A Practical Guide to Fibre Science

N. S. KAPLAN

A Practical Guide to Fibre Science

"This page is Intentionally Left Blank"

A Practical Guide to Fibre Science

N.S. Kaplan

ABHISHEK PUBLICATIONS QI.AN)IGARH ~ 17 (India)

All rights reserved. No part of this book may be reproduced in any form, electronically or otherwise, in print, photoprint, micro film or by any other means without written permission from the publisher.

ISBN 81-85733-42-2

ISBN : 978-81-85733-42-5

© Publishers First Edition : 2002 Published by: Abhishek Publications, S.C.O. 57-59, Sector 17-C, CHANDIGARH - 160017(lndia) Ph. 707562, Fax 0172-704668

Printed at Mehra Offset, Daryaganj, Delhi - 110002

Contents

1

l.

Textile Fibres

2.

Processing of Textile Fibres

23

3.

Cotton Fibres

93

4.

Cotton Mixing and Blowroom Operations

112

5.

Carding

122

6.

Effects of Fibre Preparation on Instrument Readings

132

7.

Length of Cotton Fibres

150

8.

Cotton Stickiness

166

9.

White Specks

183

10. Fibre Dynamics

194

II.

218

Roving Frame and Draw Frame

12. Metallic Card Clothing

234

13. Winding

248

14. Spinning Geometry

271

"This page is Intentionally Left Blank"

1 Textile Fibres Fibers are natural or chemical structures that can be spun into yarns. Yarns then can be woven, knitted, or bonded into fabrics. Fiber properties and behavior are directly related to fabric performance and care. Learning about fibers and their characteristics will help you to understand fabrics better. Four major natural fibers and 23 man-made fibers are available. Natural fibers come from plants and animals. The plant fibers-cotton and linen-are made of cellulose. Animal fibers, silk and wool, are made of protein. Two classes of man-made fibers are those adapted from cellulose (cellulosic) and those made entirely of chemicals (noncellulosic). Noncellulosic man-made fibers often are called synthetics. Each fiber is identified by a generic name. The Textile Fiber Products Identification Act that officially established the generic fiber classifications became effective in 1960. All fibers (natural or man-made), yarns, fabrics, and household textile articles (includes articles of wearing apparel, draperies,

Textile Technology

2

floorcoverings, furnishings, beddings, and other textiles customarily used in a household), are covered by this Act. Fibrous materials should possess certain properties for them to be useful as textile raw materials. Those properties which are essential for acceptance as a suitable raw material may be classified as "primary properties", while those which add specific desirable character or aesthetics to the end product and its use may be classified as "secondary properties". PRIMARY PROPERTIES

Length; length-width ratio Tenacity (strength) Flexibility (pliability) Acceptable extensibility for processing Cohesion Uniformity of properties Secondary Properties Physical shape (cross-section, surface contour, etc.) Specific gravity (influence weight, cover, etc.) Moisture regain and moisture absorption (comfort, static electricity, etc.) Elastic character - tensile and compression Thermoplasticity (softening point and heat-set character) Dyeability

Textile Fibres

3

Resistance to solvents, corrosive chemicals, microorganisms, and environmental conditions Flammability Luster PROPERTIES DESIRED FOR TEXTILE FIBERS

Apparel and Domestic application: Tenacity: 3 - 7 grams/denier Elongation at break: 10 - 35% Recovery from elongation: 100% at strains up to 5% Modulus of elasticity: 30 - 60 grams/denier Moisture absorbency: 2 - 5% Zero strength temperature (excessive creep and softening point): above 215 0 C High abrasion resistance (varies with type fabric structure) Dyeable Low flammability Insoluble with low swelling in water, in moderately strong acids and bases and conventional organic solvents from room temperature to 1000 C Ease of care INDUSTRIAL REQUIREMENTS

Tenacity: 7 - 8 grams/denier Elongation at break: 8 - 15%

4

Textile Techll%gtj

Modulus of elasticity: 80 grams/denier or more conditioned, 50 grams/denier wet Zero strength tempera ture: 250 0 C or above KEY FIBER PROPERTIES DETERMINED POLYMER COMPOSITION AND STRUCTURE:

• •

Meltwg Point

• • •

Elasticity and recovery from strain Tensile strength

•

Moisture absorption

• •

Dyeability

BY

Modulus

Density

Comfort

The ability of a fiber to withstand the rubbing or abrasion it gets in everyday use POLYESTER

Characteristics Strong Crisp, soft hand Resistant to stretching and shrinkage Washable or dry-cleanable Quick drying Resilient, wrinkle resistant excellent pleat retention (if heat set)

Textile Fibres

5

Abrasion resistant Resistant to most chemicals Because of its low absorbency, stain removal can be a problem Static and pilling problems

Major End Uses Apparel - essentially every form of clothing, dresses, blouses, jackets, separates, sportswear, suits, shirts, pants, rainwear, lingerie, childrenswear Home Fashions - curtains, draperies, floor coverings, fiber fill, upholstery, bedding. Comments - Of all the manufactured fibers, polyester is the most used. Polyester is the best washand-wear fiber. Unfortunately, because of the oversaturation of polyester 20 to 30 years ago, some consumers maintain a negative perception about the fiber. But, that is changing. As with the other manufactured fibers, new developments in polyester have created a new attitude towards manufactured fibers. This is true, not only for manufacturers and designers, but also for consumers. In addition, when polyester is blended with other dry-clean only fibers, like wool, acetate, or rayon, the durability of the blended fabric improves and, in some cases, the fabrics can even be made washable, if the percentage of polyester is high enough. RAYON

Characteristics -

Soft and comfortable

Textile Technology

6

Drapes well Highly absorbent Dyes and prints well No static, no pilling problems Fabric can shrink appreciably if washing dry-cleanonly rayon Washable or dry cleanable. Major End Uses Apparel - Blouses, dresses, jackets, lingerie, linings, millinery, slacks, sportshirts, sportswear, suits, ties, work clothes Home Fashions - bedspreads, blankets, curtains, draperies, sheets, slip covers, table cloths, upholstery. Comments - One of the major characteristics of rayon, also called viscose, centers around the care of the fabric. For those of you who have been around rayon a lot, you know that there are both washable and "dry clean only" rayons in the garments that you sell. Why are there both washable and non-washable rayons? Originally rayon was a "dry clean only" fiber. However, the fiber producers discovered that they could create washability in rayon by putting certain finishes on the surface of the fabric after it was knitted or woven. But this also added to the price. So, today many rayons in the marketplace remain untreated, and are therefore "dry clean only." It's very important to read the labels, and make the customer aware that just because he or she may have purchased a washable rayon last week, that doesn't mean

Textile Fibres

7

that all rayons are washable. Anytime a rayon garment, labeled "dry clean only," is washed, a risk is taken, and one of three things may happen. First the garment can shrink tremendously, sometimes as much as two or three sizes. Second, the garment may fade, or a printed pattern may bleed. And third, the fabric may lose its soft hand. The rayon that was once soft and drapeable may become stiff and harsh. There's also something important to remember when caring for the washable rayons. Most of the washable rayon garments today are labeled "hand wash, cool water, drip dry or dry flat." And, it's important that these directions are followed, because when rayon is wet, it actually loses 30% to 50% of its strength. So, hand washing, like the label says, is the best. The constant agitation of the washer, and tumbling of the dryer will beat the garment against the side of the washer and dryer. And, eventually this causes the fiber to break down, and shorten the life of the rayon garment. So, in order to get the maximum life out of your washable rayei garment, it's best to hand wash and drip/hang dry. ACETATE

Manufactured Fiber - cellulosic-based, made from wood pulp or cotton linters

Characteristics Luxurious appearance Crisp or soft hand

Textile Technology

8

Wide range of colors; dyes and prints well Excellent drapeability and softness Shrink, moth, and mildew resistant Low moisture absorbency, relatively fast' drying No pilling problem, little static problem Most acetate garments require dry-cleaning

Major End Uses Apparel- Blouses, dresses, linings, special occasion apparel, Home Fashions - Draperies, upholstery, curtains, bedspreads. Acetate is a "dry clean only" fiber. However, again, read the label, because many of the new acetate circular knits, that have been out on the market for a few years, are hand washable. So far, there is no washable woven acetate available in the marketplace. Comments - Acetate takes color extremely well. It is also very soft and drapable. Acetate has been blended with a wide variety of other fibers. Experimenting has also been done with different knitting and weaving techniques, which has resulted in the development of a variety of fabrics suitable for many markets. Prior to these developments, the major uses fpr acetate in apparel were as a liner in coats, jackets, blazers, etc., and as a major fabric in special occasion dresses - acetate velvets, crepes, taffetas, and satins were ideal for this market. Because of these new fabric developments, acetate has been elevated to the designer level with many major designers using acetate in their lines.

Textile Fibres

9

ACRYLIC

Characteristics Light-weight, soft, warm with a wool-like hand Dyes to bright colors with excellent fastness Outstanding wickability Machine washable, quick drying Resilient; retains shape; resists shrinkage, & wrinkles Flexible aesthetics for wool-like, cotton-like or blended appearance Excellent pleat retention Resistant to moths, oil and chemicals Superior resistance to sunlight degradation Static and pilling can be a problem Major End Uses Apparel : sweaters, socks, fleece, circular knit apparel, sportswear, childrenswear Home Fashions : Blankets, throws, upholstery, awnings, outdoor furniture, rugs/floor coverings Comments - Acrylic is a soft drapeable fabric which provides warmth without being heavy. It takes color beautifully. Although acrylic has traditionally been a fall/winter fabric, with a wonderful resemblance to wool, acrylic has recently been used in developing some light weight circular knits and blends which lend themselves to trans-seasonal dressing as well. Acrylic is comfortable to wear. It feels like wool. Yet, it is easy care and is machine washable or dry cleanable.

Textile Technology

10

LYOCELL

Characteristics Excellent strength Washable Shrink- and wrinkle-resistant Soft hand Excellent drape Absorbent Dyes and prints well

Major End Uses Apparel - dresses, suits, sportswear, pants, jackets, blouses, skirts. Home Fashions - curtains, draperies, upholstery, bedspreads, table linens, sheets, dish towels, bath towels. Comments - This is the newest cellulosic fiber, and a new brand name that you may have seen recently is Tencel®. This fiber is cellulosic, and it is very similar to rayon in appearance. The major difference between lyocell and rayon is that lyocell is much more durable and has a much stronger wet strength. It can also be machine washable and dryable. MICROFIBERS

Characteristics Ultra fine (less than 1.0 dpf), finer than the most delicate silk

Textile Fibres

11

Extremely drapeable Very soft, luxurious hand with a silken or suede touch Washable, dry cleanable Shrink-resistant High strength (except Rayon) Excellent pleat retention Insulates well against wind, rain and cold

Major End Uses Apparel - hosiery, blouses, dresses, separates, sportswear, ties, scarves, menswear, intimate apparel, activewear, swimwear, outerwear, rainwear. Home Fashions - curtains, draperies, upholstery, sheets, towels, blankets. Comments - Micro-fibers is not really a fiber unto itself. Rather, it refers to an ultra-fine fiber, which can be woven or knit into a very high quality fabric construction. Originally, when DuPont introduced the first microfiber in 1989, it was a polyester microfiber. However, today in addition to polyester microfibers, there are also nylon rhicrofibers that have become important in the pantyhose market, rayon microfibers, and acrylic microfibers. One of the important characteristics of micro fiber fabrics is that they can be woven so tightly that the fabric can't be penetrated by wind, rain, or cold. For this reason, raincoat manufacturers have become big users of polyester microfibers. Microfibers also have a wicking ability, which allows perspiration to pass through the fabriC. Microfibers are comfortable to wear.

Textile Technology

12

NYLON

Characteristics Lightweight Exceptional strength Good drapeability Abrasion resistant Easy to wash Resists shrinkage and wrinkling retentive

resilient, pleat

Fast drying, low moisture absorbency Can be precolored or dyed in a wide range of colors Resistant to damage from oil and many chemicals Static and pilling can be a problem Poor resistance to continuous sunlight Major End Uses Apparel - swimwear, activewear, intimate apparel, foundation garments, hosiery, blouses, dresses, sportswear, pants, jackets, skirts, raincoats, ski and snow apparel, windbreakers, childrenswear. Home Fashions - carpets, rugs, curtains, upholstery, draperies, bedspreads Other - Luggage, back packets, life vests, umbrellas, sleeping bags, tents. Comments - Nylon is one of the strongest fiber. For this reason it's used in garments that take a great deal of hard wear, like panty hose and swimwear.

Textile Fibres

13

The most popular fiber blend used in swimwear today is nylon and spandex. Although nylon is a very strong fiber, it has poor resistance to prolonged exposure to the sun. In addition, spandex breaks down from exposure to chlorine in pool water. Yet, there probably aren't a lot of old, worn out swimsuits being returned because the fabric has wore out. That's because the customer has learned through experience that most swimsuits, if worn a lot, won't last for much more than a season or two. So, in many cases, when a customer shops for swimwear, she may buy as many as two or three at a time in order to get herself through just one season. This is because she has come to know what to expect from these fibers. ELAST ANE FIBERS:(LYCRA) Elastane fibres, better known under their trade names, Lycra and Dorlastan, represent a further high point in the development of man-made fibres. Invented in 1937 in Germany, elastane has properties not found in nature, the most important being an extraordinary elasticity. Compared to rubber, elastane has both greater tear resistance and durability and a tension capacity two or three times greater, at a third of the weight. Elastane is used in all areas where a high degree of permanent elasticity is required, as, for example, in tights, sportswear, swimwear, corsetry, and in woven and knitted fabrics. When stretched, it always reverts to its original form. Elastane thus is a prerequisite for fashionable or functional apparel which is intended to cling to the body, while at the same time remaining comfortable.

Textile Technology

14

Elastane combines its good properties with both natural and man-made fibres. There are two principal methods used in processing elastane. One is to wrap the elastane fibre in a non-elastic thread - either natural or man-made. The resulting yarn has the appearance and feel of the outer fibre used. The second method involves using pure elastane threads, which are worked or woven into fabrics made from other fibres. The added elasticity makes such fabrics more comfortable to wear. Blends with elastane depend on the type of fabric and the end use.

Properties High performance and easy care. Elastane fibres can be stretched from four to seven times their length, reverting to their original length when the tension is relaxed. Elastane has the highest stretch tension of all textile raw materials. Two per cent elastane is enough to make trousers, for instance, retain their shape. For body-shaped silhouette and high stretch capacity, i.e. in swimwear, corsetry or sportswear, 15 - 40% elastane is used. Elastane fibres guarantee a high degree of comfort combined with great freedom of movement. In woven and knitted fabrics elastane increases shape retention and accelerates crease recovery. • Elastane is not sensitive to transpiration, make-up, cosmetics, sun cream or sea water. For example swimwear with elastane should be rinsed out after bathing. Elastane is easy to care for.

Textile Fibres

15

Major End Uses Apparel - articles where stretch is desired: athletic apparel, bathing suits, foundation garments, ski pants, slacks, hosiery, socks, belts. Comments - Lycra® is the most familiar spandex fiber, and is DuPont's bran~ name for its spandex fiber. An interesting fact about spandex is that it was developed as a substitute for rubber. And, when it was first introduced in 1959, it totally revolutionized the swimwear and foundations industry. Although it has poor strength, it stretches over 500%. So, the excellent stretch of spandex compensates for the fact that it's a weak fiber. SILK

Characteristics Soft or crisp hand Luxurious Drapes and tailors well Thinnest of all natural fibers Dyes and prints well Hand-washable or dry-cleanable Little problem with static, no pilling problem Only fair abrasion resistance Poor resistance to prolonged exposure to sunlight Major End Uses Apparel - dresses, blouses, skirts, jackets, pants, pants, scarves, ties.

Textile Technology

16

Home Fashion - curtains, draperies, upholstery.

COTTON Characteristics Comfortable Soft hand Absorbent Good color retention, prints well Machine-washable, dry-cleanable Good strength Drapes well Easy to handle and sew Major End Uses Apparel - Wide range of wearing apparel: blouses, shirts, dresses, childrenswear, activewear, separates, swimwear, suits, jackets, skirts, pants, sweaters, hosiery, neckwear. Home Fashions - curtains, draperies, bedspreads, comforters, throws, sheets, towels, table cloths, table mats, napkins FIBER BLENDS

Some reasons of blending are: To facilitate processing To improve properties

Textile Fibres

17

Abrasion resistance strength Absorbency Add bulk and warmth Hand Dimensional stability Resistance to wrinkling To produce multi-color fabrics To reduce cost MICRO FIBER

The first generation of man-made fibresneeded substantial improvements technically and commercially to establisha long lasting favourable relationship between producers and consumers.Ongoing research have produced specialty fibres such as high performencefibres, bio-degradeble fibres, antibiotic fibres, flame retardant fibres,ultrafine fibres etc. which has changed our way of life. The genuine breakthrough occured withthe introduction of micro fibre technology, originated in Japan in the early1970s. It was only subsequently that their advantages were recognised withregard to handle, napping potential and functional characteristics suchas air and moisture vapour permeability and insulation. The developmentof microfibres, the fourth generation of manmade fibres, has even surpassed the dream of Robert Hooke and made possible what for a long time was regarded as unthinkable.

18

Textile Technology

What a microfibre is: Until recently there was no exact definitionof micro fibres. Generally, microfibres refer to staple fibres, or individualfilaments within yarns, which have a finess less than 1 decitex (0.9' denier).Despite the term 'fibre' being used, it is generally applied to filamentyarns. To be classified as microfibre yarn the weight per 10,000 metres of yarn (dtex) is divided by the number of filaments (f), the result mustbe below 1 e.g. dtex 156 f 256 (=0.6). Althoughacrylic, viscose, polypropylene are available for the production of microfibres,polyester and polyamide are mainstream. The fabrics made from them car,be 100% micro fibre or in blends with wool, cotton or viscose. Microfibresare finer than the finest natural fibre i.e. silk (1 dpf =denierper filament) and are ~lso called 'microdenier' or 'ultrafine' fibres.They are so fine that a single filament of Belima X micro fibre weighingjust one pound can circle the earth, while another microfibre Tactel Micro is 60 times stronger and 15 times finer than silk. Production of microfibres: Microfibre spinning is now possible bymany of major fibre producers on their better existing equipments. However,economical production of high quality micro fibres will require significantchanges in future machine design and operation. There are two routes toproduce micro fibres i.e. Direct spinning (conventionalPOY spinning) Bi-component process (segment& Island-in-sea type) In the first method, single componenthiaments are extruded through very fine spinnerets (dia 0.2 mm or

Textile fibreI'

19

lower)and drawn at high draw ratio. However, more finer fibre cannot be producedbecause of filament breakage after extrusion. The second method involvesspinning of conventional sized bicomponent filaments and break them downinto smaller components later. Very fine super micro fibres (upto O.OOldpf) can be prod~ced using bicomponent technique.

Properties and applications The tightly woven microfibre fabrics impede water dropletsfrom penetrating but allow water vapours to permeate. Microfibres offer a great varietyof applications in fashion clothing owing to their extra softness, fullhandle, drape, comfort and easy-care properties. Tightly woven micro fibre fabrics exhibit an exceptional property of obstructing water droplets frompenetrating while allowing water vapour to escape resulting in increased comfort. Their improved water impermeability and lower air permeabilitymake micro fibre fabrics highly suitable for waterproof and windbreakerleisurewear and sportswear market. Microfibres are increasingly used forladies' fashion, outdoor wear and upholstery fields. The fineness of microfibresexcels in producing light weight, flowing drape and silk-like fabrics andtheir handle can be substantially improved by appropriate finishing e.g.emery treatment for peach-skin effect.

Characteristics problems Due to their fineness, the total surfacearea of microfibre yarn or fabric is far greater than ordinary fibres.Threfore

20

Textile Technology

larger quantity of size need to be applied to micro filament warpyarns. Since micro fibres have very small interstitches, with consequentdifficulties of size accessibility and duffusibility, desizing becomesquite difficult and costly. Microfibres have greater absorption area resultingin a dyeing rate four timt;!S higher than that of normal, which can causeunlevelness in dyeing. They also require more dyestuff than standard fibres to obtain the same depth of shade. Larger external surface means an incrreasein number of threads exposed to light which, on destruction of dye, isexpressed as lower lightfastness rating. Staple microfibres offer difficultyin carding. Technological developments: The difficulty in processing microfibrescan be overcome by proper selection of dyestuffs, using appropriate dyeingmachinery (air jet type) and choosing suitable processing parameters. Knowledge of the type of size used isvery important to optimise the desizing process. Pretreatment must be doneeither on tensionless open-width washers or in Overflow or Jet dyeing machine. Control of pH is important for optimum size removal (e.g. pH 10.5-11 forpolyacrylate size). In batch pretreatment process, material is circulatedat 90' C for 30 mins followed by hot, cold rinsing and neutralisation. The fabric is dried at 140150' C on stenter. Materials having 100% rrUcrofibrewarps or have a peach-skin effect should be pre-set at 180' C for 30 secbefore dyeing to ensure dimensional stability and finished appearance.Emerising (sueding) effect, which imparts a slightly napped, peach-likesurface and a pleasant soft handle, has grown in importance for

Textile Fibres

21

microfibrefabrics. Emerising treatment must always be carried out before pre-settingto prevent an uneven surface. Optimesed dyeing cycles can be workedout by controlling the temperature to account for the high rate of dyeingand to eliminate the risk of uneven dyeing. A slower dyebath cooling afterdyeing prevents crease formation. The most useful machine for microfibrefabric processing is a Jet dyeing machine(especially airflow type) as theyallow the fabric to develop a desirable bulk. Examples of such machineare Longclose Ventura Rapid Micro-Tech, Henriksen/Fong's AirJet Thies Luft-roto& soft stream SV etc. Proper dye selection (Le. compatible dyes) eliminatesproblems regarding build-up and fastness properties. Manufacturers likeYorkshire, leI and BASF offer new generation of dyes suitable for processingmicrofibres. An emerging technology for dyeing polyester by using supercriticalfluid (C02) was tested on polyestermicrofibre and initial trials have shown excellent levelness and fastnessof dyeing. Finishing very often consists of both mechanical and chemical treatments. Microfibres are being increasingly usedthroughout the world for various end-uses due to their fineness, high performancecharacteristics and their unique ability to be engineered for a specificrequirement. Extreme care must be taken during processing and handling(lf micro fibre fabrics. This requires specific equipment to be used whendyeing and finishing such delicate type of fabrics. Nylon is claimed tohave advantages over polyester in having a better cover, plus lower density,higher strength and abrasion resistance, where this is very important.Polyester is easier to spin and is available in

22

Textile Technology

finer filaments than nylon.Raised fabrics from polyester are somewhat easier to produce. This hasgiven polyester and economic advantage in apparel and sportswear markets.

2 Processing of Textile Fibres Mixing is the first and important process in the spinning process. Some information regarding "cotton mixing", is given below:-

Cotton mixing: Blow room is the process which takes care of opening, cleaning and blending of different fibres used in the mixing. The technological improvements are remarkable in this process. Important points are highlighted to refere please click the link

Blowroom process: High production carding has now become an established practice for short-staple fibres. Production capacity in recent carding machines can be increased substatially without deterioration in quality.

Carding process: Reading without thinking is like eating without digesting. Metallic card clothing played an important role to improve the production rates on revolving flat cards. High production card would not have been possible without the Metallic card clothing. Moreover the demand for high production and high quality from carding machine put wire manufacturers

Textile Technology

24

under pressure to improve their design continuously to meet the requirements. Modem metallic wire is designed for optimum carding performance during the processing of many tonnes of fibre at the highest proudction rates possible, and with the least amount of maintenance.

Card clothing 90 percent of your work can be done by your subordinates and you genuinely get paid only for 10 percent. Drawframe contributes less than 5% to production cost of yam. But its influence on quality is very big, because drawing is the final process of quality improvement in the spinning mill and quality of drawframe sliver determines the final yam quality.For more information please click

Drawing process Autoievelling Most problems are really the absence of ideas: Combing is the process which serves to improve the raw material.Combed yam is stronger, more uniform, has greater shine and is smoother and purer.The quality improvements are obtained at the cost of additional expenditure on machines, floor and personnel, together with a loss of rawmaterial.

Cambing process The greatest loss is the loss of self-confidence:

Processing of Textile Fibres

25

Roving bobbin is the ideal package form for supply of material to the ring spinning frame. It is very convenient for transport and storing.Eventhough drawframe produces a sliver that already exhibits all the characteristics required for making the yam, the roving frame is forced upon a spinner as a necessary evil for two reasons. They are: 1. higher draft

2. drawframe can feeding creates more problem

Speed frame Do important jobs now before they become urgent The ring spinning will continue to be the most widely used form of spinning machine in the near future, because ring spinning still offers the greatest flexibility in application and supplies yams of a quality that cannot be equalled by the new technologies owing to technological reasons.

Ring frame A pessimist finds difficulty in every opportunity, the optimist finds opportunity in every difficulty. -

Winding is the process which results in producing a good package of long length and fault free yam.

Most of the spinning mills use automatic winding machines. Quality of yam and package and winding machine production are improving day by day. The requirements of package quality and yam quality is also very high for the present knitters and weavers.

Textile Technology

26

Winding The more time spent on self improvement, the less there is to criticise others. Variables in a spinning mill is extremely high e.g., rawmaterial, atmospheric conditions in a plant type of machines, technology adopted, skill level, investment concepts, market requirements, etc. Since the variations are innumerable, it is a must to optimise the process parameters to produce a good quality yarn at a lower manufacturing cost. Some information and guidelines for fixing parameters is given in the following pages. Theory without Practice is sterile, and Practice without Theory is futile. Yarn occupies the intermediate position in the manufacture of fabric from raw material. Yarn tests are therefore essential, both for estimating the quality of the raw material and for controlling the fabric produced.

Characteristics The textile Industry uses compressed air power in some machinery or other, for instance blow room, comber, spinning frame, loom, splicers to name a few. With the use of more sophisticated, high production machinery the need for more and more complicated Pneumatic controls are necessitated. To have minimum breakdowns and reliable performance with minimum failure, in other words, to have good quality products, the compressed air supplied to the machine should be of the highest order, both in QUALITY and QUANTITY.

Processing of Textile Fibres

27

Atmospheric conditions have a decided effect on textile materials, especially during processing.For this reason it is essential that the temperature and moisture content of the air within the mill be controlled. The exact degree of temperature and relative humidity will vary depending upon the material and department.

Humidification It is better to make a first class soup than a second class

painting.

Spinning machines Blowroom Lakshmi Rieter

-

-

-

Trutzschler

-

Crosrol

Carding -

Lakshmi

-

Rieter

-

Trutzschler

-

Crosrol

-

MarzoH

Comber Lakshmi Rieter

28

Textile Technology

-

Toyoda

-

Marzoli

Draw frame Rieter Vouk Lakshmi Speed frame

-

-

Zinser

-

Toyoda

-

Marzoli

-

Lakshmi

Ring spinning Lakshmi Rieter Zinser

-

-

Suessen

-

Toyoda

Open end Schlafhorst Rieter Lakshmi

-

Winding Schlafhorst Savio

Processing of Textile Fibres

29

Textile resources • AKTRIN Textile Information Center

Importance of Rawmaterial in Yam Manufacturing Raw material represents about 50 to 70% of the production cost of a short-staple yarn. This fact is sufficient to indicate the significance of the rawmaterial for the yarn producer. It is not possible to use a problemfree raw material always, because cotton is a natural fibre and there are many properties which will affect the performance. If all the properties have to be good for the cotton, the rawmaterial would be too expensive. To produce a good yarn with this difficulties, an intimate knowledge of the raw material and its behaviour in processing is a must. Fibre characteristics must be classified according to a certain sequence of importance with respect to the end product and the spinning process. Moreover, such quantified characteristics must also be assessed with reference to the following what is the ideal value? what amount of variation is acceptable in the bale material? what amount of variation is acceptable in the final blend Such valuable experience, which allows one to determine the most suitable use for the raw material, can only be obtained by means of a long, intensified and direct association with the raw material, the spinning process and the end product. Low cost yarn manufacture, fulfilling of all quality requirements and a controlled

30

Textile Technology

fibre feed with known fibre properties are necessary in order to compete on the world's textile markets. Yarn prodcution begins with the rawmaterial in bales, whereby success or failure is determined by the fibre quality, its price and availability. Successful yarn producers optimise profits by a process oriented selection and mixing of the rawmaterial, followed by optimisation of the machine settings, production rates, operating elements, etc. Simultaneously, quality is ensured by means of a closed loop control system, which requires the application of supervisory system at spinning and spinning preparation, as well as a means of selecting the most sutable bale mix. Basic fibre characteristccs A textile fibre is a peculiar object. It has not truly fixed length, width, thickness, shape and cross-section. Growth of natural fibres or prodction factors of manmade fibres are responsible for this situation. An individual fibre, if examined carefully, will be seen to vary in cross-sectional area along it length. This may be the result of variations in growth rate, caused by dietary, metabolic, nutrientsupply, seasonal, weather, or other factors influencing the rate of cell development in natural fibres. Surface characteristics also play some part in increasing the variablity of fibre shape. The scales of wool, the twisted arrangement of cotton, the nodes appearing at intervals, along the cellulosic natural fibres etc. Following are the basic chareteristics of cotton fibre: fibre length fineness strength

Processing of Textile Fibres

31

maturity Rigidity fibre friction structural features The atmosphere in which physical tests on textile materials are performed. It has a relative humidity of 65 + 2 per cent and a temperature of 20 + 2° C. In tropical and sub-tropical countries, an alternative standard atmosphere for testing with a relative humidity of 65 + 2 per cent and a temperature of 27 + 2° C, may be used.

Fibre length The "length" of cotton fibres is a property of commercial value as the price is generally based on this character. To some extent it is true, as other factors being equal, longer cottons give better spinning performance than shorter ones. But the length of a cotton is an indefinite quantity, as the fibres, even in a small random bunch of a cotton, vary enormously in length. Following are the various measures of length in use in different countries: mean length upper quartile effective length Modal length 2.5% span length 50% span length

32

Textile Technology

Mean length It is the estimated quantity which theoretically signifies the arithmetic mean of the length of all the fibres present in a small but representative sample of the cotton. This quantity can be an average according to either number or weight.

Upper quartile length It is that value of length for which 75% of all the

observed values are lower, and 25% higher.

Effective length It is difficult to give a clear scientific definition. It may be defined as the upper quartile of a numerical length distribution eliminated by an arbitrary construction. The fibres eliminated are shorter than half the effective length.

Modal length It is the most frequently occurring length of the fibres in the sample and it is related to mean and median for skew distributions, as exhibited by fibre length, in the follwing way.

(Mode-Mean)

= 3(Median-Mean)

where, Median is the particular value of length above and below which exactly 50% of the fibres lie.

33

Processing of Textile Fibres

2.5% Span length It is defined as the distance spanned by 2.5% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using "DIGITAL FIBROGRAPH".

50% Span length It is defined as the distance spanned by 50% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using "DIGITAL FIBROGRAPH".

The South India Textile Research Association (SITRA) gives the following empirical relationships to estimate the Effective Length and Mean Length from the Span Lengths. Effective length Mean length

= 1.013 x 2.5% Span length + 4.39

= 1.242

x 50% Span length + 9.78

Fibre length variation Eventhough, the long and short fibres both contribute towards the length irregularity of cotton, the short fibres are particularly responsible for increasing the waste losses, and cause unevenness and reduction in strength in the yarn spun. The relative proportions of short fibres are usually different in cottons having different mean

Textile Technology

34

lengths; they may even differ in two cottons having nearly the same mean fibre length, rendering one cotton more irregular than the other.It is therefore important that in addition to the fibre length of a cotton, the degree of irregularity of its length should also be known. Variability is denoted by anyone of the following attributes. 1.

Co-efficient of variation of length (by weight or number)

2.

Irregularity percentage

3.

Dispersion percentage and percentage of short fibres

4.

Uniformity ratio

Uniformity ratio is defined as the ratio of 50% span length to 2.5% span length expressed as a percentage. Several instruments and methods are available for determination of length. Following are some shirley comb sorter Baer sorter A.N. Stapling apparatus Fibrograph uniformity ration == (50% span length / 2.5% span length) x 100 uniformity index == (mean length / upper half mean length) x 100

Short Fibers The negative effects of the presence of a high proportion

Processing of Textile Fibres

35

of short fibres is well known. A high percentage of short fibres is usually associated with: Increased yam irregularity and ends ddown which reduce quality and increase processing costs Increased number of neps and slubs whiich is detrimental to the yam appearance Higher fly liberation and machine conttamination in spinning, weaving and knitting operations. Higher wastage in combing and other opperations. While the detrimental effects of short fibres have been well established, there is still considerable debate on what constitutes a 'short fibre'. In the simplest way, short fibres are defined as those fibres which are less than 12 mm long. Initially, an estimate of the short fibres was made from the staple diagram obtained in the Baer Sorter method: Short fibre content

= (UB/OB)

x 100

While such a simple definition of short fibres is perhaps adequate for characterising raw cotton samples, it is too simple a definition to use with regard to the spinning process. The setting of all spinning machines is based on either the staple length of fibres or its equivalent which does not take into account the effect of short fibres. In this regard, the concept of 'Floating Fibre Index' defined by Hertel (1962) can be considered to ae a better parameter to consider the effect of short fibres on spinning performance. Floating fibres are defined as those fibres which are not clamped by either pair of rollers in a drafting zone.

36

Textile Technology Floating Fibre Index (FFI) was defined as FFI = «2.5% span length/mean length)-l)x(lOO)

The proportion of short fibres has an extremely great impact on yarn quality and production. The proportion of short fibres has increased substantially in recent years due to mechanical picking and hard ginning. In most of the cases the absolute short fibre proportion is specified today as the percentage of fibres shorter than 12mm. Fibrograph is the most widely used instrument in the textile industry, some information regarding fibrograph is given below.

Fibrograph Fibrograph measurements provide a relatively fast method for determining the length uniformity of the fibres in a sample of cotton in a reproducible manner. Results of fibrograph length test do not necessarily agree with those obtained by other methods for measuring lengths of cotton fibres because of the effect of fibre crimp and other factors. Fibrograph tests are more objective than commercial staple length classifications and also 'provide additional information on fibre length uniformity of cotoon fibres. The cotton quality information provided by these results is used in research studies and quality surveys, in checking commercial staple length classifications, in assembling bales of cotton into uniform lots, and for other purposes. Fibrograph measurements are based on the assumptions that a fibre is caught on the comb in proportion to its length as compared to toal length of all

Processing of Textile Fibres

37

fibres in the sample and that the point of catch for a fibre is at random along its length.

Fibre Fineness Fibre fineness is another important quality characteristic which plays a prominent part in determining the spinning value of cottons. If the same count of yarn is spun from two varieties of cotton, the yarn spun from the variety having finer fibres will have a larger number of fibres in its cross-section and hence it will be more even and strong than that spun from the sample with coarser fibres. Fineness denotes the size of the cross-section dimensions of the fibre. AS the cross-sectional features of cotton fibres are irregular, direct determination of the area of croo-section is difficult and laborious. The Index of fineness which is more commonly used is the linear density or weight per unit length of the fibre. The unit in which this quantity is expressed varies in different parts of the world. The common unit used by many countries for cotton is microgrammes per inch and the various airflow instruments developed for measuring fibre fineness are calibrated in this unit. Following are some methods of determining fibre fineness: gravimetric or dimensional measurements air-flow method vibrating string method Some of the above methods are applicable to single fibres while the majority of them deal with a mass of fibres. As

38

Textile Technology

there is considerable variation in the linear density from fibre to fibre, even amongst fibres of the same seed, single fibre methods are time-consuming and laborious as a large number of fibres have to be tested to get a fairly reliable average value. It should be pointed out here that most of the fineness determinations are likely to be affected by fibre maturity, which is an another important characteristic of cotton fibres.

Air-flow method The resistance offered to the flow of air through a plug of fibres is dpendent upon the specific surface area of the fibres. Fineness tester have been evolved on this principle for determininG fineness of cotton. The specific surface area which determines the flow of air through a cotton plug, is dependent not only upon the linear density of the fibres in the sample but also upon their maturity. Hence the micronaire readings have to be treated with caution particularly when testing samples varying widely in maturity. In the micronaire instrument, a weighed quantity of 3.24 gms of well opened cotton sample is compressed into a cylindrical container of fixed dimensions. Compressed air is forced through the sample, at a definite pressure and the volume-rate of flow of air is measured by a rotometer type flowmeter. The sample for Micronaire test should be well opened cleaned and thoroughly mixed( by hand fluffing and opening method). Out of the various air-flow instruments, the Micronaire is robust in construction, easy to operate and presents little difficulty as regards its maintenance.

Processing of Textile Fibres

39

Fibre maturity Fibre maturity is another important characteristic of cotton and is an index of the extent of development of the fibres. As is the case with other fibre properties, the maturity of cotton fibres varies not only between fibres of different samples but also between fibres of the same seed. The causes for the differences observed in maturity, is due to variations in the degree of the secondary thickening or deposition of cellulose in a fibre. A cotton fibre consists of a cuticle, a primary layer and secondary layers of cellulose surrounding the lumen or central canal. In the case of mature fibres, the secondary thickening is very high, and in some cases, the lumen is not visible. In the case of immature fibres, due t? some physiological causes, the secondary deposition of cellulose has not taken sufficiently and in extreme cases the secondary thickening is practically absent, leaving a wide lumen throughout the fibre. Hence to a cotton breeder, the presence of excessive immature fibres in a sample would indicate some defect in the plant growth. To a technologist, the presence of excessive percentage of immature fibres in a sample is undesirable as this causes excessive waste losses in processing lowering of the yarn appearance grade due to formation of neps, uneven dyeing, etc. An immature fibre will show a lower weight per unit length than a mature fibre of the same cotton, as the former will have less deposition of cellulose inside the fibre. This analogy can be extended in some cases to fibres belonging to different samples of cotton also. Hence it is essential to measure the maturity of a cotton sample in addition to determining its fineness, to check

40

Textile Technology

whether the observed fineness is an characteristic or is a result of the maturity.

inherent

Different methods of testing maturity Maturity ratio The fibres after being swollen with 18% caustic soda are examined under the microscope with suitable magnification. The fibres are classified into different maturity groups depending upon the relative dimensions of wall-thickness and lumen. However the procedures followed in different countries for sampling and classification differ in certain respects. The swollen fibres are classed into three groups as follows 1.

Normal: rod like fibres with no convolution and no continuous lumen are classed as "normal"

2.

Dead: convoluted fibres with wall thickness one-fifth or less of the maximum ribbon width are classed as "Dead"

3.

Thin-walled: The intermediate ones are classed as "thin-walled".

A combined index known as maturity ratio is used to express the results. Maturity ratio

= ((Normal

- Dead)/200) + 0.70

where, N - %ge of Normal fibres D - '%ge of Dead fibres

Processing of Textile Fibres

41

Maturity co-efficient Around 100 fibres from Baer sorter combs are spread across the glass slide(maturity slide) and the overlapping fibres are again separated with the help of a teasing needle. The free ends of the fibres are then held in the clamp on the second strip of the maturity slide which is adjustable to keep the fibres stretched to the desired extent. The fibres are then irrigated with 18% caustic soda solution and covered with a suitable slip. The slide is then placed on the microscope and examined. Fibres are classed into the following three categories: 1.

Mature: (Lumen width "L")/(wall thickness"W") less than 1

2.

Half mature: (Lumen width "L")/(wall thickness "W") is less than 2 and more than 1

3.

Immature: (Lumen width "L")/(wall thickness "W") is more than 2

IS

About four to eight slides are prepared from each sample and examined. The results are presented as percentage of Mature, half-mature and immature fibres in a sample. The results are also expressed in terms of "Maturity Coefficient" Maturity Coefficient = (M + 0.6H + 0.4 1)/100 Where, M is percentage of Mature fibres H is percentage of Half mature fibres I is percentage of Immature fibres If maturity coefficient is:

-

Less than 0.7, it is caJled as immature cotton

Textile Technology

42

between 0.7 to 0.9, it is called as medium mature cotton above 0.9, it is called as mature cotton There are other techniques for measuring maturity using Micronaire instrument. As the fineness value determined by the Micronaire is dependent both on the intrinsic fineness(perimeter of the fibre) and the maturity, it may be assumed that if the intrinsic fineness is constant then the Micronaire value is a measure of the maturity

Dyeing methods Mature and immature fibers differ in their behaviour towards various dyes. Certain dyes are preferentially taken up by the mature fibres while some dyes are preferentially absorbed by the immature fibres. Based on this observation, a differential dyeing technique was developed in the United States of America for estimating the maturity of cotton. In this technique, the sample is dyed in a bath containing a mixture of two dyes, namely Diphenyl Fast Red 5 BL and Chlorantine Fast Green BLL. The mature fibres take up the red dye preferentially, while the thin walled immature fibres take up the green dye. An estimate of the average of the sample can be visually assessed by the amount of red and green fibres.

Fibre Strength The different measures available for reporting fibre strength are: 1.

breaking strength

2.

tensile strength and

Processing of Textile Fibres

3.

43

tenacity or intrinsic strength

Coarse cottons generally give higher values for fibre strength than finer ones. In order, to compare strength of two cottons differing in fineness, it is necessary to eliminate the effect of the difference in cross-sectional area by dividing the observed fibre strength by the fibre weight per unit length. The value so obtained is known as "INTRINSIC STRENGTH or TENACITY". Tenacity is found to be better related to spinning than the breaking strength. The strength characteristics can be determined either on individual fibres or on bundle of fibres.

Single fibre strength The tenacity of fibre is dependent upon the following factors chain length of molecules in the, fibre orientation of molecules size of the crystallites distribution of the crystallites gauge length used the rate of loading type of instrument used and atmospheric conditions. The mean single fibre strength determined is expressed in units of "grams/tex". As it is seen the the unit for tenacity has the dimension of length only, and hence this property is also expressed as the "BREAKING LENGTH", which can be considered as the length of the specimen equivalent in weight to the breaking load. Since tex is the mass in grams of one kilometer of the specimen, the tenacity values expressed in grams/tex will correspond to the breaking length in kilometers.

44

Textile Technology

Dundle Fibre Strength In practice, fibres are not used individually but in groups, such as in yarns or fabrics. Thus, bundles or groups of fibres come into play during the tensile break of yarns or fabrics. Further,the correlation between spinning performance and bundle strength is atleast as high as that between spinning performance and intrinsic strength determined by testing individual fibres. The testing of bundles of fibres takes less time and involves less strain than testing individual fibres. In view of these considerations, determination of breaking strength of fibre bundles has assumed greater importance than single fibre strength tests.

Fibre Elongation There are three types of elongation:

Permanent elongation: the length which extended during loading did not recover during relaxation

Elastic elongation:The extensions through which the fibres does return

Breaking elongation:the maximum extension at which the yarn breaks i.e.permanent and elastic elongation together Elongation is specified as a percentage of the starting length. The elastic elongation is of deceisive importance, since textile products without elasticity would hardly be usable. They must be able to deforme, In order to withstand high loading, but they must also return to shatpe. The greater resistance to crease for wool compared to cotton arises, from the difference in their elongation. For cotton it is 6 -10% and for wool it is aroun 25 - 45%. For normal textile

Processing of Textile Fibres

45

goods, higher elongation are neither necessary nor desirable. They make processing in the spinning mill more difficult, especially in drawing operations.

Fibre Rigidity The Torsional rigidity of a fibre may be defined as the torque or twisting force required to twist 1 cm length of the fibre through 360 degrees and is proportional to the product of the modulus of rigidity and square of the area of cross-section, the constant of proportionality being dependent upon the shape of the cross-section of the fibre. The torsional rigidity of cotton has therefore been found to be very much dependent upon the gravimetric fineness of the fibres. As the rigidity of fibres is sensitive to the relative humidity of the surrounding atmosphere, it is essential that the tests are carried out in a conditional room where the relative humidity is kept constant. Fibre stiffness plays a significant role mainly when rolling, revolving, twisting movements are involved. A fibre which is too stiff has difficulty adapting to the movements. It is difficult to get bound into the yarn, which results in higher hairiness. Fibres which are not stiff enough have too little springiness. They do not return to shape after deformation. They have no longitudinal resistance. In most cases this leads to formation of neps. Fibre stiffness is dependent upon fibre substance and also upon the relationship between fibre length and fibre fineness. Fibres having the same structure will be stiffer, the shorter they are. The slendernesss ratio can serve as a measure of stiffness, slender ratio = fibre length / fibre diameter

46

Textile Technology

Since the fibres must wind as they are bound-in during yam formation in the ring spinning machine, the slenderness ratio also determines to some extent where the fibres will finish up.fine and/or long fibres in the middle coarse and/or short fibres at the yam periphery.

Trash content In additon to usuable fibres, cotton stock contains foreign matter of various kinds. This foreign material can lead to extreme disturbances during processing. Trash affects yam and fabric quality. Cottons with two different trash contents should not be mixed together, as it will lead to processing difficulties. Optimising process paramters will be of great difficulty under this situation, therefore it is a must to know the amount of trash and the type of trash before deciding the mixing. A popular trash measuring device is the Shirley Analyser, which separates trash and foreign matter from lint by mechanical methods. The result is an expression of trash as a percentage of the combined weight of trash and lint of a sample. This instrument is used: to give the exact value of waste figures and also the proportion of clean cotton and trash in the material to select the proper processing sequence based upon the trash content to assess the cleaning efficiency of each machine to determine the loss of good fibre in the sequence of opening and cleaning. Stricter sliver quality requirements led to the gradual evolution of opening and cleaning machinery leading to

Processing of Textile Fibres

47

a situation where blow room and carding machinery were designed to remove exclusively certain specific types of trash particles. This necessitated the segregation of the trash in the cotton sample to different grades determined by their size. This was achieved in the instruments like the Trash Separator and the Micro Dust Trash Analyser which could be considered as modified versions of the Shirley Analyser. The high volume instruments introduced the concept of optical methods of trash measurement which utilised video scanning trash-meters to identify areas darker than normal on a cotton sample surface. Here, the trash content was expressed as the percentage area covered by the trash particles. However in such methods, comparability with the conventional method could not be established in view of the non-uniform distribution of trash in a given cotton sample and the relatively smaller sample size to determine such a parameter. Consequently, it is yet to establish any significant name in the industry.

Raw Material as a factor affecting spinning Fineness determines how many fibres are present in the cross-section of a yam of particular linear density. 30 to 50 fibres are needed minimum to produce a yam fibre fineness influences: 1.

spinning limit

2.

yam strength

3.

yarn evenness

4.

yam fullness

48

Textile Technology

5.

drape of the fabric

6.

lustre

7.

handle

8.

productivity

Productivity is influenced by the end breakage rate and twist per inch required in the yarn. Immature fibres(unripe fibres) have neither adequate strength nor adequate longitudinal siffness. They therefore lead to the following: 1.

loss of yarn strength

2.

neppiness

3.

high proportion of short fibres

4.

varying dyeability

5.

processing difficulties at the card and blowroom

Fibre length is one among the most important characteristics. It influnces: 1.

spinning limit

2.

yarn strength

3.

handle of the product

4.

lustre of the product

5.

yarn hairiness

6.

prod uctivi ty

It can be assumed that fibres of under 4 - 5 mm will be

lost in processing(as waste and fly). fibres upto about 12 15 mm do not contribute to strength but only to fullness of the yarn. But fibres above these lengths produce the other positive characteristics in the yarn.

Processing of Textile Fibres

49

The proportion of short fibres has extremely great influence on the following parameters: 1.

spinning limit

2.

yam strength

3.

handle of the product

4.

lustre of the product

5.

yam hairiness 6.productivity

A large proportion of short fibre leads to strong fly contamination, strain on personnel, on the machines, on the work room and on the air-conditioning, and also to extreme drafting difficul ties. A uniform yam would have the same no of fibres in the cross-section, at all points along it. If the fibres themeselves have variations within themselves, then the yam will be more irregular. If 2.5% span length of the fibre increases, the yarn strength also icreases due to the fact that there is a greater contribution by the fibre strength for the yam strength in the case of longer fibres.

Neps are small entanglements or knots of fibres. There are two types of neps. They are: 1.

fibre neps and

2.

seed-coat neps.ln general fibre neps predominate, the core of the nep consists of unripe and dead fibres. Thus it is clear that there is a relationship between neppiness and maturity index. Neppiness is also dependent on the fibre fineness, because fine fibres have less longitudinal stiffness than coarser fibres.

50

Textile Technology

Nature produces countless fibres, most of which are not usable for textiles because of inadequate strength. The minimum strength for a textile fibre is approximately 6gms/tex ( about 6 kn breaking length). Since blending of the fibres into the yarn is achieved mainly by twisting, and can exploit 30 to 70% of the strength of the material, a lower limit of about 3 gms/tex is finally obtained for the yarn strength, which varies linearly with the fibre strength. Low micronaire value of cotton results in higher yarn tenacity. In coarser counts the influence of micronaire to increase yarn tenacity is not as significant as fine count. Fibre strength is moisture dependent. i.e. It depends strongly upon the climatic conditions and upon the time of exposure. Strength of cotton,linen etc. increases with increasing moisture content. The most important property inflencing yarn elongation is fibre elongation. Fibre strength ranks seconds in importance as a contributor to yarn elongation. Fibre fineness influences yarn elongation only after fibre elongation and strength. Other characters such as span length, uniformity ratio, maturity etc, do not contribute significantly to the yarn elongation.Yarn elongation increases with increasing twist. Coarser yarn has higher elongation than finer yarn. Yarn elongation decreases with increasing spinning tension. Yarn elongation is also influenced by traveller weight and high variation in twist insertion. For ring yarns the number of thin places increases, as the trash content and uniformity ratio increased For rotor yarns 50%span length and bundle strength has an ·influence on thin places.

Processing of Textile Fibres

51

Thick places in ringyarn is mainly affected by 50%span length, trash content and shor fibre content. The following expression helps to obtain the yarn CSP achievable at optimum twist multiplier with the available fibre properties. Lea CSP for Karded count = 280 x SQRT(FQI) + 700 13C Lea CSP for combed count = (280 x SQRT(FQI) + 700 13C)x(1+W)/100 where, FQI L

= LSM/F

= 50%

span length(mm)

S = bundle strength (g/tex) M = Maturity ratio measured by shirly FMT F = Fibre fineness (micrograms/inch)

= yam