ends. Wavetype vibration usually cannot be seen. The natural frequency of wave-type vibration in a chain is given by Equation 5.11: fW =

n 2l

gk Hz, W

(5.11)

where fW is the natural frequency of wave-type vibration in chain (in Hz). The natural frequency of wave-type vibration is usually much higher than that of either lateral or axial vibration. Often it is close to the tooth contact frequency of a drive running at moderate to high speeds. When that happens, wave vibration can increase chain tension quite a lot and cause early chain failure. Damaging wave-type vibration can also occur when the tooth contact frequency matches the second harmonic of the natural frequency of the chain, but that is beyond the scope of this book. The designer should contact an ACA roller chain manufacturer for assistance when this type of vibration is found. Roller-Tooth Vibration In roller-tooth vibration, the chain roller vibrates from the impact of the roller against the sprocket tooth each time a roller engages a tooth. The frequency of roller-tooth vibration depends on the effective contact stiffness of the roller on the tooth and the effective mass of the joint engaging the tooth. It is extremely difficult to estimate values for the effective stiffness and effective mass, so an equation for calculating the frequency of roller-tooth vibration is not given here. Experiments have found that roller-tooth vibrations have a frequency in the range of 2 kHz to 10 kHz.

NOISE As stated above, roller-tooth impact, and its resulting vibrations, are the source of most of the noise in a roller chain drive. Noise is a serious consideration in many roller chain drives. The roller chain industry has done considerable research on roller chain drive noise and has learned a lot about the many factors that cause roller chain drive noise. Even so, they did not find a way to calculate or predict with reasonable accuracy the noise that will be made by a given drive. Many factors affect the noise level of a drive. Some of these factors include the amount and type of chain loading, the amount and quality of lubrication, the number of sprocket teeth, the chain pitch, the fit between the chain and sprocket, chain wear, and sprocket wear. There may be, and probably are, additional factors that have not yet been clearly identified. Usually it is necessary to make a series of sound tests on a prototype or the actual drive to determine the noise level of the drive. One or two tests are not enough to show the normal variation in noise levels between one set of chains and sprockets and the next. Certain noise factors are related to the basic mechanics of a roller chain drive. Some of the basic findings of research on roller chain drive noise include the sound level (in decibels) increases with chain pitch, increases with chain tension, increases with the logarithm of the sprocket speed, and peaks at a frequency of about 6 kHz.



175

Roller Chain Drives

Fortunately, industry research also found that drive designers and users could do a number of things to reduce the noise from a roller chain drive. Some things that can be done to quiet a noisy drive, along with a short explanation, include • • • • • • •

Select a chain with smaller pitch. Note that multiple-strand chain may be required. Select a chain and sprocket combination that avoids resonant frequencies. Use a better type of lubrication than recommended. Tests show that superior lubrication can reduce the noise level of a drive by 6 dB or more. Ensure that the chain has adequate slack at installation and when readjusted. Tests show that a very tight chain is several decibels noisier than one that is correctly adjusted. Replace a worn chain well before it reaches the accepted 3% wear elongation limit. Tests show that noise is minimized when the chain and sprocket pitch are exactly the same. Replace sprockets before the teeth are noticeably hook shaped. A worn, hook-shaped tooth form is much noisier than a new tooth form. Consider using precision grade sprockets with hardened teeth for high-speed drives. This maintains the desired exact match of chain and sprocket pitch for a longer time.

There may be other ways to quiet or avoid a noisy drive. Contact an ACA roller chain manufacturer for assistance with reducing drive noise.

ACKNOWLEDGMENT Parts of S. W. Nicol and J. N. Fawcett, “Vibrational characteristics of roller chain drives,” Engineering, January 1977, pp. 30–32, were used in preparing the section on vibration.



6 Engineering Steel Chain Drives TYPICAL APPLICATIONS Engineering steel chain drives are very economical and efficient. Their design permits them to tolerate more exposure to dirt, moisture, and foreign debris than roller chains. Engineering steel chain drives are widely used in exposed drives on construction and mining equipment and on the drives for large conveyors in many industries. Figure 6-1 and Figure 6-2 show typical engineering steel chain drives.

SCOPE This chapter covers selecting engineering steel chain drives with only one driver and one driven sprocket using ANS engineering steel chains conforming to the ASME B29.10 standard, “Heavy Duty Offset Sidebar Power Transmission Roller Chains and Sprocket Teeth.” Table 6-1 lists dimensions and maximum allowable working loads for eight of the more popular sizes of chain covered in ASME B29.10. Even though they are not covered by ASME B29.10, nonstandard size, straight sidebar, and multiple-strand engineering steel chains are widely used in power transmission applications and are available from ACA engineering steel chain manufacturers. Consult an ACA engineering steel chain manufacturer for assistance on drives using nonstandard and multiple-strand chains. The following guidelines and procedures are intended to help a drive designer manually select a suitable engineering steel chain drive as quickly and efficiently as possible.

GENERAL ENGINEERING STEEL CHAIN DRIVE SELECTION GUIDELINES SELECTION OPTIONS Several different chain and sprocket combinations may be found for a particular application. It is good practice to make two or three alternative selections and then make a final selection based on cost, space and weight constraints, required life, or other important factors.

CHAIN PITCH The smallest pitch chain that will transmit the required power at the specified speed usually is the best selection. Higher speeds generally require a smaller pitch chain.

NUMBER

OF

SPROCKET TEETH

Small Sprocket The small sprocket must be large enough to accept the specified shaft diameter and keyway. A sprocket is effectively a polygon, and the chain strand rises and falls as each roller engages a sprocket tooth. This oscillation is called chordal action and causes cyclic chain velocity variation, as explained in chapter 5.

177



178


FIGURE 6-1 Typical engineering steel offset sidebar chain drives.

FIGURE 6-2 More typical engineering steel offset sidebar chain drives.

If the speed is slow (in the drip or manual lubrication range), the small sprocket may have as few as nine teeth. Even then, the chain and sprockets may have more power capacity than cold rolled shafting when the small sprocket has only nine teeth. The small sprocket in a typical engineering steel chain drive should have about 12 teeth. If speeds are high (in the oil stream lubrication range), the small sprocket should have at least 15 teeth. Each link is the same in offset sidebar chains, so there is no penalty for using sprockets with an even number of teeth. An offset sidebar chain must be installed to run in the proper direction to obtain maximum wear life, as explained in chapter 14. If straight sidebar chain is selected, the small sprocket should have an odd number of teeth, as explained for roller chain in chapter 5.



Engineering Steel Chain Drives

179

TABLE 6-1 General dimensions and working loads for ANS engineering steel drive chains

Max. Dimension Pin Ends to Chain Centerline, from: Roller Diameter

Distance between Sidebars

Max. Chain Height

Cottered Ends

Headed Ends

Max. Working Load

Average Chain Weight

ANS Number

Pitch P

R

W

U

J

H

lb.

lb./ft.

2010

2.500

1.250

1.500

1.875

1.875

1.688

4,650

7.8–8.6

2512

3.067

1.625

1.562

2.375

2.188

1.875

6,000

12.0-13.2

2814

3.500

1.750

1.500

2.375

2.438

2.188

7,600

15.8-17.3

3315

4.073

1.781

1.938

2.500

2.812

2.500

10,000

18.0-18.7

3618

4.500

2.250

2.062

3.125

3.000

2.562

12,000

22.0-25.4

4020

5.000

2.500

2.750

3.625

3.562

3.062

17,500

33.9-36.0

4824

6.000

3.000

3.000

4.125

3.875

3.500

23,600

45.0-46.5

5628

7.000

3.500

3.250

5.250

4.500

4.000

30,500

66.0-67.5

The largest sprockets practical should be chosen for low speed ratio (1:1 to 2:1) drives with the slack span on top. This reduces the possibility of contact between the chain strands as the chain wears. Large Sprocket The number of teeth on the large sprocket limits maximum allowable chain wear elongation. When chain wear elongation, over the arc of engagement, nears one-half pitch, the chain can jump teeth and damage the chain or sprocket. Maximum permissible chain wear elongation, in percent, is 200/number of teeth on the large sprocket. The large sprocket normally should have 60 teeth or less; this permits a maximum wear elongation of 3.3%. A sprocket with 40 teeth is the largest that can utilize the widely accepted maximum allowable chain wear elongation of 5% for offset sidebar chains.

CHAIN WRAP

ON

SMALL SPROCKET

Chain wrap should be at least 135 degrees, or three teeth, on the small sprocket. The chain can jump teeth and damage the chain or sprocket if chain adjustment is not very closely maintained with a wrap of less than 135 degrees.



180


DRIVE RATIO The drive ratio is the speed of the faster shaft divided by the speed of the slower shaft. The drive ratio normally should not be more than 6:1 in a single-stage drive. Larger drive ratios may be used with careful design and very good maintenance, but a two-stage drive is usually better. Check highratio drives carefully to ensure there is adequate wrap on the small sprocket.

CHAIN LENGTH Chain length must always be an integral number of pitches. If straight sidebar chain is used, the chain length should be an even number of pitches to avoid the use of one offset link in the chain.

CENTER DISTANCE Minimum Center Distance To avoid tooth interference, the minimum center distance is one-half the sum of the sprocket outside diameters. To ensure adequate wrap on the small sprocket, a suggested minimum center distance is the sum of the outside diameter of the large sprocket plus one-half the outside diameter of the small sprocket. Practical Center Distance It is good practice to set the center distance at 30 to 50 times the chain pitch. The longest practical center distance is about 80 times the chain pitch because chain sag and catenary tension become very large. Adjustable Centers Chain drive designers should provide adjustable centers, commonly a moveable motor mount, whenever possible. The range of adjustment should be equal to at least 11/2 pitches of chain. Fixed Centers If adjustable centers cannot be provided, then an idler or tensioning shoe should be used to maintain adequate slack span tension. In the rare instance when an idler cannot be used, the designer must calculate and specify an exact center distance. The designer should make a conservative selection (overchain the drive somewhat) and specify oil bath or oil stream lubrication to minimize wear.

IDLER SPROCKETS When adjustable centers cannot be provided, an idler sprocket can be used to maintain correct slack span tension (Figure 6-3). An idler sprocket should have at least as many teeth as the small sprocket and should engage the slack span of the chain. An idler sprocket engaging the taut strand will reduce the chain’s service life because there will be more articulations under load. The chain should engage at least three teeth on the idler sprocket. Where two consecutive sprockets mesh with opposite sides of the chain, leave at least three free pitches of chain between the points of engagement.

DRIVE ARRANGEMENTS A variety of commonly used drive arrangements are shown in Figure 6-4. Consult an ACA engineering steel chain manufacturer about other drive arrangements.




181

FIGURE 6-3 Drive chain arrangements.

FIGURE 6-4 Slack side tension and sag.

CHAIN WEAR

AND

SAG

As was explained in chapter 3, chains elongate as they wear. Wear elongation is limited to a maximum of about 3% to 6% in most engineering steel chain drives. Elongation appears as sag in the slack span as shown in Figure 6-5. The designer must provide sufficient clearance to prevent



182


FIGURE 6-5 Quick selector chart for engineering steel drive chain.

the chain from contacting the bottom of the chain case or other parts of the machine. Information on calculating chain sag and catenary tension can be found in chapter 9, and information on the design of chain cases can be found in chapter 13.

MULTIPLE-SPEED DRIVES When a drive operates over a range of speeds and loads, the designer must ensure that the selected chain and sprockets have adequate capacity under the most severe operating conditions. These conditions often, but not always, are the highest and lowest operating speeds.

MULTIPLE DRIVEN SPROCKETS Engineering steel chain drives with multiple driven sprockets are not uncommon. The drive designer should consult the specific ACA engineering steel chain manufacturer for advice on drives with multiple driven sprockets. The equations to calculate the required chain length on multiple-sprocket drives are complex. The chain length usually is determined from a large-scale layout or from multistage geometric calculations.

MULTIPLE-STRAND CHAIN Although ASME B29.10 covers only single-strand chain, many manufacturers offer multiple-strand engineering steel drive chains. Where the transmitted power or speed is too high or the space is too small for a single-strand chain with sufficient capacity, the designer may want to use multiple




183

strand chain. Consult an ACA engineering steel chain manufacturer for assistance with selecting multiple-strand engineering steel drive chains.

ENGINEERING STEEL CHAIN DRIVE SELECTION PROCEDURE STEP 1: OBTAIN NECESSARY INFORMATION Obtain the following listed information before selecting a roller chain drive. Make every effort to obtain all of the needed information. • • • • • • • • • • •

Type of power source. Type of driven equipment. Power required, or input power. Size and speed of the driver shaft. Size and speed of the driven shaft. Shaft center distance and drive arrangement. Available center distance adjustment, if any. Space restrictions. Available lubrication. Environmental conditions. Operating hours per day.

In addition, the designer should determine if there are any unusual drive conditions, such as • • • • • • •

Higher than listed speeds. Inadequate lubrication. Corrosive or very abrasive conditions. Very high shock or inertial (starting) loads. Temperatures greater than 150˚F or less than 0˚F. Multiple driven shafts. Other than precision-cut sprocket teeth (cast or flame cut).

If any of the listed or other unusual drive conditions are found, contact an ACA engineering steel chain manufacturer for assistance. ACA engineering steel chain manufacturers offer special chains designed to operate in specific hostile environments.

STEP 2: DETERMINE

THE

SERVICE FACTOR

The nominal required power, or input power, is usually given. Peak power may be much larger, depending on the type of power source and driven equipment. Drive designers use service factors to account for the difference between nominal and peak power. The load characteristics of various types of driven equipment are shown in Table 6-2. Service factors, to estimate the difference between nominal and peak loads induced by combinations of different types of power sources and driven equipment, are shown in Table 6-3. It is not a coincidence that these tables are nearly identical to the similar tables for roller chain (Table 5-2). The effects of the load characteristics of the driven equipment and the characteristics of the power source are essentially the same for all types of chain. Engineering steel chain drives often operate unprotected from the environment and are exposed to more dirt, moisture, and foreign materials than roller chains. Thus, a service factor for environment, shown in Table 6-4, is applied to engineering steel chain drives to compensate for the more adverse environments.



184


TABLE 6-2 Load characteristics

TABLE 6-3 Service factors for chain loading Type of Input Power Type of Driven Load Smooth Moderate Shock Heavy Shock

Internal Combustion Engine with Hydraulic Drive 1.0 1.2 1.4

Electric Motor or Turbine 1.0 1.3 1.5

Internal Combustion Engine with Mechanical Drive 1.2 1.4 1.7

TABLE 6-4 Service factors for environment Atmospheric Conditions


Relatively clean and moderate temperature Moderately dirty and moderate temperature Exposed to weather, very dirty, abrasive, midly corrosive and reasonably high temperatures

1.0 1.2 1.4



185

TABLE 6-5 Service factors for operating time Daily Operating Rrange

8–10 hours 10–24 hours

1.0 1.4

Engineering steel chain drives also often operate intermittently, with long idle periods between operating periods. A service factor for operating time, shown in Table 6-5, is applied to engineering steel chain drives to account for the effects of long idle periods. Finally, calculate the combined service factor by multiplying the individual service factors from Table 6-3, Table 6-4, and Table 6-5 together as shown in Equation 6.1:

( )( )( SF )

SFCombined = SF1 SF2

STEP 3: CALCULATE

THE

3

(6.1)

DESIGN POWER

Calculate the design power by multiplying the nominal required power, or input power, by the combined service factor obtained from Equation 6.1: HPDesign = HP × SFCombined

STEP 4: SELECT

A

(6.2)


Enter the quick selector chart (Figure 6-5) with the design horsepower and the speed of the small sprocket (faster shaft). The area under which the two lines intersect indicates the pitch size (chain number) of the preliminary chain selected.

STEP 5: SELECT

THE

SMALL SPROCKET

AND

SPECIFIC CHAIN SIZE

Select the Small Sprocket Take the preliminary chain selection and enter the specific horsepower ratings, either the charts (Figure 6-6 through Figure 6-13) or the tables (Table 6-6 through Table 6-13) with the faster shaft speed. Follow that line up on the chart or the column down in the table until the design power is reached or exceeded. The number of teeth on the small sprocket may be read on the next higher rating line on the chart or from the leftmost column of the table. Check this selection against the sprocket manufacturer’s catalog to ensure that it will accommodate the specified shaft size. Also check the selection to ensure that the number of teeth on the sprocket is appropriate for the shaft speed. Select Specific Chain Size It is suggested that the drive designer select a small sprocket and chain from at least the next smaller and next larger pitch sizes. The designer may then select the chain that best meets the user’s particular requirements. If no specific selection can be made (speed too high or power too large), contact an ACA engineering steel chain manufacturer for assistance. They may have a nonstandard chain that is adequate.



186


FIGURE 6-6 Horsepower rating curves for no. 2010, 2.500-in. pitch chain.

STEP 6: SELECT

THE

LARGE SPROCKET

Calculate the number of teeth on the large sprocket by multiplying the number of teeth on the small sprocket by the desired drive ratio (faster shaft speed/slower shaft speed). Round the result to the nearest integral number of teeth. Check the sprocket sizes and center distance to be sure the drive will fit within any space restrictions. If it does not fit, return to the previous step and consider multiple-strand chain. If the drive ratio is critical, one may adjust the number of teeth on the small and large sprockets to obtain an exact, or more nearly exact, drive ratio. If the drive ratio is not critical, one may adjust the number of teeth on the small and large sprockets to obtain an acceptable drive ratio and permit the use of stock sprockets.

STEP 7: CALCULATE CHAIN LENGTH Chain length is a function of the center distance and the number of teeth on each of the sprockets. Chain length must be an integral number of pitches, and preferably an even number of pitches when straight sidebar chain is used, to avoid using one offset link. Sometimes an exact chain length cannot be calculated because sprockets are polygons and the required length of the chain may change as it engages each sprocket tooth. However, a good approximation of the required chain length can be calculated using Equation 6.3, and is adequate when the center distance is adjustable by at least plus or minus one-half pitch. Note that Equation 6.3 is identical to Equation 5.2 for roller chains:




187


(

)

N−n N+n L = 2C + + 2 4π 2 C

2

(6.3)

where C is the center distance (in pitches), L is the chain length (in pitches), N is the number of teeth on the large sprocket, and n is the number of teeth on the small sprocket.

STEP 8: CALCULATE

THE


The calculated chain length is often fractional. If so, the designer must select a whole number of pitches and determine the center distance from that. An approximate center distance can be calculated using Equation 6.4, and is acceptable when the center distance is adjustable by at least plus or minus one-half pitch:

(

N−n ⎛ N+n N + n⎞ L− + ⎜L − −8 ⎟ 2 2 ⎠ ⎝ 4π 2 C= 4 2


)

2

.

(6.4)


188



A more nearly exact center distance C can be calculated using Equation 6.5:

(

C ′ = KCD 2 L − N − n

)

pitches.

(6.5)

L−n , and may be obtained from Table 5-5. N−n The center distance obtained using Equation 6.5 is a maximum. Any tolerance applied must be negative only. If a positive tolerance is applied, it may damage the chain or other components of the drive. The factor KCD is derived from the term

STEP 9: SELECT

THE

TYPE

OF

LUBRICATION

The designer should select the type of lubrication recommended in the power rating charts or tables. More detailed information on engineering steel chain drive lubrication can be found in chapter 13.

SAMPLE ENGINEERING STEEL CHAIN DRIVE SELECTION STEP 1: OBTAIN REQUIRED INFORMATION Select a suitable drive for a conveyor that runs at 72 ft/min. with a total conveyor load of 6500 lb. The head shaft turns at 12 rpm. Power will be supplied from an electric motor through a reducer




189


whose output shaft turns at 30 rpm. The drive will be open and exposed to moderately dirty conditions. Normal operating time will be 8 hr/day. Moderate shock loads are expected. Therefore the required information is • • •

Type of power source: electric motor. Type of driven equipment: conveyor with moderate shocks. Power required, or input power:

HPRe quired = • • • • • • • •

(

)( )

6, 500 ⋅ 72 WP ⋅ S = 14..18 HP. = 33, 000 33, 000

Size and speed of the driver shaft: to be determined. Size and speed of the driven shaft: to be determined. Shaft center distance and drive arrangement: to be determined. Available center distance adjustment, if any: to be determined. Space restrictions: to be determined. Available lubrication: to be determined. Environmental conditions: moderately dirty Operating time: 8 hr/day.



190



STEP 2: DETERMINE

THE

SERVICE FACTOR

From Table 6-3, Table 6-4, and Table 6-5, the service factors are moderate shock loads, 1.3; moderately dirty, 1.2; 8 hr/day operating time, 1.0; and the combined service factor is SFCombined = 1.3 × 1.2 × 1.0 = 1.56.

STEP 3: CALCULATE

THE

DESIGN HORSEPOWER

Applying the combined service factor to the calculated required power yields HPDesign = 1.56 × 14.18 = 22.12.

STEP 4: SELECT

A


Enter the quick selector chart (Figure 6-5) with the speed of the small sprocket (30 rpm) and the design horsepower (22.12 hp). These values intersect between the lines for chains ANS 2512 and ANS 2814. The preliminary selection is ANS 2814.




191


STEP 5A: SELECT

THE

SMALL SPROCKET

In the chart for ANS 2814 chain (Figure 6-8), the intersection of 30 rpm and 22.12 hp falls below the 9-tooth line. In the chart for ANS 2512 chain (Figure 6-7), the intersection of 30 rpm and 22.12 hp falls between the 9-tooth and the 12-tooth lines. In Table 6-7, for ANS 2512 chain, we find that an 11-tooth sprocket is adequate. Checking Table 6-6, for ANS 2010 chain, we find that an 18tooth sprocket is required. Check to be sure that an 11-tooth sprocket for ANS 2512 chain will accommodate the specified shaft size. The designer may use the procedures described in Chapter 4 to select appropriate shaft and hub sizes.

STEP 5B: SELECT

A

SPECIFIC CHAIN SIZE

Even on a nine-tooth sprocket, ANS 2814 chain has about 20% excess capacity. This selection would substantially overchain the drive and might be more costly than necessary. An ANS 2010 chain on an 18-tooth sprocket requires much more space than an ANS 2512 chain on a 9-tooth sprocket. This could cause interference problems, and it might be more costly than necessary. An ANS 2512 chain on an 11-tooth sprocket is the correct selection.



192



STEP 6: SELECT

THE

LARGE SPROCKET

The drive ratio is 30/12 = 2.5, so the large sprocket should have 11 × 2.5 = 27.5, or 28 teeth.

STEP 7: CALCULATE CHAIN LENGTH A center distance of 30 to 50 times the pitch is good practice. For this example, choose a center distance of 40 pitches, then calculate the required chain length using Equation 6.3:

(

)

2

28 + 11 28 − 11 L = 2 40 + + = 80 + 19.5 + 0.18 = 99.68, 2 4π 2 ( 40 )

( )

therefore 100 pitches of ANS 2512 chain are required for this drive.

STEP 8: CALCULATE

THE


A center distance of 40 pitches, or 40 × 3.067 = 122.7 in., was chosen. If we provide at least ±41/2 in. of adjustment, we do not need to calculate a more accurate center distance.

STEP 9: SELECT

THE

TYPE

OF

LUBRICATION

In Table 6-7, for ANS 2512 chain, 30 rpm is right on the borderline. Manual lubrication should be sufficient.




193


BASIS OF HORSEPOWER RATINGS GENERAL Much research by ACA members has produced reliable power ratings for ANS engineering steel chain drives conforming to the ASME B29.10 standard. The power capacity of roller chain drives, operating within standard conditions, is limited by link plate fatigue strength, roller and bushing impact fatigue, galling between the pin and bushing, and the type of lubrication. The standard conditions are a chain length of 100 pitches, a service factor of one, a well-aligned, two-sprocket drive on parallel horizontal shafts, use of the recommended type of lubrication, and an expected service life of approximately 15,000 hr.

EQUATIONS

FOR

ENGINEERING STEEL CHAIN HORSEPOWER RATINGS

The equations for heavy-duty offset sidebar chain power ratings are quite complex and are not published. If the drive designer has any questions about power ratings, or how they are applied, he or she should consult an ACA engineering steel chain manufacturer.

HORSEPOWER RATING CURVES

AND

TABLES

FOR

ANS CHAINS

IN

ASME B29.10

The horsepower rating tables for ANS chains conforming to the ASME B29.10, at the listed standard conditions, follow.



194

TABLE 6-6 Horsepower ratings for no. 2010, 2.500-in. pitch chain









195


196










197


198


ALTERNATE SELECTION METHOD GENERAL The alternate method must be used when horsepower rating curves or tables are not available. The alternate method uses rated working loads that are listed in ACA engineering steel chain manufacturers’ catalogs. There is not a uniform relationship between the rated working load and the ultimate tensile strength of the chain. Use only the working load published by the ACA engineering steel chain manufacturer. An individual should never attempt to derive a working load by multiplying or dividing the ultimate tensile strength by some general factor.

SELECTION PROCEDURE Determine Required Working Load The chain pull is often given. That value is multiplied by the combined service factor from Equation 6.1 to obtain the required working load. If the input power is given, use the design horsepower from Step 2 and Equation 6.5 to calculate the required working load:

WLRe quired =

396000 ⋅ HPDesign npR

,

(6.5)

where n is the number of teeth on small sprocket, P is the chain pitch (in inches), and R is the rotational speed of the small sprocket (in rpm). Construct Selection Table The designer must then determine the number of teeth on the small sprocket n and the chain pitch P. This can be done by rearranging Equation 6.5 to Equation 6.6 to calculate the required number of teeth:

n=

396000 ⋅ HPDesign p ⋅ R ⋅ WLRated

.

(6.6)

Using the given information and rated working loads from Table 6-1, construct a table containing at least three pitches of chain and resulting numbers of teeth from 9 to 15. The designer may use the procedures described in chapter 4 to calculate appropriate shaft and hub sizes, and add these to the constructed table. Select Chain and Sprocket Size From the constructed tabulation, select a chain with adequate rated working load and a sprocket with adequate bore capacity. Chain length and center distance are calculated as in step 7 and step 8, above. The alternate selection procedure ends here. There is no guidance on lubrication or other drive parameters. The drive designer should consult an ACA engineering steel chain manufacturer for assistance on these issues.




199

TABLE 6-14 Constructed Chain Selection Table

ANS number 2512 2814 3315 3315

Chain pitch, P 3.067 3.500 4.073 4.073

No. of teeth on small sprocket, n 16 11 8? 9

Calculated required working load, WLReq. 5950 7584 8960 7965

Chain rated working load, WLRated 6000 7600 10,000 10,000

Chain clearance (maximum hub) diameter, CCD 12.99 9.49 — 8.64

Maximum chain height, U 2.375 2.375 — 2.500

Sprocket pitch diameter, PD 15.72 12.42 — 11.91

SAMPLE SELECTION We will use the same sample drive conditions as given above for the drive selection using rating curves and tables. Determine Required Working Load Obtain the design horsepower, 22.12 hp, as calculated in step 3 of the prior sample selection, then begin construction of the selection table. Construct Selection Table Use Equation 6.6 to construct a selection table containing at least three sizes of chain. Table 6-14 is the constructed sample selection table.

SELECT CHAIN

AND

SPROCKET SIZE

From the tabulation, it appears that ANS 2814 chain on an 11-tooth sprocket is the best selection. The rated working load of 7600 lb. just exceeds the required working load of 7584 lb. ANS 2512 chain on a 16-tooth sprocket will take up much more space than ANS 2814 chain on an 11-tooth sprocket. The rated working load of the ANS 3315 chain on a nine-tooth sprocket greatly exceeds the required working load. It would be an obvious case of overchaining.

ALTERNATE SELECTION METHOD COMPARED CURVES

TO

SELECTION

WITH

HORSEPOWER

Selecting the chain and sprocket by the rating curves and tables yielded an ANS 2512 chain on an 11-tooth sprocket. Selecting the chain and sprocket by working loads yielded an ANS 2814 chain on an 11-tooth sprocket. The example of sample selection illustrates very well the advantages of using the horsepower rating curves and tables. Selection by the rating curves and tables is based on testing that included most, if not all, of the necessary factors. Conversely, selection by working loads is based on bearing pressures and arbitrary ratios to ultimate or yield strengths. Selection by working loads also does not give any guidance on selecting the proper lubrication for the drive. The designer should consult an ACA engineering steel chain manufacturer or another reference for that.



7 Silent Chain Drives This chapter provides guidelines and procedures for selecting silent chain and sprockets for drives. The use of silent chain for conveying is not discussed here; such information can be obtained from the chain manufacturer. In general, silent chain transmits power efficiently, smoothly, and quietly at speeds and loads that exceed the capability of most other chains and belts. Figure 7-1 through Figure 7-3 show typical silent chain drives. Power capacity ranges from a fraction of a horsepower to more than 2000 hp and speeds can exceed 7000 ft/min. Many silent chains employ two pin joints that wear very uniformly as they operate. This means that each pitch of these chains elongates consistently, so they deliver smooth, low-vibration, performance throughout their life. Figure 7-4 shows this uniform wear. The initial cost for silent chain and sprockets is often higher than for other types of chain, but long life and reduced life cycle costs often justify the added expense. There are many different silent chain designs and configurations. There are high-performance silent chains that handle large amounts of power at very high speeds. This chapter covers selecting silent chain drives that use chains and sprockets that conform to the ASME B29.2 standard. Consult the manufacturer for help with selecting chains not described by the standard or drives with more than two sprockets.

GENERAL GUIDELINES FOR SILENT CHAIN DRIVE SELECTION OPTIONS ENCOUNTERED

IN

DRIVE SELECTION

Selecting a silent chain drive consists of choosing a chain and sprockets that best satisfy the specified requirements. In most cases, this is a multistep process, the first step of which is obtaining a chain and sprockets that fit in the available space and that will work at the required loads and speeds. Often, more than one combination of chain and sprocket sizes will work in a given situation, so it is good practice to consider two or three alternatives. A final selection is made from the alternatives by considering other important factors such as cost, stock availability, and desired life. Most chain manufacturers offer drive selection manuals and technical assistance to aid in the selection of their products. Many also offer computer programs to simplify the selection process. One should consult the chain manufacturer for help when selecting drives that have large capital costs or operate in unusual and extreme conditions.

CHAIN PITCH Generally, small pitches operate smoother at high speeds. Larger pitches offer higher torque capacity, but at lower speeds.

CHAIN WIDTH Silent chain power capacity is rated in units of power per unit of chain width. For any given pitch, increased chain width results in greater chain strength, increased power capacity, and increased cost. When several chain widths satisfy the specified requirements, narrower chain widths are generally more readily obtained and less costly. Wider chains will provide a more robust, shockresistant drive. 201



202



SERVICE FACTORS Table 7-1 lists service factors. Service factors are used to account for the load characteristics of the power sources and the driven machinery. The proper service factors must be used when selecting a silent chain drive to obtain satisfactory operation and long drive life. Failure to use correct service factors can result in premature drive failures.

NUMBER

OF

SPROCKET TEETH

Sprockets should have at least 21 teeth for long drive life and smooth operation. Drives using sprockets with fewer teeth are likely to have increased vibration and noise because of chordal action (see Figure 5-2 and Figure 5-3, and the explanation used for roller chain). Each sprocket must be large enough to accommodate the bore and keyway specified for the shaft on which it will be mounted. Table 7-2 lists the maximum recommended bore and minimum hub diameter for standard silent chain sprockets with up to 33 teeth. An ANS silent chain sprocket cannot have fewer than 12 teeth. The number of teeth on the large sprocket should generally be no more than 120. As silent chain wears, the effective pitch increases and the chain wraps a larger pitch diameter farther out on sprocket teeth. When elongation becomes excessive, the chain may begin to skip or jump sprocket teeth, damaging the chain or sprockets. The estimated maximum permissible chain elongation, in percent, is 200/N, where N is the number of teeth on the larger sprocket.



203

Silent Chain Drives


HARDENING

OF

SPROCKET TEETH

Sprocket teeth should be hardened to maximize drive life. In some instances, where sprockets are large, have more than 50 teeth, and loads and speeds are nominal, unhardened teeth may provide satisfactory life.

CHAIN WRAP

ON THE

SMALLER SPROCKET

The chain should wrap at least 120 degrees on the small sprocket to ensure proper engagement and prevent tooth jumping. This condition will always be satisfied if the drive ratio is 3:1 or less. The arc of contact can be calculated using Equation 7.1: ⎛ D−d⎞ , A = 180 − 2 arcsin ⎜ ⎝ 2C ⎟⎠


(7.1)


204



FIGURE 7-4 Uniform wear of silent chain.

where A is the arc of contact (in degrees), D is the large sprocket diameter (in inches), d is the small sprocket diameter (in inches), and C is the center distance (in inches).

DRIVE RATIO Drive ratios of up to 12:1 are possible with silent chain drives. However, it is usually more economical and practical to use ratios of 8:1 or less. Higher ratios are often better achieved using a two-stage drive.

CHAIN LENGTH Chain length should be an even number of pitches. Chains with an odd number of pitches must use offset links that reduce power capacity and increase costs. Also, offset links may not be available for many styles and widths of silent chain.



205

Silent Chain Drives

TABLE 7-1 Service Factors Prime mover type

Prime mover type Application Agitators Pure liquid Liquid, variable density Bakery machinery Dough mixer Brewing and distilling equipment Bottling machinery Kettles, cookers, mash tubs Scale hopper (frequent starts) Brick and clay machinery Auger machines, cutting tables Brick machines, dry press, granulator Mixer, pug mill, rolls Centrifuges Compressors Centrifugal and rotary Reciprocating (1 or 2 cycles) Reciprocating (3 or more cycles) Cranes and hoists Main hoist (medium duty) Main hoist (heavy duty) Crushing machinery Ball mills, crushing rolls, jaw crushers Dredges Conveyors, cable reels Jigs, screens Fans and blowers Centrifugal, propeller, vane Positive blowers Grain mill machinery Sifters, purifiers, separators Grinders and hammer mills Roller mills

A

B

1.1 1.2

1.3 1.4

1.2

1.4

1 1 1.2

1.2 1.2 1.4

1.3 1.4 1.4 1.4

1.5 1.6 1.6 1.6

1.1 1.6 1.3

1.3 1.8 1.5

1.2 1.4

1.4 1.6

1.6

1.8

1.4 1.6

1.6 1.8

1.3 1.5

1.5 1.7

1.1 1.2 1.3

1.3 1.4 1.5

Application Generators and exciters Machine tools Boring mills, milling machines Grinders, lathes, drill press Beaters, Yankee dryer Calendars, dryer, paper machines Chippers, winder drums Barker, mechanical Printing machinery Embossing press, flat-bed press, folder Linotype machines, paper cutter, rotary press Magazine, newspaper presses Pumps Centrifugal, gear, lobe, vane Dredge Pipe line Reciprocating (1 or 2 cycles) Reciprocating (3 or more cycles) Rubber and plastics machinery Banbury mills Calenders, rolls, tubers, tire building Banbury mills Mixers Extruders Screens Conical, revolving Rotary, gravel, stone, vibrating Stokers Textile industry Batchers, calenders, looms

A 1.2

B 1.4

1.1 1 1.3 1.2 1.5 1.6

1.3 1.2 1.5 1.4 1.7 1.8

1.2 1.1 1.5

1.4 1.3 1.7

1.2 1.6 1.4 1.6 1.3

1.4 1.8 1.6 1.8 1.5

1.5 1.5 1.6 1.5

1.7 1.7 1.8 1.7

1.2 1.5 1.1

1.4 1.7 1.3

1.1

1.3

Type "A" prime mover: internal combustion engine with hydraulic coupling, or torque converter, or an electric motor, turbine, or hydraulic motor. Type "B" prime mover: internal combustion engine with mechanical drive.

SHAFT CENTER DISTANCE Where the center distance is not predetermined, it is usually best to use the smallest center distance that will provide 120 degrees or more of wrap on the small sprocket and is otherwise practical in the application. For a given drive ratio, shorter center distances require less chain. This reduces the number of parts subjected to wear and decreases overall cost. Longer center distances require a longer chain, which may be subject to whipping and accelerated wear, and they may need more maintenance.



206


MINIMUM CENTER DISTANCE The minimum center distance must be large enough to prevent sprocket interference and it must provide 120 degrees of chain wrap on the small sprocket. There will be no sprocket interference as long as the center distance is greater than the sum of the sprocket outside diameters. If the speed ratio is 3:1 or less, adequate wrap will be obtained, regardless of the center distance. For larger speed ratios, the amount of chain wrap at the chosen center distance can be calculated using Equation 7.1.

PRACTICAL CENTER DISTANCE In general, center distances should not exceed 60 pitches. With larger center distances, chain sag may be excessive.

ADJUSTABLE CENTER DISTANCE Whenever possible, provide some way to adjust the center distance. This will allow a chain to be retensioned as it wears and can improve operation throughout the life of a drive. One can estimate the amount of adjustment needed for a given drive. This is done by multiplying the maximum allowable elongation (in percent/100) by the initial center distance. Where possible, an adjustment equal to approximately two pitches of chain should be allowed.

FIXED CENTER DISTANCE When center distance must be fixed and there is no idler or other means of slack take-up, it is very important that the drive be designed to provide the correct amount of chain tension. This is typically done by using a center distance that is exact for the chain length and sprockets used. In some cases, chain manufacturers may recommend that the exact center distance be increased by a small amount. This is to ensure that the chain is correctly tensioned after a brief run-in period. It is also common practice to use a chain that is wider than the minimum width required for the application. This effectively reduces the bearing stresses in the chain, reduces the wear rate, and prolongs the life of the fixed center drive. Consult the chain manufacturer for specific advice on fixed center drives.

CLEARANCE

FOR

CHAIN SAG

As chains wear and elongate, some amount of sag will develop in the slack strand, as shown in Figure 5-8. It is important to provide enough clearance around the drive to allow for this condition. Chapter 14 provides information on the design of chain casings and enclosures.

IDLER SPROCKETS An idler sprocket or shoe-type tensioning device may be used in the slack chain strand to maintain proper chain tension. As shown in Figure 7-2, an idler sprocket must be installed on the inside of the drive, while a shoe tensioner must be installed on the outside of the drive. Before using a shoe tensioner, make sure that the silent chain being used is compatible. Many silent chains are not designed to “backbend,” and using a shoe tensioner can cause severe damage.

DRIVE ARRANGEMENTS Some common preferred drive arrangements are shown in Figure 5-10.



Silent Chain Drives

207

FIGURE 7-5 Duplex drive illustrations.

Variable Speed Drives When a drive must operate over a range of conditions, make sure the chain is capable of handling the maximum loads and speeds. In some cases, the duty cycle (the percentage of time the drive operates at various load and speed conditions) is well established. That must be considered, along with expected chain life, before making a final chain selection. Multiple Driven Sprockets Duplex silent chain, designed to drive sprockets from either surface of the chain, is often employed when multiple sprockets must be driven (see Figure 7-5). Duplex chain designs vary greatly and the chain manufacturer should be consulted when designing a duplex drive.



208


TABLE 7-2 Maximum Bores for Silent Chain Sprockets Bores with standard keyways Chain pitch

Number of teeth 17 19 21 23 25 27 29 31 33

0.37 0.875 1.25 1.3125 1.5 1.75 1.875 2.0625 2.125 2.3125

50 1.375 1.625 1.875 2.125 2.375 2.625 2.8125 3.0625 3.25

.50 1.75 2 2.3125 2.625 2.9375 3.25 3.625 3.8125 4.25

.625 2.0625 2.375 2.75 3.25 3.625 3.9375 4.375 4.5 4.9375

0.75 2.75 3.25 3.75 4.25 4.75 5.3125 5.5625 6.3125 6.9375

11.52 4.125 4.75 5.5 6.5 7.375 7.875 9 9.9375 10.6875

5.25 6 7 7.75 8.875 9.625 10.625 11.125 12.375

SILENT CHAIN DRIVE SELECTION PROCEDURE STEP 1: OBTAIN INFORMATION Selection of a complete silent chain drive begins with the gathering of as much of the following information as possible: • • • • • • • • •

Type of power source. Type of equipment to be driven. Power to be transmitted or input power. Driving shaft information: speed, diameter, keyway size. Driven shaft information: speed, diameter, keyway size. Shaft center distance and amount of adjustment available. Drive arrangement. Space restrictions. Available lubrication.

STEP 2: CHOOSE

THE

SERVICE FACTOR

Choose an appropriate service factor for the power source, type of driven load, daily duty cycle, and operating conditions. Table 7-1 provides a list of base service factors for a few different types of equipment. For example, a centrifugal blower application powered by an electric motor would have a service factor of 1.3. Extensive lists of base service factors are available in the ASME B29.2 standard and from most chain manufacturers.

STEP 3: CALCULATE

THE

DESIGN POWER

Calculate the design power by multiplying the input power by the service factor determined in step 2.

STEP 4: SELECT PRELIMINARY PITCH Select a preliminary chain pitch with the pitch selection chart in Figure 7-6. Enter the chart with the speed of the small sprocket (faster shaft) and the design power computed in step 3. Often more than one chain pitch will work in a given application. If the preliminary pitch selection results in



209

Silent Chain Drives

FIGURE 7-6 Pitch selection chart.

a chain size that is impractical, choose the next larger or smaller pitch and repeat the selection process.

STEP 5: SELECT

THE

SMALL SPROCKET

Select the number of teeth on the small sprocket, then verify in Table 7-2 that it will accommodate the shaft diameter and keyway. Remember that the best performance is obtained when sprockets have 21 or more teeth.

STEP 6: DETERMINE

THE

CHAIN WIDTH

Use the power capacity tables (Table 7-3 through Table 7-9) to determine the chain width. Enter the table appropriate for the pitch selected in step 4, using the speed and number of teeth on the small sprocket to locate the power capacity per inch of chain width. Compute the minimum recommended chain width (in inches) by dividing the design horsepower by the power capacity per inch of chain width. If the computed chain width is not readily available, the designer may have to choose a wider chain or larger sprocket.

STEP 7: SELECT

THE

LARGE SPROCKET

Select the number of teeth on the large sprocket by multiplying the number of teeth on the small sprocket by the desired speed ratio.

STEP 8: CALCULATE

THE

CHAIN LENGTH

Calculate the chain length, in pitches, using Equation 5.2. If the computed length is fractional, round off to the nearest even integer. Chains with an odd number of pitches require an offset section; that is generally undesirable.


210



Silent Chain Drives

TABLE 7-3 Horsepower ratings for 3/8 -in. pitch silent chain

211



Silent Chain Drives





212


213



Silent Chain Drives





214

TABLE 7-7 Horsepower ratings for 1-in. pitch silent chain

215



Silent Chain Drives

TABLE 7-8 Horsepower ratings for 1 1/2 -in. pitch silent chain




216

TABLE 7-9 Horsepower ratings for 2-in. pitch silent chain


217

Silent Chain Drives

STEP 9: CALCULATE

THE


Calculate the final center distance for the chain length selected. If the center distance is adjustable, or some other means of chain tensioning is available, the final center distance can be calculated with Equation 5.3. If the center distance is fixed, the final center distance should be calculated iteratively using Equation 5.1 or obtained from the chain manufacturer.

STEP 10: SELECT

THE

LUBRICATION METHOD

Identify the preferred method of chain lubrication by entering the power capacity table used in step 6 with the small sprocket’s speed and number of teeth. Refer to chapter 12 for additional information on lubricant properties and recommended flow rates.

SAMPLE SILENT CHAIN DRIVE SELECTION STEP 1: OBTAIN INFORMATION Power source: electric motor Type of driven equipment: fan, centrifugal Input power: 35 hp Driving shaft: 1750 rpm, 1 1/2-in. shaft diameter Driven shaft: 800 rpm, 2 1/2-in. shaft diameter Center distance: 28 in., adjustment available Drive arrangement: acceptable Space restrictions: none Lubrication available: yes

STEP 2: CHOOSE

THE

SERVICE FACTOR

From Table 7-1 service factor, 1.3.

STEP 3: CALCULATE

THE

DESIGN POWER Design power = 1.3 × 35 hp = 45.5 hp.

STEP 4: SELECT

THE

PRELIMINARY PITCH

Entering the pitch selection chart (Figure 7-6 at 1750 rpm, select a 1/2-in. pitch).

STEP 5: SELECT

THE

SMALL SPROCKET

A minimum of 21 teeth is recommended. From Table 7-2, the maximum bore for a 21-tooth sprocket is 1.88 in. This is larger than the shaft diameter of 1.5 in., so the sprocket choice is acceptable.

STEP 6: DETERMINE

THE

CHAIN WIDTH

Enter Table 7-4 with the speed and number of teeth on the small sprocket and locate the power capacity per inch of chain width (interpolation is required in this example). Power capacity = 33.5 hp/in. of width Divide the design power by the power capacity to obtain the chain width:



218


Minimum width = 45.5 hp/33.5 = 1.336 in. This is not a readily available width, so choose the nearest larger chain that is available, 1 1/2 in. wide in this case. The availability of various chain widths must be determined by consulting the chain manufacturer or reseller.

STEP 7: SELECT

THE

LARGE SPROCKET

The speed ratio is calculated as 1750/800 = 2.19. Therefore the large sprocket must have 2.19 × 21 teeth = 46 teeth.

STEP 8: CALCULATE

THE

CHAIN LENGTH

The center distance in pitches equals 28/0.5 = 56. Calculate the chain length, in pitches, using Equation 5.2:

(

)

2

⎛ 28 ⎞ 46 + 21 46 − 21 + + L = 2⎜ = 112 + 33.5 + 0.283 = 145.78 pitches. 2 ⎛ 28 ⎞ ⎝ 0.5 ⎟⎠ 4π 2 ⎜ ⎝ 0.5 ⎠⎟ Rounding to the next larger, even number of pitches, the chain length equals 146 pitches.

STEP 9: CALCULATE

THE


Since adjustment is available, the final center distance is calculated using Equation 5.3:

(

)

46 − 21 ⎛ 46 + 21 46 + 21 ⎞ + ⎜ 146 − −8 146 − ⎟ 2 2 ⎠ ⎝ 4π 2 C= 4 pitches, or 28.05 in. 2

STEP 10: SELECT

THE

2

=

146 − 33.5 + 12656 − 126.65 = 56.09 4

LUBRICATION METHOD

The lubrication method indicated by Table 7-4 is oil bath or slinger disk. These are the minimum required; forced feed lubrication would also be suitable.

DERIVATION OF SILENT CHAIN POWER RATINGS The power capacity of silent chain drives operating under typical conditions is limited by the fatigue strength of the chain, which is largely determined by the fatigue strength of the load carrying links within the chain. Because silent chain link plate designs vary with different manufacturers, link strength and chain power capacity also vary. The ASME B29.2 standard defines important silent chain and sprocket dimensions so consumers can be certain that “standard” chain and sprockets from different manufacturers are dimensionally compatible. However, because chain link design and power capacity varies, the standard does not specify power ratings for standard silent chains. Instead, the standard is published with supplemental horsepower tables that contain the power capacities of commonly available silent chains. Consult specific chain manufacturers to determine how the power capacity of their chain compares to the supplemental horsepower table.



8 Tension Linkage Chains Tension linkage chains are a series of chain products that are both catalog standard and manufactured for special purposes. The main use of a tension linkage chain is to move a load slowly or intermittently over a given distance. They also are used to reliably hold a load in position when it is not moving. Tension linkage chains generally move back and forth rather than through a complete revolution. Tension linkage chains are used in a variety of ways. They may be used for hoisting, supporting counterweights, or pulling objects through forming operations. The loads in these applications can range from a few ounces to several thousand pounds. The wide range of loads requires many different sizes and types of products to meet the different requirements. Examples of the different sizes of tension linkage chains can be seen in Figure 8-1. Speed and frequency of movement will often determine the type of product that is used. Applications that move frequently and faster may require a product that has features that reduce wear. On the other hand, applications with slow and infrequent movements may not need the same features. Both types of applications will be discussed later. Special types of roller chain, leaf chain, and block chain can be used as tension linkages. Some of these products are described in the American National Standards, but many are manufacturers’ specials and can only be found in their catalogs or by contacting them directly. Some of these products will be discussed in greater detail. Engineering steel chains in various styles of bar-link or block and bar chain are used for tension linkages. These types of chains will be discussed later.

ROLLER CHAINS AS TENSION LINKAGES Standard and special roller chains are often used for static or slow-moving tensile applications. They are used where compactness and flexibility or engagement with a sprocket is needed. Some examples of these applications are for supporting a floating machine head, manual and electric hoists, and steering mechanisms on lift trucks. A standard series of roller chains is available for use on overhead hoists. These chains are covered by the ASME B29.24 standard. This series of load chains for overhead hoists has the same dimensions as the drive chains in ASME B29.1, but they must meet higher performance requirements. It is best to contact the hoist manufacturer about replacement chain for a hoist, and the hoist designer should consult the chain manufacturer directly when selecting a roller load chain for an overhead hoist. A roller load chain on an overhead hoist is shown in Figure 8-2. Rollerless chains are also used as tension linkages where a chain with the wear resistance of a hardened bushing is needed. Most of these chains have the same basic dimensions as standard roller chain, but they do not have the free-turning roller over the bushings. Because of this feature, these chains usually do not run on sprockets. Rollerless chains are not described by an American National Standard. However, they may be identified with numbers taken from ASME B29.1. The chain number ends with a “5,” indicating the rollerless feature. For example, a 3/4 -in. pitch no. 60 chain without a roller becomes a no. 65 chain. Tension linkage chains generally experience high loads at low speeds. They do not fall within the published horsepower tables given in chapter 5. Do not attempt to use horsepower ratings to select tension linkage chains. There are many types and sizes of chains available for use as tension

219



220


FIGURE 8-1 Comparison of chains showing sizes of tension linkage chains.

linkages. One should contact the chain manufacturer for help in choosing a chain type and size. Figure 8-3 shows several roller chains being used for actuation.

TENSION LINKAGES USING LEAF CHAIN Leaf chain probably is the chain most commonly used for tension linkages. Leaf chain is designed specifically for use where the chain does not engage a sprocket or travel through a complete chain revolution. Leaf chain was briefly described in chapter 2 and an example is shown in Figure 8-4. Complete information on leaf chain is contained in the ASME B29.8 standard. Figure 8-5 shows the most common use of leaf chain, a lift truck or fork lift. The chain is used to lift a load by transferring the motion from a hydraulic cylinder to the movable forks. The chain is anchored at one end to the rigid mast, while the other end is attached to the movable forks. The hydraulic cylinder pushes against the chain using a sheave that rotates as the cylinder moves upward. The mechanical advantage of this system is that the load moves at twice the speed of the cylinder. Figure 8-6 shows a leaf chain used as a counterbalance chain on a large machine tool and Figure 8-7 shows a special type of leaf chain used in a pipe vise.

DIMENSIONS AND ARRANGEMENTS OF LEAF CHAIN Figure 8-8 shows the standard leaf chain lacings and Table 8-1 gives the basic dimensions of leaf chains contained in the ASME B29.8 standard. The chain number describes both the pitch size and lacing. The letters “BL” indicate heavy series chain is the basis for link thickness and pin diameter. The first number represents the pitch size, the same as for standard roller chain. The next two numbers describe the lacing. For example, BL 422 is 1/2 -in. pitch with 2 × 2 lacing. The tensile strength for leaf chain is specified in ASME B29.8. It should never be used as the working load. Working loads should always be obtained from the leaf chain manufacturer. Toler-



Tension Linkage Chains

FIGURE 8-2 Roller load chain on an overhead hoist.

FIGURE 8-3 Roller chains used for actuation.


221


222


FIGURE 8-4 Typical leaf chain.

FIGURE 8-5 Leaf chain on a hydraulic lift truck.

ances for chain length and other specific dimensional features should be obtained from either ASME B29.8 or the leaf chain manufacturer. Clevises are normally used to connect the ends of a leaf chain. They are available in either outside or inside designs. Basic dimensions can be obtained by using the information found in Figure 8-9. However, the more detailed dimensions for designing a clevis must be obtained from ASME B29.8. Clevises must be manufactured to ensure equal load distribution across the entire width of the chain. Clevis connections to the equipment must also be designed to avoid misalignment. Materials of adequate strength are to be specified for both the clevis and the connecting pin. This information can be obtained from the leaf chain manufacturer. Sheaves that allow the leaf chain to travel around a corner should be designed according to the requirements in ASME B29.8. Figure 8-10 gives the general dimensions. Using sheaves with less than the recommended diameter of five times the pitch should be verified by extensive testing. Sheaves should always be mounted with bushings or bearings that allow free rotation. The sheaves must be mounted rigidly enough to maintain good alignment and prevent unequal loading of the chain. The sheave must never interfere with the smooth operation of the chain. Other styles of leaf chain are available from some manufacturers. These chains are special and do not conform to any industry or American National Standards. Examples of these types are wrench chains and laminated block chains. One feature of wrench chain is the extended pins that are used to clamp the chain in position. Some types of laminated block chains have openings that allow the chain to be used with a toothed device similar to a sprocket. These and all other special types of chains can be found in manufacturers catalogs. Pictures of the two special-purpose types of leaf chain mentioned can be found in Figure 8-11.




223

FIGURE 8-6 Leaf chain used on a machine tool as a counterbalance chain.

FIGURE 8-7 Pipe vise using a special leaf chain.

TENSION LINKAGES USING ENGINEERING STEEL CHAINS The engineering steel chains normally used in tension linkages are relatively heavy chains. They are usually the bar-link or block and bar types of chain, and they are much larger in size and much stronger than the leaf and other chains used for lighter tension linkages. Some tension linkage chains of the engineering steel bar-link type are among the heaviest, most massive, and durable chains ever built. Their effectiveness depends on strength and not speed.



224

FIGURE 8-8 Standard leaf chain lacings and dimensions.





225

FIGURE 8-8 (Continued)

Chains of this type have been designed and built with an ultimate strength of more than 3 million pounds. Figure 8-12 shows how massive chains of this type must sometimes be. Some engineering steel chains used for tension linkages were shown in Figure 1-22, Figure 2-24, and Figure 2-25. These chains are not covered by any standards, but extensive listings of smaller sizes are contained in engineering steel chain catalogs. These smaller sizes are still some very heavy chains. Larger sizes are usually designed for an application and built to order. Most heavy tension linkage chains are simple designs. They usually consist of heavy blocks, bars, and leaves with heat-treated pins. The other components are not always hardened. Barlink and leaf chains are very similar in concept and function, but manufacturing methods differ greatly.

CHARACTERISTICS OF ENGINEERING STEEL CHAIN TENSION LINKAGES There usually are no rigid rules to guide the engineer in choosing the type of tension linkage to be used in a given instance, but chain has the following advantages: • •

Chain action is positive when it meshes with a sprocket. Chain articulation (or flexing) is confined to specially treated bearing surfaces.



226

TABLE 8-1 Leaf chains: general dimensions





227

Connecting link with interference fit cover plates

Outside Clevis

FIGURE 8-9 Clevises for leaf chains.

FIGURE 8-10 General dimensions of leaf chain sheaves.

FIGURE 8-11 Two special-purpose types of leaf chain.

FIGURE 8-12 Huge tension linkage chain for dam gates.


Inside Clevis


228


• • •

Chains are often a better choice for very heavy tension linkages because they can be designed to handle very heavy loads. Chains used in tension linkage applications are easy to lubricate, and regular lubrication extends the chain’s life. Chains are easy to install. End terminals, or connectors, simplify attaching the chain to the load.

DRAW BENCH APPLICATIONS Draw benches (Figure 8-13) are machines used to draw wire and tubular shapes from materials such as steel, copper, and aluminum. On continuous benches, a heavy block with a hook that engages the chain slowly draws the metal through a series of dies to produce the desired size of wire or tubing. At the end of the stroke, the hook disengages from the chain and the draw block returns to its starting position. In this application, the chain operates continuously, picking up the load with each pass of the draw block. On reversing benches (Figure 8-14), the block is connected to and pulled with a high-capacity chain (lower chain), then it is retracted with a smaller, less costly chain (above). Most draw bench chains are heavy-duty types of bar-link chain. In chains intended for draw bench service, all parts are hardened, bearing surfaces are machined, and pins are securely riveted to endure the stresses of draw bench operation. Figure 8-15 shows typical draw bench chains. As shown in Figure 2-24, designs with a single block alternating with two sidebars are used for the least rigorous kinds of draw bench work. Their ultimate strength range is from 30,000 lb to 200,000 lb. Designs in which two and three sidebars alternate may have an ultimate strength well in excess of 3 million pounds and are used for very heavy duty work. The pitches of bar-link chains used in draw bench service may be as short as 2 in. or as long as 12 in. The weights of such chains may run from 4 lb/ft to 400 lb/ft. Giant bushed rollerless chains (Figure 8-1) are being used more often on high-speed draw benches. This construction provides larger wear areas that are hardened to high levels for maximum

FIGURE 8-13 Draw bench using special engineering steel chain.




229

FIGURE 8-14 Reversing draw bench using bar-link ES chain.

FIGURE 8-15 Typical draw bench chains.

wear resistance. The construction also allows the use of a full complement of sprocket teeth for smoother operation or more compact drives.

TENSION LINKAGE CHAINS FOR DAM AND LOCK GATES Tension linkage chains are widely used to raise and lower dam gates and draw bridges and to open and close canal lock gates. Bar-link chain has been popular for these uses because of its simple design and relatively low cost, but other types of tension linkage chain are being used with increasing frequency. The giant roller chain shown in Figure 8-16 has a relubrication feature. This allows greasing of the inner chain joint for protection against corrosion and wear. It is installed to lift and hold a frequently used navigation lock gate that weighs one million pounds.



230


FIGURE 8-16 Tension linkage chain used in locks on the Mississippi River.

FIGURE 8-17 ES chains moving steel billets in an inspection operation.

OTHER APPLICATIONS Engineering steel tension linkage chains are used in the hold-down apparatus of rock drills and the ladle-tilting devices in steel mills and foundries. They are used in hydraulic lifts and counterweight balances on the arms of radial drills. And they are used in transmission systems between doubleacting hydraulic cylinders and their shafts. Two such unusual applications are shown in Figure 8-17 and Figure 8-18. The kinds of chain that are chosen for these applications depend on the circumstances. When chain movement is infrequent, a bar-link chain should be considered. When the chain rotates




231

FIGURE 8-18 Bar-link chain operates a clamshell digging mechanism.

FIGURE 8-19 Diagram of catenary to maintain correct tension on draw bench.

frequently relative to the sprockets, rollers, and sheaves, a bushed roller chain, with its smoother sprocket action, may be the better choice. The environment and access for lubrication are also factors. There are many variables to be considered when selecting engineering steel chains for tension linkages. The designer should consult with manufacturers for more information.

CATENARY TENSION AND CHAIN SAG The return strands of heavy bar-link chains must be considered carefully when they run over sprockets and are horizontally arranged. Most steel mill installations are in this category. Generally the numbers of teeth in the drive sprocket are very small and loads are very high, and the surroundings are usually soaked with good high-pressure lubricants. In such a situation, it is essential that adequate slack-side chain tension at the drive be maintained so that the chain cannot jump teeth at peak loads. Slack-side tension is usually maintained with a deep catenary at the head shaft end of the return strand, as shown in Figure 8-19. In most steel mills, doing so is relatively easy, as ample space usually exists in the basement under the mill main floor. The chain manufacturer should inform the user about the amount of sag needed to maintain adequate tension on the slack side of the drive sprocket. A method for calculating the tension produced by a given amount of sag is given in chapter 10.



Steel 9 Engineering Chain Conveyors Engineering steel conveyor chains are the workhorses of the conveying field. They are designed to convey heavy loads and to absorb severe shock loading. In addition, they are expected to operate well in corrosive and very abrasive conditions with little or no protection. Engineering steel conveyor chains may carry heavy weights, such as automobiles on final assembly lines, or they may need to absorb a blow from a log, perhaps 18 in. in diameter and 10 ft long, being dropped endwise on the conveyor from more than 10 ft above the conveyor. Conveyors using engineering steel chains have to operate in all kinds of weather, in sand and saltwater, and in the chemical and abrasive environments of everything from coal, taconite, and granite to sugar cane bagasse and hot lime.

TYPES OF ENGINEERING STEEL CHAIN CONVEYORS GENERAL Engineering steel chains are used on conveyors in an enormous variety of applications, although most installations can be resolved into one of the types of conveyors described in this chapter. Conveying applications may be classified in many ways. The materials handled may be “bulk,” such as sand or grain, or “unit,” such as television sets or cartons. The conveyor chain also may carry the material or push or scrape it. The material conveyed and how it is to be placed on and taken off the conveyor really dictates the type of conveyor to be used. For example, if the materials to be handled are individual large objects, which can be slid on and off the conveyor, a floor, carrier, or slat conveyor usually will be used. If the material to be handled is a bulk material, such as coal or sawdust, or even logs, the material will be carried by the conveyor or pushed along in a trough by a drag or scraper conveyor chain. This chapter describes the more common basic types of chain conveyors to help the reader understand how each type of chain conveyor functions and to recognize the chain attachments required to support, move, and discharge the material from the conveyor. The chain conveyors discussed are arranged according to the type of service the conveyor performs and the types of attachments added to engineering steel chains that help them perform their required function.

PLAIN CHAIN CONVEYORS Many objects can be conveyed on plain engineering steel chains without any attachments, slats, or fixtures. Figure 9-1 is a sketch of a typical application. Here, the objects being conveyed, pulp yard logs, are rolled onto the conveyor at one end and are discharged over the head shaft of the conveyor. Although no protruding attachments are present, chains with high sidebars are sometimes used as the logs rest on the edges of the chain sidebars. The engineering steel chains used on such conveyors may be set up to roll or to slide, depending on the details of the operation. Engineering steel roller chains, steelbushed rollerless chains, welded steel chains, and bar-link steel chains are all used in this style of conveyor. Figure 9-2 to Figure 9-7 illustrate the wide variety of applications in which plain chain conveyors can be used. In all these applications, two or more parallel strands of chain are used. The chains 233



234

FIGURE 9-1 Drawing of a plain chain conveyor.

FIGURE 9-2 Chain conveyors in a cannery.

FIGURE 9-3 Welded steel conveyor carrying cants.




Engineering Steel Chain Conveyors

FIGURE 9-4 Bushed rollerless conveyor carrying stainless steel sheets.

FIGURE 9-5 Bar-link conveyor carrying cases in a dairy.

FIGURE 9-6 Bushed rollerless conveyor and transfer carrying boxes.


235


236


FIGURE 9-7 Bushed rollerless conveyor carrying pulpwood logs.

carry the weight of the material and the frictional drag of the chains on the material carries it along. Such conveyors are usually level or nearly so. Slopes are relatively mild and are usually downhill toward the head shaft. Any lubrication of the chain must be provided with care to maintain adequate friction between the chain and the conveyed material. Many plain chain conveyors use chains without rollers. Although roller conveyor chains have the advantage of low friction, means such as high sidebars, must be provided to prevent the rollers from making contact with the materials conveyed. As illustrated in Figure 9-6, plain chain conveyors are often used in mechanized transfer devices. The possibility of hang-ups from misaligned objects is greatly reduced by the lack of attachments on a plain chain conveyor.

PUSHER CHAIN CONVEYORS When an article or part can slide or roll or be moved on rollers or wheels, the most economical method of conveying it in a definite path is frequently a pusher chain conveyor. These conveyors have one or more endless strands of chain with suitable attachments to push the loads. By definition, pusher chain conveyors usually do not support the materials conveyed. Rather, the load slides or rolls on rails with the top of the chain below the level of the rails and the chain pusher attachments rising between them to push the material along. A typical such arrangement is shown in Figure 9-8. The designer should be very careful laying out this type of conveyor. He or she should be sure that the entry and discharge of material, particularly the latter, is not be restricted. Some conveyors of this type are used in highly mechanized manufacturing systems. In this case, they are furnished with movable “pusher dog” attachments that retract below the tops of the rails to disengage the material. The designer should contact the chain manufacturer for advice on installing conveyors of this type. Photographs of typical pusher chain conveyors are shown in Figure 9-9 to Figure 9-13. It should be noted that the applications shown, all from either the steel or the forest products industries, involve mostly long, narrow objects. Figure 9-12 shows what appears to be an exception to the concept that pusher chain conveyors do not support the material conveyed. However, in this type of installation, the V-trough protects the chain from being contacted to any large degree by the larger logs. The sides of the trough actually support the load. In effect, the chain slides in a groove at the bottom of the trough.




237

FIGURE 9-8 Drawing of a pusher chain conveyor.

FIGURE 9-9 ES roller chain transferring pipe.

CARRIER CHAIN CONVEYORS Carrier chain conveyors are built with attachments that are either connected to or are an integral part of the chain. They form a carrying medium or continuous surface for an individual part. Figure 9-14 is a sketch of a carrier chain conveyor that uses roller conveyor chain with flat-top attachments on every link. It is carrying large coils of steel. Carrier chain conveyors are widely used to convey parts and assemblies. Many of the attachments used in carrier chains are of special design to conform to the shape of the objects being handled. Chains are usually standard roller conveyor or bar-link chains. They can be arranged to travel paths in horizontal, inclined, or combination patterns and contours, and are built in a wide range of types and sizes. Special designs can be furnished for handling objects from medicinal pills to 100,000 lb coils of strip steel. Figure 9-15 and Figure 9-16 show two carrier conveyors handling coils of steel strip, but they each handle them in different ways. The conveyor shown in Figure 9-15 handles the coils nested in shallow V-block attachments. The attachments are spaced every sixth link in a bar-link chain



238


FIGURE 9-10 Inclined conveyor carrying logs to a debarker.

FIGURE 9-11 Rack conveyor carrying cooling pipe.

equipped with outboard rollers (probably with antifriction bearings). The coils can be discharged from the conveyor by taking the chain below the floor level and rolling the coils away. The conveyor shown in Figure 9-16 transports the coils on their ends on a roller conveyor chain with flat-top attachments on every link. Coils are picked up from the conveyor by a machine made for the purpose. The whole arrangement is planned to keep scratches or marring of the finished steel surfaces to a minimum.




239

FIGURE 9-12 Bushed rollerless jack ladder conveyor carrying logs.

FIGURE 9-13 Bushed rollerless conveyor carrying pulpwood.

SLAT CONVEYORS Figure 9-17 is a drawing of a basic slat conveyor. This type of conveyor consists of two or more endless strands of chain with attached noninterlocking wooden slats or metal flights to carry the material. Roller conveyor chains are generally used for slat conveyors. The chains usually have closely spaced attachments of styles A or K (see Figure 2-20 and Figure 2-30) to which the slats or flights are attached. Unit handling applications are the major use for conveyors of this type. The most common uses are to move products for shipping and processing, such as in appliance assembly lines. Most slat conveyors have a chain at each side with the slats between. When loads are very heavy or the conveyor is very wide, added strands of chain in the center might be needed to prevent excessive flight deflection and chain wear. Slats or flights are usually extended to cover the chains at the side for safety reasons and to prevent material from dropping through the conveyor. Sometimes conditions are such that lubrication cannot be provided, such as on a meat packing line, where frequent wash down is necessary. Then, chains with plastic bushed rollers are sometimes used. Several chain manufacturers provide such chain as a part of their standard product line. Examples of slat conveyors are shown in Figure 9-18 through Figure 9-20. The conveyor shown in Figure 9-18 is quite large and unusual. The material handled—pineapples—is a bulk material rather than the unit product handled by most slat conveyors. The problem of retention on the



240

FIGURE 9-14 Drawing of a carrier chain conveyor.

FIGURE 9-15 ES roller chain carrying steel coils.





241

FIGURE 9-16 ES roller chain carrying steel coils on end.

FIGURE 9-17 Drawing of a slat conveyor.

conveyor was solved in this instance by providing skirt boards above the conveyor edges. Figure 9-20 shows a large, slow-moving conveyor on which furniture is assembled.

APRON

OR

PAN CONVEYORS

Apron conveyors or feeders consist of die-formed steel aprons or pans mounted on two or three strands of chain. The effect in operation is that of a moving trough, with discharge over the head shaft as shown in Figure 9-21. This type of conveyor is used extensively for handling all types of loose and bulk materials, ranging from fines to large irregular lumps. Apron conveyors are used to carry materials such as coal, coke, lime, sand, stone, sugar cane, and ingot molds. Apron conveyors are commonly used where abrasion, impact, and high temperatures must be considered. These conveyors can be furnished in extremely heavy-duty versions with great strength and rigidity. This allows them to operate well under severe operating conditions. Usually the ends are welded to the die-formed sections of apron conveyor pans. Chain attachments are specifically chosen to allow the apron flights to be easily mounted. Engineering steel conveyor roller chains are mostly used for apron conveyors. However, some steel bushed rollerless chain with outboard rollers is used on heavy-duty conveyors.



242


FIGURE 9-18 ES roller chain slat conveyor carrying pineapples.

FIGURE 9-19 ES roller chain slat conveyor carrying packaged meat.

“Leak-proof” apron conveyors are so called because the flights and sides are formed with interlocking “beads” and offsets such that minimal clearances allow the conveyor to retain very fine material. These chains have been used in the mining and foundry industries for years. Apron conveyors can be used as inclined conveyors. Extra “lifter” blades are used to let conveyors operate at a steeper angle than is normally permitted by the angle of repose of the




FIGURE 9-20 ES roller chain slat conveyor carrying office furniture.

FIGURE 9-21 Drawing of an apron conveyor.

FIGURE 9-22 ES roller chain apron conveyor carrying coal.


243


244


FIGURE 9-23 Drawing of a scraper conveyor.

FIGURE 9-24 Drawing of a scraper conveyor on an earthmover.

material being handled. Aprons are well adapted for use as feeders for rock crushers, elevating systems, picking systems, and in power plants using coal conveyors, such as that shown in Figure 9-22.

SCRAPER FLIGHT CONVEYORS A sketch of a scraper flight conveyor is shown in Figure 9-23. This type of conveyor is used to move bulk materials. The flights are suspended into the material from above to force the material conveyed to slide along a trough or deck. Thus, the trough, and not the chain of the conveyor, supports the material. The usual arrangement of the strands is as in Figure 9-24, with the conveying strand being below and the return on top. Conveyors so arranged are usually loaded from the sides. The alternative is to drop the material through the return strand. Discharge is through the conveyor trough just in front of or below the head shaft. In this type of conveyor, the chains are usually placed above the material, but if it is a twostrand conveyor, the chains may be placed at the sides. For single-strand conveyors, the chain is centered. But in both cases, the chain does not usually operate in the material conveyed. Engineering




245

FIGURE 9-25 Photo of a scraper conveyor on an earthmover.

FIGURE 9-26 Drawing of a drag conveyor.

steel roller conveyor chain, steel bushed rollerless chain, welded steel, and bar-link chain are all used in scraper conveyor applications. A wide variety of attachments are also used; style G (see Figure 2-30) is popular and type A, used with flight wings on the flights, is an arrangement that is also common. In the latter design, the chain and attachment connections are not rigid. Flights are made from a wide range of materials. Fabricated steel, cast steel or cast iron, injection molded or extruded plastic, sawn plastic, and wood have all been used successfully. The choice of material depends on the characteristics of the material being conveyed and the other details of the application. Scraper conveyors are widely used to handle bulk materials such as coal, ashes, potash, lime, grains, and other bulk materials. As shown in Figure 9-25, short, heavy-duty scraper conveyors are used to load elevator scrapers used on construction jobs, where large amounts of dirt must be moved.

DRAG CONVEYORS Drag conveyors are used to handle bulk materials. They are very similar to scraper conveyors both in function and the types of materials handled. The drag conveyor sketched in Figure 9-26 is quite typical and shows the main difference between scraper and drag conveyors. Drag chains normally run in the material on the bottom of the conveyor trough. Several drag chain strands, operating side by side in a trough, is very common in this type of conveyor. Chains for drag conveyors may have separate flights connected to attachments on the chain. Such a conveyor is shown in Figure 9-27, the flights being wooden and placed flat on the conveyor deck. The chain, an engineering steel bushed rollerless type, travels on top of the flights, being connected to them with type A attachments. Both the chain and flights run in the material. Probably the most common type of drag conveyor chain has the drag feature built into the construction of the links. Engineering welded steel drag chain (see Figure 2-27), shown in Figure



246


FIGURE 9-27 Drag conveyor moving wood chips.

9-26, is such a chain. Conveyors using such chain normally have a low initial cost and provide good service life under severe conditions. Drag conveyors may be arranged as shown in Figure 9-26, with the return on top and discharge through the conveyor trough at, or just before, the head shaft. Some drag conveyors have the loaded strand on top and discharge over the head shaft. In such cases, the sprockets serve as a continuation of the conveyor deck. For conveyors with wide troughs, sprockets with extended flanges or “wings” (see Figure 4-21) are sometimes used to ensure discharge over the head shaft. Drag conveyors are used to handle abrasive bulk material such as sand, coal, ashes, coke, and cement. They are also used to handle other materials, such as sawdust and wood chips. In fact, they can be used to convey just about any bulk material that can be discharged by gravity.

CROSSBAR CONVEYORS Crossbar conveyors are mainly used in surface treating and finishing lines, where parts suspended from the conveyor are dipped and dried. Crossbar conveyors normally have two strands of chain connected with crossbars, as shown in Figure 9-28. Parts hung from the crossbars can thus be dipped in a series of treating and preparation tanks. The parts can then be passed through a paint dip and drying oven, and all of this can be done without removing the parts from the conveyor. The double-strand design with crossbars permits better control and positioning of the parts than on similar conveyors with a single strand of chain. The chains used on such conveyors are engineering steel roller conveyor or steel bushed rollerless chains. The latter are usually used when the chain is subjected to high temperatures in drying ovens. Crossbar conveyors are often used in the appliance and automobile industries. They are also widely used in foundries and the agricultural equipment industry. The conveyors can be arranged




247

FIGURE 9-28 Drawing of a crossbar conveyor.

FIGURE 9-29 Crossbar conveyor carrying painted metal parts.

in various paths from inclined to serpentine. Figure 9-29 shows a crossbar conveyor used in a continuous paint dipping and drying line.

IN-FLOOR CONVEYORS In-floor conveyors are used in a wide variety of industrial applications. One popular type, shown in Figure 9-30, is the tow cart type. It is frequently used to transfer boxes of materials between warehousing and shipping areas. This style of conveyor has to traverse horizontal curves, so it



248


FIGURE 9-30 Drawing of an in-floor chain conveyor.

FIGURE 9-31 An in-floor conveyor carrying cases in a dairy.

often uses bar-link-type chain lying on its side or it may use bar-link chain with special features enabling it to be flexed both vertically and horizontally. Some conveyors of this type are part of complex systems with remote computer-controlled features to discharge or pick up the carts at will. Some types of in-floor conveyors handle objects directly on the chains, unloading with diverter bars, as shown in Figure 9-31. Another type of in-floor conveyor that uses heavy steel bar-linktype chain with closely spaced flat tops is widely used to move automobiles and other vehicles down assembly lines. Outboard rollers on the chain, running on tracks under the floor, support the chains in these conveyors, including the weight of the vehicles. The outboard rollers are often equipped with antifriction bearings. These types of conveyors are also used to carry and store materials, components, and subassemblies feeding the final assembly line.




OTHER TYPES

OF

249

CONVEYORS

Most conveyors that use standard engineering steel chains and attachments fall into one of the categories described in this chapter. However, some must meet specialized needs. In either case, contact a manufacturer of engineering steel chains for help.

ENGINEERING STEEL CHAIN CONVEYOR SELECTION GUIDELINES CONVEYOR TYPE The designer must carefully decide which of the two basic conveying modes should be used to obtain the most useful and economical chain conveyor for the application. The two conveying modes are as follows: • •

The material is supported and carried entirely on the chain and attachments. Carrier, apron, pan, slat, crossbar, and in-floor conveyors fit in this category. The material being conveyed is pushed, scraped, dragged, or otherwise slid along a conveyor deck. The chain does not support the material. Pusher, drag, and scraper conveyors fit in this category.

The final decision on which conveyor type to use should be made only after checking the following: • • • • • • •

Advantages and disadvantages of each type. Initial installation and operating costs. Service life required and maintenance costs. Physical and chemical properties of the material or items to be conveyed. Conveying speed required. Distance to be conveyed. Loading methods.

One of the best actions is to use a similar chain conveyor installation that has given good performance and service life. One should contact an engineering steel chain manufacturer for help in selecting a conveyor. Much experience is usually needed to make a good selection.

CONVEYOR WIDTH

AND

HEIGHT

The chain conveyor must be wide enough and high enough to handle the objects or materials carried on it. A designer must be careful to consider all physical restrictions before deciding on the size of the chain conveyor. This requirement would seem to apply mainly to conveyors handling unit products, but it is also important to consider the width and height of those handling bulk materials. The designer must also consider the dimensions of the chutes or other equipment that deliver the material to the conveyor and those that discharge it.

CONVEYOR LENGTH

AND

SHAFT CENTER DISTANCE

Conveyor length is limited by the frictional drag from the weight of the chain and product and the rated working load of the chain. As the conveyor gets longer, the drag increases and there is less available capacity to carry the product.



250


Shaft center distance is often the same as the conveyor length, but sometimes it is a longer. The shaft center distance may be made longer to accommodate additional equipment at the ends of the conveyor. Conveyor chains stretch elastically when a load less than the yield strength is applied. When the load is removed, the chain returns to its original length. If the conveyor is very long (more than about 20 feet), this elastic stretch can cause problems. The chain may not align properly with loading or transfer points, and in extreme cases, the chain can jump teeth on the tail shaft sprocket. Consult the chain manufacturer for advice on chain elongation under load. Long shaft center distances and sprockets with a very small number of teeth can cause severe surge and vibration in a conveyor. This can happen when the resonant frequency of the conveyor chain matches the sprocket tooth contact frequency. If either of the above problems occurs, splitting the conveyor into two sections with a transfer point often solves the problem.

LOADING

THE

CONVEYOR

Loading any conveyor should be done as gently as possible to reduce impact. If possible, the load should be placed or slid onto the conveyor to reduce the pulsation and surging caused by rough loading. In laying out chutes or hoppers for direct discharge onto a conveyor, it is desirable to place the load as near the center of the conveyor span as possible. Otherwise, the chain on one side of the conveyor may wear more rapidly than the chain on the opposite side.

CONVEYOR SPEED The speed at which the conveyor travels and the material carried per unit of length set the capacity of the conveyor. The nature of the material, how it is loaded or unloaded from the conveyor, what happens while it is on the conveyor, and how it is discharged often dictate the conveyor speed. Table 9-1 lists basic conveyor types and the ranges of speed typical for each type. From this table, an estimate can be made of the speed of the conveyor to be selected.

CONVEYOR CAPACITY Conveyors for Parts and Packages The capacity of these unit conveyors can be determined by multiplying the items per linear foot of conveyor by the conveyor speed in feet per hour. Conveyors for Bulk Material The capacity of these bulk conveyors can be determined by Equation 9.1: TABLE 9-1 Recommended operating speed ranges Conveyor type Slat or flat-top conveyor Carrier conveyora Assembly line conveyor Drag and scraper conveyors Apron conveyor a

Material conveyed directly on chain.


Speed (ft/min) 50–150 50–150 5–15 50–100 10–60


251


W=

T (2000lb / ton ) 33.3T = , S (60 min/ hr ) S

(9.1)

where W is the weight (in pounds) of the conveyed load per foot of conveyor, S is the speed of the conveyor (in ft/min), and T is the weight (in ton/hr). The speed in Equation 9.1 is estimated, so some juggling of speed and capacity per foot may be needed later.

CONVEYOR CHAIN SUPPORTS The return strand of chain conveyors usually needs to be supported when the conveyor is more than 15 feet long. That is because an unsupported return strand, hanging as a catenary, can greatly increase the chain pull. The chain pull normally will be much less when the return strand is supported. In addition, the sag in a return strand elongated from wear sometimes will “hang up” on obstructions the chain cleared when the conveyor was new. Supporting the return strand also will minimize pulsation and whip. Load-carrying strands are normally supported by tracks or guides, although spaced rollers are sometimes used. Return strands are often supported by guides or spaced rollers. Figure 932 illustrates in cross section the carrying and return strands of four different styles of conveyors. When designing supports for a conveyor, be sure that the span of the centerlines of the sprockets on shafts matches the span of the centerlines of the pairs of mating chains and tracks or ways. When flanged rollers are used on rails to support the conveyor, recognize that the gauge of the track will be longer than the span of the centerlines of the chains. The difference will often be found as a listed dimension in manufacturers’ catalogs under the heading “track gauge.” The reason for the difference is that the track is gauged to the center of the faces of the rollers, excluding the space occupied by the flanges. The flanges are normally on the inside of the rails.

CONVEYOR DRIVE Two important factors in the design of a conveyor are how to power the conveyor and where to apply this power. These factors should be considered very early in the design process. Whenever possible, power should be applied to the conveyor at the head shaft. The head shaft usually is at the discharge end of the conveyor; then, only the carrying span of the conveyor chains will be under maximum tension when it is operating. The wear life of conveyor chains is a function of the load and the time it is under load. Thus conveyor chains that are driven from the tail shaft, where the entire chain loop is always under load, have a shorter chain life. Normal practice is to drive chain conveyors by another chain and sprockets. For best results, this secondary drive should have its tensioned span parallel to the tensioned run of the chain conveyor (see Figure 9-33). It is sometimes good to use a compensating sprocket to drive the head shaft of long-pitch chain conveyors, as shown in Figure 9-33. This reduces conveyor surge due to chordal action and permits the use of smaller diameter sprockets.



252


FIGURE 9-32 Typical methods of supporting the carrying and return strands in a conveyor.

FIGURE 9-33 Compensating sprocket and head shaft.

SPROCKETS Sprocket Size Both sprockets are the same size in most conveyors. The recommended number of teeth on the drive sprocket is found by the procedure given later in this chapter. If space will not permit a sprocket with the recommended number of teeth, select a sprocket with as many teeth as space will permit.




253

FIGURE 9-34 Keyed in-line sprockets.

FIGURE 9-35 Chain tension take-ups.

Matched Sprockets On multiple-strand conveyors, correct head sprocket alignment is extremely important (see Figure 9-34). Sprockets should be ordered in sets, keyed in line, matched, and tagged. One tail shaft sprocket should be keyed to the shaft to turn the shaft in its bearings. The others should be allowed to turn freely between set collars to position automatically should uneven wear occur between the strands.

TAKE-UPS Most conveyors require control of chain tension through the use of take-ups. Take-ups are devices for adjusting shaft center distances. They are normally installed at the loading end of a conveyor. Take-ups should be provided on all chain conveyors to adjust for elongation as the chain joints wear. Take-ups also are used to provide slack in the chain for installation and maintenance. Takeups should be adjusted while the conveyor is operating to obtain the best results. There are four basic types of take-ups: screw, spring, gravity, and catenary. The four types are shown in Figure 9-35.



254


FIGURE 9-36 Chain conveyor with catenary section.

CATENARY TENSION

AND

CHAIN SAG

In most long conveyors, the return span of chain should be supported over most of its length. The weight of the unsupported span, or a portion of a span, adds to the chain pull. This must be considered, along with the bearing and shaft loads, when calculating the total working load on the chain. The added pull from catenary tension is not included when calculating the power needed to run the conveyor. When a catenary take-up is used (see Figure 9-36), some length of the return span remains unsupported. It creates a place for any excess chain to accumulate as wear takes place. The catenary also gives enough tension to the slack span so that the conveyor is not likely to jump teeth under a heavy load. Ample space should be provided for chain sag in the catenary. Attempting to operate with too little depth of sag in a long catenary will result in high bearing loads as well as increased loads on the chain. Chain sag should not be less than 3% of the unsupported span. The procedure for calculating catenary sag and tension is given later in this chapter.

MATCHED STRANDS Matching Left-Hand and Right-Hand Strands Right- and left-hand strands are required in all multiple-strand installations where the chain attachments are not symmetrical. In this situation, right- and left-hand strands must be specified when ordering (see Figure 9-37). Specifying of right- and left-hand conveyor strands should not be

FIGURE 9-37 Right-hand and left-hand strands where attachments are not symmetrical.




255

confused with the concept of left- and right-hand attachments, discussed in chapter 3 and in the next section. Direction of Travel for Left- and Right-Hand Strands As was noted elsewhere, not all chains and attachments used in conveyor service are symmetrical. It should be noted that many such chains have a recommended direction of travel relative to the head sprocket. When there is such a recommendation, it should be clearly shown on the conveyor drawings or be part of the contractor’s specifications. Matching and Tagging Strands for Length Using matched strands helps ensure correct alignment across the strands. It is particularly important where through rods, scraper flights, or other carrying attachments are used. Strands operating out of alignment throw a greater load on one chain. This causes excessive wear on the chain and/or attachments, and on the sprockets. Multiple-strand chain conveyors should be checked regularly to make sure that the chains are operating in proper alignment with each other. When chains are required for multiple-strand operation, it is important to specify to the manufacturer “matched and tagged chain” along with the number of strands required. The chains will then be measured at the factory and a number tag will be attached to each strand (see Figure 9-38). Each matching group of strands is tagged with the same number and, whenever possible, will be wired and shipped together. The tags should not be removed until the chain is assembled. The strands must be coupled so that those with the same number are installed side by side. All chain is made to length tolerance specifications. The matching of strands ensures that sections of chain, with lengths at opposite ends of the tolerance range, are not placed opposite one another in the conveyor installation. Figure 9-39 shows the effect of two strands that are not equal in pitch. One strand becomes overloaded or the chain becomes twisted when engaging the sprockets.

ENVIRONMENT Temperature Standard engineering steel chain is expected to perform well in an outdoor temperature range of from 0˚F (–18˚C) to 150˚F (65˚C). Special materials or lubricants may be needed for use in higher or lower temperatures. Call an engineering steel chain manufacturer for help when using these chains in extremely high or low temperatures.

FIGURE 9-38 Matched and tagged chain strands.



256


FIGURE 9-39 Effect of two strands of unequal length.

Corrosion and Abrasion Standard engineering steel chain must often work outdoors and in mildly corrosive and abrasive conditions. These are normal conditions in many industrial uses for engineering steel chain. Contact an engineering steel chain manufacturer for help when using these chains in very corrosive or abrasive conditions.

LUBRICATION Lubricating engineering steel conveyor chains is covered in chapter 13.

ENGINEERING STEEL CONVEYOR CHAIN SELECTION PROCEDURE STEP 1: OBTAIN NECESSARY INFORMATION The following information is needed to design a conveyor using engineering steel chain: •

• • • • • •

Conveyor configuration • Type • Mode • Layout (including height of lift or incline angle) Conveyor width and height Conveyor length and shaft center distance Conveyor speed Kind of material to be handled Weight of material to be handled per foot of conveyor length Loading characteristics



257


• • • •

•

Estimated weight of carriers (slats, flights, pans, etc.) and weight of chain, including attachments, per foot of chain Size and spacing of attachments and/or carriers Diameters of shafts and sprockets Environment • Temperature • Corrosion • Abrasion Available lubrication

STEP 2: SELECT GENERAL CHAIN TYPE

AND

ESTIMATE WEIGHT

After deciding on the conveyor type and mode, a suitable type of chain is determined using Table 9-2, then a coarse estimate of the weight of that chain can be obtained from Table 9-3. These tables give only very general information about the chain. The designer must consult one or more of American Chain Association manufacturers’ catalogs for the basic data and details of the chain used in the conveyor. These catalogs give the necessary data on rated working loads, pitches, dimensions, weights, and other details for the chains being considered.

STEP 3: SELECT CHAIN SUPPORTS Select the method of supporting the chain in the conveying and return runs from Figure 9-32. If the conveyor is very short, it might not need supports on the return run. Calculate the catenary tension to see if return supports are needed. TABLE 9-2 Chain type selection



258


TABLE 9-3 Ranges of average weights per foot of ES chain conveyors Conveyor type and conveyor chain type Carrier, apron, pan, or slat conveyors: roller-type enineering chain Pusher, scraper, or drag conveyors Rollerless-type engineering chain Drag chain Bar-link-type chain

Average weight range (lb/ft) of chain conveyor 10–20

5–20 8–20 10–50

TABLE 9-4 Coefficients of sliding friction, chain Coefficient fs Dry 0.33 0.50 — 0.35 0.44

Steel on Steel Cast Iron or Cast Steel on same surface Steel on Bronze Steel on Hardwood As Cast: Iron or Steel on Wood

STEP 4: OBTAIN NEEDED COEFFICIENTS

OF

Lubricated 0.20 0.40 0.15 0.25 —

FRICTION

Chain Sliding Friction Where the chain slides on the edges of its plates on ways of steel or other materials, use the sliding coefficient of friction (fs) shown in Table 9-4. If the chain carries the material (mode 1), this factor applies to the weight of both the conveyor and the material. If the chain only pushes the material (mode 2), this factor applies only to the weight of the conveyor. Chain Rolling Friction When the chain rolls on rails or in a track, use the rolling coefficient of friction (fr) shown in Table 9-5. If the chain carries the material (mode 1), this factor applies to the weight of both the conveyor and the material. If the chain only pushes the material (mode 2), this factor applies only to the weight of the conveyor. Material Sliding Friction When the material slides on a deck or in the bottom of a trough, use the coefficient of friction (fw) shown in Table 9-6. Coefficients of friction for only a few common materials are shown in Table 9-6. Coefficients of friction for materials not listed may be found in handbooks and catalogs.

STEP 5: CALCULATE ADDITIONAL CHAIN PULL When bulk materials slide against containing walls of conveyor troughs they cause an additional pull on the conveyor. This factor, J, can be calculated by referring to Figure 9-40 and using Equation 9.2.



259


TABLE 9-5 Coefficients of rolling friction, chain Coefficient, fr*

Roller Outside Diameter

Dry 0.22 0.20 0.16 0.14 0.12 0.11 0.10 — —

1- 1/2 ” 2” 2- 1/2 ” 3” 4” 5” 6” Roller Bearings Ball Bearings in Hardened Races

Lubricated 0.16 0.15 0.12 0.09 0.08 0.07 0.06 0.015 0.01

* Approximate values developed from standard chains. To calculate rolling friction (fr) for other size rollers use the following formula: fr = fs ×

d 0.1 + where : D D

fr D d fs

= Coefficient of rolling friction = OD of roller = ID of roller = sliding coefficient (0.33 for steel chain, dry)

TABLE 9-6 Coefficients of sliding friction, conveyed materials Coal on Steel Crushed Stone or Sand on Steel Cement on Steel Wood on Wood

Dry 0.33 0.33 0.80 0.55

Coeffeicent, fw Lubricated — — — —

FIGURE 9-40 Cross-section of material conveyed in a trough.


(9-6)


260


TABLE 9-7 R-factor values Material

R 14.0 35.0 7.5 7.0 5.5 14.0

Coal Coke Limestone Gravel Sand Ashes

J=

Ch 2 , R

(9.2)

where J is the additional chain pull (in lb), h is the height of the material in the trough (in inches), C is the distance the material is carried on the conveyor (in ft), and R is the drag factor for various materials (see Table 9-7).

STEP 6: CALCULATE BASIC CHAIN PULL Select the equations given for the layout that was chosen. The formulas work for either mode 1 (material is carried on the chain) or mode 2 (material is pushed on a deck) type conveyors. The material weight on the chain is zero in mode 2 and the term drops out. All of these equations for chain pull assume that the same supports are used for the return span as for the conveying span. Also, the term J for additional chain pull applies only when the material is pushed in a trough and the skirt boards are stationary. Terms used in the equations are: Horizontal Conveyors (see Figure 9-41)

FIGURE 9-41 Horizontal conveyor layout.

When the material is moved but not supported by the chain: P = C(2.1MfM + Wfw) + J.

(9.3)

When the material is supported by the chain: P = CfM(2.1M + W) + J. Note that in this case, fw = fM, so only the value of fM is needed in the equation.


(9.4)


261


Inclined Conveyors (see Figure 9-42)

FIGURE 9-42 Inclined conveyor layout.

When the material is moved but not fully supported by the chain: P = C(MfMcos α + Wfwcos α + Msin α + Wsin α) + C(MfMcos α – Msin α) + J.

(9.5)

Note that when the term (MfMcos α Msin α) is a positive value, multiply it by 1.1 to allow for tail shaft friction. Also note that cos α = b/C and sin α = a/C. When the material is fully supported by the chain: P = CfMcos α(2.1M + W) + (CWsin α) + J.

(9.6)

Note that in this case, fw = fM, so only the value of fM is needed in the equation. Vertical Conveyors (see Figure 9-43)

FIGURE 9-43 Vertical conveyor layout.

P = C(M + W) + P1, where P is the conveyor chain pull (in lb), C is the length of the conveyor (in ft), M is the weight of the chain, attachments, and carriers (in lb/ft), W is the weight of the conveyed material (in lb/ft), fM is the coefficient of friction for the chain (it may be either fs or fr, whichever applies), fs is the coefficient of sliding friction for the chain (from Table 9-4), fr is the coefficient of rolling friction for the chain (from Table 9-5),


(9.7)


262


TABLE 9-8 Speed correction factors

fw is the coefficient of sliding friction for the material (from Table 9-6), and P1 is the take-up tension (in lb).

STEP 7: SELECT

THE

SPROCKET SIZE

In Table 9-8, in the columns for conveyor operating speed, read down to the number nearest 1.00. This will be in the vicinity of the heavy dividing line. Read across to the left to find the number of sprocket teeth. This is the ideal sprocket size. If available space will not accommodate the ideal sprocket size, select a sprocket with as many teeth as the space will permit.

STEP 8: CALCULATE

THE

COMBINED SERVICE FACTOR

Calculate the combined service factor, V, using Equation 9.8. The values for the four individual factors are obtained from Table 9-9. V = VSVLVOVT

(9.8)

where VS is the factor for frequency of shock, VL is the factor for character of loading, VO is the factor for operating conditions, and VT is the factor for daily operating time.

STEP 9: CALCULATE

THE

PRELIMINARY CHAIN DESIGN PULL

Calculate the preliminary design chain pull using Equation 9.9:



263


TABLE 9-9 Service factors VS Frequency of shocks Infrequent

VL Character of loading Uniform or steady

Frequent

Moderate shock

VO Operating conditions Relatively clean and moderate temperature Moderately dusty Unprotected from weather, dirty or corrosive conditions, or unusual temperatures within permissible operating range

Heavy shock

VT Daily operating time 8–10 hr 24 hr

Factor 1.0 1.2 1.4

1.5

PDesign = PVE.

(9.9)

Multiply the basic chain pull (from Equation 9.3 through Equation 9.7) by the combined service factor (from Equation 9.8) and the speed correction factor (from Table 9-8).

STEP 10: SELECT

THE


The preliminary design chain pull applies to all the strands of chain in the conveyor. If two or more strands of chain are used, which is usually the case, multiply the preliminary design chain pull by 1.2 and divide by the number of strands of chain in the conveyor. This will be the required working load per strand of chain. American Chain Association manufacturers that supply engineering steel chains for conveyors list rated working loads for such chains in their catalogs. These rated working loads should be interpreted as “maximum allowable working loads.” Operating the chain at loads greater than the rating will usually limit their service life. A chain should be selected that has a rated working load at least equal to and preferably greater than the required working load per strand of chain calculated above. Chain pitch should be as long as is found to be compatible with sprocket size, as selected earlier. Manufacturers will usually list standard chains in two or three popular pitches with similar or identical working loads. The best economics are obtained by using standard chains of longer pitches, but sprockets with the same number of teeth will be proportionately larger for longer pitch chains. If sprockets with fewer teeth are then chosen, the speed correction factor will increase the conveyor pull accordingly.

STEP 11: CALCULATE CATENARY SAG

AND

TENSION

If a catenary section is present, the designer should now determine the depth of sag so that the needed clearance can be provided. Also, the designer should calculate the catenary tension to be sure the rated working load of the selected chain is sufficient. D = 0.375 LE PC =


L2W , 96 D

(9.10)

(9.11)


264


where D is the depth of sag of the conveyor (in inches), L is the straight-line distance between points of support (in inches), E is the amount of excess chain in the catenary (in inches), S is the length of the catenary in the slack span (in inches), PC is the catenary tension (in lb), and W is the weight of chain per foot including attachments and carriers (in lb/ft). The depth of sag and catenary tension can also be determined using Table 9-10 and Table 9-11. TABLE 9-10 Amount of chain sag for various centers

TABLE 9-11 Catenary tension



265


STEP 12: RECALCULATE

THE

REQUIRED WORKING LOAD

AND

SELECT FINAL CHAIN

Repeat steps 6 through 9 using the actual chain and attachment weights. These should be taken from the manufacturer’s catalog from which the chain was selected. Once a specific chain is selected, repeating steps 6 through 9 will give a somewhat different design chain pull and required chain working load. Remember to include the catenary tension if a catenary section is present. The listed allowable chain working load taken from the catalog must be greater than or equal to the calculated required chain working load for the application, and the listed allowable chain working load should be greater than the calculated required chain working load for the application. If it is not, a chain with a higher working load (and probably weight) should be selected. Recheck the calculations again until a chain with satisfactory working load is selected.

STEP 13: CALCULATE

THE

REQUIRED CHAIN LENGTH

Both sprockets (head shaft and tail shaft) are the same size in most conveyors. In this case, the chain length can be calculated using Equation 9.12: LP = N +

2C ′ , P

(9.12)

where LP is the required chain length (in pitches), N is the number of teeth on the sprockets, C′ is the shaft center distance (in inches), and P is the chain pitch (in inches).

STEP 14: CALCULATE

THE

REQUIRED POWER

The horsepower required at the input shaft of the conveyor is calculated using Equation 9.13 and Equation 9.14. For horizontal and inclined conveyors: HP =

1.1PS , 33000

(9.13)

and for vertical conveyors:

HP =


(

)

1.1 WC + 0.1MC S 33000

.

(9.14)


10 Roller Chain Conveyors Several types of roller chains are used in conveyors. Many are of the single-pitch design covered in the ASME B29.1 standard, many more are double-pitch conveyor chains covered in ASME B29.4, and a few are hollow pin, covered in ASME B29.27. Small or large (carrier) rollers are available in the double-pitch series of conveyor roller chains; thus the chains can slide or roll on tracks or support rails. The conveyed material can be moved by bars, flights, slats, pusher lugs, and other types of components. The large and small roller types were shown in Figure 2-10 and Figure 2-11. A wide variety of standard and special attachments are available for these chains. Most of the standard attachments are shown in Figure 10-1 to Figure 10-8. Attachments can also be modified for special needs. The hole size and location can be altered or the attachments can be altered to provide special geometry of bend, contour, or other forms. Figure 10-9 shows a group of special attachments. When modified attachments are needed, consult a roller chain manufacturer. Many attachment sizes and types are available in stainless steel.

TYPES OF ROLLER CHAIN CONVEYORS Nine types of chain conveyors were described in the chapter on engineering steel chain conveyors. The descriptions are very detailed and are not repeated here. Designers should refer to chapter 9 for more information. Roller chains can be used on any of the listed conveyor types. However, good practice dictates against using roller chain in a few of those conveyor types. The most common uses for roller chains probably are in carrier and slat conveyors. Roller chains are seldom used in apron or scraper conveyors that carry bulk materials. This is because the small clearances in roller chain easily become packed and clogged with the loose conveyed material. If roller chain is used in one of these conveyor types, the chain should be well shielded from the loose material. Roller chains are almost never used in drag conveyors. The chain runs in the conveyed material in a drag conveyor and the chain cannot be shielded from the loose material. This chapter does not cover roller chains conveying bulk materials in drag or scraper conveyor applications. The designer should consult an ACA roller chain manufacturer for help with these applications.

ROLLER CHAIN CONVEYOR SELECTION GUIDELINES CONVEYOR TYPE The designer must decide which of the two basic conveying modes will be used. The two conveying modes are • •

The material is supported and carried entirely on the chain and attachments. Carrier, apron, pan, slat, crossbar, and in-floor conveyors fit in this category. The material conveyed is pushed, scraped, or otherwise slid along a conveyor deck. The chain does not support the material. Pusher and scraper conveyors fit in this category.

267



268

FIGURE 10-1 Straight attachment plates for precision roller chain.

FIGURE 10-2 Bent attachment plates for precision roller chain.

FIGURE 10-3 Extended pins for precision roller chain.

FIGURE 10-4 DP straight attachment, 1H.

FIGURE 10-5 DP straight attachment, 2H.




Roller Chain Conveyors

FIGURE 10-6 DP bent attachment, 1H.

FIGURE 10-7 DP bent attachment, 2H.

FIGURE 10-8 DP extended pins.

FIGURE 10-9 Special RC attachments.


269


270


The final decision on which conveyor type to use should be made only after considering the following: • • • • • •

Advantages and disadvantages of each type. Initial installation and operating costs. Service life required and maintenance costs. Conveyor speed. Conveyor length. Loading methods.

For unusual or complex conveyors, one should contact a roller chain manufacturer for help in selecting a conveyor. Much experience is usually needed to make a good selection in these cases.

CONVEYOR WIDTH

AND

CLEARANCE HEIGHT

The chain conveyor must be wide enough to handle the objects or materials carried on it. There also must be enough clearance height to permit the attachments, fixtures, and the carried material to pass, and there must be enough clearance height in the return run to clear the attachments and fixtures. The designer must be careful to consider all physical restrictions before deciding on the size of the chain conveyor.

CONVEYOR LENGTH

AND


Conveyor length is limited by the frictional drag from the weight of the chain and product and the rated working load of the chain. As the conveyor gets longer, the drag increases and there is less available capacity to carry the product. Shaft center distance is often the same as the conveyor length, but sometimes it is longer. The shaft center distance may be made longer to accommodate additional loading and unloading equipment at the ends of the conveyor.

LOADING

THE

CONVEYOR

Loading any conveyor should be done as gently as possible to reduce the impact. If possible, the load should be placed or slid onto the conveyor to reduce the vibration and surging caused by rough loading. Chutes or hoppers that load the conveyor should place the load as near the center of the conveyor span between the chains as possible. Otherwise the chain on one side of the conveyor may wear more rapidly than that on the opposite side.

CONVEYOR CAPACITY Conveyor capacity is the amount of material, in pounds or units, carried per unit of time. The capacity of the conveyor is found by Equation 10.1: WC = 60WS, where WC is the conveyor capacity (in lb/hr or units/hr), W is the amount of material carried (in lb/ft or units/ft), and S is the conveyor speed (in ft/min).


(10.1)



271

CONVEYOR SPEED The required conveyor capacity determines the conveyor speed. The type of material and what is done to it on the conveyor limit the conveyor speed. How the material is loaded onto and discharged from the conveyor may also limit conveyor speed.

ACCUMULATION Sometimes the user wants to stop the material flow without stopping the conveyor. In this case, an accumulation section is needed. Accumulation sections are often used in pusher and carrier chain conveyors. A device either raises the material or lowers the chain and the material then sits on stationary strips or a deck while the chain conveyor runs freely below the material. Stopping the material flow in this way does not increase the chain pull. In fact, it reduces the chain pull slightly. Accumulation sections are sometimes used in slat conveyors. In this case, a device stops and holds the material in place while the conveyor slides under the material. Stopping the material flow in this way greatly increases the chain pull, so the accumulation section should be kept as short as possible. Stopping the material flow on the conveyor while the conveyor continues to run can generate a lot of heat, so the time the material is held in the accumulation section should be as brief as possible.

CHAIN TYPES Precision Roller Chains Precision roller chains with attachments are often used in conveyors. These chains and standard attachments for them are listed in the ASME B29.1 standard. Some manufacturers offer precision roller chain with straight-edged link plates for conveyor use. Precision roller chains are usually used where sprocket sizes are limited and where smooth operation is very important. Double-Pitch Conveyor Roller Chains Double-pitch conveyor roller chains are also used in conveyors. These chains, and standard attachments for them, are listed in ASME B29.4. Double-pitch conveyor roller chains have straight-edged link plates and come with either small- or large-diameter rollers. Chains with small-diameter rollers are normally used in vertical conveyors or short conveyors where the chain slides on the edges of the link plates. Chains with large-diameter rollers are normally used in longer conveyors where it is important to reduce the drag caused by friction. Hollow Pin Roller Chains Hollow pin chains are used almost exclusively in crossbar conveyors. Hollow pin chains come in both single-pitch and double-pitch versions. The double-pitch chains come with either small- or large-diameter rollers.

CHAIN PITCH Conveyor chains are usually selected on the basis of working load and working load is related to chain pitch. In addition, carrier size or required attachment spacing may control chain pitch. Shortpitch chains (35–80) are normally used in short conveyors or where smooth operation is needed. Longer pitch chains (100–200, or C2040–C2160) are usually used in longer conveyors where speeds are slower.



272


CHAIN ATTACHMENTS Figure 10-1 through Figure 10-3 show standard attachments for precision roller chains (in ASME B29.1) and Figure 10-4 through Figure 10-8 show standard attachments for double-pitch conveyor roller chains (in ASME B29.4). Figure 10-9 shows some special attachments. Figure 10-10 and Figure 10-11 show how attachments can be used. Figure 10-10 shows how attachments can be used on single-strand chain. At the left, the use of V-blocks held by A-1 and M-1 attachments is shown. They are frequently used to handle cylindrical objects. In the center, the upper and middle illustrations show rollers mounted on the chain with M1 and D-1 attachments. The roller mounted on the M-1 attachment is intended to provide rolling contact with either the objects conveyed or a “hold-down” and the roller on the D-1 attachment is usually to support the chain in rolling contact. The lower center view shows a D-3 attachment with a rubber block used to provide a high-friction conveying surface. The upper right illustration shows an angle iron attached to a K-2 attachment that serves as a pusher. The lower right drawing shows a tapped carrier block mounted on a chain with M-2 attachments. Figure 10-11 shows three double-strand setups. On the left are slats mounted on A-1 attachments. In the center M-35 attachments are used as spacers to convey and position long objects. On the right, tubing is assembled on D-3 attachments to form a conveying surface. The setup on the right could also have been done using through-crossbars in hollow pin chains.

CONVEYOR CHAIN SUPPORTS Load-carrying strands are normally supported by tracks or guides. If the conveyor chain has largediameter rollers, the chain usually rides on the rollers in a track. If the conveyor chain has smalldiameter rollers, the chain usually slides on the link plate edges. When the conveyor chain has

FIGURE 10-10 Use of RC attachments.

FIGURE 10-11 Use of attachments on parallel strands.




273

small-diameter rollers, the loaded span should not ride on the chain rollers on a rail. The rollers may not turn and flat spots may be worn on the rollers. The return strand of chain conveyors should be supported when the shaft center distance is equal to more than 80 pitches of the chain. That is because a long unsupported return strand hangs in a catenary and can greatly increase the chain pull. The chain pull normally will be much less when the return strand is supported. In addition, the sag in a return strand elongated from wear will sometimes “hang up” on obstructions it cleared when the conveyor was new. Supporting the return strand also reduces pulsation and whip. In most conveyors, the return strand slides on the link plate edges or the carriers on a track or deck. Even when the loaded strand rides on large-diameter rollers, the return strand still slides on a track or deck. That is because the attachments or carriers often obstruct the rollers in the return strand.

CONVEYOR DRIVE Power should be applied to the conveyor at the head shaft. The head shaft is usually at the discharge end of the conveyor, then only the carrying span of the conveyor chains will be under maximum tension when it is operating. The wear life of conveyor chains is a function of the load and the time it is under load. Thus conveyor chains that are driven from the tail shaft, where the entire chain loop is always under load, have a shorter chain life. Also, when conveyor chains are driven from the tail shaft, excess slack chain can accumulate in the carrying run just after the tail sprocket (Figure 10-12). This can cause conveyor loading problems or cause the chain to jump sprocket teeth.

SPROCKETS Sprocket Size Both sprockets are the same size in most conveyors. For double-pitch chain, as few as six effective teeth can be used on very-slow-speed conveyors where smooth operation is not essential. However, a minimum of 15 effective teeth is desirable. For single-pitch chain, sprockets should have at least 15 teeth. Where smooth operation is very important, sprockets should have 21 or more effective teeth to reduce the effect of chordal action. If space will not permit a sprocket with the recommended number of teeth, select a sprocket with as many teeth as space will permit. Hardened Sprocket Teeth Sprockets with hardened teeth should be used where any of the following conditions exist: • •

Abrasive environment. A small number of teeth; less than 15.

FIGURE 10-12 Excess chain slack at the tail shaft.



274


FIGURE 10-13 Keyed in-line sprockets.

• •

High speeds; more than 150 ft/min. High loads: more than 50% of rating.

Matched Sprockets On multiple-strand conveyors, correct head sprocket alignment is extremely important (see Figure 10-13). Sprockets should be ordered in sets, keyed in line, matched, and tagged. One tail shaft sprocket should be keyed to the shaft to turn the shaft in its bearings. The others should be allowed to turn freely between set collars to position automatically should uneven wear occur between the strands.

TAKE-UPS Most conveyors require control of chain tension through the use of take-ups. Take-ups are devices for adjusting shaft center distances. They are normally installed at the loading end of a conveyor. Take-ups should be provided on all chain conveyors to adjust for elongation as the chain joints wear. Take-ups are also used to provide slack in the chain for installation or maintenance. Takeups should be adjusted while the conveyor is operating to obtain the best results. There are four basic types of take-ups. They are the screw type, spring type, gravity type, and catenary type. The four types are shown in Figure 10-14.

FIGURE 10-14 Chain tension take-ups.



275


CATENARY TENSION

AND

CHAIN SAG

In most long conveyors, the return span of chain should be supported over most of its length. The weight of the unsupported span, or a portion of the span, adds to the chain pull and must be considered, along with bearing and shaft loads, when calculating the total working load on the chain. The added pull from catenary tension is not included when calculating the power needed to run the conveyor. When a catenary take-up is used (see Figure 10-14), a length of the return span equal to 30 to 50 pitches of the chain may remain unsupported. It creates a place for any excess chain to accumulate as wear takes place. This catenary also gives enough tension to the slack span so that the conveyor is not likely to jump teeth under a heavy load. Ample space should be provided for chain sag in the catenary. Attempting to operate with too little depth of sag in a long catenary will result in high bearing loads as well as increased loads on the chain. Chain sag should not be less than 3% of the unsupported span. The procedure for calculating catenary sag and tension is provided later in this chapter.

ELASTICITY Roller chains stretch when they are loaded. If the load is less than the yield strength of the chain, it will return to very nearly its original length when the load is removed. The amount of this elastic stretch can be readily calculated because roller chains are of proportional design. The amount of elastic elongation may be found by Equation (10.2a) and Equation (10.2b): d = 0.15PC/12,500p2 for single-pitch chains

(10.2a)

d = 0.15PC/3125p2 for double-pitch chains,

(10.2b)

where d is the total amount of elastic elongation (in inches), P is the chain pull (in lb), C is the conveyor length (in ft), and p is the chain pitch (in inches). Elastic stretch can be a large amount in long conveyors. One should calculate the amount of stretch when the conveyor is more than 20 ft long and anything on the conveyor must be located within 0.5 in. One should always calculate the elastic stretch when the chain is used for precision indexing.

MULTIPLE-STRAND CONVEYORS GENERAL Sometimes one strand of chain does not have enough load capacity or it will not handle the conveyor width. Two or more strands of chain are then needed, making a multiple-strand conveyor. Multiplestrand conveyors work well and give long life as long as a few important guidelines are followed.

MATCHING LEFT-HAND

AND

RIGHT-HAND STRANDS

Left-hand and right-hand strands are required in all multiple-strand installations where the chain attachments are not symmetrical. In this situation, right- and left-hand strands must be specified when ordering (see Figure 10-15). There is no uniform definition of what a left-hand or right-hand chain is. That also must be agreed upon between the user and supplier when the chain is ordered.



276


FIGURE 10-15 Right-hand and left-hand strands where attachments are not symmetrical.

FIGURE 10-16 Matched and tagged chain set.

Specifying of right-hand and left-hand conveyor strands should not be confused with the concept of left-hand and right-hand attachments. Again, there is no uniform definition of what left-hand or right-hand attachments are. That also must be agreed upon between the user and supplier when the chain is ordered.

DIRECTION

OF

TRAVEL

FOR

LEFT-

AND

RIGHT-HAND STRANDS

Not all chains and attachments used in conveyor service are symmetrical. Many chains must travel in a particular direction relative to the head sprockets. When this is the case, the direction of travel should be clearly shown on the conveyor drawings or be part of the contractor’s specifications. Left-hand and right-hand strands are often involved in such cases. Sometimes repair parts refer to left-hand and right-hand attachments. Then, adequate specifications are needed to let the conveyor chain attain its full usefulness.

MATCHING

AND

TAGGING STRANDS

FOR

LENGTH

Using matched strands helps ensure correct alignment across the strands. It is particularly important where through-rods or other carrying attachments are used. Strands operating out of alignment put a greater load on one chain, causing excessive wear on the chain and/or attachments and the sprockets. Multiple-strand chain conveyors should be checked regularly to make sure that the chains are operating in proper alignment with each other. When chains are required for multiple-strand operation, it is important to specify to the manufacturer “matched and tagged chain” together with the number of strands required. The chains will then be measured at the factory and a number tag attached to each strand (see Figure 10-16). Each matching group of strands is tagged with the same number and, whenever possible, will be wired and shipped together. The tags should not be removed until the chain is assembled. The strands must be coupled so that those with the same number are installed side by side.



277


FIGURE 10-17 Effect of two strands of unequal length.

All standard chains must meet standard length tolerances. Matching chain strands ensures that sections of chain with lengths at opposite ends of the tolerance range are not placed together in the conveyor. Figure 10-17 shows the effect of two strands that are not equal in pitch. One strand becomes overloaded or the chain becomes twisted when engaging the sprockets.

PRECISION INDEXING GENERAL Roller chains are used in packaging machines, assembly machines, and other processing machines that require precise placement of items. These machines almost always handle single items. Figure 10-18 shows part of a packaging machine without the safety guards. In these machines, items must be put in a specific place, with very small tolerances. It is a very demanding use and roller chain performs well in these machines if a few critical guidelines are followed.

MACHINE DESIGN Roller chains can be made to position parts close enough for many automated operations. However, a machine must sometimes put items in a specific place, within extremely close tolerances. In this case it may be better to have the chain position the item close to the desired position and use another means, such as pilot pins, to move the item into the exact position. The machine designer should work closely with an ACA manufacturer to obtain a precise and reliable machine.

MATCHING

AND

TAGGING STRANDS

FOR

LENGTH

Most precision indexing applications require strands to be matched for length to limits that are closer than standard. A chain manufacturer usually must do the special matching. All of the information on matching and tagging strands for length given earlier applies here. There are several classes of matching limits for conveyor roller chains. Only three of the more common classes are



278


FIGURE 10-18 Roller chain on a packaging machine.

given here. Not all manufacturers offer the same classes or limits. Check with the particular manufacturer before issuing specifications. Standard length tolerances normally apply regardless of how closely the chains are matched. In other words, all of the chains in one set can be matched for length (be the same length) as close as 0.002 in/ft, but the next set may differ in length by as much as 0.032 in/ft. Common Match for Length For this class of match, the manufacturer normally uses special procedures to select or make the parts and assemble the chain. This ensures that the difference in length between the strands in a set is no more than 0.006 in./ft to 0.008 in./ft. There usually is a nominal extra charge for this class of matching. Close Match for Length For this class of match, the manufacturer normally uses special procedures to make the parts, assemble the chain, and measure and match the strands. This ensures that the difference in length between the strands in a set is no more than 0.002 in./ft to 0.004 in./ft. There is usually a large extra charge for this class of matching. Specific Length In this case, the user negotiates with a manufacturer to make multiple sets of chain to a specific length within a closer-than-standard length tolerance. There are no uniform standard tolerances for this class of matching. Each manufacturer sets their own tolerances and no two manufacturers are likely to have the same tolerances. There is usually a very large extra charge for this.



279


Single-Strand Chains for Precision Indexing Sometimes a long single-strand chain is used for precision indexing. A long single chain is made in short sections for easier handling. In this case, each section of chain should be matched for length to the other sections. This ensures that the chain will index uniformly no matter which section is active. Uniform Attachment Spacing within a Chain A basic, but sometimes overlooked need in precision indexing is that the spacing between each of the attachments in the chain must be nearly the same. The manufacturer may have to use special procedures to ensure that the spacing is as uniform as is needed, and this may increase the cost of the chain.

ENVIRONMENT TEMPERATURE Standard roller chains, with conventional lubrication, should perform well in an ambient temperature range of 0˚F (–18˚C) to 150˚F (65˚C). With special high-temperature lubricants, standard steel roller chains can be used in temperatures up to 350˚F (177˚C), and with extra clearance, standard steel roller chains can be used in temperatures up to 500˚F (260°C). However, some tempering of the steel in the chain will occur at this temperature and the pins and bushings will soften somewhat and become less resistant to wear. Consult a roller chain manufacturer for help when using these chains in extremely high or low temperatures. There are several types of stainless steel chains available for use in high temperatures.

CORROSION Carbon and alloy steel roller chains are not well suited to corrosive conditions, but there are plated chains available for use outdoors and in wet conditions. There are also stainless steel chains available for use in caustic or acidic conditions. Finally, there are a few types of stainless steel chains that are very resistant to stress corrosion cracking. Consult a roller chain manufacturer for material recommendations when a hostile environment is known or anticipated.

ABRASION Standard conveyor roller chains do not work very well in very abrasive conditions. Special conveyor chains designed to keep abrasive material out of the bearing areas usually work much better. Consult an ACA roller chain manufacturer for help with selecting a chain for use in abrasive conditions.

LUBRICATION Lubricating engineering steel conveyor chains is covered in chapter 13.

ROLLER CONVEYOR CHAIN SELECTION PROCEDURE STEP 1: OBTAIN NECESSARY INFORMATION •

Conveyor configuration • Type • Mode • Layout (including height of lift or incline angle)



280


• • • • • • • • •

Conveyor width and height Conveyor length and shaft center distance Conveyor speed Kind of material to be handled Weight of material to be handled per foot of conveyor length Size and spacing of attachments and/or carriers Estimated weight of carriers (slats, flights, pans, etc.) and weight of chain, including attachments, per foot of chain Diameters of shafts and sprockets Environment • Temperature • Corrosion • Abrasion • Available lubrication

STEP 2: SELECT PRELIMINARY CHAIN TYPE

AND

ESTIMATE WEIGHT

After deciding on the conveyor type, mode, and layout, select a suitable type of chain from Table 10-1, Table 10-2, or Table 10-3. The size of the crossbars, slats, pans, or carriers should be known. This usually requires a particular attachment spacing and chain pitch. An approximate weight for the chain may then be obtained from Table 10-1, Table 10-2, or Table 10-3. If the chain pitch has not yet been selected, a coarse estimate of the weight of the chain is 2.0 lb/ft. These tables give only very general information about the chain. The designer should see one or more of ACA manufacturers’ catalogs for more detailed data on the chain used in the conveyor. These catalogs give chain pitch, rated working loads, dimensions, chain and attachment weights, and other details for the chains being considered. TABLE 10-1 Technical data, double-pitch conveyor roller chains Chain number

Chain pitch (in.)

Small roller series C-2040 C-2050 C-2060H C-2080H C-2100H C-2120H C-2160H

1 1 1/4 1 1/2 2 2 1/2 3 4

3700 6100 8500 14500 24000 34000 58000

0.34 0.58 1.05 1.40 2.48 3.60 6.42

Large roller series C-2042 C-2052 C-2062H C-2082H C-2102H C-2122H C-2162

1 1 1/4 1 1/2 2 2 1/2 3 4

3700 6100 8500 14500 24000 34000 58000

0.50 0.81 1.42 2.13 3.51 5.48 9.34


Average ultimate tensile strength (lb)

Weight per foot (lb) without attachments


281


TABLE 10-2 Technical data, single-pitch precision roller chains Chain number 40 50 60 80 100 120 140 160

Chain pitch (in.) 1/2 5/8 3/4 1 1-1/4 1-1/2 1-3/4 2

Average ultimate tensile strength (lb) 3700 6100 8500 14500 24000 34000 46000 58000

Weight per foot (lb) without attachments 0.41 0.68 0.99 1.73 2.51 3.69 5.00 6.53

TABLE 10-3 Technical data; hollow pin roller chains Chain number 40 HP 50 HP 60 HP 80 HP C2040 C2042 C2050 C2052 C2060 C2062 C2080 C2082

Chain pitch (in.) 0.500 0.625 0.750 1.00

Average ultimate tensile strength (lb) 2400 4400 6000 11,000

Approximate weight (lb/ft) without attachments 0.37 0.60 0.86 1.60

1.00 1.00 1.25 1.25 1.50 1.50 2.00 2.00

2400 2400 4400 4400 6000 6000 11,000 11,000

0.31 0.54 0.50 0.83 0.75 1.20 1.50 2.25

HP HP HP HP HP HP HP HP

STEP 3: SELECT CHAIN SUPPORTS Select the method of supporting the chain in the conveying and return runs. Remember that they sometimes are not the same. When the conveyor is short (less than or equal to 160 pitches of chain) or travels at low speed (less than 75 ft/min), letting the chain slide in the conveying run is acceptable. But when the conveyor is longer or travels at higher speeds, having the chain roll in the conveying run is a better choice. Similarly, when the conveyor is short or travels at low speed, letting the chain slide in the return run is acceptable. Putting wear pads on the chains or carriers and having them run on a low-friction material in the return run will reduce the frictional drag and wear. When the conveyor is long or travels at high speed, it is better to have the chain ride on roller supports in the return run. If the conveyor is very short (less than or equal to 80 pitches of chain), it might not need supports on the return run. Calculate the catenary tension to see if return supports are needed.



282



OF

FRICTION

Chain Sliding Friction Where the chain slides on the edges of its plates on ways of steel or other materials, use the sliding coefficient of friction (fs), taken from Table 10-4. If the chain carries the material (mode 1), this factor applies to the weight of both the conveyor and material. If the chain only pushes the material (mode 2), this factor applies only to the weight of the conveyor. This factor applies only to the weight of the conveyor in the return run when the chain rolls in the active run, but slides in the return run. Also use the sliding coefficient of friction when the chain rides on a small-diameter roller on a guide rail. Chain Rolling Friction When the chain rolls on rails or in a track, use the rolling coefficient of friction (fr), shown in Table 10-5. If the chain carries the material (mode 1), this factor applies to the weight of both the conveyor and material. If the chain only pushes the material (mode 2), this factor applies only to the weight of the conveyor. Letting the chain ride on small-diameter rollers in the conveying run is not recommended. Small-diameter rollers may not turn and flat spots may be worn on them. In spite of that, many conveyors are designed to have the chain ride on small-diameter rollers. If the chain rides on smalldiameter rollers, use the coefficient of friction for sliding chain. When the chain rides on smalldiameter rollers, friction and wear may be reduced when the rollers ride on a low-friction material. Still, the user may see flat spots on some rollers.

TABLE 10-4 Coefficient of friction for chain sliding Condition Statica Sliding

Dry 0.33 0.27

Lubricated 0.24 0.21

a

Use static coefficient of friction for speeds of 3 ft/min or less.

TABLE 10-5 Coefficient of friction for chain rolling with large rollers Statica Chain number C-2042 C-2052 C-2062H C-2082H C-2102 C-2122H C-2162H a

Dry 0.17 0.16 0.16 0.15 0.14 0.14 0.13

Lubricated 0.12 0.11 0.11 0.10 0.09 0.09 0.08

Rolling Dry 0.14 0.13 0.13 0.12 0.11 0.11 0.10

Use static coefficient of friction for speeds of 3 ft/min or less.


Lubricated 0.10 0.09 0.09 0.08 0.07 0.07 0.07


283


TABLE 10-6 Coefficient of friction for sliding material Product material Paper 0.40 0.35 0.30 0.40

Slat, carrier, or deck material Steel Plastic Low-friction plastic Wood

Plastic 0.30 0.25 0.20 0.30

Wood 0.40 0.30 0.25 0.40

Steel 0.40 0.30 0.20 0.40

All coefficients are for dry conditions. All values are approximate. Each can vary considerably from the listed value.

Material Sliding Friction When the material slides on a conveyor deck or slides on the chain carriers in an accumulation section, use the coefficient of friction (fw) for sliding material, shown in Table 10-6. Approximate coefficients of friction for only a few common materials are shown in Table 10-6. Coefficients of friction for materials not listed may be found in handbooks and catalogs. Note that bulk materials are not listed. Roller chains are seldom used to convey bulk materials because fines can clog the chain clearances and prevent lubricant from reaching critical areas.

STEP 5: CALCULATE PRELIMINARY CHAIN PULL Select the equations given for the layout that was chosen. The formulas work for either mode 1 (material is carried on the chain) or mode 2 (material is pushed on a deck) conveyors. The material weight on the chain is zero in mode 2 and the term drops out. All of these equations for chain pull assume that the same supports are used for the return span as are used for the conveying span. If the supports for the return span are different than for the conveying span, the term 2.1CMfM will have to be split into two parts: 1.0CMfM for the conveying span and 1.1CMfM for the return span. In most of the equations, the term 0.1MfM is included to account for tail shaft friction. The symbols used in the equations are P, conveyor chain pull (in lb); C, length of the conveyor (in ft); CA, length of the accumulation section (in ft); M, weight of the chain, attachments, and carriers (in lb/ft); W, weight of the conveyed material (in lb/ft); fM, coefficient of friction for the chain (it may be either fs or fr, whichever applies); fs, coefficient of friction for the chain sliding, from Table 10-4; fr, coefficient of friction for the chain rolling, from Table 10-5; fw, coefficient of friction for the material sliding, from Table 10-6; P1, take-up tension (in lb); and PA, added chain pull from accumulation (in lb): PA = CAWfw

(10.3)

Horizontal Conveyors (see Figure 10-19) When the material is moved but not supported by the chain: P = C(2.1MfM + Wfw).


(10.4)


284


FIGURE 10-19 Horizontal conveyor layout.

When the material is supported by the chain: P = CfM(2.1M + W) + PA.

(10.5)

Note that in this case, fw = fM, so only the value of fM is needed in the equation. Inclined Conveyors (see Figure 10-20)

FIGURE 10-20 Inclined conveyor layout.

When the material is moved but not fully supported by the chain: P = C(MfMcos α + Wfwcos α + Msin α + Wsin α) + C(MfMcos α Msin α).

(10.6)

Note that cos α = b/C and sin α = a/C. Also, when the term (MfMcos α Msin α) is a positive value, multiply it by 1.1 to allow for tail shaft friction. When the material is fully supported by the chain: P = CfMcos α(2.1M + W) + (CWsin α).

(10.7)

Note that in this case, fw = fM, so only the value of fM is needed in the equation. It should also be noted that accumulation sections are not often used in inclined conveyors. Vertical Conveyors (see Figure 10-21)

FIGURE 10-21 Vertical conveyor layout.



285


TABLE 10-7 Working loads for conveyor roller chains Pinch (in.) 1.00 1.25 1.50 2.00 2.50 3.00 4.00

Chain speed (ft/min) 5 530 870 1215 2070 3425 4855 8585

25 525 865 1205 2055 3400 4815 8210

50 510 840 1170 2000 3310 4690 8000

75 490 805 1125 1915 3175 4495 7670

100 465 765 1065 1815 3000 4250 7250

200 335 555 775 1320 2180 3090 5275

P = C(M + W) + P1.

STEP 6: SELECT

THE

300 230 380 530 905 1500 2125 3625

400 160 265 370 630 1040 1480 2520

500 115 190 265 455 750 1065 1815

(10.8)


The preliminary chain pull applies to all the strands of chain in the conveyor. If two or more strands of chain are used, which is often the case, multiply the preliminary design chain pull by 1.2 and divide by the number of strands of chain in the conveyor. This will be the required working load per strand of chain. Enter Table 10-7 with the preliminary chain pull and the conveyor speed. Scan down the column for chain speed until a working load is found that equals or exceeds the preliminary chain pull. Read the minimum required chain size in the leftmost column. Table 10-7 was developed to apply only to double-pitch conveyor chains. However, the working loads listed in Table 10-7 apply just as well to single-pitch chains (with one-half the listed pitch). Table 10-7 does not apply to hollow pin chains. Consult an ACA roller chain manufacturer about working loads for hollow pin chain. Chain pitch must be compatible with attachment spacing. That is, the attachment spacing divided by the pitch must be a whole number. If it is not, try adjusting the carrier or attachment spacing, or select a different chain pitch and consider using more or fewer strands of chain.


AND

TENSION

If a catenary section is present, the designer should now determine the depth of sag so that the needed clearance can be given. The designer should also calculate the catenary tension to be sure the rated working load of the selected chain is sufficient. The terms in the following equations are defined in Figure 10-22. 3 S 2 − 3 L2 4

(10.9)

M ⎛ S2 D ⎞ + 12 ⎜⎝ 8 D 2 ⎟⎠

(10.10)

M ⎛ 28 D 2 + 3 L2 ⎞ ⎟ 12 ⎜⎝ 24 D ⎠

(10.11)

D=

PC =

PC =



286


FIGURE 10-22 Conveyor with catenary section.

where D is the depth of sag of the conveyor (in inches); L is the straight-line distance between points of support (in inches); S is the length of the catenary in the slack span (in inches); PC is the catenary tension (in lb); and M is the weight of the chain per foot including attachments and carriers (in lb/ft). The depth of sag and catenary tension may also be determined from Table 10-8 and Table 10-9.

STEP 8: RECALCULATE THE REQUIRED WORKING LOAD AND SELECT THE FINAL CHAIN Repeat steps 5 through 7 using the actual chain and attachment weights. Those are taken from the manufacturer’s catalog from which the chain was selected. Once a specific chain is selected, repeating steps 5 through 7 will give a somewhat different design chain pull and required chain working load. Remember to include the catenary tension if a catenary section is present. The working load listed for the chain in the catalog must be greater than or equal to the calculated required working load for the application. If it is not, a chain with a higher working load (and, probably, weight) should be selected. Then recheck the calculations again until a chain with satisfactory working load is selected.

STEP 9: SELECT

THE

SPROCKET SIZE

A sprocket with at least 15 effective teeth should be selected. If the conveyor runs at high speed (more than 100 ft/min) or smooth operation is very important, a sprocket with at least 21 effective teeth should be selected. If available space will not accommodate the suggested minimum sprocket size, select a sprocket with as many teeth as space will permit.

STEP 10: CALCULATE

THE


Both sprockets (head shaft and tail shaft) are the same size in most conveyors. In this case, the chain length may be calculated using Equation 10.12: LP = N +

2C ′ , p

(10.12)

where LP is the required chain length (in pitches), N is the number of teeth on the sprockets, C′ is the shaft center distance (in inches), and p is the chain pitch (in inches).



287


TABLE 10-8 Catenary sag

STEP 11: CALCULATE

THE

REQUIRED POWER

The horsepower required at the input shaft of the conveyor is calculated using Equation 10.13 and Equation 10.14. For horizontal and inclined conveyors: HP = For vertical conveyors:


1.1PS . 33000

(10.13)


288


TABLE 10-9 Catenary tension

HP =

STEP 12: SELECT

THE

(

)

1.1 WC + 0.1MC S 33000

.

(10.14)

LUBRICATION METHOD

Select a method of lubricating the conveyor chain using the information given in chapter 13.

SAMPLE ROLLER CHAIN CONVEYOR SELECTION STEP 1: OBTAIN NECESSARY INFORMATION A user wants to select a slat conveyor to carry cartons of canned foods. The conveyor is to carry the cartons horizontally between a carton filling station and a tape sealing station. The cartons measure 1 ft × 2 ft × 10 in. The 2-ft dimension will be across the width of the conveyor. The conveyor must carry the cartons a distance of 78 ft. The desired conveyor speed is 200 ft/min.



289


The conveyor will carry cartons, or unit material. Each carton weighs 48 lb and they are placed on the conveyor with 4 in. between cartons. So 48 lb/(12 in. + 4 in.) = 3 lb/in., and 3 lb/in. × 12 in./ft = 36 lb/ft. Each slat is 1 in. wide × 2 ft long. It is desired to install them on 3-in. centers. Each slat weighs 1.91 lb; 1.91 lb/3 in. = 0.637 lb/in. and 0.637 lb/in. × 12 in./ft = 7.64 lb/ft. No chain has been selected, so an estimated chain weight of 2 lb/ft will be used. This yields an estimated total weight of 7.64 lb/ft + 2.0 lb/ft = 9.64 lb/ft for the chain and slats. The shaft and sprocket sizes may be as recommended by the conveyor designer. The environment is a typical food canning plant. The temperature range will be 60˚F to 90˚F. There are no notable abrasive or corrosive conditions. The user will use the recommended lubrication method.

STEP 2: SELECT PRELIMINARY CHAIN TYPE

AND

ESTIMATE WEIGHT

A C2062H chain may be selected. The chain pitch is 1.5 in., so the slats can be mounted on 3-in. centers by installing them on bent attachment link plates on every pin link. The weight of C2062H chain is obtained from Table 10-1 and it is 1.42 lb/ft. The added weight of a bent attachment link plate is obtained from the manufacturer’s catalog and is 0.03 lb/plate. There are (12 in./ft/3 in.) four attachment plates per foot on each chain, so the added weight of the attachment plates is 0.03 lb/plate × 4 plates/ft = 0.12 lb/ft. The weight of the chain with attachment plates is 1.42 lb/ft + 0.12 lb/ft = 1.54 lb/ft. Two strands of chain are required so the total weight of the chains is 2 × 1.54 lb/ft = 3.08 lb/ft. Finally, adding the weight of the slats to the weight of the two strands of chain gives a total conveyor weight of 3.08 lb/ft + 7.64 lb/ft = 10.72 lb/ft.

STEP 3: SELECT CHAIN SUPPORTS The conveyor length is 78 ft. That is quite long for a roller chain conveyor, so the chain will roll in guide tracks on both the conveying and return runs.

STEP 4: OBTAIN COEFFICIENTS

OF

FRICTION

The material is carried on the chains and the chains roll in guide tracks, and the user will use the recommended type of lubrication. So only the lubricated rolling coefficient of friction is need. From Table 10-5, that is 0.09.

STEP 5: CALCULATE PRELIMINARY CHAIN PULL There is no accumulation section in this conveyor, so Equation 10.5 can be used without the term PA, and that gives us: P = CfM(2.1M + W) = 78 × 0.09[(2.1 × 10.72) + 36] = 7.02 × [22.5 + 36] = 7.02 × 58.5 = 410 lb.

STEP 6: SELECT

THE


The design chain pull is 1.2 × 410 lb = 492 lb, and 492 lb/2 = 246 lb. Entering Table 10-7 with a chain pitch of 1.5 in. and a conveyor speed of 200 ft/min, we find that the capacity of C2062H chain is 775 lb. That is much more than the required capacity of 246 lb. The capacity of C2042 chain is 335 lb and that is adequate. However, the attachments on C2042 chain would have to be placed on every third pitch. Attachment plates on every third pitch must alternate between pin links and roller links. That is usually much more costly than putting every attachment plate on a pin link. The conveyor designer can make the final choice based on cost.



290



AND

TENSION

A conveyor that is 78 ft long probably should have a catenary section. The length of the catenary section should be about 60 in. (40 pitches). A suggested amount of sag is about 5% of the length of the catenary, or 3 in. From Table 10-8, one finds that there should be about 0.4 in. of excess chain in the catenary. Then from Table 10-9, one finds that 0.4 in. of excess chain increases the chain pull by 10 lb for a chain that weighs 1 lb/ft. Multiplying 10 lb by the chain and slat weight of 10.72 lb gives an added chain pull of 107 lb. The added chain pull per strand is 107 lb × 1.2 = 128 lb, and 128/2 = 64 lb.

STEP 8: RECALCULATE THE REQUIRED WORKING LOAD AND SELECT THE FINAL CHAIN Now one must add the catenary chain pull to the design chain pull. This gives 246 lb + 64 lb = 310 lb. The selected chain must have a capacity of at least 310 lb. The capacity of C2062H chain is 775 lb. It is more than adequate. The weight of the C2042 chain with attachments would be less than for the C2062H chain. The capacity of the C2042 chain is 335 lb. A C2042 chain might be adequate.

STEP 9: SELECT

THE

SPROCKET SIZE

A sprocket with at least 15 effective teeth should be selected. A better choice would be a sprocket with 15 1/2 effective teeth. Then each tooth would contact a roller every second revolution and sprocket life would be much longer.

STEP 10: CALCULATE

THE


The required chain length can be obtained using Equation 10.12. Assuming the shaft center distance is the same as the conveyor length and sprockets with 15 1/2 effective teeth will be used, the minimum required chain length, LP, is LP = 15.5 + [(2 × 78 × 12)/1.5] = 15.5 + [1872/1.5] = 15.5 + 1248 = 1263.5 pitches. The total must be rounded up to 1264 pitches because the attachment spacing is every second pitch. Then the length in pitches is converted to inches and feet. The specified chain length, L, is L = 1264/1.5 = 842.67 in., and that is equal to 70.22 ft.

STEP 11: CALCULATE

THE

REQUIRED POWER

The required power to run the conveyor is calculated by Equation 10.13: HP = (1.1 × 410 × 200)/33000 = 90200/33000 = 2.73.

STEP 12: SELECT

THE

LUBRICATION METHOD

According to the information given in chapter 13, this conveyor should have drip-type lubrication.

ADDED STEP: CALCULATE ELASTIC STRETCH The example conveyor is more than 20 ft long, so the elastic stretch should be calculated. From step 8, the total chain pull is 310 lb. Substituting the total chain pull of 310 lb and the conveyor length of 78 ft into Equation 10.2b gives the following:



291


d=

0.15 ⋅ 310 ⋅ 78

( )

3125 ⋅ 1.5

2

=

3978 = 0.52 in. 7031

This conveyor simply transfers product from one machine to another. So an elastic stretch of 0.52 in. should not cause a problem.



11 Chains for Bucket Elevators A bucket elevator is broadly defined as a specialized type of conveyor used to lift bulk materials in a vertical or nearly vertical plane using carrying buckets. It will handle nearly any loose material that does not contain lumps too big for the buckets and not too sticky to be discharged. Typical bucket elevators are shown in Figure 11-1 to Figure 11-3. Typically a bucket elevator consists of three basic components: a head end, a foot end, and intermediate sections (see Figure 11-2 and Figure 11-3). The head end assembly includes the head shaft and sprocket, bearings, drive assembly, supporting structure, buckets, chain, and casing. The foot end includes the foot shaft and sprocket, bearings with a take-up, supporting structure, casing, buckets, and chain. Intermediate sections normally consist of the elevator supporting structure and casing, plus buckets and chain. In most instances, elevator casings are used to support the machinery and control dust. However, when conditions permit, open elevators may be used and include supporting structure only (Figure 11-2). Elevator buckets are bolted to one or two strands of endless carrying chain. Material is loaded into the buckets via a hopper and loading leg at the “boot” in a continuous elevator, or is scooped up by the buckets as they round the lower sprocket in a centrifugal discharge elevator. The material is discharged by centrifugal force or gravity as the buckets overturn at the head sprocket.

ELEVATORS USING ENGINEERING STEEL CHAINS Typical examples of the types of chain used in elevators are shown in Figure 2-29. In most applications, straight sidebar, hardened bushing rollerless chain is used, however, most continuous high-capacity elevators use straight sidebar, hardened bushing roller chain whose rollers ride on vertical guides integral with the elevator casing. In some applications, instead of straight sidebar chain, the offset sidebar type can be used. Table 11-1 lists chains of various pitches and designs with typical working loads. Bucket elevators equipped with engineering steel chains can lift enormous quantities of heavy materials to considerable heights. “Supercapacity” elevators have been designed to lift up to 750 tons/hr of material weighing 125 lb/ft as high as 120 ft. Special chains can be engineered for even better performance. Since there are many different elevator designs, the following discussion is limited to medium and heavy-duty types, with emphasis on chain, attachments, buckets, and sprockets. There are four basic types of bucket elevators: centrifugal discharge, positive or perfect discharge, continuous bucket, and supercapacity. These are shown in Figure 11-4 and are described in the following paragraphs.

CENTRIFUGAL DISCHARGE ELEVATORS The centrifugal discharge elevator (Figure 11-5 and Figure 11-6) is designed so that the buckets scoop material from the boot and discharge it by centrifugal force as they pass over the head sprocket. It is, therefore, a comparatively high-speed elevator. The average centrifugal discharge elevator head shaft speed varies with the diameter of the head sprocket and the nature of the material, but is usually between 35 rpm and 50 rpm. Elevators handling grain, cement, and so on, with largediameter head sprockets and high-speed buckets may run at much higher speeds. Centrifugal

293



294


FIGURE 11-1 Typical bucket elevators.

discharge elevators work best with fine, loose material, such as ashes or crushed coal, that can be thrown from the buckets and is not easily degraded. Because the chain runs through the material in the boot when the buckets are loaded, steel bushed rollerless chain should be used. This is because chains with rollers often become loaded with dust between the rollers and bushings. If any moisture is present, this tends to cake the material, preventing the rollers from turning. The pitch of the chain will vary depending on the size of the buckets and the weight of the material, but since the speed must be relatively high, a chain pitch of 6 in. is used in most applications. A single strand of steel bushed rollerless chain will carry most loads on a centrifugal discharge elevator. Attachments When a single strand of chain is used, the buckets are bolted to K-type attachments (see Figure 11-7). The selection of the number of holes depends on the forces and impact developed. For larger capacities, K attachments having more than two holes are used with buckets up to 24 in. wide. For elevators requiring larger chains and buckets, consult the chain manufacturer. Double-strand chain in centrifugal discharge elevators is not recommended.



Chains for Bucket Elevators

295

FIGURE 11-2 Open inclined elevator.

Elevator Buckets Buckets for centrifugal discharge elevators come in many styles, as shown in Figure 11-8. For heavy, moderately abrasive loads, style AA malleable iron or pearlitic malleable iron buckets are used. Specially shaped buckets are available for large capacities or for fine or wet material. Reinforced welded steel buckets are used for high-speed cement or grain elevators. Style A cast elevator buckets are used when very small buckets are required for handling coal, cement, ash, sand, stone, gravel, and similar materials. They are furnished in either malleable or pearlitic malleable iron. Style AA cast elevator buckets, which have generally replaced style A in popularity, are designed similar to style A except that a heavy reinforcing band is cast along the front. Style AA buckets are furnished in either malleable or pearlitic malleable iron. Style AA-RB cast elevator buckets are used for handling heavy abrasive products under severe service and impact conditions. Buckets are designed similar to style AA with reinforcing ribs on the front and with backs twice the normal thickness. They may be furnished in either malleable or pearlitic malleable iron.



296


FIGURE 11-3 Enclosed vertical elevator.

Style AC cast elevator buckets are designed specifically to increase elevator capacity by closer bucket spacing. Style AC buckets are used for handling material such as raw meal, crushed clinker, and finished cement. Air ports are provided in the bottom of the bucket to act as a relief valve for faster loading and unloading of light, fluffy materials. Style B cast elevator buckets are used on inclined elevators for handling coarsely broken materials such as coke, stone, ore, etc. Clean discharge at relatively slow speeds is made possible by the low-front design. Style B buckets are furnished in either malleable or pearlitic malleable iron. Style C cast elevator buckets are designed to handle materials that tend to stick or pack in buckets, such as clay, sugar, salt, wet grain, and finely pulverized wet ore. Style C buckets are furnished in either malleable or pearlitic malleable iron. Style SC cast elevator buckets are designed primarily for handling foundry sand. SC buckets have an extra heavy body with a reinforcing band cast along the front edge and around the ends to resist abrasion, and are furnished in either malleable or pearlitic malleable iron. Salem steel elevator buckets are used for powdered or granular free-flowing materials. They are formed from one piece of sheet metal and have a smooth round contour for clean handling and delivery of materials. There are no seams in front or on the ends of these buckets. The back is reinforced for strength and durability.


297




TABLE 11-1 Typical engineering steel chains for elevators


298

FIGURE 11-4 Types of elevators.

FIGURE 11-5 Centrifugal discharge elevator with foot-end take-up.





299

FIGURE 11-6 Centrifugal discharge elevator with head-end take-up.

Continuous elevator buckets are used for gritty, bulky material with relatively large lump sizes at slower speeds than centrifugal discharge elevators. They may be either regular or supercapacity and may be either cast or fabricated depending on size or usage. Buckets made of nonmetallic materials, such as high-density polyethylene and nylon, are also available for special handling requirements. The manner in which buckets are spaced along the chain depends on the design of the particular installation. As a rule, for cast malleable iron buckets the spaces are 21/2 to 3 times the projection of the bucket, the principle being that the load discharged from one bucket should be thrown clear of the preceding bucket (see Figure 11-9). Buckets are commonly attached to every third or fourth chain pitch. Exceptions to the above are for specially designed buckets or high-speed discharge.



300


FIGURE 11-7 Bucket attached to a single strand of chain with a K attachment.

FIGURE 11-8 Typical elevator buckets.




301

FIGURE 11-9 Bucket spacing.

FIGURE 11-10 Bucket length.

The bucket length may be governed by the rule of thumb that it may not exceed five times the chain bushing length (see Figure 11-10).

POSITIVE DISCHARGE ELEVATORS The positive discharge or perfect discharge elevator (Figure 11-11) moves slowly (rarely more than 120 ft/min). The buckets are completely inverted over the discharge spout by a pair of snub wheels. This deliberate method of discharge is intended for cohesive, powdery, and granular material and for sluggish loads that stick in the buckets. Pulverized coal, powdered feldspar, and wet sugar beet pulp are typical loads. Positive discharge elevator buckets are end hung between a double strand of engineering steel chain. An A attachment with an A bucket wing is the most commonly used mount (see Figure 11-12). Usually positive discharge elevators take the same standard malleable iron buckets as centrifugal discharge elevators, but there are also specifically contoured steel buckets for handling sticky materials. The buckets must be spaced to keep the loads from being dumped onto the preceding bucket.

CONTINUOUS BUCKET ELEVATORS The continuous bucket or continuous discharge elevator usually operates at speeds of 100 ft/min to 125 ft/min. It is unique in that the buckets are spaced continuously and have flat fronts and



302


FIGURE 11-11 Positive or perfect discharge elevator.

FIGURE 11-12 An A attachment with bucket wing for end-mounting buckets.



303


projecting sides so that each bucket acts as a chute for material discharged by the bucket directly behind it. This combination of continuous buckets and moderate speed makes the capacity of the continuous bucket elevator nearly twice that of the positive discharge elevator, but less than that of the high-speed centrifugal discharge elevator. The continuous buckets are usually fed through a loading leg or chute. This method of loading, together with the gentle method of discharge, makes the elevator especially suitable for material that is easily degraded. Regular Capacity Continuous Bucket Elevators Regular capacity vertical and inclined elevators operate at about the same speeds (100 ft/min to 125 ft/min, depending on the material) and use steel bushed rollerless chain for severe work. Vertical elevators are enclosed in a steel casing (Figure 11-13), while inclined elevators usually work on a simple frame and are used for outdoor work where it is not important to contain material within a casing or exclude outside contaminants. Engineering steel chain may be installed in single or double strands, depending on the length of the bucket and how much strength is needed. If a single strand is chosen, K attachments are used. For double strands, either A or G attachments are generally preferred. Continuous elevator buckets are made of welded steel and can be furnished in many standard and custom designs, all of them with projecting sides that may overlap to varying degrees depending on how smooth a chute is needed to discharge the material without spilling (see Figure 11-14). As a rule, the finer the material, the deeper the overlap.

SUPERCAPACITY ELEVATORS A special kind of continuous bucket elevator is the supercapacity type (see Figure 11-15). Its extra long buckets are end hung between two strands of chain and carry heavy loads, from fine sand to large lumps of coal and ore. Since the supercapacity elevator carries very heavy loads and since a smooth run is necessary for effective discharge, long-pitch bushed straight sidebar roller chain is normally used. The rollers are between the sidebars, and this design allows the chain to roll smoothly between angle tracks fixed to the inside of the casing on vertical elevators, or part of the frame on inclined elevators. The material is fed directly into the buckets from a hopper so that it does not enter the chain joint and wear the inside diameter of the roller and outside diameter of the bushing as it would with scoop-type loading. Supercapacity buckets are mounted to G attachments (Figure 2-25), and their capacity is explained not only by their bucket length but also by the fact that the double strand of chain allows them to extend beyond the chain centerline, as shown at the right in Figure 11-4. The sides of the bucket extend outward far more than those of the regular capacity continuous buckets and are shaped so that, when inverted, each bucket forms a deep trough to receive the material being discharged from the following bucket.

TAKE-UPS Some type of take-up must always be used in elevator installations. Types of take-ups are shown in Figure 11-16. They are used primarily to maintain sufficient tension on the chain to ensure proper seating on the sprocket and to compensate for elongation of the chain due to wear. They are especially useful when installing chain in the elevator casing by allowing the reduction of shaft center distances. In a standard basic elevator, either foot-end or head-end take-ups may be used. A foot-end installation is preferable, but for elevating materials that require frequent clean out or which tend to pack excessively, head-end take-ups are recommended.



304


FIGURE 11-13 Regular capacity continuous bucket elevator.

DESIGN AND SELECTION OF CHAIN AND BUCKET ELEVATORS Although the various manufacturers’ standard elevators vary somewhat in type and ratings, Table 11-2 gives an approximate comparison of what the four basic types can do. Note that there is some



305


FIGURE 11-14 Typical overlapping bucket assembly at discharge.

overlapping. Generally, however, centrifugal discharge elevators are used for rapid conveying of free-flowing granular materials, and are popular for elevating coal, sand, cement, etc. Positive discharge elevators are used for rather fine materials that tend to stick to the bucket or adhere to each other. Continuous bucket elevators may be used for some of the same materials as centrifugal elevators and are commonly used for gravel and similar mixed and lumpy materials. Continuous elevators are slower, have lower capacities, and require less maintenance when conveying heavy or variable loads. The supercapacity elevators are the workhorses of the group. They are used not only for conveying the materials shown in Table 11-2, but for conveying almost any heavy bulk material at high capacities over long centers.

SELECTING ENGINEERING STEEL ELEVATOR CHAIN The following two rules of thumb apply in nearly all cases: •

•

Use engineering steel bushed straight sidebar rollerless chain for elevators in which the chain hangs free and in which the chain is exposed to the conveyed material as it is scooped up during loading. Use engineering steel bushed straight sidebar roller chain for elevators in which the chain rides on tracks; generally supercapacity elevators.

Prior to selecting the chain and sprockets, the following should be known or determined: • • • • •

Required capacity (in ton/hr). Elevator chain and bucket speed (in ft/min). The distance between the sprocket centers. The size of the elevator buckets. The weight of the material per foot of elevator as determined by the equation W =


33.33T , S

(11.1)


306


FIGURE 11-15 Supercapacity vertical elevator.

• • • •

where T is the capacity (in ton/hr), S is the chain and bucket speed (in ft/min), W is the weight of the material per foot of elevator. Service conditions such as the abrasiveness of the material; clean, corrosive, hot, or cold environment; degree and frequency of shock; operating hours per day. Aeration for pulverized materials and its effect on material density. The weight of moving parts (buckets, attachments, chain) per foot of elevator.

Some of these items can only be approximated at this point. For example, the user does not know the weight of the chain until he or she selects it, so a back-check should be made when the selection is completed.



307


FIGURE 11-16 Types of take-ups.

SELECTION STEPS STEP 1: DETERMINE

THE

CHAIN PITCH

In nearly all cases this is predetermined by bucket size and spacing. With continuous buckets and supercapacity elevators, one bucket per pitch is normally used and should never exceed two pitches of chain when the chain pitch is 6 in. or less. In other types, one bucket every three or four pitches may be used if the spacing falls within the range of 2 1/2 to 3 times the projection for AA buckets, which are generally used. AC buckets are usually spaced every second pitch. In all cases, choose a pitch length that will permit proper spacing to give the required capacity at the correct speed for the head sprocket diameter. Specific chains and pitch lengths are usually selected from styles and sizes that have become known through regular use as typical elevator chains (see Table 11-3).



308


TABLE 11-2 Maximum capacities of standard chain and bucket elevators

TABLE 11-3 Maximum revolutions per minute as a function of chain pitch and the number of sprocket teeth

STEP 2: DETERMINE

THE

SPROCKET SIZE

Tentatively determine the size of the sprocket in terms of the number of teeth, chain pitch, and revolutions per minute using Table 11-4 and Table 11-5. In general, the more teeth in the sprocket, the smoother the operation. When material is discharged by centrifugal force, its trajectory is determined by the sprocket diameter and revolutions per minute. The basic equation for revolutions per minute is



309


TABLE 11-4 Maximum linear speeds for conveyor and elevator chains

TABLE 11-5 Service factors

Minimum head shaft speed = 44.3/R,

(11.2)

where R is the distance (in ft) from the center of rotation to the center of gravity of the discharged material.



310


FIGURE 11-17 Diagram for maximum chain pull equation.

Good elevator design requires proper balance between these factors. (For calculating sprocket pitch diameter from the pitch and the number of teeth, see Table 4-6.)

STEP 3: CALCULATE

THE

MAXIMUM CHAIN PULL

In a vertical chain elevator the main elements of pull are the weight of the chain and buckets, the weight of the material, the pull induced by the digging or loading action of the buckets, the load induced by the take-up, and the friction that occurs with the movement of components (bearings, chain joints, etc.). If the elevator is inclined, an additional factor induced by the catenary effect of the return run (if hanging free) must be taken into consideration. Inclined elevators with a catenary return run will not be covered in this discussion. The maximum chain pull (P) can be calculated using Equation 11.3 (see Figure 11-17): P = W2 + W3 + W4 + Q + P1/2, lb

(11.3)

where P is the maximum chain pull (in lb), W2 is the total weight of either the carrying or return strand of chain, W3 is the total weight of the buckets on either the carrying or return strand of chain, W4 is the total weight of the material in the buckets on the carrying strand of chain (anticipated surge conditions or bucket overfill must be considered), Q is the chain pull (tension) induced by the digging or loading action in the boot and other miscellaneous elevator friction, and P1 is the take-up tension. W2, W3, and W4 can be readily found. For instance, the weight of the chain can be found by multiplying the weight per foot of the selected chain by the elevator centers. The weights of the buckets and the weight of the material can be found in a similar manner.



311


The chain pull due to the digging action of the boot or the loading action of the carrying leg (Q) as well as the friction throughout the elevator can be calculated using Equation 11.4: Q = 12JW5/d × boot sprocket diameter (in inches),

(11.4)

where W5 is the weight of the material in one bucket (in lb), d is the bucket spacing (in inches), and J is the empirical corrective factor with the following values for stated conditions: 1.0 for centrifugal elevators handling coarse lumpy material, 0.67 for centrifugal elevators handling fine free-flowing material, 0.50 for continuous bucket elevators. Service factors are applied to find the design working load of the elevator chain (see step 5). In setting the take-up in the elevator, care should be taken to prevent extra tension in the elevator chain. If such is necessary, an additional factor must be included in the basic chain pull equation. Should additional equipment be driven from the elevator foot shaft, such tensions must be calculated, converted to pounds, and included in the basic equation. When vertical elevators decrease in sprocket center distance, the Q value becomes relatively greater in importance. If adjustments for difficult conditions must be made, the J corrective factor can be adjusted to suit. Additional Chain Pull Equations The take-up tension, P1, for screw-type take-ups with proper adjustment tension should be as near zero as possible. Take-up tension for gravity take-ups should be equal to the tail carriage machinery plus any force from added weights (Figure 11-17). Tension P2 (Figure 11-17) can be determined using Equation 11.5: P2 = W2 + W3 + P1/2, lb.

(11.5)

The point of least tension, P3 (Figure 11-17) , theoretically should be zero, and can be determined using Equation 11.6: P3 = P1/2.

(11.6)

Finally, tension P4 (Figure 11-17) can be determined by Equation 11.7: P4 = Q + P3.

STEP 4: FIND

THE

DESIGN PULL

AND

(11.7)


The design pull, PDes, is obtained by multiplying the total pull P by the factors for chain and speed and service conditions, as shown in Equation 11.8: PDes = P × F1 × F2 × F3 × F4,

(11.8)

where F1 is the service factor for frequency of shock (from Table 11-5), F2 is the service factor for character of chain loading (from Table 11-5), F3 is the service factor for atmospheric conditions (from Table 11-5), and F4 is the service factor for the daily operating time range (from Table 11-5).

STEP 5: SELECT

A

CHAIN

Select a chain whose maximum rated working load is greater than or equal to the design pull. Table 11-1 lists such chains of the steel bushed rollerless and long-pitch roller conveyor types deemed



312


suitable for bucket elevator service and listed in the standards ASME B29.12 and B29.15. For these, Table 11-1 shows ANS designations, working loads, and weights of plain chain and of a few styles of attachments. Although Table 11-1 provides enough information to make a tentative chain selection, there may be many other factors involved, and it is desirable to consult chain and bucket elevator catalogs before a final selection is made.

STEP 6: SPROCKET, TRACTION WHEEL, HUB,

AND

SHAFT SELECTION

Sprocket, traction wheel, hub, and shaft selection information is presented in chapter 4.

ELEVATOR CHAIN SELECTION EXAMPLE A centrifugal discharge bucket elevator has been selected to handle 3/4 -in. lump coal to a belt system feeding surge bins. Buckets and some components are already on hand and should be used, if possible. Requirements are as follows: • • • • • • • • • • • •

Required capacity of bucket elevator: 60 ton/hr. Elevator chain and bucket speed: 240 ft/min. Distance between centers: 70 ft. Size of the elevator buckets: 16 in. × 8 in. Capacity of the buckets: 0.34 ft3. Weight of the buckets: 21 lb each. Weight of the material per foot of elevator, as per Equation 11.1. Service conditions (see Table 11-5): (1) frequency of shock—occasional frozen lumps in winter, otherwise smooth; factor: 1.1; (2) shock is moderate; factor: 1.2. Atmospheric conditions: exposed to weather; very dirty; material handled is mildly corrosive; quite corrosive when wet; factor: 1.3. Daily operating range: 12 to 14 hr; factor: 1.2. Aeration is not a factor. Weight of moving parts: assume the standard 6-in. pitch ANS S110 chain (weighing 6.3 lb/ft for plain chain) will have adequate capacity. If it does not, then S111 chain, weighing 10.2 lb/ft, will have to be used (Table 11-2). The chain will have K-2 attachments for the buckets, spacing not yet established. For S110 chain, K-2 attachments weigh 8.6 lb/ft; for S111 chain they weigh 15.2 lb/ft.

STEP 1: DETERMINE CHAIN PITCH The buckets to be used are 16 in. × 8 in. and have a rated capacity of 0.34 ft3. The bulk density of the material is 50 lb/ft3, so the buckets will carry 0.34 ft3 × 50 lb/ ft3 = 17 lb each. To achieve a capacity of 60 tons/hr, the elevator has to carry an average of 8.33 lb/ft, so the maximum permissible bucket spacing is 17 × 12/8.33 = 24.49 in. Therefore, buckets every fourth link of a 6-in. pitch chain will produce the rated capacity.

STEP 2: DETERMINE

THE

SPROCKET SIZE

On a centrifugal discharge bucket elevator, the shaft revolutions per minute, coupled with the radius of the bucket center, must be such that the bucket will discharge the material. Against this is that chains have limits to the speeds at which they may be operated. From Table 11-3 and Table 11-4, maximum allowable speeds of a 6-in. pitch chain in bucket elevator service is 37 rpm shaft speed and 203 ft/min linear chain speed over an 11-tooth sprocket. Over a 12-tooth sprocket, these values are 41 rpm and 246 ft/min, and for a 13-tooth sprocket they



313


are 44 rpm and 286 ft/min. On this basis, with a chain speed of 240 ft/min required to achieve capacity, a 12-tooth sprocket will do the job. Next, the minimum shaft revolutions per minute necessary so that bucket discharge will be satisfactory must be determined. Calculating the pitch diameter of a 12-tooth sprocket for 6-in. pitch chain (securing the necessary angle cosecant from Table 4-7): 6 in. × 3.8637 = 23.18 in. Then, assuming that the center of gravity of the material being discharged is approximately 5 in. outside the sprocket pitch radius, the R of centrifugal discharge, from Equation 11.2, is R = (23.18/2 + 5)/12 = 1.38 ft. Minimum shaft speed is thus 44.3/1.38 = 37.7 rpm. Then, operating at 240 ft/min, the shaft speed will be 240 × 2/12 = 40 rpm. While a 12-tooth sprocket is adequate, many engineers will use a larger sprocket, both for better discharge and to permit a higher allowable chain speed.

STEP 3: CALCULATE

THE

MAXIMUM CHAIN PULL

The total chain pull can be calculated using Equation 11.3. There is 70 ft between centers, 75% of the chain will be plain chain that weighs 6.3 lb/ft, and 25% of the chain will be chain with attachments that weighs 8.6 lb/ft. So the weight of either the carrying or return strands, W2, will be (6.3 × 70 × 0.75) + (8.6 × 70 × 0.25) = 330.75 + 150.5 = 481.25 lb. There is a bucket every 2 ft of chain and the weight of each bucket is 21 lb. So the weight of the buckets on either the carrying or return strands, W3, will be (70/2) × 21 = 35 × 21 = 735 lb. Since there are 35 buckets with a capacity of 0.34 ft3 each, and the material weighs 50 lb/ft3, the weight of the material on the carrying strand, W4, will be (70/2) × 0.34 × 50 = 595 lb. This can be compared to the required weight of the material per foot of elevator, which is 8.33 × 70 = 583 lb. The digging load, Q, is determined next using Equation 11.4. Assuming that the factor, J, is estimated to be approximately 0.85 (about midway between 0.67 and 1.0) because the material is considered to have relatively small lumps with fairly free-flowing characteristics: Q = (12 × 17 × 0.85 × 23.18)/(4 × 6) = 167 lb. The take-up tension, P1, is assumed to be 2000 lb because the elevator will need a fairly heavy gravity take-up that will give somewhat and yet resist the digging loads from the occasional wet caked or sometimes frozen lumps of crushed coal from a storage yard that can momentarily be quite high. Then the total chain pull is calculated using Equation 11.3:



314


P = 481 + 735 + 595 + 167 + (2000/2) = 2978 lb. Finally, referring to Figure 11- 21, we have P2 = 481 + 735 + 1000 = 2216 lb, P3 = 1000 lb, P4 = 167 + 1000 = 1167 lb.

STEP 4: FIND

THE

DESIGN PULL

AND


The design pull is calculated using Equation 11.8, using the chain pull calculated from Equation 11.3 and the service factors obtained from Table 11-5: PDes = 2978 lb × 1.1 × 1.2 × 1.3 × 1.2 = 6132 lb.

STEP 5: SELECT

THE

CHAIN

The chain tentatively selected, ANS S110, with a rated working load of 6300 lb, is adequate. Again, some engineers would decide to use a heavier chain, depending on such factors as how important the installation might be to an operation or other factors which are not part of these calculations.

STEP 6: SPROCKET, TRACTION WHEEL, HUB,

AND

SHAFT SELECTION

This step was covered in chapter 4.

ROLLER CHAIN EQUIPPED BUCKET ELEVATORS Most bucket elevators using roller chain are used for unit handling or food or chemical bulk handling applications. Generally speaking, standard and extended pitch conveyor series (ASME B29.4) roller chains with straight-edge link plates are normally used in bucket elevator applications. Specifications for roller chains in bucket elevators are determined in exactly the same manner as for engineering steel chains; the necessary information concerning working loads, chain weights, and static or rolling friction (if needed) can be found in Table 10-4, Table 10-5, and Table 10-7.

PIVOTED BUCKET OR PAN CONVEYORS Figure 11-18 shows a style of equipment widely used to handle materials vertically, with this particular unit often being seen in food processing plants. The concept carries different names in various applications. In food handling applications, such as that in Figure 11-18, which commonly use roller chains, it is called a bucket elevator. With engineering steel chains, and in a much larger version such as would be used to handle coal in a power plant (Figure 11-19, a common and effective application), it is called a pivoted bucket conveyor. On long slopes, with no vertical run, the concept is sometimes called a pivoted pan conveyor, when the pivoting carrier has but two shafts. Figure 11-20 is a diagram of a typical pivoted bucket conveyor path with six shafts, and Figure 11-21 shows the method of discharge in diagram form.



315


FIGURE 11-18 Pivoted bucket elevator using roller chain.

OPERATION PRACTICES The advice on the maintenance and lubrication of conveyor chains, as given for conveyor chains in chapter 12, can be applied to chains used in bucket elevators as well, except where it is modified by the following remarks.

ELEVATOR STOPPAGE In normal operation, the elevator should always be emptied if it is stopped. If the elevator is stopped while it is loaded (as in a power failure, for instance), the chain will run backward. A backstop should be used to prevent this. One type of backstop is a wheel keyed either to the head or foot shaft that turns forward with the shaft. The slightest backward motion brakes the wheel and the elevator is immobilized until the forward motion is resumed. Figure 11-22 shows a typical backstop.

INSPECTION The inspection door on the side of the elevator casing makes the chain accessible for inspection and repair. Check the chain, attachments, and buckets as you would those on a bulk-handling conveyor. If the chain pitch has stretched appreciably, adjust the take-ups.



316


FIGURE 11-19 Discharge portion of a pivoted bucket conveyor.

FIGURE 11-20 Diagram of the bucket path of the conveyor in Figure 11-19.




317

FIGURE 11-21 Diagram of the discharge arrangement of pivoted buckets.

FIGURE 11-22 Typical backstop.

OPERATION If for any reason the elevator is out of service for a time, it should be run regularly to prevent freeze-up. As a rule, it should be run at least once a week, and it should be turned over every day if it is handling sticky material. Otherwise the material may harden and the chain will be severely strained when the elevator is started up again.

LUBRICATION Bushed roller and bushed rollerless chains, whether used on elevators or conveyors, are lubricated in the same manner. For details, see chapter 12.



Chain 12 Flat-Top Conveyors Many types of flat-top chains are used in conveyors. This chapter covers only a limited number of unit link flat-top chains all with 1 1/2 -in. pitch. The four basic types of flat-top chain covered in this chapter are shown in Figure 3-43 through Figure 3-46. The steel chains considered here are available in carbon steel or stainless steel. The plastic chains considered here are available in plain acetal and low-friction acetal. Several other types of flat-top chains are available, but space does not permit covering them in this book. There is a series of flat-top chains that use modified no. 40 or no. 60 base roller chains and have top plates that snap on to the base chains. The plastic chains can be made from many other plastics than acetal, and there are special side-grip, high-friction, and low back-pressure, flattop chains for unusual conveying needs. If the user has unusual needs, they should contact an ACA flat-top chain manufacturer for help with selecting the proper flat-top chain. Nine types of chain conveyors were described in the chapter on engineering steel chain conveyors. Most of those descriptions do not apply to flat-top chain conveyors. Most flat-top chain forms a special kind of slat conveyor, and that is the only type covered in this chapter.

FLAT-TOP CHAIN CONVEYOR SELECTION GUIDELINES CONVEYOR LAYOUT A straight-running layout usually is the simplest, most efficient, and least costly, and should be used whenever possible. However, parts of the machine may be in the way and the locations of other parts of the process may not be in line. In these cases, one cannot use a straight-running conveyor. One might have to use several shorter straight-running conveyors with transfers to change direction, or one might use side-flexing flat-top chain to make the necessary turns. When a conveyor must travel around a corner, side-flexing flat-top chain offers some advantages. The cost of added motors, sprockets, and transfer plates or turntables may be avoided, and product tipping, jamming, and slipping at the transfers is eliminated. At the same time, the designer needs to observe a few guidelines when using side-flexing flattop chains. Use as few corners and as small an angle as possible. Use as large a turning radius as possible. Use lubrication in the corners to reduce friction and wear. And design the conveyor so the drive is as far from the last corner as possible. Figure 12-1 shows poor and good practice for laying out a curved conveyor. This chapter covers only simple horizontal flat-top conveyors that move product from one point to another. If any part of the conveyor is inclined, or if it has transfers, contact an ACA flat-top chain manufacturer for help.

CONVEYOR WIDTH

AND

CLEARANCE HEIGHT

The flat-top chain conveyor must be wide enough to handle the widest object carried on it. Also, if speed is limited by other factors, two or more flat-top chains may have to be used in parallel to produce the needed output. This will increase conveyor width. There also must be enough clearance height to permit the carried material to pass, as well as enough clearance height in the return run 319



320


FIGURE 12-1 Poor and good locations of drive.

to allow the chain to pass under the conveyor. A designer must be careful to consider all physical restrictions before deciding on the size of the chain conveyor.

CONVEYOR LENGTH

AND


Conveyor length is limited by the frictional drag from the weight of the chain and product and the rated working load of the chain. As the conveyor gets longer, the drag increases and there is less available capacity to carry the product. Shaft center distance is often the same as the conveyor length, but sometimes it is longer. The shaft center distance may be made longer to accommodate additional loading and unloading equipment at the ends of the conveyor. Flat-top chain conveyors generally should not be more than 100 ft long.

LOADING

THE

CONVEYOR

Loading any conveyor should be done as gently as possible to reduce impact. The load should, if possible, be placed or slid onto the conveyor to reduce the pulsation and surging caused by rough loading. Chutes or hoppers that load the conveyor should place the load as near the center of the conveyor width as possible. Otherwise the chain may wear unevenly or be damaged by the off-center load.

CONVEYOR CAPACITY Conveyor capacity is the amount of material, in pounds or units, carried per unit of time. The capacity of the conveyor is found using Equation 12.1: WC = 60WS, where WC is the conveyor capacity (in lb/hr or units/hr), W is the amount of material carried (in lb/ft or units/ft), and S is the conveyor speed (in ft/min).


(12.1)


Flat-Top Chain Conveyors

321

Please note that oval or rectangular containers normally can only run in single file. Conveying such containers in multiple rows can cause jamming or cause the containers to be oriented incorrectly.

CONVEYOR SPEED The required conveyor capacity is used to set the needed conveyor speed. The types of material used in the chain and wear strips limit the maximum conveyor speed. Also, the type of lubrication limits the maximum speed. The way the material is loaded onto and discharged from the conveyor may also limit conveyor speed. Flat-top conveyor chains normally should not run faster than about 300 ft/min.

ACCUMULATION Sometimes the flow of product must be stopped while the conveyor keeps running. Product then accumulates on that section of the conveyor. Stopping the product flow in an accumulation section increases the chain pull. The accumulation section should be as short as possible to keep the increase in chain pull to a minimum, and the accumulation section should only be in a straight section of the conveyor for the same reason. Also, the time the material is stopped should be as brief as possible to keep the heat generated to a minimum. The adjusted chain pull depends on two factors. One is the increased chain pull from frictional drag. The other is the percentage of time that accumulation occurs.

CHAIN TYPES The flat-top chains considered in this chapter may be made from carbon steel, stainless steel, acetal, or low-friction acetal. They also may be made in straight-running or side-flexing styles. The material and style of the chain selected depends on the product conveyed and the conditions. Tables to help select a suitable material for the chain are provided later in this chapter. Carbon Steel Flat-Top Chain Carbon steel flat-top chains normally are made from cold-finished carbon or low-alloy steel. Some carbon steel in flat-top chains is hardened for better abrasion resistance. Carbon steel flat-top chains are good for conveying paper, glassware, and metal parts in dry abrasive conditions. Stainless Steel Flat-Top Chain Most stainless steel flat-top chains are made from cold-finished austenitic stainless steel. They have very good resistance to many different corrosives and the stainless steel is often hardened by cold work for better abrasion resistance. Stainless steel flat-top chains are good for conveying bottles and other products where the spillage might be corrosive. They are also good for use in food and beverage processing, where the equipment must be cleaned regularly. Plastic Flat-Top Chains Plastic flat-top chains are usually made from acetal or low-friction acetal. Acetal chains have reasonably low friction and acceptable corrosion resistance. They are good for conveying aluminum cans in breweries and soft drink plants, and they do not make much noise. Low-friction acetal chains have very low friction. They are good for conveying paperboard cartons where no lubrication is permitted.



322


Side-Flexing Flat-Top Chains Side-flexing flat-top chains may be made from any of the four materials that were mentioned above. They are used where the conveyor must travel around a corner and it is not practical to use transfers. However, they should only be used where needed because their rated working loads are less than an equivalent straight-running chain.

LOAD-CARRYING STRAND WAYS

AND

WEAR STRIPS

Ways or wear strips normally are used to support the load-carrying strands of a flat-top chain conveyor. A wide variety of materials can be used in wear strips for flat-top chains, but the most commonly used materials are listed below. Carbon Steel Carbon steel ways are usually made from cold-finished bars or strips. They should have a surface finish of 32 to 63 microinches Ra and should be hardened to 25 to 30 Rc. Abrasive particles are not likely to imbed in steel wear strips. So carbon steel ways are good for use in noncorrosive, abrasive, or high-temperature applications. Stainless Steel Stainless steel ways are usually made from austenitic cold-finished bars or strips. Stainless steel offers the best corrosion resistance. They should have a surface finish of 32 to 63 microinches Ra and should have a one-quarter hard temper with a hardness of 25 to 35 Rc. Softer annealed grades of austenitic stainless steel should be avoided because they will not have the abrasion resistance of the one-quarter hard temper. Abrasive particles are not likely to imbed in steel wear strips. Thus, stainless steel ways are good for use in corrosive, abrasive, or high-temperature applications. Nylatron Nylatron ways consist of nylon with a molybdenum disulfide filler. They have a high PV rating and low friction and wear. They should have a surface finish of 32 to 125 microinches Ra. Nylatron ways are good for use in dry applications. They are especially good for use in thermoplastic sideflexing chain corners when no lubrication is used. Nylatron should not be used in wet applications because the nylon will absorb moisture and swell. Ultra High Molecular Weight Polyethylene Ultra high molecular weight polyethylene (UHMWPE) ways are usually made from extruded bars or strips. They have lower friction than metal ways and good corrosion resistance to many industrial fluids. They should have a surface finish of 32 to 125 microinches Ra. UHMWPE ways are good for use in dry or wet applications with straight-running or side-flexing flat-top chains. They do not absorb water and are not affected by moisture. Other Teflon and lubricant-impregnated wood are sometimes used in wear strips. Teflon wear strips should only be used in low-speed and low-load applications. Lubricant-impregnated wood can be used in some dry abrasive applications.




323

FIGURE 12-2 Typical wear strips for straight-running flat-top chain.

FIGURE 12-3 Typical wear strips for side-flexing flat-top chain with bevels.

FIGURE 12-4 Typical wear strips for side-flexing flat-top chain with tabs.

A table for selecting wear strip materials is provided later in this chapter. The conveyor designer should study the catalogs and engineering manuals of an ACA flat-top chain manufacturer for more help in selecting wear strips. Typical installations of load-carrying wear strips for straight-running flat-top chain are shown in Figure 12-2. Side-flexing chains must have special support in the corners to prevent the chain from being pulled out of the channel. Typical installations of side-flexing chain wear strips for flattop chains with bevels and tabs are shown in Figure 12-3 and Figure 12-4.



324


FIGURE 12-5 Typical perforated continuous return way.

RETURN STRAND SUPPORTS

AND

WEAR STRIPS

The return strand of flat-top chain conveyors should be supported when the shaft center distance is more than about 5 ft. This is because a long unsupported return strand hangs in a catenary and can greatly increase chain pull. The same materials are used in wear strips for the return strand as are used in wear strips for the load-carrying strand. They are selected in the same way and from the same table. Wear strips should support the full width of the chain in the return strand. If a continuous sheet is used, it should be perforated to allow foreign materials to pass through it. This is shown in Figure 12-5. A serpentine-type return also may be used to allow foreign materials to pass through. This is shown in Figure 12-6. Side-flexing chains with tabs may be supported by the tabs in the return strand. That reduces wear on the carrying surface of the chain when running in the return section. Side-flexing chains must have special support in the corners to prevent the chain from being pulled out of the channel. Typical installations of curved return strand wear strips for flat-top chains with bevels and tabs are shown in Figure 12-7 and Figure 12-8. If the conveyor is very long, or if very low drag is needed, roller return supports can be used. Such a system is shown in Figure 12-9. The diameter of the rollers in a roller return should be at least two times the minimum back-flex radius of the chain, and dimension “A” should be 1.5 to 2 times dimension “B” to provide a catenary section.




325

FIGURE 12-6 Typical serpentine return way.

MULTIPLE-STRAND CONVEYORS Sometimes one strand of chain does not have enough load capacity or is not wide enough to handle the product. Two or more strands of chain are then needed to make a multiple-strand conveyor. Remember that round or square containers can be conveyed in multiple rows, but oval or rectangular containers should only be conveyed in single file. For multiple-strand conveyors, the head shaft sprockets (drivers) need to be keyed in line, but only one tail shaft sprocket, usually the center sprocket, needs to be keyed to the shaft. This reduces the chances of product tipping and spilling. Make sure there is enough clearance between adjacent strands to prevent interference. Suggested corner section layouts that give adequate clearance are shown in Figure 12-10. Straight sections should be designed to maintain the same side clearance.

CATENARY TENSION

AND

CHAIN SAG

A catenary section should be used in flat-top conveyors that are more than about 5 ft long. A catenary section provides a place for any excess chain to accumulate as wear occurs. The catenary also gives enough tension to the slack span so that the conveyor is not likely to jump teeth under a heavy load. A typical catenary section is shown in Figure 12-11. The catenary section should be located as close to the drive as possible. Vertical chain sag should be maintained within the recommended range shown in Figure 12-11. When sag exceeds the recommended maximum, it should be adjusted by removing one or more links from the chain.



326


FIGURE 12-7 Typical bevel-style curve return.

FIGURE 12-8 Typical tab-style curve return.

Take-ups are not recommended for flat-top conveyors. Ample space must be provided for chain sag in the catenary to prevent the chain from snagging or hitting any machine members or other obstructions. As was stated earlier, most long conveyors should have the return span of chain supported over most of its length. The weight of the unsupported span, or a portion of a span, adds to the chain pull. This must be considered, along with the bearing and shaft loads, when calculating the total working load on the chain. The added pull from catenary tension is not included when calculating the power needed to run the conveyor. The procedure for calculating catenary sag and tension is provided later in this chapter.




327

FIGURE 12-9 Typical roller return.

FIGURE 12-10 Side clearance in multiple-strand flat-top chain conveyors.

FIGURE 12-11 Catenary for flat-top chain conveyor.

ENTRY RADIUS The return support should have a large radius on the end where the chain travels from the catenary onto the support. The minimum entry radius should be greater than the minimum back-flex radius for the chain. Typical back-flex radii are provided in a table later in this chapter. For specific backflex radii, refer to the chain manufacturer’s catalog. A diagram of a typical entry radius is shown in Figure 12-12.



328


FIGURE 12-12 Entry radius for sliding returns.

CONVEYOR DRIVE Power should be applied to the conveyor at the head shaft and the driven head shaft should always be at the discharge end of the conveyor. There must be at least 18 in. of straight run from the head shaft to any turns in the conveyor, which provides enough room for the catenary.

SPROCKETS Sprocket Size Both sprockets are the same size in most conveyors. The chains considered in this chapter normally engage every other tooth on the sprocket, so the effective number of teeth is one-half the actual number of teeth on the sprocket. The sprockets in a flat-top chain conveyor should have at least 19 teeth for most general uses and should have 23 teeth or more for smoothest operation. If space will not permit a sprocket with the recommended number of teeth, select a sprocket with as many teeth as space will permit. The sprockets should have an odd number of actual teeth. With an odd number of teeth, each tooth on the sprocket engages the chain every other revolution. Thus tooth wear is automatically equalized. Sprocket Material Sprockets for flat-top chains can be made from several different materials. The material in the sprockets must be compatible with the chain that runs on it. The material in the sprockets also must be able to operate at the temperature and in the environment in which the conveyor runs. Conveyor designers should refer to the catalogs and engineering manuals of an ACA flat-top chain manufacturer for more information on selecting sprocket materials.

INDEXING: FREQUENT STOPS

AND

STARTS

Starting a conveyor while it is loaded causes a momentary increase in chain pull. Many conveyors start less than once per hour and no adjustment to the design chain pull needs to be made in these cases. Some conveyors start several times per hour, and a few conveyors start many times per hour in a repeating cycle. The latter condition is typical of an indexing conveyor. Any time a conveyor starts five times per hour or more, the design chain pull must be adjusted by a starting factor. A table of starting factors is provided later in this chapter.




329

TABLE 12-1 Temperature guide Chain or wear strip material Acetal UHMWPE Nylon Carbon steel Stainless steel Lubricant-impregnated wood

Minimum temperature, ˚F Dry -40 -100 -40 -100 -40 -50

Maximum temperature, ˚F Dry 180 180 170 350 800 160

Wet 150 160 150 250 250 160

ENVIRONMENT Temperature The lowest and highest temperatures in which flat-top chains and wear strips should be used depend on whether there is moisture present or not. Acceptable temperature ranges for some materials are shown in Table 12-1. When different materials are used in the same conveyor, the more restrictive temperature limit must be used. Corrosion Carbon and alloy steel flat-top chains are not well suited to corrosive conditions. However, there are flat-top chains made from materials for use outdoors, in wet conditions, or in some corrosive chemicals. See Table 12-2 for chain and wear strip materials when the conveyor must work in corrosive chemicals. Consult an ACA flat-top chain manufacturer for help in selecting chain or wear strip materials for corrosive chemicals not listed in Table 12-2. Abrasion Abrasive materials such as dirt, sand, glass, or metal particles cause conveying chains and wear strips to wear very fast. When a chain is working in abrasive conditions, use a chain and wear strips with hard wear surfaces. If possible, use controls to reduce the amount of abrasive material affecting the chain and wear strips. A table to help select chains and wear strips to be used in abrasive conditions is given later in this chapter. Consult an ACA flat-top chain manufacturer for help with selecting a chain for use in abrasive conditions. Lubrication Lubricating flat-top conveyor chains is covered in chapter 13.

FLAT-TOP CONVEYOR CHAIN SELECTION PROCEDURE STEP 1: OBTAIN NECESSARY INFORMATION The following information is needed: • • •

Conveyor layout Conveyor length and shaft center distance Product to be conveyed



330


TABLE 12-2 Corrosion resistance guide Corrosive product Acetic acid (>5% up to 50%) Acetone Alcohol Ammonia Beer Beverages: soft drinks Benzene Brine (pickle) Carbon tetrachloride Chlorine Citric acid Formaldehyde Fruit juices Gasoline Hydrogen peroxide Isopropyl alcohol Lactic acid Milk Nitric acid (low concentrations) Oil (vegetable or mineral) Paraffin Phosphoric acid (up to 10%) Soap and water Sodium chloride Sodium hydroxide (up to 25%) Stearic acid Toluene (toluol) Turpentine Vegetable juices Vinegar Water (fresh) Whiskey Wine Xylene

Carbon steel U U S M S S S U M U U S U S U S U S U S S U M U U U S – M U U S S S

Stainless steel M S S S S S S M M U S S S S S S S S S S S S S M S S S S S S S S S S

S, satisfactory; M, marginal; U, unsatisfactory.

• • • • • • • • • •

Unit or bulk product Product dimensions Weight of product per foot of conveyor length Product arrangement and spacing on conveyor Required output rate Conveyor width and height Conveyor speed Weight per foot of chain Diameters of shafts and sprockets Environment • Temperature


Acetal U S S U S S S M S U M S S S U S S S U S S U S S S M M S S S S S S S

Nylon, Nylatron M M S S S S S M S U M S S S U S M S U S S U S S U S S S S S S S S S

UHMWPE S S S S S S M S M S S S S M S S S S S S S S S S S S U U S S S S S M



331

TABLE 12-3 Chain material selection Carbon steel

Stainless steel

Acetal

Abrasives Present Absent



Lubricated with soap and water R A R A A A

Lubricated with water only A R N R N A

Not lubricated A A A A A A

Not lubricated N R N R N A

Top plate material

Conveyed product Paper, plastic, cans China, glass, bottles Metal parts

Lubricated oil A A R

with

Paper, plastic, cans China, glass, bottles Metal parts

Not lubricated R A R A R R

A A R

R, recommended; A, acceptable; N, not recommended.

• • • • •

• Corrosion • Abrasion Other conditions Accumulation Frequent stops and starts or indexing Space limitations Available lubrication

STEP 2: SELECT CHAIN MATERIAL After deciding on the conveyor layout and type, select a suitable chain material from Table 12-3. The table provides only general information about flat-top chain materials. The designer should contact an ACA flat-top chain manufacturer for more detailed information on selecting flat-top chain materials.

STEP 3: SELECT WEAR STRIP MATERIAL Select the wear strip material from Table 12-4. Here again, the table gives only general information about wear strip materials. The designer should contact an ACA flat-top chain manufacturer for more detailed information on selecting wear strip materials.


OF

FRICTION

Friction between Chain and Wear Strips Obtain the coefficient of friction between the chain and wear strips from Table 12-5. Friction between Chain and Product If product accumulates anywhere on the conveyor, obtain the coefficient of friction between the chain and product from Table 12-6.



332


TABLE 12-4 Wear strip material selection Top plate material

Carbon steel

Stainless steel

Acetal

Wear strip material




Lubricated with oil R N

Lubricated with soap and water R N

Lubricated with water only R N

Carbon steel Stainless steel

A

N

R

N

R

A

Nylon, Nylatron

A

A

A

A

A

R

UHMWPE

A

R

A

R

A

A

Lubed wood

A

N

A

A

A

A

Not lubricated

Not lubricated

Not lubricated

Carbon steel

R

A

A

A

A

A

Stainless steel

R

A

R

A

R

A

Nylon, Nylatron

N

N

N

N

A

R

UHMWPE

A

R

A

R

A

A

Lubed wood

N

N

A

A

A

A

R, recommended; A, acceptable; N, not recommended.

TABLE 12-5 Friction between chain and wear strips Wear strip material Chain material Carbon steel Stainless steel

Regular acetal Lowfriction acetal

Lubrication Dry Oil Dry Water Soap and water Oil Dry Water Soap and water Dry Water Soap and water

NR, not recommended


Steel 0.50 0.20 0.50 NR NR 0.20 0.30 NR NR 0.25 NR NR

Stainless steel NR NR 0.50 0.40 0.20 0.20 0.30 0.23 0.15 0.25 0.20 0.15

Nylon 0.40 0.20 0.40 0.30 0.20 0.20 0.25 0.21 0.15 0.20 0.18 0.15

UHMWPE 0.30 0.20 0.40 0.30 0.20 0.20 0.25 0.21 0.15 0.20 0.18 0.15

Lubed wood 0.15 NR 0.15 NR NR NR NR NR NR NR NR NR



333

TABLE 12-6 Friction between chain and product Chain material Carbon steel

Lubrication Dry Oil

Aluminum 0.28 —

Glass 0.35 —

Returnable glass bottles 0.47 —

Nonreturnable glass bottles 0.35 —

Paper 0.40 NR

Plastic 0.30 NR

Steel 0.35 0.15

Dry Water Soap and Water Oil

0.28 0.19 0.12 —

0.35 0.25 0.15 —

0.47 0.31 0.21 —

0.35 0.25 0.15 —

0.40 NR NR NR

0.30 0.20 0.10 —

0.35 0.25 0.15 0.15

Regular acetal

Dry Water Soap and water

0.25 0.17 0.12

0.20 0.15 0.10

0.27 0.18 0.14

0.20 0.15 0.10

0.33 NR NR

0.25 0.20 0.15

0.30 0.22 0.15

Low-friction acetal

Dry Water Soap and water

0.20 0.15 0.12

0.15 0.13 0.10

0.20 0.16 0.14

0.15 0.13 0.10

0.30 NR NR

0.20 0.18 0.15

0.25 0.20 0.15

Stainless steel

NR, not recommended; —, not tested.

STEP 5: OBTAIN CORNER FACTORS If the conveyor has corner sections, there will be added drag between the chain and the inside of the corner wear strips. Obtain the corner factor for each corner section from Table 12-7.

STEP 6: CALCULATE BASIC CHAIN PULL A flat-top chain conveyor layout is shown in Figure 12-13. The sample layout has two straight sections, a 90-degree corner, and a 180-degree corner. The equations given later are keyed to the section labels of the sample conveyor. Only the final equation, which applies to the section ending at point 4, is needed for a straight-running conveyor. All of these equations for chain pull assume that the same wear strips are used for the return span as are used in the conveying span. The symbols used in the equations are P, basic conveyor chain pull (in lb); Pw, required chain working load (in lb); C, length of the conveyor (in ft); C1, C2, C3, C4, length of the conveyor sections (in ft); Ca, length of the accumulation section (in ft); and M, weight of the chain (in lb/ft; for calculating the basic chain pull, the designer may use an estimated weight of 1 lb/ft for plastic chains and 2 lb/ft for steel chains); W, weight of the conveyed material (in lb/ft); fs, coefficient of friction between the chain and wear strips (from Table 12-5); fw, coefficient of friction between the material and chain (from Table 12-6); Kc, corner factor (from Table 12-7); Ka, slippage (accumulation) factor (from Table 12-8); Kv, speed factor (from Table 12-9 or Table 12-10); Ks, frequent starts factor (from Table 12-11); and PA, added chain pull from accumulation (in lb),



334


TABLE 12-7 Corner factors Corner track material Chain material Carbon steel or stainless teel

Regular acetal

Low-friction acetal

Corner angle

Steel or stainless steel

Nylatron or UHMWPE

30 60 90 120 150 180

Dry 1.25 1.65 2.00 2.50 3.10 3.50

Well lubricated 1.10 1.25 1.40 1.60 1.80 2.00

Dry 1.20 1.50 1.80 2.20 2.70 3.00

Well lubricated 1.10 1.25 1.40 1.60 1.80 2.00

30 60 90 120 150 180

1.25 1.45 1.70 2.05 2.40 2.70

1.15 1.20 1.25 1.40 1.55 1.65

1.20 1.40 1.60 1.90 2.20 2.50

1.10 1.15 1.20 1.30 1.40 1.50

30 60 90 120 150 180

1.20 1.35 1.50 1.85 2.00 2.40

1.10 1.20 1.25 1.40 1.55 1.65

1.15 1.20 1.30 1.50 1.60 1.80

1.10 1.15 1.20 1.30 1.40 1.50

Curve angle factor is 1.0 for straight sections.

FIGURE 12-13 Flat-top chain conveyor layout.

PA = CaWfwKa.


(12.2)



335

TABLE 12-8 Slippage (accumulation) factor Percent of time slippage occurs 0 10 20 30 40 50 or more

Slippage factor 0.0 0.5 0.7 0.8 0.9 1.0

TABLE 12-9 Speed factor for steel chains Speed, ft/min 5 6–10 11–20 21–50 51–150 151–250 251–300

Factor 1.00 1.25 1.50 2.00 2.50 3.00 3.20

TABLE 12-10 Speed factor for plastic chains Speed, ft/min 5 or less 6 through 15 16 through 35 36 through 75 76 through 125 126 through 200 201 through 300

Factor 1.00 1.50 2.00 2.50 3.00 3.50 4.00

TABLE 12-11 Frequent starts factor No. of Starts Per Hour 0 5 10 15 20 25 or more


Starts Factor 1.0 1.4 1.7 1.8 1.9 2.0


336


Straight Running Conveyors If the conveyor is straight running, only section C4 in Figure 12-13 applies: P = Cfs(2M + W) + PA

(12.3)

Curved Conveyors If the conveyor is curved, all sections in Figure 12-13 may apply. Begin at the tail shaft and work toward the driver shaft. Calculate the chain pull in sections as follows:

STEP 7: CALCULATE

THE

At point 1: P1 = [C1fs(2M + W) + PA1]Kc(180)

(12.4)

At point 2: P2 = P1 + C2fs(2M + W) + PA2

(12.5)

At point 3: P3 = [P2 + C3fs(2M + W) + PA3]Kc(90)

(12.6)

At point 4: P4 = P3 + C4fs(2M + W) + PA4.

(12.7)

PRELIMINARY REQUIRED WORKING LOAD

Calculate the preliminary required working load using Equation 12.8: Pw = PKvKs.

STEP 8: CALCULATE

THE

CATENARY SAG

AND

(12.8)

TENSION

If a catenary section is present, the designer should determine the depth of sag so that the needed clearance can be provided. Also, calculate the catenary tension to be sure the rated working load of the selected chain is sufficient. D = 0.375C c E

PC =

Cc2 M , 96 D

(12.9)

(12.10)

where D is the depth of sag of the conveyor (in inches), Cc is the straight-line distance between points of support (in inches), L is the length of the catenary in the slack span (in inches), E is the amount of excess chain in the catenary (in inches) (E = L Cc), PC is the catenary tension (in lb), and M is the weight of the chain per foot (in lb/ft). The depth of sag and catenary tension may also be determined from Table 9-10 and Table 9-11.




337

TABLE 12-12 Straight-running flat-top chain dimensions and capacities Chain Number 815

Chain Material CS SS

Top Plate Thickness 0.125

Top Plate Width 2.25 2.63 3.25 4.00 4.50 6.00 7.50

Weight Lb/ft 143 1.60 1.84 2.14 2.34 2.94 3.54

Maximum Load 625

Min. Back Flex Radius 6.50

820

AC LF

0.156

3.25 4.00 4.50 6.00 7.50

0.56 0.64 0.69 0.84 0.99

365

1.50

831

AC LF

0.188

3.25 4.50 7.50

0.61 0.75 1.08

365

1.50

821

AC LF

0.188

7.50 10.0 12.0

1.70 2.00 2.20

625

1.50

STEP 9: DETERMINE

THE

TOP PLATE WIDTH

Using Tables 12-12 and 12-13, determine the top plate width from the width of the product and the number of rows of product. If the total width of the product is greater than a single available top plate, two or more chains may be used running in parallel. Remember that oval and rectangular containers should only be run in single file. The preliminary required working load applies to all the strands of chain in the conveyor. If two or more strands of chain are used, divide by the number of strands of chain in the conveyor. This will be the required working load per strand of chain.

STEP 10: SELECT

THE

CHAIN

AND

RECALCULATE

THE


Add the catenary tension (PC) to the preliminary required working load (Pw). Using the total, select a chain with an adequate working load from Tables 12-12 and 12-13. The values in Table 12-12 are typical values taken from a compilation of published data. Check the manufacturer’s catalog for the specific brand of chain chosen to be sure that the dimensions and working load are acceptable. Repeat steps 6 through 8 using the actual chain weight taken from the manufacturer’s catalog from which the chain was selected. Once a specific chain is selected, repeating steps 6 through 8 will give a somewhat different design chain pull and required chain working load. The working load listed for the chain in the catalog must be greater than or equal to the calculated required working load for the application. If it is not, a chain with a higher working load should be selected or the conveyor should be divided into more strands. Then, recheck the calculations until a chain with satisfactory working load is selected.



338


TABLE 12-13 Side-flexing flat-top chain dimensions and capacities Chain Number 879 BEV

Chain Material AC LF

Top Plate Thickness 0.188

Top Plate Width 3.25 4.50

Weight Lb/ft 0.55 0.64

Maximum Load 425

Min. Back Flex Radius 18 24

879 TAB

AC LF

0.188

3.25 4.50

0.70 0.76

425

18 24

880 BEV

AC LF

0.156

3.25 4.50

0.60 0.70

425

18 24

880 TAB

AC LF

0.156

3.25 4.50

0.63 0.73

425

18 24

882 BEV

AC LF

0.188

4.50 7.50 10.0

1.30 1.60 1.90

625

24

882 TAB

AC LF

0.188

4.50 7.50 10.0 12.0

1.33 1.63 1.90 2.13

625

24

881 BEV

CS SS

0.125

3.25 4.50 7.50

2.00 2.50 3.70

625

24

881 TAB

CS SS

0.125

3.25 4.50 7.50

2.00 2.50 3.70

625

24

Note: Minimum back flex radius for all listed side flexing chains is 1.50 inches.

STEP 11: SELECT

A

SPROCKET SIZE

Select a sprocket with at least 91/2 effective teeth. If the conveyor runs at high speed (more than 100 ft/min), or smooth operation is very important, select a sprocket with at least 111/2 effective teeth. If available space will not accommodate the suggested minimum sprocket size, select a sprocket with as many teeth as the space will permit.

STEP 12: CALCULATE

THE


Both sprockets (head shaft and tail shaft) are the same size in most flat-top chain conveyors. In this case, the chain length can be calculated using Equation 12.11: LP = N + 24C/p,

(12.11)

where LP is the required chain length (in pitches), N is the number of teeth on the sprockets, C is the shaft center distance (in ft), and p is the chain pitch (in inches).




STEP 13: CALCULATE

THE

339

REQUIRED POWER

The horsepower required at the input shaft of the conveyor is calculated using Equation 12.12: hp = PS/33,000.

STEP 14: SELECT

THE

(12.12)

LUBRICATION METHOD

Select a method of lubricating the conveyor chain using the information provided in chapter 13.

SAMPLE FLAT-TOP CHAIN CONVEYOR SELECTION STEP 1: OBTAIN NECESSARY INFORMATION Conveyor layout: Conveyor runs straight for 2 ft, turns 90 degrees to the right and runs straight again for 12 ft. Conveyor length: C = 2 + 1.2 + 12 = 15.2 ft. Product conveyed: Filled 12 oz. soft drink cans; weight, 0.85 lb each. Cans are 2.6 in diameter. Weight per foot = (12/2.6) × 0.85 = 3.92 lb/ft. Cans to be conveyed single file with no space between. Need an output rate of 60,000 cans/hr. Conveyor width: To accommodate can diameter. Conveyor speed: Using Equation 12.1. WC = 60,000 cans/hr and W = 12/2.6 = 4.6 units/ft, thus S = 60000/(60 × 4.6) = 217 ft/min. Weight of chain: To be determined; estimate 1.0 lb/ft. Diameters of shafts and sprockets: To be determined. Environment: Some corrosion possible. Soap and water to be used as lubricant. Other conditions: None. Available lubrication: Soap and water.

STEP 2: SELECT CHAIN MATERIAL From Table 12-3, an acetal is selected for the chain material. Stainless steel or low-friction acetal also could have been selected, but acetal is less costly and is acceptable for the conditions.

STEP 3: SELECT WEAR STRIP MATERIAL From Table 12-4, UHMWPE is selected for the wear strip material. Nylon was not selected because it absorbs water. Stainless steel was not selected because it is more costly and difficult to work with.


OF

FRICTION

Only the coefficient of friction between the chain and wear strips is needed. From Table 12-5, it is 0.15.

STEP 5: OBTAIN CORNER FACTORS With chain material of regular acetal, wear strip material of UHMWPE, a corner angle of 90 degrees, and well-lubricated operation, the corner factor from Table 12-7 is 1.20.

STEP 6: CALCULATE BASIC CHAIN PULL For this sample selection, Equation 12.5 through Equation 12.7 are used:



340


At point 1: P1 = 0.0. At point 2: P2 = 2.0 × 0.15 × [(2.0 × 1.0) + 3.92] = 1.8 lb. At point 3: P3 = [1.8 + (1.2 × 0.15 × 5.92)] × 1.20 = 3.4 lb. At point 4: P4 = 3.4 + (12 × 0.15 × 5.92) = 14 lb.

STEP 7: CALCULATE

THE

PRELIMINARY REQUIRED WORKING LOAD

Calculate the preliminary required working load using Equation 12.8: Pw = PKv = 14 × 4.0 = 56 lb.


AND

TENSION

A catenary that is 24 in. long, with a minimum sag of 3 in. will be used. Equation 12.10 gives a catenary tension of 2 lb.

STEP 9: DETERMINE

THE

TOP PLATE WIDTH

The can diameter is 2.6 in. and the product is conveyed single file, so a top plate width of 3.25 in. is adequate.

STEP 10: SELECT

A

CHAIN

AND

RECALCULATE

THE


Entering Table 12-13 with the required working load of 58 lb (Pw + PC) shows that an 880 BEV or 880 TAB chain is more than adequate. Assuming that an 880 TAB chain is selected, the required working load is recalculated using the actual chain weight of 0.73 lb/ft. At point 2: P2 = 2.0 × 0.15 × [(2.0 × 0.73) + 3.92] = 1.6 lb. At point 3: P3 = [1.6 + (1.2 × 0.15 × 5.38)] × 1.20 = 3.1 lb. At point 4: P4 = 3.1 + (12 × 0.15 × 5.38) = 12.8 lb. The preliminary required working load is Pw = PKv = 12.8 × 4.0 = 51.2 lb, and the catenary tension is only 1.5 lb. The final required working load is 52.7 lb, so the 880 TAB chain is still more than adequate.

STEP 11: SELECT

A

SPROCKET SIZE

This conveyor will be running at more than 100 ft/min, so a sprocket with 11 1/2 effective teeth (23 actual teeth) is selected.

STEP 12: CALCULATE

THE


Assume that the shaft center distance is the same as the conveyor length, thus




341

Lp = 11.5 + [(24 × 15.2)/1.5] = 254.7 pitches. This is rounded up to 255 pitches.

STEP 13: CALCULATE

THE

REQUIRED POWER

The power required by this conveyor is calculated using Equation 12.12: hp = (51.2 × 217)/33,000 = 0.33 hp.

STEP 14: SELECT

THE

LUBRICATION METHOD

This conveyor is to be lubricated with soap and water.

SELECTION SOFTWARE Some manufacturers offer software to select flat-top conveyor chains. These programs eliminate much of the work in selecting flat-top conveyor chains. However, be sure to read and follow all of the cautions and restrictions that come with your software.



13 Chain Lubrication Good lubrication must be provided to obtain the longest life from a chain. Several chain manufacturers offer chains that can operate with little lubrication. Most of these chains use a sintered metal bushing or joint seal to extend the life of the factory lubrication. These chains give very good service on certain applications, but many times a standard chain with good lubrication performs very well at a lower overall cost. In drives, lubrication is as much a part of the rating as the load and speed. This is clearly shown in the horsepower tables for roller chain, engineering steel chain, and silent chain, in chapters 5, 6, and 7. In conveyors, good lubrication is needed to get long chain life and to keep the unit working properly. Effective lubrication for a chain is a matter of applying the correct lubricant where it is most needed. The main problem is getting enough clean lubricant to the bearing surfaces of pins, bushings, and rollers. This is made even more difficult by the fact that chains are moving and it is almost impossible to get direct access to the bearing surfaces. These factors apply to nearly all chains, but the details can differ widely with the type of application and the kind of chain used.

PURPOSE OF LUBRICATION Chains need good lubrication for six important reasons: • • • • • •

Lubrication Lubrication Lubrication Lubrication Lubrication Lubrication

helps prevents wear of the pin-bushing joint. cushions impact loads. dissipates heat. flushes away wear debris and other foreign materials. smoothes chain to sprocket contact. prevents rust and corrosion.

LUBRICANT CHARACTERISTICS The lubricant used for most chains should have the following characteristics: • • • •

Low enough viscosity to penetrate into the critical bearing surfaces. Enough viscosity, or suitable additives, to maintain the lubricating film under the prevailing bearing pressures. Clean and free from corrosives. Capability to maintain lubricating qualities under the prevailing operating conditions.

These requirements are usually met by a good grade of nondetergent petroleum-base oil. Detergent oils generally are not needed, but oils with antifoaming, antirust, or film-strengthening additives may be needed. Low-grade or impure oils should be avoided. Low-grade oils will not lubricate the chain effectively, and acids or abrasives in the oil may damage the chain beyond repair. Most manufacturers apply a petroleum jelly (petrolatum) or grease to the chain at the factory. Some slow-moving chains work very well with little or no lubrication added to that applied at the factory. Very heavy oils and greases should not be used to lubricate a chain in service. They are

343



344


usually too thick to penetrate into the bearing surfaces of the chain where they are most needed, and high-viscosity oils can reduce the efficiency of a chain drive. There is an exception to not using grease on chains in service. Grease can be used on large chains that have fittings to inject the grease into critical bearing areas.

LUBRICATION OF DRIVE CHAINS All of the chains used in drives have the same general lubrication needs. The horsepower tables in chapters 5, 6, and 7 show three types of lubrication. All of the tables show manual, oil bath, and oil stream lubrication. These three types of lubrication are an important part of the ratings. It is just as important to use the correct type of lubrication as it is to keep the load and speed within the limits.

LUBRICANT FLOW Figure 13-1 shows a cross section of an engineering steel drive chain. The clearances are exaggerated to show the paths that the lubricant must follow to reach the bearing areas. One can see that there are two different bearing pairs. The inside surface of the roller and the outside surface of the bushing form one pair. The inside surface of the bushing and the outside surface of the pin form the other pair. It is important to apply the oil to the upper edges of the link plates. This ensures that the oil can penetrate to the critical bearing surfaces. Figure 13-2 shows where lubricant should be applied in a drive. Lubricant should be applied to the slack span so that the clearances will be more open for oil to flow through them, and it

FIGURE 13-1 Paths of lubricant to the bearing surfaces of a chain.

FIGURE 13-2 Application of lubricant to a chain drive.



Chain Lubrication

345

TABLE 13-1 Recommended oil viscosity for various temperatures Temperature range, ˚F –50 to +50 –20 to +80 +10 to +110 +20 to +130 +30 to +140 +40 to +150

Recommended viscosity grade SAE 5 SAE 10 SAE 20 SAE 30 SAE 40 SAE 50

When the temperature range permits a choice, use the heavier grade.

should be applied to the inside of the chain loop. This is so gravity and centrifugal force help the lubricant to flow into the chain and not simply drip off.

LUBRICANT VISCOSITY Table 13-1 shows the recommended oil viscosity for various temperature ranges.

LUBRICATION TYPES FOR CHAIN DRIVES Three types of lubrication are shown in the horsepower tables for roller chain, engineering steel chain, and silent chain in chapters 5, 6, and 7. They are Type I, manual or drip lubrication. Type II, oil bath or slinger disk lubrication. Type III, oil stream lubrication. The type of lubrication recommended in the rating tables depends on the chain speed and the amount of power transmitted. The lubrication type obtained from the rating table is the minimum needed. Using a better type—for example, type III instead of type II—will usually give longer chain wear life. A better type may also be needed for harsh operating conditions. Using an inferior type of lubrication will usually reduce the chain wear life. Also, using an inferior type of lubrication can damage or destroy the chain in a very short time. Consult an ACA chain manufacturer for help if you are unsure of what lubrication to use.

MANUAL LUBRICATION Note: Manual lubrication is to be done only when the drive is stopped and power to the drive is locked out. For manual lubrication, a person applies oil to the chain with a brush or a spout can. Oil should be applied to the chain once each eight hours of operation. The time may be longer if it has been found adequate for that drive. The amount and frequency of applying oil to the chain must be sufficient to prevent a red-brown (rust) discoloration of the oil in the joints. That discoloration tells the user that the lubrication is not adequate.

DRIP LUBRICATION For drip lubrication, oil is continuously dripped onto the upper edges of the link plates, or sidebars, from a drip lubricator. The drip rate ranges from 4 to 20 or more drops per minute. The drip rate



346


FIGURE 13-3 Drip lubrication.

FIGURE 13-4 Oil bath lubrication.

must be sufficient to prevent a red-brown (rust) discoloration of the oil in the joints. Care must be taken to prevent the oil drops from being misdirected. For multiple-strand chains, a drip lubricator needs a distribution pipe to feed oil drops to all of the rows of link plates. Wick packing is normally used to distribute oil uniformly to all of the holes in the pipe. Figure 13-3 shows a drip lubricator for multiple-strand chain.

OIL BATH LUBRICATION For oil bath lubrication, a short section of the chain runs through the oil in the bottom of the chain casing. Figure 13-4 shows a chain in a casing with oil bath lubrication. The oil level should just reach the pitch line of the chain at its lowest point in operation. A long section of chain should not run through the oil bath. This can cause oil foaming and overheating.



Chain Lubrication

347

FIGURE 13-5 Slinger disk lubrication.

SLINGER DISK LUBRICATION In slinger disk lubrication, the chain operates above the oil level. A disk on one shaft picks up oil from the sump and slings it against a collector plate. The oil then flows into a trough that drops it onto the upper edges of the link plates in the lower span of the chain. Figure 13-5 shows a chain in a casing with slinger disk lubrication. The diameter of the disk should give a rim speed between 600 ft/min and 8000 ft/min. Lower speeds may not pick up the oil effectively. Higher speeds can cause oil foaming and overheating. In both oil bath and slinger disk lubrication, the temperature of the chain and oil should not be more than 180˚F. Also, the oil flow rate must be sufficient to prevent a red-brown (rust) discoloration of the oil in the joints.

OIL STREAM LUBRICATION In oil stream lubrication, a pump delivers oil under pressure to a nozzle that directs a stream or spray of oil onto the chain. Excess oil collects in the bottom of the chain casing and is returned to the pump suction reservoir. Figure 13-6 shows a typical oil stream system. The oil should be applied evenly across the entire width of the chain to ensure that oil reaches all bearing surfaces. Figure13-7 shows a cross section of a roller chain using oil stream lubrication. Again, clearances are exaggerated to show the flow of lubricant from the spray nozzle to the bearing surfaces. Oil stream lubrication is needed for chains that operate at high speeds and transmit large amounts of power. The oil stream not only lubricates the chain, it cools the chain and carries away wear debris. The minimum oil flow rate for the amount of power being transmitted is shown in Table 13-2.

CHAIN CASINGS Figure 13-8 shows a typical chain casing. Chain casings are an aid to chain lubrication. They contain the oil used to lubricate the chain. Chain casings are required for oil bath, slinger disk, and oil stream types of lubrication. They are also good for manual or drip lubrication.



348


FIGURE 13-6 Oil stream lubrication.

FIGURE 13-7 Oil distribution with oil stream lubrication.

Chain casings protect the drive from being damaged by debris or contamination. They can also serve as guards to prevent people from coming in contact with the drive. Chain casings are normally made of sheet metal and are often stiffened by steel angles or embossed ribs. They usually have access doors or panels for inspection and maintenance. Figure 13-9 is a drawing that shows the main dimensions of a chain casing. There must be ample clearance around the chain inside the casing. Otherwise the drive may run too hot and the life of the chain may be reduced. There should be at least 3 in. of clearance around the periphery of the chain and there should be at least 0.75 in. of clearance on each side of the chain. Consult an ACA chain manufacturer for details on designing a chain casing.



Chain Lubrication

349

TABLE 13-2 Flow of oil required for chain drives Horsepower Transmitted 50 100 150 200 250 300

Minimum G.P.M. of Oil Required 1/ 4 1/ 2 3/ 4 1 1 1/4 1 1/2

400 500 600 700

2 2 1/2 3 3 1/4

800 900 1000

3 3/4 4 1/4 4 3/4

1500 2000

7 10

FIGURE 13-8 Typical chain casing.

FIGURE 13-9 Chain casing dimensions.

As a chain wears, elongation accumulates in the slack span. In time, the chain sag can become large enough to strike the bottom of the casing. This can damage both the chain and the casing. Thus there must be enough clearance in the bottom of a chain casing to allow for the expected



350


FIGURE 13-10 Casing clearance to accommodate chain wear.

chain elongation. The added clearance needed to accommodate various percentages of chain wear elongation can be estimated from Figure 13-10.

TEMPERATURE INCREASE IN A CHAIN CASING When a chain casing is used, it may need to be sized for adequate heat dissipation. The temperature increase of the oil in a chain casing can be estimated using Equation 13.1: T=

50.9 HP , AK

(13.1)

where T is the temperature increase (in ˚F), HP is the transmitted power (in hp), A is the area of the casing exposed to air circulation (in ft2), K is the radiation constant (BTU/ft2h˚F). K is 2.0 for still air, 2.7 for normal free air circulation, and 4.5 for rapid air circulation. Good practice states that the operating temperature should not be more than about 180˚F (temperature increase plus ambient temperature). If the calculated temperature is more than 180˚F, one should use a larger casing or an oil cooler. Then, recalculate the temperature increase to see if the change reduced the operating temperature to 180˚F or less. A quick estimate of the temperature increase and casing area can be made using the following procedure with Figure 13-11. 1. Compute the value of x and plot point 1. 2. Draw a vertical line from the x value (point 1) to intersect the appropriate centers (point 2). 3. Draw a horizontal line from the centers (point 2) and read the projected casing area (point 3). 4. At the intersection of the appropriate HP and the horizontal line (point 4) from step 3, draw a vertical line and read the approximate casing temperature increase (point 5). The values for x can be calculated from Equation 13.2 or Equation 13.3:



Chain Lubrication

351

For standard size casings: X=

P (t + T ) + Wc + 9 6

(13.2)

For oversize casings: X = R1 + R2 + W,

(13.3)

where P is the chain pitch (in inches), t is the number of teeth on the small sprocket, T is the number of teeth on the large sprocket, Wc is the chain width (in inches), W is the casing width (in inches), R1 is the casing radius at the small end (in inches), R2 is the casing radius at the large end (in inches), and A is the exposed casing area (in ft2).

LUBRICATION OF EXPOSED DRIVE CHAINS Some chain drives are used on mobile equipment where the chain is exposed to the weather and other elements. These drives can only be lubricated manually. Most of these drives use engineering steel chain. Two typical examples are welded steel mill chains used to drive sludge collectors and heavy-duty offset sidebar chains for propel drives on power shovels. The chains used in such applications are often packed with extreme pressure grease at the factory. The purpose of this is to provide satisfactory lubrication only for the first few hours of operation. It is difficult to effectively lubricate these chains in service, and in some environments it is impractical. For example, these chains are often immersed in mud and water for a long time without being cleaned or lubricated. Chains will rust rapidly under such conditions. In addition, internal rust and accumulated dirt may clog the chain clearances so that no lubricant can enter, even if it is applied. Joint flexure may also be impaired, resulting in poor sprocket action and reduced chain life. Chains used in such applications need to be cleaned and relubricated regularly. This can greatly increase their wear life and it may prevent chain failure from poor sprocket-chain interaction. Exposed drives sometimes have to work in abrasive environments. It is always good practice to lubricate these chains. Even though the abrasive mixed with lubricating oil forms a lapping compound, lubrication is recommended because the effects of no lubrication—galling, seizing, and scoring—can destroy the chain faster than abrasive wear. Drive chains that must work where mud and dirt accumulate should be cleaned and relubricated periodically. Otherwise, caking may seal the joints, prevent effective lubrication, and lead to rapid corrosive wear.

LUBRICATION OF CONVEYOR, BUCKET ELEVATOR, AND TENSION LINKAGE CHAINS It is often difficult to lubricate chains used in conveyors, bucket elevators, and tension linkages. They normally cannot be enclosed in a chain casing or protective housing. They have to work in the open and they are exposed to spillage of the product being carried.

LUBRICANTS In most cases, oil is recommended as a lubricant for conveyor chains. The same oil that is recommended for drive chains, at the same temperature ranges, can be used for conveyor chains. Grease may be used only if it is injected into the joint through lubrication fittings on the pins,



352


bushings, or rollers. Special lubricants may be needed when the chains run in high temperatures or other unusual conditions. Lubrication for some unusual conditions is covered later in this chapter.

TYPES

OF

LUBRICATION

Manual or drip lubrication is often used for chains that work in a relatively clean atmosphere. The methods of applying lubricant are the same as for drive chains. In manual lubrication, oil is applied with a brush or spout can. In drip lubrication, oil is constantly dripped on the chain. In both cases, the oil should be applied to the upper edges of the link plates or sidebars.

CONVEYOR LUBRICATION

IN

ABRASIVE CONDITIONS

Some conveyor chains have to work in dusty or abrasive conditions. The abrasive then mixes with the oil and forms a slurry that makes the chain wear faster. Even so, conveyor chains that run in abrasive conditions should be lubricated. A chain running in abrasives usually wears faster without lubrication than with it. Wiping the abrasive off the chain with a cloth or brush before applying the oil can extend chain life. Clearing debris off the chain can be automated when drip-type oiling is used. Rotating cleaning wheels or brushes can be mounted just ahead of the drip oiler to clear the debris off the chain. When large chains run in abrasive conditions, their life can be greatly increased by lubricating them internally. Figure 13-12 shows a flanged cast roller, equipped with an oil can fitting. Oil can be added to chains with these rollers on a regular schedule. Figure 13-13 shows a cross section through chain joints where grease may be injected through grease pressure fittings in the ends of pins. Both the roller and bushing are lubricated through the pressure fitting in the end of the pin or rod. The pins or rods should be at least 5/8 in. in diameter to be drilled for grease fittings. The major advantage of lubricating chains this way is that dirt, grit, and debris are not carried into the internal clearances of the chain. The grease from the inside flushes out foreign materials. The grease and dirt usually cake to form a solid barrier against the foreign materials entering. The disadvantage is cost and the need to lubricate each joint in each chain individually, as shown in Figure 13-14. Rollers with antifriction bearings are sometimes installed on heavy-duty chains. Such a roller is shown in Figure 13-15. Such rollers may have removable caps for grease packing or may be equipped with grease pressure fittings. Rollers with antifriction bearings are normally used as outboard rollers on heavy-duty chains so they will not to be subject to sprocket impact.

LUBRICATION

OF

FLAT-TOP CONVEYOR CHAINS

A flat-top chain conveyor is basically a special type of slat conveyor. Some of the lubrication advice for other conveyor chains also applies to flat-top conveyor chains. However, many flat-top chain conveyors have features that demand special lubrication. Flat-top chain conveyors should be lubricated whenever possible as shown in Figure 13-16. Lubrication reduces friction and chain pull, and lubrication increases the life of the chain and wear strips. Lubricant Flow As with other types of chain, flat-top chain needs good lubrication in the joints. Even more important, flat-top chain conveyors need good lubrication between the top plates and the wear strips. If lubrication is allowed, be sure to get good lubrication between the top plates and the product in the accumulation section.



Chain Lubrication

353

FIGURE 13-11 Required chain casing area.

FIGURE 13-12 Roller with oil fitting.

When lubricating side-flexing flat-top chains, the lubricant must be applied at the entrance of the inside corner track. Steel side-flexing chains should always be lubricated in the corners. Figure 13-17 shows the proper locations for corner track lubrication.



354


FIGURE 13-13 Grease fittings in the end of a pin or rod.

FIGURE 13-14 Injecting grease into a fitting.

FIGURE 13-15 Roller with antifriction bearings.

Lubricants Oil-Base Lubricants Vegetable oils, mineral oils, or grease can be used with plastic or steel flat-top chains. Oil-base lubricants should be used on all steel chains whenever practical. The same oil that is used on drive chains, at the same temperature ranges, can be used on flat-top chains. Grease should be used only when it can be directed to critical points in the conveyor. If grease is used, it is also good to lubricate the chain joints separately with oil.



Chain Lubrication

355

Water-Soluble Lubricants and Soaps These are excellent lubricants that also help clean the chain. However, they usually can only be used with plastic or stainless steel chains. Water rapidly corrodes carbon steel chains. Water Only Water can be used to lubricate flat-top chain conveyors, but plain water should be used only if oil or a soap and water mix cannot be used. Water is not as good as oil or soap and water because of its higher friction and poorer cleaning ability. Water should only be used to lubricate plastic or stainless steel chains because water rapidly corrodes carbon steel chains. No Lubricant (Dry) Sometimes no lubricant can be permitted on a flat-top chain conveyor. For those cases, a lowfriction acetal chain with Nylatron corners can be used. This combination offers the lowest coefficient of friction. Carbon steel chains should not be run dry. Stainless steel chains can be run dry, but lubrication will greatly increase wear life and help reduce noise.

TYPES

OF

LUBRICATION

Manual Lubrication In manual lubrication, oil or grease is periodically brushed or sprayed on the chain, sprockets, and wear strips. For best results, manual lubrication should be applied at least once every eight hours of operation. Manual lubrication should only be used on very short, slow-moving, flat-top chain conveyors. Drip or Oil Stream Lubrication In drip lubrication, oil, soap and water, or plain water is dripped onto the chain and wear strips. As the drip rate increases, the drops turn into a stream. This is still considered to be a form of drip lubrication. Typical oil stream lubrication of a flat-top chain conveyor is shown in Figure 13-16. One must be sure that lubrication reaches all critical points in the conveyor. It is especially important to get lubrication between the chain top plates and the wear strips. Pump Lubrication In pump lubrication, lubrication is pumped through piping to the specific points in the conveyor. Pump lubrication probably is the best type of lubrication to use on long, high-speed, or curving conveyors. The piping system can direct lubrication to where it is most needed.

HIGH-TEMPERATURE LUBRICATION The first question is what is a high temperature for chains? A temperature of more than 150˚F may be considered a high temperature for many chains. This is a practical limit for standard steel and plastic chains using common petroleum lubricants. Special lubricants are usually needed when temperatures are more than 150˚F, and special chains may be needed when temperatures are more than 350˚F.

CHAIN DESIGN

AND

MATERIALS

Most plastic chains should not be used when the temperature is more than 150˚F (wet) to 180˚F (dry). Special heat-resistant plastics can be used in temperatures up to 250˚F, but only for a limited



356


FIGURE 13-16 Flat-top chain conveyor lubrication.

FIGURE 13-17 Flat-top chain corner track lubrication.

time. Most standard steel chains can be used in temperatures up to 350˚F. Extra-clearance chains are usually needed for use in temperatures from 350˚F to 500˚F, and heat-resistant stainless steel chains are suggested for temperatures above 500˚F. The user should consult an ACA chain manufacturer for more specific information about using their chains in high temperatures.



Chain Lubrication

357

HIGH-TEMPERATURE LUBRICANTS Petroleum-Based Lubricants Some petroleum-based oils and greases can work at temperatures up to about 250˚F. However, many petroleum oils should be used only at 180˚F or less. Petroleum-based lubricants rapidly break down at higher temperatures. They lose their lubricity and form carbon deposits that can prevent fresh lubricant from reaching the critical joint areas. Petroleum Oil with Solids In this case, a solid lubricant such as graphite or molybdenum disulfide (MoS2) is mixed with light petroleum oil. The fluid is used to carry the solid to points that need lubrication. The fluid is then evaporated off by heat. This type of lubricant is often used where the chain is directly exposed to a heat source (flame) and can be used in temperatures of 550˚F to 1000˚F. They are often the only types of lubricant that can be used in these very high temperatures. Petroleum oils with solids cost about twice as much as petroleum oils. Synthetic Lubricants Several types of synthetic lubricants can be used in high temperatures. Depending on the exact type, they can work in temperatures of 300˚F to as high as 700˚F. Development in this field is occurring rapidly, so it is not practical to review the available types of synthetic lubricants here. The user should consult an ACA chain manufacturer and the lubricant manufacturer for help in using synthetic lubricants in high temperatures.

FOOD GRADE LUBRICATION Many chains are used in food and beverage processing. Some chains are used to convey the product through various processing steps, others are used to drive the conveyors and other parts of the processing equipment. In these operations, leaks from a casing or drips from a chain can cause the lubricant to come in contact with the food. Thus, the chain must use a food grade lubricant to avoid contaminating the product. Many chains are also used on exposed drives on agricultural equipment. Food grade oils are sometimes used on these chains to prevent drips from contaminating the soil. Lubricant Flow and Application Chains in food processing operations are lubricated the same as any other chain drive or conveyor and the lubricant must reach the same critical areas. However, the lubricant used must be a food grade lubricant and the lubrication system must meet all sanitation requirements for food processing machinery. Lubricants The National Sanitation Foundation (NSF) classifies food grade lubricants as NSF/H1. The H1 designation applies to lubricants that may come in contact with edible product. These food grade lubricants may be either mineral (petroleum-based) oils and greases or synthetic oils and greases. Only food grade oils are discussed here because grease should not be used for lubricating a chain in service. Food grade lubricants must be nontoxic, colorless, odorless, and tasteless.



358


Mineral Oils Food grade oils may be made from technical, or USP, white mineral oil. Additives to resist wear, high bearing pressures, oxidation, and corrosion are usually blended with the base oil. Mineralbased food grade oils can be used in temperatures up to about 180˚F. Synthetic Oils Food grade oils also may be made from synthetic fluids that are not petroleum based. These oils are specially made to have better lubricity and oxidation resistance than mineral oils. Here again, additives to resist wear, high bearing pressures, oxidation, and corrosion are usually blended with the base oil. Most synthetic oils can be used in temperatures up to 250˚F, and some special synthetic food grade oils can be used in temperatures as high as 400˚F to 600˚F. Summary There are many things to consider when planning to use a food grade lubricant. Chain users should consult with both the chain manufacturer and the lubricant supplier for help with using food grade lubricants.

CONCLUSION There always are many things to consider when planning a chain lubrication system. Advances are constantly being made in chain and lubricant technology. Designers should consult an ACA chain manufacturer and a lubricant supplier for the latest information before deciding what lubrication system to use.



14 Chain Installation It is vital to set up the drive or conveyor properly and install the chain correctly to get the longest life and best performance from the chain. Almost all chain ratings are based on having sprockets that are well aligned and not excessively worn. The ratings also require that the shafts and bearings be rigidly mounted and in good condition. Also, the chain must be properly connected and mounted with the right amount of slack. Failing to do any of these things can seriously reduce the life and capacity of the drive or conveyor.

SAFETY PRECAUTIONS Serious personal injury can result if safety rules are not followed. Observe the following safety precautions when installing a chain. • • • • • •

•

Shut off the power to the equipment and lock out the power switches before installing chains. Always wear safety glasses to protect your eyes. Wear protective clothing, gloves, and safety shoes as appropriate. Support the chain to prevent uncontrolled movement of the chain or parts. Restrain shafts and sprockets from free rotation where such rotation could permit uncontrolled chain movement and cause personal injury or equipment damage. Use pressing equipment to remove or install press fit pins or link plates. Keep tooling in good condition and use it properly. If pressing equipment is not available, contact the chain manufacturer for additional guidance. Know and understand the chain construction, including the correct direction for pin removal and insertion, before connecting or disconnecting a chain.

CHAIN GUARDING Any chain can break in service from the effects of wear and exposure to the atmosphere. Sturdy guarding should be furnished to prevent personal injury or property damage. Persons often work near operating chain drives or conveyors. Guarding should be designed to prevent persons from coming in contact with the chain and sprockets during normal operation. If a chain breaks while operating on sprockets at speed, the chain can be thrown off the sprockets with considerable force. Guarding should be strong enough to contain a broken chain that may be thrown off the sprockets when operating at speed. Sometimes a broken chain can release a load. If that is possible, a brake or other restraining device should be furnished to stop and hold the load if the chain breaks.

INSTALLATION STEPS The main steps for installing a chain on a drive or a conveyor include the following: • •

Check the condition of all components. Align the shafts, sprockets, and ways.

359



360


• • • • • • •

CHECK

Prepare the chain for installation. Install the chain on the drive or conveyor. Inspect the installation. Adjust the initial chain tension. Set up the lubrication system. Check the installation for proper function. Install guards. THE

CONDITION

OF

ALL COMPONENTS

Inspect the shafts, bearings, sprockets, and guards to ensure they are in good condition. Be sure that none are excessively worn or damaged. Check all bearing mounts to be sure they are correctly positioned and secure. If the chain is not new, be sure it is clean, well lubricated, and not excessively worn or damaged. If the sprockets are not new, be sure they are not excessively worn or damaged. Criteria for inspecting shafts and bearings should be obtained from the suppliers of those components. Criteria for inspecting the chain and sprockets can be found in chapter 15.

ALIGN

THE

SHAFTS, SPROCKETS,

AND

WAYS

Align Shafts (Angular Alignment) Figure 14-1 is a drawing that shows how to align the shafts. Carefully level each shaft with a machinist’s spirit level set directly on the shaft. When multiple-strand sprockets are used, the level may be set across the teeth. Make the shafts parallel using a feeler bar. After setting to parallel, recheck the shaft levels. Repeat the adjustments until both level and alignment are satisfactory. Shafts should be aligned to within 0.050 in./ft, or 0.25 degrees for most single-strand roller chain drives and conveyors. That same limit applies to most silent chain drives up to 1-in. wide. A somewhat larger limit may be used for engineering steel drives. High-speed, high-power, and multiple-strand roller chain drives should be aligned to the limit obtained by Equation 14.1: ø = 0.00133C/pn,

(14.1)

where ø is the maximum angular misalignment (in in./ft; 0.21 in./ft ≈ 1˚), C is the drive center distance (in inches), p is the chain pitch (in inches), and n is the number of strands. Equation 14.1 also shows that angular alignment is more critical for short center distances. Consult the silent chain, engineering steel chain, or flat-top chain manufacturer for angular misalignment limits for those drives or conveyors. Align Sprockets (Axial Alignment) First, if a shaft can float axially, block the shaft in its running position before aligning the sprockets. Also, be sure to secure the sprockets against axial movement by tightening the setscrews. When preparing a conveyor with multiple strands of chain, make sure the sprockets are spaced correctly on the shafts. Figure 14-2 is a drawing that shows how to align the sprockets. The axial alignment of the sprockets may be checked with a straightedge laid against the finished surfaces on the sides of the



Chain Installation

361

FIGURE 14-1 Aligning shafts.

FIGURE 14-2 Aligning sprockets.

sprockets. Piano wire may be used if the center distance is too large to use a straightedge. Laser instruments may also be used to check sprocket alignment. The latter are especially good for checking the long center distances of conveyors. The maximum amount of axial misalignment for roller chain drives and conveyors can be obtained using Equation 14.2: δ = 0.045p,

(14.2)

where δ is the maximum axial misalignment (in inches). Consult the silent chain, engineering steel chain, or flat-top chain manufacturer for axial misalignment limits for those drives or conveyors. Align Ways or Wear Strips When preparing a conveyor, carefully align the ways axially with the sprockets. This is so the chain transfers from the ways to the sprocket smoothly without catching or binding. Most chain manufacturers can provide limits for axial alignment of the ways. Conveyor ways must also be aligned vertically with the sprockets. In most cases, the pitch line of the chain on the ways should be at or slightly above the pitch line of the chain on the sprockets (Figure 14-3). Most chain manufacturers can provide limits for vertical alignment of the ways.

PREPARE

THE

CHAIN

FOR INSTALLATION

Unroll or Uncoil the Chain and Lay It Out Remove the chain from its packaging and unroll or uncoil the chain and lay it out on a bench or on the floor. Use care to not twist or bend the chain. Inspect the Chain Compare the chain to the specifications to be sure that the chain matches what was ordered. Inspect the chain to ensure that it has not been damaged in shipment or storage. Be sure that the attachments,



362


FIGURE 14-3 Vertical sprocket alignment.

if any, are correctly positioned and aligned. Determine the correct direction of travel for offset sidebar chains or multiple strands of chain with unsymmetrical attachments. If the chains are matched in sets, be sure that the sections are placed in the correct position and sequence. Disconnect or Connect to the Correct Length If the chain is not purchased to a specific length from the factory, it usually must be disconnected and/or connected to the needed length. Many chains come in a standard 10-ft lengths. This is seldom the needed length for a drive or a conveyor, so often the chain must be disconnected to a shorter length or connected to a longer length. Very basic directions for disconnecting and connecting the several different types of chain follow. More detailed guidance may be obtained from ACA publications or the chain manufacturer. Disconnect and Connect Roller Chain These directions cover only single-strand roller chains and connecting links with slip fit cover plates. If the chain is multiple-strand roller chain or if the connecting link has a press fit cover plate, see the ACA publication Connect and Disconnect Guide for ANS Roller Chains. Additional information can also be obtained from the chain manufacturer. Disconnect

If the chain is a riveted type, grind off the pin heads on one side of a pin link. If the chain is a cottered type, remove the cotter, or cotters, in one pin link. Not doing this can damage the chain bushings when the headed pins are pressed out. If pressing equipment with appropriate tooling is available, mount the chain in a chain vise (Figure 14-4). Then press the pins out of one pin link plate (Figure 14-5). If pressing equipment is not available, the pins may be pressed out of the pin link plate with a pin extractor (Figure 14-6). The pin links removed from the chain normally are not reusable. Connect

Bring the end roller links of each section together. Inset the pins of the connecting link through the bushings of the two roller links. Slide the cover plate on the ends of the connecting pins and install the cotters or the spring clip. Then push the connecting pins back into the chain until the cover plate is snug against the retainers. Referring to Figure 3-11 and Figure 3-16 will help the user see how the connecting links go into the chain.



Chain Installation

363

FIGURE 14-4 Roller chain in a chain vise.

FIGURE 14-5 Pressing pins out of a roller chain.

Install a spring clip with the closed (solid) end toward the direction of chain travel (Figure 14-7). Spread the legs of the cotters to no more than a 90-degree angle (Figure 14-8). Spreading them more than that can damage the cotter and result in early breakage. Be sure that the joint flexes freely after the connection is finished. Disconnect and Connect Silent Chain These directions cover only silent chain with two pin joints and side guides, and using a connector with a washer. For other types of joints and connectors, and for center guide chains, see the ACA publication Connect and Disconnect Guide for Silent Chains. Additional information can also be obtained from the chain manufacturer. Disconnect

Grind off one pin head at a side link (Figure 14-9). Removing the pins without grinding off the heads will damage the chain. Then remove both the long and short pins from the joint (Figure 14-10).



364


FIGURE 14-6 Pressing a pin out of a roller chain with a pin extractor.

FIGURE 14-7 Direction to install spring clip.

FIGURE 14-8 Spread cotter. Connect

Bring the two ends of the chains together. Be sure the holes in the link plates are aligned (Figure 14-11). Insert a drilled connecting pin through the holes in the link plates (Figure 14-12). Then insert a short pin next to the drilled pin. Make sure the convex pin surfaces face each other (Figure 14-13). Put a washer over the end of the drilled pin and secure it with a roll pin or a cotter (Figure 14-14). If a cotter is used, spread the legs of the cotter to no more than a 90-degree



Chain Installation

365

FIGURE 14-9 Grind off one pin head.

FIGURE 14-10 Remove both long and short pins.

FIGURE 14-11 Bring ends together and align holes.

angle. Spreading them more than that can damage the cotter and result in early breakage. Be sure that the joint flexes freely after the connection is finished. Disconnect and Connect Engineering Steel Chain These directions cover only a few of the more common types of engineering steel chains and connectors. For types of chain or connectors not listed here, see the ACA publication Connect and Disconnect Guide for Engineering Steel and Cast Chains. Additional information can also be obtained from the chain manufacturer.



366


FIGURE 14-12 Insert drilled pin.

FIGURE 14-13 Insert short pin.

FIGURE 14-14 Put washer on pin and secure.

Many engineering steel chains are very large and the press fits of the pins in the sidebars are very heavy. Connecting such chains into strands for installation must be carefully planned. This is both for safety and to avoid damaging the chains. The forces needed to install the pins are so large that pressing equipment is usually needed to disconnect and connect these chains. Many different styles of pins are used in engineering steel chains (Figure 14-15). Be sure to find out in which direction the pin may be pressed out of the chain before disconnecting a chain.



Chain Installation

367

FIGURE 14-15 Styles of pins used in engineering steel chains.

FIGURE 14-16 Pressing pins out of straight sidebar engineering steel chain.

FIGURE 14-17 Pressing a sidebar onto the pins of a straight sidebar engineering steel chain.

Straight Sidebar Chain Disconnect

If the chain is a riveted type, grind off the pin heads on one side of an outside link. If the chain has retainers or cotter pins, remove the retainers or cotters in one outside link. Not doing this can damage the chain bushings when the headed pins are pressed out. Support the top sidebar of the outside link. Then press the pins out of the top sidebar (Figure 14-16). Connect

If the sidebar that is furnished with the connecting link is a slip fit on the pins, the connecting link can be assembled just like that for a roller chain. However, if the sidebar is a press fit on the pins, the cover plate must be pressed onto the pins. The cover plate should be pressed equally onto both pins at the same time (Figure 14-17). Then install the retainers into the connecting pins. Sometimes, when the chain pitch is long, individual connecting pins are furnished for straight sidebar engineering steel chain. When this is the case, place a drilled anvil under one hole of the



368


FIGURE 14-18 Pressing a pin into a straight sidebar engineering steel chain.

FIGURE 14-19 Pressing a pin out of an offset sidebar engineering steel chain.

loose sidebar. Carefully align the holes in both sidebars and the inside link. Insert the pin by hand as far as it will go. Carefully align any flats or keys on the pin with the corresponding recesses in the sidebar holes. Press the pin into the holes of the sidebars (Figure 14-18). Repeat the procedure at the other end of the sidebar. Finally, install the retainers into the connecting pins. Be sure that the joint flexes freely after the connection is finished. Offset Sidebar Chain Disconnect

Usually only one pin must be pressed out of an offset sidebar chain because every link is the same. If the pins are riveted or staked, grind the head off of one pin on the proper side of the chain. If the chain has retainers or cotter pins, remove a retainer or cotter pin from the proper side of the chain. Put a drilled anvil under the pin that is to be removed. Then press that pin out of the sidebars (Figure 14-19). Connect

Place a drilled anvil under the hole in the sidebar on the proper side of the chain. Carefully align the holes in both sidebars and the narrow end of the next link. Insert the pin by hand as far as it will go. Carefully align any flats or keys on the pin with the corresponding recesses in the sidebar holes. Press the pin into the holes of the sidebars (Figure 14-20). Then install the retainers into the connecting pin. Be sure that the joint flexes freely after the connection is finished. Disconnect and Connect Flat-Top Chain In many cases, the chain pin is also used as a connecting pin in flat-top chain. This is because the pins are held in place by a press fit or knurl on one end of the pin. One must know the correct direction for removing and inserting pins before disconnecting or connecting a flat-top chain.



Chain Installation

369

FIGURE 14-20 Pressing a pin into an offset sidebar engineering steel chain.

FIGURE 14-21 Pressing a pin out of steel flat-top chain.

FIGURE 14-22 Pressing a pin into steel flat-top chain. Disconnect Steel Flat-Top Chain

Many steel flat-top chains have the pin press fitted in one curl. Determine which end of the pin is in the press fit curl. Then press the pin out of the chain from the end with the press fit curl (Figure 14-21). To connect steel flat-top chain, find if the chain has a press fit curl. If so, press the straight pin into the chain from the end opposite the press fit curl (Figure 14-22). If all of the curls have the same size hole, the chain will need a shouldered connecting pin. In this case, press the pin into the chain with the smaller diameter leading (the same as for plastic chain as shown later). Be sure that the joint flexes freely after the connection is finished. Plastic Flat-Top Chain

Many plastic flat-top chains have the pin held in one barrel by a knurl on one end of the pin. Find the end of the pin with the knurl. Then press the pin out of the chain from the end opposite the knurled end (Figure 14-23). Some plastic flat-top chains have a counterbored hole on one side. Find the correct direction to insert the knurled pin, then press the pin into the chain with the knurled end trailing (Figure 14-24). Be sure that the joint flexes freely after the connection is finished.



370


FIGURE 14-23 Pressing a pin out of plastic flat-top chain.

FIGURE 14-24 Pressing a pin into plastic flat-top chain.

INSTALL CARRIERS, FLIGHTS, CROSS RODS, ETC. If the chain is to be used in a conveyor, and there are no obstructions to prevent doing so, install any carriers, flights, or cross rods on the chain now. Of course, if obstructions will not allow this, any carriers, etc. will have to be installed after the chains are installed in the conveyor.

INSTALL

THE

CHAIN

When the chain is connected to the correct length, it is ready to be installed on the drive or conveyor. All installations require three basic steps: •

• •

Place the chain on the sprockets in a drive or thread the chain into its designed path and over the sprockets in a conveyor. Make sure offset sidebar chains travel in the correct direction. Make the final connection in the chain to make it endless. Inspect the installation to be sure that the installation is complete and that the chain path is clear.

These three steps seem very simple, but there are many details to be considered in each one. The details are covered in the following paragraphs. Place the Chain on the Drive or in the Conveyor and Connect Installation and Connection Many roller and silent chains can be easily placed on the sprockets of a drive by hand. Pull the ends of the chain together around one sprocket with the rollers seated in the sprocket teeth. Hold the ends in place on the sprocket and connect the chain endless as described earlier. Figure 14-25 shows the final connection on a roller chain drive. The general procedure is the same for installing larger chains on drives, but additional equipment is often needed to install engineering steel chains, large roller chains, or very wide silent chains. A hoist may be needed to lift the chain into place. A “come-along” may be needed to pull the ends of the chain together on the sprocket. Planks or rods may be needed to support the chain between the sprockets. And clamps may be needed to hold the chain in place while the final connection is made. NOTE: Carefully follow all of the manufacturers safety warnings when using a hoist or “comealong.” Normally, one should lay out and connect the sections of a chain for conveyors on a bench or on the floor. If possible, install any flights or carriers at that time, then thread the chain into the



Chain Installation

371

FIGURE 14-25 Final connection on a roller chain drive.

conveyor. If there is a catenary section just after the head shaft, it is often good to start feeding the chain into the return run there. Be careful to pull the chain straight into the conveyor; do not twist or camber the chain. Finally, pull the ends of the chain together on the head shaft sprocket and connect the chain endless. Just as for drives, additional special equipment is usually needed to install large heavy chains on conveyors. A hoist may be needed to pull the chain into the conveyor, and clamps may be needed to hold the chain in place while the final connection is made. In very large conveyors, the chain sections may have to be connected as they are put into the conveyor, and carriers or flights may have to be installed after the chain is in the conveyor. A block and tackle or “come-along” is usually needed to pull the chain into a bucket elevator, and the final connection is usually made at the tail shaft in a bucket elevator. This is because the chain tension is lowest there. Ask the chain or machine supplier for advice on installing large chain in a conveyor or bucket elevator.

DIRECTION

OF

TRAVEL

Offset sidebar chains should be installed to run in a given direction to obtain the least pin and bushing wear. The basic idea is shown in Figure 14-26. The general rule for direction of chain travel for offset sidebar chains is as follows. The narrow or roller end of the link in the tight strand should always face the smaller sprocket. Regardless of whether it is a driver or a driven sprocket. As a roller enters or leaves a sprocket, the chain joint articulates. The smaller the sprocket, the larger the angle of articulation. When the wide or pin end of the link faces the sprocket tooth, all of the sliding between the pin and the bushing bore is under full load. Wear between the pin and the bushing bore is at a maximum. Wear elongation is more rapid in this case, and the chain will need to be replaced more often. When the narrow end of the offset link faces the sprocket, sliding also takes place between the pin and bushing bore, but the load quickly decreases between these parts as articulation starts. The full load between the sprocket tooth and the tight-side strand is transferred from roller to bushing to sidebar. Wear between the pin and the bushing bore is at a minimum. Wear elongation is less rapid in this case and the chain will need to be replaced less often. Wear elongation is probably the major reason to replace a chain. So the direction of travel that gives the least amount of wear between the pin and bushing bore should be the correct direction.



372


FIGURE 14-26 Proper direction of travel for offset sidebar chains.

When the drive ratio is not one-to-one, the narrow or roller end of the link in the tight strand should face the smaller sprocket because the angle of articulation is larger. In this case, the greater the difference in sprocket size, the more wear life may be increased. The usual drive reduces the speed. That is, the drive sprocket is smaller and turns faster than the driven sprocket. But there are many drives that increase the speed. Therefore, a rule based on driver or driven sprockets cannot be used to determine the direction of chain travel.

INSPECT

THE INSTALLATION

Inspect the newly installed equipment with care before applying power to it. This inspection should include at least the following items: • • • • • • • •

Chains must be in the proper position on the sprockets. The direction of chain travel and the direction of sprocket rotation must be correct. All chain connectors must be correctly installed. Any cotters, or other retainers, must be correctly in place and secure. All setscrews should be in place and tight. All bolts and nuts should be in place and nuts should be tight, with lock washers or other retainers as needed. The chains, including any outboard rollers, should be lubricated as needed. Other bearings related to the chain should be checked for proper lubrication. Any other factors that might hurt the operation of the chain should be checked and corrected.

ADJUST INITIAL CHAIN TENSION Drives First, turn the sprockets opposite each other to put all of the slack in one span. Put a straightedge between the two rollers that are first engaged on each sprocket in the slack span. This is the straightline distance between engagement points. Use a scale to measure the total midspan movement (AC) in the slack span (Figure 14-27).



Chain Installation

373

FIGURE 14-27 Adjusting initial tension in a chain drive.

FIGURE 14-28 Amount of chain sag in a horizontal catenary.

The total movement (AC) should be between 4% and 6% of the straight-line distance between engagement points for drives that are horizontal or inclined up to 45 degrees from horizontal. In a horizontal drive, the depth of sag is approximately 0.433 × AC. The total movement (AC) should be only 2% to 3% of the straight-line distance between engagement points for drives that are vertical or inclined more than 45 degrees from horizontal. Conveyors For horizontal conveyors, measure the sag in the catenary section shown in Figure 14-28. Put a straightedge between the last roller engaging the sprocket and the first roller on the return support (L). Then use a scale to measure the depth of sag (D). Adjust the chain tension to give the amount of sag recommended by the chain manufacturer. No sag is generally recommended for vertical conveyors and bucket elevators. Adjust the initial chain tension to the amount, and using the method, recommended by the chain manufacturer.

SETUP LUBRICATION Install and set up the lubrication system. Make sure that all reservoirs are filled. Make sure that all lines are properly connected and clear, and make sure that the lubricant is directed onto the chain as it was designed.



374

CHECK CHAIN OPERATION


AND

RUN-IN

Turn the driveshaft slowly (preferably by hand) to see that the chain works as it should. Some large machines may have to be jogged with the power on. When this is the case, be sure to follow all safety rules to protect personnel and not damage the machinery. The chain should be pulled through its path for at least one full cycle. Make sure the chain works as it is supposed to through its entire path. Check carefully to ensure that the chain works smoothly and does not catch or bind on the sprockets or in the tracks. It is good to run the chain with no load for a few hours. This seats all of the bearing surfaces and gives the lubricant an opportunity to penetrate all of the internal bearing surfaces. After this run-in period, check and retighten any fasteners as needed. Also, check and readjust the initial chain tension if needed.

INSTALL GUARDS If the chain does not run in a casing, it should be enclosed in guards to prevent personnel from being injured by coming in contact with the chain or sprockets. More information can be found in the American National Standards, ASME B15.1 and ASME B20.1. Before installing the guards, inspect them to ensure that they are not broken or damaged. Install the guards, making sure that all fasteners are in place and secure. Make sure that any safety devices, such as presence sensors and interlocks, are in the correct position and are working properly.

CONCLUSION Most standard chain applications that are installed following the directions in this chapter will give good service. However, improved methods and chains are constantly being developed. Contact your chain and sprocket supplier to get the latest information.



Inspection and 15 Chain Maintenance A good inspection and maintenance program will help most chains run better and longer. It is usually much better to correct problems found in an inspection than to have to repair the chain drive or conveyor after a breakdown. Regular inspection and maintenance often costs less than repairing breakdowns. Most chains will show signs of trouble long before a breakdown. If problems are found in a regular inspection, they can be corrected before a breakdown, reducing lost production time. Hidden damage from a breakdown is often not found during repairs. Thus, another breakdown may occur soon after repairs are made. An inspection program for each chain installation should be established and followed. A checklist of items to inspect should be made and a record of maintenance action kept. Trends can be tracked that way and the chain can be adjusted or replaced before a costly failure occurs.

SAFETY PRECAUTIONS Serious personal injury can result if safety rules are not followed. Observe the following safety precautions when inspecting, maintaining, or replacing a chain. • • • • • •

•

Shut off the power to the equipment and lock out the power switches before inspecting, adjusting, repairing, or replacing chains. Always wear safety glasses to protect your eyes. Wear protective clothing, gloves, and safety shoes as appropriate. Support the chain to prevent uncontrolled movement of the chain or parts. Restrain shafts and sprockets from free rotation where such rotation could permit uncontrolled chain movement and cause personal injury or equipment damage. Use pressing equipment to remove or install press fit pins or link plates. Keep tooling in good condition and use it properly. If pressing equipment is not available, contact the chain manufacturer for additional guidance. Know and understand chain construction, including the correct direction for pin removal and insertion, before connecting or disconnecting a chain.

INSPECTION PROGRAM All inspection programs should include the items listed below. These items apply to both drives and conveyors. • • • • • •

Inspect Inspect Inspect Inspect Inspect Inspect

for for for for for for

signs of interference. chain or sprocket damage. signs of misalignment of the shafts, sprockets, or ways. dirt or corrosion. proper lubrication. sprocket wear.

375



376


• • •

Inspect for chain wear. Inspect for correct chain initial tension. Inspect for good guarding condition.

This is a list of only the major items that should be inspected regularly. There may be more items that apply to a given application. Any other items should be added to the list. Many chain and sprocket problems are described or shown in Table 15-1. Maintenance personnel should have a copy of Table 15-1 on hand when inspecting a chain drive or conveyor. The actions that may be required to correct these problems are briefly described in Table 15-1 and are discussed later in this chapter.

INSPECTION AND MAINTENANCE OF CHAIN DRIVES INTERFERENCE Look for signs of interference between the chain or sprockets and any other parts of the machine. One sign of interference is a battered link plate or sidebar edges. Other signs of interference include battered pin ends, bent pins, and broken rollers. TABLE 15-1 Chain drive and conveyor inspection and maintenance guide



Chain Inspection and Maintenance

377

TABLE 15-1 Chain drive and conveyor inspection and maintenance guide (continued)

Rubbing between the chain or sprockets and other objects can cause unusual wear. Impact between the chain and a solid object can cause the chain to break from fatigue. Refer to Table 15-1 for more information.

CHAIN

OR

SPROCKET DAMAGE

Inspect the chain for any missing, cracked, deformed, corroded, or broken parts. If any are found, search for the cause and correct it. Then replace the entire damaged chain. Even though the rest of the chain may appear to be in good condition, there may be hidden damage. Refer to Table 15-1 for more information. Inspect the sprockets for chipped, broken, or deformed teeth. If any of these problems are found, find the cause and correct it. Then replace the damaged sprocket. Carefully inspect the other sprockets in the drive. If they show any signs of damage, consider replacing them too.

MISALIGNMENT Inspect roller chains for unusual wear on the inside of the roller link plates. Inspect engineering steel chains for unusual wear inside the narrow ends of the offset links. Inspect silent chains for



378



uneven wear across the width of the chain. Inspect all chains for signs of uneven wear of the pins from one side of the chain to the other. Refer to Table 15-1 for more information. Inspect the sprockets of roller and engineering steel chains for unusual wear on one side of the teeth. Inspect the sprockets of silent chains for uneven wear across the face of the teeth. Refer to Table 15-1 for more information.

DIRT

AND

CORROSION

Inspect the chain for dirt packed between link plates or sidebars. Also check for tight rollers or tight joints. This could indicate that dirt is packed between the rollers and bushings or that dirt is packed between the pin and bushings. Dirt in these clearance spaces can prevent lubricant from entering critical bearing areas. Refer to Table 15-1 for more information. Inspect the drive for dirt packed between the sprocket teeth and the rollers of roller or engineering steel chains. Inspect for dirt packed between the sprocket teeth and the link plates of silent chain. Dirt in these spaces can stretch the chain or damage rollers. Refer to Table 15-1 for more information. Inspect the chain for cracked link plates or sidebars. Inspect the chain for discolored or pitted parts. These are signs that the chain may have been exposed to a corrosive substance or that the lubricant has been contaminated.




379


LUBRICATION Inspect the chain for tight joints or rust around the joints. These are signs of a lubrication failure. Refer to Table 15-1 for more information. For all types of lubrication, check the type and grade of lubricant. Be sure it is the correct type and grade. For manual lubrication, make sure that the lubrication schedule is being followed and make sure that the oil is being properly applied. For drip lubrication, inspect the filling of the reservoir cups and the rate of feed. Check that the feed pipes are not clogged. Be sure that the lubricant is being directed onto the chain correctly. For bath or slinger disk systems, inspect the oil level. Make sure that there is no sludge and make sure that the lubricant is being directed onto the chain correctly. For oil stream systems, inspect the oil level in the reservoir. Check the pump drive and the delivery pressure. Make sure that there is no clogging of the piping or nozzles and make sure that the lubricant is being directed onto the chain correctly. These inspections are only to verify that the lubrication schedule and procedures are followed. They do not take the place of a proper lubrication system as described in chapter 13.



380



This table shows only some of the more common chain problems and possible causes and cures. It is only a general guide for troubleshooting. The user should always consult the chain manufacturer when a chain fails.

SPROCKET WEAR Inspect the sprockets for signs of worn teeth. As roller chain sprocket teeth wear in a drive, the teeth begin to take on a “hooked” shape. A badly worn roller chain drive sprocket is shown in Figure 15-1. Engineering steel drive sprockets wear in a similar way. Idler sprockets for roller and engineering steel chain drives wear in a different way. There is not much pressure on the working faces of the teeth on an idler sprocket. So idler sprockets usually wear at the bottom of the tooth space. A badly worn idler sprocket for roller chain is shown in Figure 15-2. When the tooth space is worn deeply enough, the chain rollers may bind against the tooth tips as they enter and leave the idler sprocket. It is very hard to measure sprocket wear directly. The sprocket teeth shown in Figure 15-1 and Figure 15-2 are very badly worn and should be replaced. But some sprockets with less wear than shown in Figure 15-1 may also need to be replaced. If a new chain sticks, clings, or binds as it disengages from a sprocket tooth, the tooth may be worn out and the sprocket may need to be replaced. If a high-speed drive is very noisy or runs rough, the sprockets may be worn badly enough that they need to be replaced. Reversing the sprocket on the shaft can sometimes extend the life of a worn sprocket. But this is only possible if the flange is centered on the hub, or if there is space to do so. Sprockets for silent chain wear in a much different way, but noise and rough running still may indicate that the sprockets are worn and need to be replaced. Contact an ACA silent chain manufacturer for more information about silent chain sprocket wear.

CHAIN WEAR Rotate two sprockets opposite each other to get a tight section of chain. Measure that tight section of chain, as shown in Figure 15-3. The section of chain that is measured should be at least 1 ft long or contain at least eight pitches of chain.




381

FIGURE 15-1 Worn roller chain drive sprocket.

In most roller and silent chain drives, the chain is considered worn out when wear elongation reaches 3%. In other words, when the measured length is 3% more than the nominal length, the chain is worn out. For example, the nominal length over 24 pitches of 1/2 -in. pitch chain is 12 in. When the measured length over 24 pitches of that chain reaches 12 in., the chain is worn out. Three-eighths of an inch is 3.1% of 1 ft. In most engineering steel chain drives, the chain is considered worn out when wear elongation reaches 4% or 5%. In drives where the large sprocket has more than 66 teeth, the allowable wear elongation may be much less than 3%. In this case, wear elongation, in percent, is limited to 200/N (where N is the number of teeth on the largest sprocket). In high-speed roller chain drives, wear elongation may be limited to 1% or less. This is due to the pin links and roller links wearing at different rates, as described in chapter 3. When the chain is worn beyond its functional limits, it must be replaced. Do not put a new roller chain or engineering steel chain on very worn sprockets. The chain tension will not be spread over several teeth (Figure 4-28). The tension will be concentrated on the final roller engaging the sprocket. That effect is shown in Figure 15-4. A new chain is also subjected to an impact load as each roller leaves the worn sprocket. This effect is shown in Figure 15-5.

CHAIN TENSION Check the initial chain tension. If the initial tension or sag is not within the recommended range, adjust it as needed. This is done just as it is for a newly installed chain. The procedure is described in chapter 14 and is illustrated in Figures 14-27 and 14-28. If the available adjustment is not large enough, the chain may have to be shortened. Engineering steel chains can be shortened by removing one link. Roller and silent chains can be shortened by



382


FIGURE 15-2 Worn roller chain idler sprocket.

FIGURE 15-3 Measuring chain for wear.

removing two links. If removing two links shortens the chain too much, an offset link may need to be installed in roller or silent chain.

GUARDING Inspect the guarding to be sure it is in good condition. Guards must not be bent or deformed so much that intended clearances are reduced. Any intended openings in the guards (mesh) must not




383

FIGURE 15-4 New roller chain on a worn sprocket.

be enlarged and the guarding must not be broken or damaged. This is especially important at or near the mounting points. Make sure that all fasteners are in good condition and secure. Be sure that any safety devices, such as presence sensors or interlocks, are in the proper position and are operating properly. If the guarding does not meet these requirements, it must be repaired or replaced.

INSPECTION AND MAINTENANCE OF CHAIN CONVEYORS AND BUCKET ELEVATORS Much of the inspection and maintenance of conveyors and bucket elevators is the same as for drives. Lubrication, sprocket wear, and chain tension are as important for conveyors as they are for drives. However, some items for conveyors are more important than for drives and those items need to be checked more closely.

INTERFERENCE Look for signs of interference between the chain or sprockets and any other parts of the machine. Check for contact between the chain and any outside objects. Most chains for conveyors and bucket elevators have attachments; carriers, flights, buckets, or crossbars may be added to the chain. These added items increase the chances for interference with a machine member or outside objects.



384


FIGURE 15-5 a -the worn tooth carries roller A well past the normal disengagement point. b - The slack span tension pulls roller A out of the “hook” on the worn tooth. c - The chain snaps back and roller B impacts the next tooth.




385

Buckets of bucket elevators can be worn and deformed, sometimes causing hang-ups. If any interference is found, it should be corrected immediately.

MISALIGNMENT Look for signs of misalignment between the chain and the sprockets and ways. Usually conveyor chains are longer than drive chains, and they are commonly used in pairs or sets. Conveyor chains also normally travel in ways or guides, so conveyors often are much more affected by misalignment. If too much misalignment is found, correct it as described in chapter 14.

DIRT

AND

CORROSION

Inspect for dirt on the chains and sprockets the same way as for drives. Also inspect for dirt buildup between the chain and tracks or guides. Chains used on conveyors usually cannot be shielded from the material they carry, nor can they be protected from their normal working conditions. Conveyor chains are often affected much more by dirt buildup because of this. Dirt or foreign material between aprons, flights, or slats can cause bending and let material leak. Continued dirt buildup can cause the aprons, flights, or slats to break. This can lead to larger materials entering the breaks and causing a conveyor wreck. If problems from dirt are found, clean the chain and conveyor as completely as possible. If that is not satisfactory, remove the chain and clean it thoroughly before putting it back in service. If conditions are extremely dirty, the chain may need to be replaced. Inspect for signs of corrosion the same way as for drives. Here again conveyor chains are usually much more affected by corrosion than drive chains because they cannot be shielded or protected. The signs of corrosion are often serious chain damage, in which case the entire chain should be replaced.

CHAIN WEAR Inspect for chain wear the same as for drives. Conveyor chains are usually longer than drive chains and conveyor chains sometimes must place objects with precision. Thus conveyor chains may not be allowed to wear as much as drive chains. The limit on wear elongation may be reduced to as little as 1% or 2%. When the chain is worn beyond its functional limit, it must be replaced. Conveyor chains are often used in pairs or sets. The difference in wear between the chains in a set can sometimes cause the conveyor to not work properly. Sometimes the difference in wear between the chains in a set can cause attachments to break. When the difference in wear between the chains in a set causes problems, the chains must be replaced as a set.

SURGE Long, very slow conveyors are sometimes subject to surge. Surge is often caused by a stick-slip condition. Better lubrication or a slight increase in speed may remedy the situation.

INSPECTION AND MAINTENANCE OF TENSION LINKAGE CHAINS Inspecting and maintaining tension linkage chains is too critical to cover here. Inspection and maintenance of leaf chains are covered in the ASME B29.8 standard. Inspection and maintenance of roller load chains for overhead hoists are covered in the ASME B29.24 standard. Guidance on inspection and maintenance of other tension linkage chains should be obtained from the chain manufacturer.



386


REPLACING AND REPAIRING CHAINS REMOVING

AND

REPLACING CHAIN

To remove a chain, find the connecting link. Remove the connecting link using the reverse procedure of installing it. If a connecting link cannot be found, disconnect the chain using the procedure described in chapter 14. The main difference is the chain must be disconnected on the drive or conveyor instead of on a bench. Install the chain using the procedure described in chapter 14. Do not put a new chain on badly worn sprockets. The impact forces may damage or destroy the chain, as described earlier.

REPAIRING CHAIN A chain can be repaired if the damage is slight and the wear is minor. Make sure that any damage is local before repairing the chain. Use repair links or sections from the original chain manufacturer and ask the manufacturer for advice on making the repair. Repairing very worn or damaged chains is not recommended. Damaged links or sections should not be replaced in a broken chain. It is very likely that there is unseen damage in the chain and that another failure may occur. Damage should only be repaired in an emergency. For example, damaged parts can be replaced to keep a vital machine running until a new chain is obtained. Also, new links are shorter than worn links and create a shock every time the new link passes over a sprocket. In chains with more than one strand, new links can cause strand mismatch. In both cases, the new link does not seat the same as the worn links on sprocket teeth. This can cause the chain to break or damage the sprockets. Single parts should not be replaced in a chain.

PROTECTING IDLE CHAINS AND SPROCKETS PROTECTING IDLE DRIVES If a chain is to be stored, remove it from the sprockets. Clean it and cover it with heavy grease and wrap it in heavy, grease-resistant paper. Store the chain where it will be protected from corrosion or damage. The sprockets may be left in place on the shafts. Cover each with heavy grease and protect them from damage. Before putting the drive in service again, thoroughly clean the chain and sprockets to remove the protective grease. Then relubricate the chain and reinstall it.

PROTECTING IDLE CONVEYORS If the chain is to be stored, remove it from the sprockets and disconnect it into sections. Then clean, coil, and apply a rust-preventive coating. Store the chain where it will be protected from corrosion or damage. The sprockets may be left in place on the shafts. Cover each with heavy grease and protect them from damage. Before putting the drive in service again, thoroughly clean the chain and sprockets to remove the protective coating. Then relubricate the chain, reconnect the sections, and reinstall it.

CONCLUSION This chapter covers only the basics of chain maintenance. Much more information can be found in other ACA and chain manufacturers’ publications. Anyone who is responsible for the maintenance of chain drives and conveyors should learn all they can and take advantage of all available information.


Standard Handbook of Chains: Chains for Power Transmission and Material Handling (Mechanical Engineering (Marcell Dekker): A Series of Textbooks and Reference Books)

Standard Handbook of Chains: Chains for Power Transmission and Material Handling,

Liquid Pipeline Hydraulics (Mechanical Engineering (Marcell Dekker): A Series of Textbooks and Reference Books)

Intermediate Heat Transfer (Mechanical Engineering (Marcell Dekker))

Mechanical Life Cycle Handbook (Mechanical Engineering (Marcell Dekker))

Mechanical Properties of Engineered Materials (Mechanical Engineering (Marcell Dekker))

Mechanical Life Cycle Handbook (Mechanical Engineering (Marcell Dekker))

Pressure Sensors (Mechanical Engineering (Marcell Dekker))

Heat Exchanger Design Handbook (Mechanical Engineering (Marcell Dekker))

Handbook of Materials Selection for Engineering Applications (Mechanical Engineering (Marcell Dekker))

Engineering Documentation Control Practices & Procedures (Mechanical Engineering (Marcell Dekker))

Designing for Product Sound Quality (Mechanical Engineering (Marcell Dekker))

Chains of Darkness, Chains of Light

Chains

Chains of Darkness, Chains of Light

Chains of Darkness, Chains of Light

Chains

Structural Analysis of Polymeric Composite Materials (Mechanical Engineering, 165) (Mechanical Engineering (Marcell Dekker))

Modeling and Simulation for Material Selection and Mechanical Design (Dekker Mechanical Engineering)

Applied Finite Element Modeling (Mechanical Engineering (Marcell Dekker))

Applied Computational Fluid Dynamics (Mechanical Engineering Series) (Dekker Mechanical Engineering)

Chains

Chains

Standards for Engineering Design and Manufacturing (Dekker Mechanical Engineering)

Steam Plant Calculations Manual (Mechanical Engineering (Marcell Dekker))

Turbomachinery: Design and Theory (Dekker Mechanical Engineering)

Principles of Biomechanics (Dekker Mechanical Engineering)

Theory of Dimensioning (Dekker Mechanical Engineering)

Damage Mechanics (Dekker Mechanical Engineering)

Chains of Command

Master of Chains

Standard Handbook of Chains: Chains for Power Transmission and Material Handling (Mechanical Engineering (Marcell Dekker): A Series of Textbooks and Reference Books)