1-Page View
2-Page View
Search
Table of Contents
Next
e-version
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
Heres how easy it is to use the e-version of the International Journal of Powder Metallurgy with these built-in navigation buttons Use this button to go to the previous page
Use these buttons to toggle between a 1-page view (shown below) and a view of 2 facing pages
Use this button to go to the next page
Use this button to go to the table of contents of this issue, from where you can go anywhere with a single click
Use this button to access the most powerful feature of the e-version of the Journal: the search capability. In some versions of the Adobe Reader, clicking this button will bring up the following window:
If this is the case, click on the arrow next to Find: and then click on Open Full Reader Search which will bring up the following window:
Type in the term you want to search for, click on the Search button, and the results will include every instance of the term in the current issue.
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
Previous
1-Page View
EDITORIAL REVIEW COMMITTEE P.W. Taubenblat, FAPMI, Chairman I.E. Anderson, FAPMI T. Ando S.G. Caldwell S.C. Deevi D. Dombrowski J.J. Dunkley Z. Fang B.L. Ferguson W. Frazier K. Kulkarni, FAPMI K.S. Kumar T.F. Murphy, FAPMI J.W. Newkirk P.D. Nurthen J.H. Perepezko P.K. Samal H.I. Sanderow, FAPMI D.W. Smith, FAPMI R. Tandon T.A. Tomlin D.T. Whychell, Sr., FAPMI M. Wright, PMT A. Zavaliangos INTERNATIONAL LIAISON COMMITTEE D. Whittaker (UK) Chairman V. Arnhold (Germany) E.C. Barba (Mexico) P. Beiss, FAPMI (Germany) C. Blais (Canada) P. Blanchard (France) G.F. Bocchini (Italy) F. Chagnon (Canada) C-L Chu (Taiwan) O. Coube (Europe) H. Danninger (Austria) U. Engström (Sweden) O. Grinder (Sweden) S. Guo (China) F-L Han (China) K.S. Hwang (Taiwan) Y.D. Kim (Korea) G. L’Espérance, FAPMI (Canada) H. Miura (Japan) C.B. Molins (Spain) R.L. Orban (Romania) T.L. Pecanha (Brazil) F. Petzoldt (Germany) G.B. Schaffer (Australia) L. Sigl (Austria) Y. Takeda (Japan) G.S. Upadhyaya (India) Publisher C. James Trombino, CAE
[email protected] Editor-in-Chief Alan Lawley, FAPMI
[email protected] Managing Editor James P. Adams
[email protected] Contributing Editor Peter K. Johnson
[email protected] Advertising Manager Jessica S. Tamasi
[email protected] Copy Editor Donni Magid
[email protected] Production Assistant Dora Schember
[email protected] President of APMI International Nicholas T. Mares
[email protected] Executive Director/CEO, APMI International C. James Trombino, CAE
[email protected] 2-Page View
Search
Table of Contents
Next
international journal of
powder metallurgy Contents 2 4 6 9
45/1 January/February 2009
Editor’s Note PM Industry News in Review PMT Spotlight On …Zachary Z. Zebrovious Consultants’ Corner David Whittaker
ENGINEERING & TECHNOLOGY 13 Engineering the Green State of Powder Products D. Whittaker
RESEARCH & DEVELOPMENT 19 Optimization of Metal Powder-Mixing Parameters for Chemical Homogeneity and Agglomeration N. Vlachos and I.T.H. Chang
29 Effect of Axial and Radial Metal Powder Mixing on Chemical Homogeneity and Agglomeration N. Vlachos and I.T.H. Chang
OUTSTANDING TECHNICAL PAPER: PM2008 WORLD CONGRESS 38 Development of a Dual-Phase Precipitation-Hardening PM Stainless Steel C.T. Schade, T.F. Murphy, A. Lawley and R.D. Doherty
HISTORICAL PROFILE 47 The Origin and Role of APMI International in North America’s PM Industry K.H. Roll
DEPARTMENTS 57 APMI Membership Application 58 Web Site Directory 64 Advertisers’ Index Cover: APMI Executive Director Kempton H. Roll addressing an APMI luncheon at the 1963 conference at the Sheraton-Cadillac hotel in Detroit. The International Journal of Powder Metallurgy (ISSN No. 0888-7462) is a professional publication serving the scientific and technological needs and interests of the powder metallurgist and the metal powder producing and consuming industries. Advertising carried in the Journal is selected so as to meet these needs and interests. Unrelated advertising cannot be accepted. Published bimonthly by APMI International, 105 College Road East, Princeton, N.J. 08540-6692 USA. Telephone (609) 4527700. Periodical postage paid at Princeton, New Jersey, and at additional mailing offices. Copyright © 2009 by APMI International. Subscription rates to non-members; USA, Canada and Mexico: $100.00 individuals, $230.00 institutions; overseas: additional $40.00 postage; single issues $55.00. Printed in USA by Cadmus Communications Corporation, P.O. Box 27367, Richmond, Virginia 23261-7367. Postmaster send address changes to the International Journal of Powder Metallurgy, 105 College Road East, Princeton, New Jersey 08540 USA USPS#267-120 ADVERTISING INFORMATION Jessica Tamasi, APMI International INTERNATIONAL 105 College Road East, Princeton, New Jersey 08540-6692 USA Tel: (609) 452-7700 • Fax: (609) 987-8523 • E-mail:
[email protected] Previous
1-Page View
2-Page View
Search
Table of Contents
Next
EDITOR’S NOTE
I
t’s time to celebrate on the occasion of the Golden Anniversary of APMI International. Founding Executive Director Kempton H. Roll traces the intriguing history of this unique international professional society from its birth in 1959 to the present. In his inimitable style, Kemp chronicles the events leading to the formation, growth, and importance of the society to the PM industry. This is the 16th year of the MPIF Outstanding Technical Paper Award competition. The recipients of the award, selected by the Federation’s Technical Board from the PM2008 World Congress technical program, are from the Hoeganaes Corporation and Drexel University. Their collaborative study details the development of a dual-phase precipitation-hardening stainless steel. A unique feature of the new low-cost alloy is its ability to increase in both strength and ductility on aging. We extend a welcome to David Whittaker, chair of the Journal’s International Liaison Committee, in the “Consultants’ Corner.” Topics addressed embrace future prospects for PM titanium applications and guidance to end-user designers on high-performance press-and-sinter parts. Kudos to Animesh Bose, the 2009 APMI Fellow Award recipient. A long-time professional peer, Animesh has made seminal contributions to the PM industry in powder injection molding technology, refractory metals, carbides, and hardmetals. A major collaborative project in the United Kingdom under the title “Engineering the Green State of Powder Products” has provided knowledge and insight into the net-shape forming of powder compacts by die pressing. David Whittaker’s article highlights important outcomes from the program involving six academic research groups and more than 20 industrial partners. Two articles in this issue of the Journal by Vlachos and Chang give insight into the program module on the formulation and mixing of constituent powders in relation to chemical homogeneity and agglomeration.
Alan Lawley Editor-in-Chief
Attention to global economic woes focuses primarily on financial institutions, housing, and manufacturing. In this climate, it is not surprising that projections on R&D support are less than encouraging. According to the Battelle Memorial Institute’s annual report, U.S. inflation-adjusted investment in R&D is set to fall in 2009 after a decade of uninterrupted growth, as corporations and the federal government move into a belt-tightening mode. The drop is expected to be ~1.6% in the U.S., while global R&D spending in inflation-adjusted dollars is expected to be flat in 2009. At best, the PM industry is likely to mirror these projections.
2
Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
PM INDUSTRY NEWS IN REVIEW The following items have appeared in PM Newsbytes since the previous issue of the Journal. To read a fuller treatment of any of these items, go to www.apmiinternational.org, login to the “Members Only” section, and click on “Expanded Stories from PM Newsbytes.”
Hopeful Signs in New Transmissions New transmission types offering improved fuel savings are receiving a lot of attention among automotive powertrain engineers, reports Automotive News. They include sixspeed transmissions, manuals, continuously variable, and dualclutch designs. Tungsten Bucking Price Trend Tungsten raw material prices in the U.S. have thus far remained steady but may soon be in freefall, reports American Metals Market. The reason, according to metal dealers and traders, is that demand has disappeared. Outlook Darkens GKN plc, London, UK, issued a statement about deteriorating market conditions, primarily based on new reductions from automotive customers in the last two months of the year. GKN’s global production schedules in November and December are 20 percent lower than forecast in October. Aerospace Industry Relies on Porous Metal Products Mott Corporation, Farmington, Conn., supplies porous metal products that meet stringent aerospace requirements, including the filtration for the onboard air monitoring system in the International Space Station. Important aerospace applications cover flow
4
restriction and surge protection, filtration to prevent clogging of downstream instrumentation, and pressure stabilizers and vents for sensitive environments. Hoeganaes Ending Powder Production in New Jersey Hoeganaes Corporation announced that it will close the last remaining powder production operations in Cinnaminson, New Jersey, during February 2009. The company will continue making ferrous powders at other plants in Tennessee, Pennsylvania, Germany, and Romania. Tantalum Mining Operation Suspended H.C. Starck, Goslar, Germany, announced its regrets about the decision of Talison Minerals Pty. Ltd. to halt mining at the world’s largest tantalum operation in Wodgina, Australia. The miner’s decision is based on the downturn in worldwide demand for consumer electronics, a major user of tantalum products, Starck reports. Solder Powder Business Growing in China Atomising Systems Limited, Sheffield, England, has sold a centrifugal solder powder atomizer to HuaYuan Technologies, Huizhou City, China. The unit produces lead-free tin–silver–copper powders for electronic solder pastes.
PM Sales and Earnings Rise Mask Uncertain Future Miba AG, Laarkirchen, Austria, a supplier to the international automotive industry, posted a four percent rise in sales to 298 million euros (about $405 million) for the first three quarters of its 2008 fiscal year. Earnings before interest and taxes increased from 18 million euros (about $24 million) to 32.4 million euros (about $44 million). Joint Ventures Completed North American Tungsten Corp. Ltd. (NTC), Vancouver, B.C., Canada, has finalized agreements with Tundra Particle Technologies LLC, White Bear Lake, Minn., and its sister company Tundra Composites (TC) to produce and sell commercial tungsten products made from tungsten concentrate. In addition, NTC has received a license for TC’s patented tungsten composites manufacturing process. Press Maker to Restructure ReConditioning, Manufacturing and Marketing Cincinnati Incorporated will combine its satellite facility for re-conditioning metal powder compacting presses into its 500,000 sq. ft. main manufacturing plant in Harrison, Ohio. The transition, scheduled for completion by March 31, 2009, will also include restructuring the company’s powder metal marketing and service groups. ijpm Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
PM INDUSTRY NEWS IN REVIEW
Capstan Adds PM Parts Operation Capstan Inc., Carson, Calif., has acquired the assets of the MPP–Anaheim div. of Metal Powder Products Company (MPP), report Capstan partners Mark Paullin and Chris Doughty. Operating plants in California, Massachusetts, Tennessee, and Jalisco, Mexico, Capstan is the largest individually owned PM parts company in North America. Metaldyne Reduces Costs Metaldyne Corporation, an Asahi Tec company, Plymouth, Mich., has announced actions to reduce structural costs, balance capacity with OEM vehicle production cuts, and focus on core products. The company has reduced headquarters staff, eliminated a leased facility housing its North American Chassis Products business unit, and is consolidating headquarters in one building.
Jet Sieve and Tolling Available Minox-Elcan, Mamaroneck, N.Y., offers the MLS 200 Jet Sieve for small volumes and testing dry materials from 20 to 1,000 microns. Operating with standard 8-inch sieves, the unit prevents inaccurate results due to screen blinding and dedusts statically bound fines, the company reports. PM Equipment Auction The assets of PM parts maker Falcon Diversified Manufacturing Inc. (FDM), Battle Creek, Mich., will be sold at public auction on January 28. The company was formed in 2006 by Ron Holcomb who purchased the assets of Paradigm Sintered Products while in Chapter 11 bankruptcy. ijpm
PURCHASER & PROCESSOR
Powder Metal Scrap (800) 313-9672 Since 1946
Ferrous & Non-Ferrous Metals Green, Sintered, Floor Sweeps, Furnace & Maintenance Scrap
1403 Fourth St. • Kalamazoo, MI 49048 • Tel: 269-342-0183 • Fax: 269-342-0185 Robert Lando E-mail:
[email protected] Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
5
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
SPOTLIGHT ON ...
ZACHARY Z. ZEBROVIOUS, PMT Education: BS, Industrial & Systems Engineering, Virginia Institute of Technology, 2001 MBA, University of Wisconsin–Whitewater, 2008 Why did you study powder metallurgy/particulate materials? The family tool & die business, Compacting Tooling, Inc. (CTI), is probably what started my interest in powder metallurgy (PM). After spending many of my early years working my way through the shop, moving on to working for a PM parts producer seemed like a natural progression. It was also a move towards a position that was more closely aligned with my undergraduate degree. When did your interest in engineering/ science begin? I do not recall that I had a solid interest in engineering per se until I started working in the family business. As a kid, I had a variety of different interests. I loved to build and paint scalemodel cars and airplanes, yet at the same time I also enjoyed playing a variety of sports. I was also a voracious reader at an early age. So it was hard for me to make a decision. My 8th grade yearbook listed law, medicine, and engineering as future possibilities. But once I got a chance to “get my hands dirty” and create something out of metal, while getting paid, I was hooked. What was your first job in PM? What did you do? My first job was as a janitor during high school at CTI…seriously. I pushed a broom, mopped floors, cleaned the chips out of the mills and lathes, and scraped grit off grinding tables. During the Christmas break of my freshman year in high school, I learned how to strip down the reservoir tank on an Eltee EDM machine so that I could clean out about 5 years’ worth of sludge and grime. For those who want to try it, wear elbow-length gloves…the black sludge stains the skin! I think it took a week to sweat it out. After that experi-
6
ence, I spent just about every summer and break working in the shop. I started working full-time immediately after I graduated from VT. Describe your career path, companies worked for, and responsibilities. My career path is short as I have only worked for two companies in my lifetime. I managed to work my way through the various areas of tool & die manufacturing: heat treatment, turning, milling, jig/NC grinding, OD grinding, surface grinding, finishing/lapping, inspection & CAD/CAM. After graduating from college, I moved directly into production management. I took over many of the day-to-day operations (with the help of a great team) while my father concentrated on quoting and maintaining open lines of communication with our customers. In 2004, my parents decided to retire after 34 years in the business and I made the personal decision to move on. A team of our former employees purchased the company, and I came to SSI as a process engineer. My career at SSI has kept me primarily in the fully dense and structural components business units (BUs). After completing my introductory period, I moved into the fully dense BU as their process engineer. I like to think that my experience in this department helped me to develop a solid foundation in PM concepts. With much larger shrink factors (around 7% on average), learning the nuances of density control and powder flow were important. I also received a solid introduction to the basics of metallurgy and an understanding of microstructures. With time and experience, SSI moved me into a product/process role within their structural components BU. To date, this has been a Process Engineer SSI Technologies, Inc. 3330 Palmer Drive Janesville, Wisconsin 53546 Phone: 608-373-2843 E-mail:
[email protected] Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
SPOTLIGHT ON ...ZACHARY Z. ZEBROVIOUS, PMT
perfect fit as I have been given a chance to work with low- and high-temperature sintering, multilevel pressing, secondary machining operations, and some automation projects. Also, I have been able to work with a much wider spectrum of customers. Some are automotive-oriented while others are not. And I have gained the ability to work with both foreign and domestic customers and suppliers. I truly appreciate the variety of opportunities that my current position offers. What gives you the most satisfaction in your career? I enjoy the challenge of fabricating “problem” parts and the variety of issues that my position offers. I enjoy speaking with customers and learning about how our components are integrated into their systems. Most of all, I enjoy succeeding in developing a PM part or resolving an issue with one of my components. If I did not deal with “challenges” on a daily basis I do not think that I would be in the same field. Despite the constant challenges posed by the domestic automotive
Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
industry and global competition, I find that I have enjoyed my career path thus far. List your MPIF/APMI activities. I have been somewhat lax in attending APMI International events. The Chicago Chapter does not hold a large number of meetings, so I have tried to attend those that did not interfere with my graduate school schedule. The same holds for many of the seminars that are held throughout the year. Going back to school at night has really cut back on the amount of free time in my schedule. Hopefully, I will have opportunities in the coming years to become more involved. I do enjoy reading the International Journal of Powder Metallurgy. What major changes/trend(s) in the PM industry have you seen? I have not been involved in the PM industry long enough to witness significant changes. The major trends that I have seen have involved a move towards leaner production systems with shorter lead times, increasing pressure from customers to
7
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
SPOTLIGHT ON ...ZACHARY Z. ZEBROVIOUS, PMT
reduce prices, and an ever-increasing focus on product quality and tighter tolerances. This progression seems natural as economies continue to open up globally. The trend that I am not excited about, however, is the reluctance of young people in the U.S. to consider manufacturing as a viable and rewarding career path. From my limited experience, finding and retaining talented staff with both a mechanical aptitude and a strong work ethic has become increasingly difficult to manage. In my opinion, being able to figure out the solution to this problem is what will help define and drive domestic manufacturing in the future. Why did you choose to pursue PMT certification? SSI was the primary driver behind my obtaining PMT certification, since becoming certified was one of my goals. Obtaining certification was an excellent way to lear n about PM in a short amount of time. SSI had a group of us take the ASM International PM course which did an excellent job of explaining all of the nuances involved in the technology, from powder processing to molding to the various forms of sintering. It was also an excellent crash course for the PMT certification examination. Having certification has given me confidence that I am proficient in the core areas of PM technology. Working to obtain certification has also given me the background informa-
8
tion that is essential to being a competent engineer within the PM industry. How have you benefited from PMT certification in your career? The knowledge I obtained while studying for the certification examination has been useful on a daily basis. In addition to using statistics and mathematics regularly, my job requires that I understand how powder particles flow, how they are compacted, how they react when heated, and how PM materials can be effectively machined. Certification has helped to build my knowledge base of PM principles. What are your current interests, hobbies, and activities outside of work? I have far too many hobbies and participate in far too many activities for my own good! I recently adopted my first greyhound, Titan, and am hoping to have him attempt some lure coursing events next summer. I spend time in the gymnasium weight lifting, and I enjoy running and biking. I am a tinkerer, so at any given time I usually have two or three projects going on in my house. My move to Wisconsin also introduced me to sportbikes. I found that I have an addiction to twisty roadracing tracks and the sound of an engine at 10,000 RPM! ijpm
Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
CONSULTANTS’ CORNER
DAVID WHITTAKER* Q A
How do you rate the prospects for future growth of titanium PM applications? It is tempting to simplify this answer by saying that a reduced titanium powder price is the key to such prospects. However, it is not as straightforward as that; it depends on the particular user sector and application in mind. So, let us consider a number of different potential user sectors. The automotive and general engineering sectors certainly have an active interest in the benefits that titanium alloys could offer, including high specific strength, a density ~45% less than that of steel, and corrosion resistance about four times better than that of stainless steel. With the exception of unique motorsport applications, titanium would generally have to replace the ferrous materials currently used in the target applications. In this type of application, therefore, the cost of the starting material will be absolutely paramount in determining potential cost competitiveness. Even on a cost/specific-strength basis, titanium is currently 25 times more expensive than steel! There has been considerable development activity in such applications back in the 1980s, particularly in North America. I recollect at least one SAE paper on the subject, which referred to applications that, from memory, included valve spring retainer caps and the ubiquitous connecting rod. This development activity was in part stimulated by the existence at the time of a source of a potentially low-cost titanium powder feedstock—titanium sponge fines, the by-product from a Hunter process extraction plant. When this source disappeared, so did the prospects of these developments translating into production applications. To reactivate interest in such applications, lowercost powders would certainly be required. The current costs of commercial titanium or titanium alloy powders span the range from >$320/kg for the highest grade plasma-spray-atomized powders, through
$200–$260/kg for plasma rotating electrode (PREP) and gas-atomized grades, and $65–$200/kg for titanium hydride/dehydride (Ti-HDH) grades. Although there has been reported development activity that uses Ti-HDH powder mixed with elemental or master-alloy additions as feedstock, this type of application is really waiting for one of the many emerging powder-production processes, promoted as being potentially low cost, to deliver on their potential. There was a time when one of these emerging processes, a UK invention, the FFC Cambridge electrolytic de-oxidation process, looked to be the frontrunner. This process involved electrolysis in a molten salt electrolyte to strip oxygen ions away from a cathode, made by pressing low-cost TiO2 powder, to leave titanium. At the development stage, this process promised significant energy-efficiency benefits compared with the Kroll process for titanium sponge and, as a direct powder -production process, large cost-reduction benefits. However, the process has subsequently run into scale-up problems. Achievable electrolysis rates have proven to be severely limited by the need to reduce residual oxygen content sufficiently, and to avoid unwanted reactions between the cathode and electrolyte materials that produce compounds rather than the pure metal. Also, “wasted” background current (associated with electron conduction through the electrolyte) has meant that the achievable energy efficiency to date has only beaten that of the Kroll process by a factor of about two, rather than the factor of six or seven originally envisaged. The emerging U.S. process that must be rated as being closest to commercial reality is the Armstrong process developed by International T itanium
*Consultant, David Whittaker & Associates, 231 Coalway Road, Merryhill, Wolverhampton WV3 7NG, UK; Phone: 44 1902 338498; E-mail:
[email protected] Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
9
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
CONSULTANTS’ CORNER
Powder, L.L.C., which relies on the reduction of TiCl4 with molten sodium. There is a now a strong development focus on the application of this powder type. Now, let us turn to other user sectors, where issues other than the material cost are dominant (although, of course, even these sectors would welcome the availability of lower-cost powders as long as they satisfy attendant quality requirements). In the aerospace sector, both airplane engine and airframe manufacturers are expressing an interest in PM titanium-alloy components. The driving force here is the need for cost reductions in components that are already specified as titanium-alloy products and are currently machined from wrought titaniumalloy feedstock. Such components currently exhibit low material- utilization rates, with “fly-to-buy” ratios often being 4, the design parameter has a significant effect on the quality characteristic. Also, the right-hand columns in Tables III and IV give the percentage *Statistically, the F test (named after Fisher) is used to determine which design parameters have a significant effect on the quality characteristic. The F-ratio is the ratio of mean square error to residual, and is traditionally used to determine the significance of a factor.
24
Figure 7. Combination of BSE and X-ray map, (a) 35 v/o fill ratio, 30 rpm mixing speed, 20 min mixing time, and (b) 50 v/o fill ratio, 20 rpm mixing speed, 5 min mixing time
Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
Previous
1-Page View
2-Page View
Search
Next
Table of Contents
OPTIMIZATION OF METAL POWDER-MIXING PARAMETERS FOR CHEMICAL HOMOGENEITY AND AGGLOMERATION
where nm is the total mean S:N, ni′ is the mean S:N at the optimal level and n is the number of the main design parameters that affect the quality characteristic. It is obvious from Table III that mixing speed (factor B) and time (factor C) significantly affect the standard deviation of the chemical volume ratio of ferrosilicon to iron. Also, it can be seen in Table IV that the strongest influence on the average number of particles in each aggregate is exerted by the volume-fill ratio of the double-cone mixer/blender (factor A), mixing speed (factor B), and the interaction between the volume-fill ratio and mixing time (A*C). The level average response can be based upon the S:N data. The analysis is performed by averaging the S:N of each level of each factor and plotting the values in graphical form. The level average responses from plots based on the S:N data help to optimize the objective function under study. The peak points in these plots correspond to the optimum condition. The responses of S:N values for control factors are displayed in Tables V and VI, and the level average response plots for various quality characteristics based upon the S:N are shown in Figure 8. Based on the S:N average effect response (Table V and Figure 8 (b)) and ANOVA analysis, the optimal testing parameters for the standard deviation of the chemical volume ratio of ferrosilicon to iron, were the mixing speed at level 3 and mixing time at level 3. Thus, the optimum mixing condition is 30 rpm rotation speed in the double-cone mixer/blender, 45 min mixing time, with any fill ratio (as noted previously, the fill ratio does not influence the standard deviation). Consequently, the factors B3 and C3, which are significant, are used to calculate the standard deviation of the chemical volume ratio of ferrosilicon to iron at the optimum conditions. This was done using equation (3), and found to be 2.260. Similarly, Table IV shows the ANOVA results with respect to the number of particles in each aggregate. Based on the S:N response in Table VI, the level average response plots (Figure 8(a)) and ANOVA analysis, the optimal testing parameters for the average number of particles in each aggregate, are the volume-fill ratio of the double-cone mixer/blender at level 3 (factor A), mixing speed at level 1 (factor B), and the interaction (A*C) between the volume-fill ratio and the mixing time at level 1. Thus, the optimum mixing condition is Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
TABLE III. ANALYSIS OF VARIANCE FOR S:N VALUES OF CHEMICAL SEGREGATION Source
Filling Ratio Speed (rpm) Time (min) Filling Ratio*Speed Filling Ratio*Time Speed*Time Residual Error Total
Degree of Freedom (DOF)
Sum of Squares
Mean of Squares
F
Contribution (%)
2 2 2 4 4 4 8 26
5.669 31.683 31.268 24.885 22.583 28.286 30.707 175.081
2.834 15.842 15.634 6.221 5.646 7.071 3.838
0.74 4.13 4.07 1.62 1.47 1.84
3.238 18.096 17.859 14.213 12.899 16.156 17.539 100
TABLE IV. ANALYSIS OF VARIANCE FOR S:N VALUES OF AVERAGE NUMBER OF PARTICLES IN EACH AGGREGATE Source
Filling Ratio Speed (rpm) Time (min) Filling Ratio*Speed Filling Ratio*Time Speed*Time Residual Error Total
Degree of Freedom (DOF)
Sum of Squares
Mean of Squares
F
Contribution (%)
2 2 2 4 4 4 8 26
12.073 7.208 2.222 4.431 14.314 8.553 7.101 55.903
6.0365 3.6041 1.1112 1.1078 3.5785 2.1383 0.8876
6.80 4.06 1.25 1.25 4.03 2.41
21.596 12.894 3.975 7.926 25.605 15.300 12.702 100
TABLE V. AVERAGE EFFECT RESPONSE FOR S:N ON CHEMICAL SEGREGATION* (A) (B) (C) Filling Blending Blending (A*B) Ratio Speed (rpm) Time (min) Level 1 -10.180 Level 2 -9.243 Level 3 -10.247 Min-Max 1.004 Rank 6
-10.109 -11.094 -8.468 2.626 1
(A*C)
-11.128 -9.066 -9.230 -10.037 -11.121 -9.447 -8.505 -9.484 -10.993 2.623 2.055 1.763 2 4 5
(B*C) No. of Revolutions -8.459 -10.672 -10.540 2.213 3
*Standard deviation TABLE VI. AVERAGE EFFECT RESPONSE FOR S:N ON AGGLOMERATION (A) (B) (C) Filling Blending Blending (A*B) Ratio Speed (rpm) Time (min) Level 1 Level 2 Level 3 Min-Max Rank
-7.943 -6.779 -6.363 1.580 1
-6.354 -7.610 -7.121 1.256 2
-7.331 -6.643 -7.110 0.688 6
(A*C)
-6.502 -6.464 -7.123 -6.696 -7.459 -7.924 0.957 1.460 5 3
(B*C) No. of Revolutions -6.759 -7.699 -6.626 1.073 4
25
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
OPTIMIZATION OF METAL POWDER-MIXING PARAMETERS FOR CHEMICAL HOMOGENEITY AND AGGLOMERATION
Figure 8. (a) Level average response graphs for S:N and chemical segregation, (b) Level average response graphs for S:N and average number of particles in each aggregate
a 65 v/o fill ratio for the asymmetrical doublecone mixer/blender, 15 rpm rotation speed, with any mixing time (fill ratio does not influence the average number of particles in each aggregate). Factors A3, C1, and A*C1, which are significant, are used to calculate the average number of particles in each aggregate using equation (3), which is 1.804. If only the main factors are taken into account, i.e., A3 (= 65 v/o fill ratio), B2 (20 rpm rotation speed), and C1 (= 10 min mixing time), the average number of particles in each aggregate is 1.841. The first calculation yielded a smaller value, confirming that the revised optimum is superior. DISCUSSION Rotational Speed A detailed statistical analysis is performed on the effect of cohesive/free-flowing powders in a
26
non-uniform binary system consisting of particles of different sizes. It is shown that the homogeneity and the size of the agglomerates of the free-flowing/cohesive mixtures are a function of mixing rotational speed, namely, facilitating better mixing properties with a small increasing size of aggregates at higher rotational speeds. For small particles or cohesive powders, cohesive forces (attributed primarily to van der Waals interactions for intimate contact) between particles become comparable with particle weights, and small particles can stick to one another in relatively rigid aggregates. According to Chaudhuri et al.,19 the velocity profile of intensely cohesive material shows that single particles do not flow independently; rather, groups of particles act together when force is applied to the entire mass (avalanching). Thus, no mixing is observed. Instead, a cohesive material layer pushes the freeflowing layer and the constituents remain segregated. Also, the cohesive material forms a band and tends to flow coherently in the same direction, hindering the mixing process and creating large agglomerates.19 Higher tumbler speeds (30 rpm) transmit more shear to the system, breaking up the coherent particle bonds, resulting in improved mixing. According to Brone and Muzzio, 1 and Sudah, Coffin-Beach and Muzzio,20 this is because, at rotation rates >10 rpm, the dynamic angle of repose increases and the cascading surface (the region where the material is in rapid flow driven by gravity) becomes curved, with the curvature increasing as the rotational rate is increased, becoming S-shaped.1,20 Consequently, at 30 rpm particles entering the cascading zone of the mixer have enough inertia to separate slightly from the bulk surface and follow free-fall trajectories until they reach (approximately) the center of the mixer and break the aggregates of cohesive material. In addition, as the rotational speed increases, the cascading surface is larger. In general, a larger cascading surface should increase the number of particles in the mixing zone and improve mixing quality. According to Shinbrot, Zeggio and Muzzio21 and Alexander et al.,22–23 at low rotational speeds, trajectory segregation induced by surface flow separates large and small particles. At this location, the mixture of large and small particles enters a bend in the flow, and large particles travel further in the original flow direction before turning. Also, Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
OPTIMIZATION OF METAL POWDER-MIXING PARAMETERS FOR CHEMICAL HOMOGENEITY AND AGGLOMERATION
large particles have a tendency to flow outward more readily than smaller particles (larger particles have more inertia and less sur face friction/unit mass). Thus, at low rotational speeds, pattern formation is characterized by separation of components into an inner band of smaller particles surrounded by an outer band of larger particles. With low rotational speeds, there is a tendency to increase size segregation and consequently increase chemical segregation in a non-uniform binary system. At higher tumbler rotational speeds, particle velocities increase mixture crashes into the wall, breaking the cohesiveness of fine particles. Large particles again move towards the surface, but travel faster downwards. The large particles reach the bottom of the granular cascade with less outward displacement than in slower tumblers, and they recoil further inward than smaller particles when they reach the container wall. Thus, small particles percolate through the mix while large particles remain on the surface. Moreover, for finer, more cohesive particles (1 if there are real differences. Taguchi Method The aim of the Taguchi approach is to identify the best product or process characteristic that minimizes sensitivity to noise. The Taguchi design can be used to define the effect of mixing conditions on characteristic properties and the best combination of conditions.24,25 This simple and systematic approach is used to optimize design for performance, quality and cost. 13,14 In the Taguchi approach, orthogonal arrays and ANOVA are used as the analytical tools. ANOVA can estimate the effect of a factor on the characteristic properties, and experiments can be performed with minimum replication, using the orthogonal arrays. Conventional statistical experimental design can determine the optimal conditions on the basis of the measured values of the characteristic properties, while the Taguchi method can determine the experimental conditions resulting in the least variability from the optimal condition. The variability is expressed by signal-to-noise ratio (S:N). The terms “signal” and “noise” represent the desirable and undesirable values for the output characteristic, respectively. The Taguchi method uses the S:N value to measure the quality characteristic deviating from the desired value. The experimental condition having the maximum S:N is considered as the optimal condition as the variability characteristics are inversely proportional to the S:N.13,14 There are three categories of quality characteristics in the analysis of the S:N, namely, “thelower -the-better,” “the-higher -the-better,” and “the-nominal-the better.”24,25 In this study, thelower-the-better quality characteristic was used. The S:N value of each level of testing parameters was computed based on the S:N analysis. “Thelower-the-better” is usually the chosen S:N for all undesirable characteristics such as “defects,” for which the ideal value is zero. Also, when an ideal value is finite and its maximum or minimum values are defined, the difference between measured data and the ideal value is expected to be as small as possible. The generic form of the S:N then becomes: S:N = -log (1/n ) Σy2i
(4)
where yi is the primary response and n is the number of repetitions of each experiment. Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
Experimental Methods Quantitative experiments were performed using a free-flowing powder and a cohesive ferrosilicon powder (Figure 1) loaded into horizontal layers in a non-symmetrical double-cone mixer/blender, with a volume capacity of 1 L. The iron powder had a mean diameter of 102.5 µm and an apparent density of 3.041 g/cm3. The ferrosilicon powder had a mean diameter of 25 µm and an apparent density of 2.081 g/cm3. The nominal composition of the mixture was 6 w/o ferrosilicon and 94 w/o Fe (equivalent to 9.38 v/o ferrosilicon and 90.62 v/o iron). Mixing was performed using a Pharmatec Multi-blender MB 015. Fill levels between 35 v/o and 65 v/o were used and speeds between 15 and 30 rpm were evaluated. Each experiment was run for a predetermined mixing time, between 10 and 45 min. Subsequently, quantitative data were obtained utilizing image analysis, using a combination of scanning electron microscopy (SEM) and image analyzer software. The factors that influence the homogeneity of the mixture in the axial and radial orientations used in this experiment included only the mixing conditions and not the characteristics of the components. Thus, the primary parameters were the volume-fill ratio of the double-cone mixer/ blender, the rotational speed (rpm) and the time (min), which were optimized to achieve the desired results. These parameters and their levels are cited in Table II.
Figure 1. (a) Iron powder (irregular shape) and (b) ferrosilicon powder (large particles have irregular shape, smaller particles are spherical). SEM
TABLE II. MIXING PARAMETERS AND LEVELS Variables
Fill Ratio
Level 1 Level 2 Level 3
35 50 65
Rotational Speed (rpm) Time (min) 15 20 30
10 20 45
31
Previous
1-Page View
2-Page View
Search
Table of Contents
Next
EFFECT OF AXIAL AND RADIAL METAL POWDER MIXING ON CHEMICAL HOMOGENEITY AND AGGLOMERATION
At the completion of each experiment, the entire mixture was solidified inside the mixing vessel to preserve the structure of the mixture during subsequent characterization, using an infiltrant solution of low viscosity, following the technique described by Vlachos and Chang. 26 After curing the liquid infiltrant, the structure was extracted from the vessel and sliced by means of a band saw. Seven cross sections were examined using a 35 v/o volume-fill ratio and nine sections for the other volume-fill ratios. The composition of the slices was characterized by a combination of SEM, EDS (Inca software), and image analysis software (KS400, 3.0). A representative backscattered SEM micrograph of one of the samples of mixed iron/ferrosilicon powder is shown in Figure 2; this micrograph shows that the solidified binding agent forms bridges between the particles. The number of samples for the 35 v/o, 50 v/o, and 65 v/o fill levels were 90, 110, and 130, respectively.26 Two X-ray maps were created from one backscattered electron image (BSE), Figure 3. The first showed both iron and ferrosilicon powders, and the second showed only ferrosilicon powders, using Fe Kα and Si Kα X-ray lines (bright pixels). The estimated v/o is equal to the ratio of the number of pixels that belong to the phase analyzed to the total number of pixels in the image (determined via image analysis based on a pixel counting technique).26 Therefore, the calculated volume ratio (V R ) of ferrosilicon to iron is expressed as: Ferrosilicon Si VR = —————— = ——————— Iron Fe(TOTAL) – Si
Figure 3. Representative X-ray maps of iron/ferrosilicon mix (from Figure 4), showing (a) iron and ferrosilicon, and (b) ferrosilicon using Fe Kα and Si Kα X-ray lines
powder mixtures in different orientations. The cited parameters and their levels produced the L27 orthogonal matrix. All output responses need to be kept to a minimum.
(5)
Si = Number of bright pixels in Si Kα X-ray map Fe(TOTAL) = November of bright pixels in Fe K α X-ray map To test agglomeration, 100 isolated ferrosilicon particles were measured by dispersing them on a carbon disc and using the method described. The number of pixels per particle was measured and the average number for 100 particles calculated. Subsequently, the size of each agglomerate and the average size of the agglomerates for each of the mixing conditions were calculated For the Taguchi design and subsequent analysis, Minitab (version 15.0) software was used. The standard deviation σ (STDV) was used as a response for testing chemical segregation in the
32
Figure 2. Representative micrograph of iron/ferrosilicon mixture. SEM/BSE
RESULTS & DISCUSSION Effect of Axial and Radial Mixing on Uniformity and Agglomeration of Mixes For the purpose of these studies, the orientation of the areas of the mixture sectioned horizontally is defined as the X-orientation (axial mixing), and the orientation perpendicular to the axial mixing as the Y-orientation (radial mixing). The Zorientation is a combination of axial and radial mixing. To investigate any orientation effects on mixedness, three spaced sites in each orientation were used (except for the 35 v/o fill ratio in the Y and Z orientation). These sites were labeled X1, X2, X3; Y1, Y2, Y3; and Z1, Z2, Z3, respectively. Each site was sampled multiple times and the mean of the ratios of ferrosilicon to iron taken. The value of this ratio changes, depending on the Volume 45, Issue 1, 2009 International Journal of Powder Metallurgy
Previous
1-Page View
2-Page View
Next
Table of Contents
Search
EFFECT OF AXIAL AND RADIAL METAL POWDER MIXING ON CHEMICAL HOMOGENEITY AND AGGLOMERATION
TABLE III. MIXING CONDITIONS, MEAN VALUE OF FERROSILICON-TO-IRON RATIO OF EACH SURFACE, AND AVERAGE NUMBER OF PARTICLES PER AGGREGATE PER ORIENTATION No. 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
Factors
X- Axial Mixing
F.R.
Sp.
T.
X1
X2
X3
35 35 35 35 35 35 35 35 35 50 50 50 50 50 50 50 50 50 65 65 65 65 65 65 65 65 65
15 15 15 20 20 20 30 30 30 15 15 15 20 20 20 30 30 30 15 15 15 20 20 20 30 30 30
10 20 45 10 20 45 10 20 45 10 20 45 10 20 45 10 20 45 10 20 45 10 20 45 10 20 45
6.47 5.26 9.49 6.90 9.77 7.58 9.41 8.39 8.61 7.30 8.73 6.99 13.54 7.89 9.34 6.66 9.83 9.42 5.15 4.72 5.72 12.95 11.65 9.01 9.75 7.39 9,40
8.40 5.21 11.40 7.92 9.91 9.11 13.02 8.60 11.03 9.90 12.65 10.09 4.40 9.87 10.23 9.88 10.35 9.75 6.54 9.77 13.97 15.03 12.22 10.11 9.56 9.51 9.18
9.55 9.53 8.04 6.13 9.08 7.28 7.42 8.80 11.19 9.09 10.46 10.25 9.06 12.17 9.47 9.43 11.02 9.57 7.71 8.51 10.95 17.48 9.31 9.85 12.19 10.04 10.68
Y- Radial Mixing
Xave Agglomeration STDV Y1 8.14 6.66 9.65 6.98 9.59 7.99 9.95 8.59 10.28 8.76 10.61 9.11 9.00 9.98 9.68 8.66 10.40 9.58 6.47 7.67 10.21 15.15 11.06 9.65 10.50 8.98 9.75
1.891 2.088 2.352 2.053 1.992 2.648 2.147 2.142 2.059 2.117 2.392 1.947 3.036 2.353 2.195 2.066 2.382 2.100 1.843 1.863 2.359 2.964 1.647 2.003 2.165 2.235 2.232
1.55 1.09 1.41 2.76 3.12 3.91 2.21 1.73 1.71 1.86 1.92 1.69 2.90 2.97 1.01 1.33 1.68 1.69 1.28 2.46 2.11 3.30 3.00 1.84 1.90 1.50 1.66
mixing conditions. In addition, the average number of particles in each aggregate was investigated in the X and Y orientations. The overall test arrangements and the resultant outputs are listed in Table III. An ANOVA statistical procedure was used to determine whether the means from two or more samples were drawn from populations with the same mean value. The ANOVA results are listed in Table IV. These results reveal that there is a significant difference in the uniformity of the mixture between radial and axial mixing with p-values of 0.832 and 0.027 respectively, at the significance level α = 0.05. As the p-value is a measure of how much evidence there is to support the “no-significant difference” hypothesis, the higher the p-value, the more evidence there is. As the axial mixing has a p-value