Magnetics Business & Technology - Summer 2012 - (Page 30)

SPONTANEOUS THOUGHTS A Column by Dr. StAn trout The End of Axial Pressing? Whether we like it or not, we now live in an era of relatively magnets are aligned independently, before they are pressed. high and fluctuating rare earth prices. While some people yearn Pick up product information from any sintered NdFeB producer for the days of cheap rare earths, the idea that they will return any and you will see the magnetic properties of magnets pressed by time soon seems unrealistic. Rather, it is important to recognize these three methods are not the same. You will likely notice an imthat we are in the midst of a major paradigm shift that demands provement from axial to transverse to isostatic, a sure sign that the our attention and action. What does seem very ability to align powder improves from axial to realistic and practical today is reviewing our transverse to isostatic pressing. As an example, designs to be sure that we are making the best this trend is demonstrated nicely by the maguse of our magnets. netic properties of Vacodym 633, shown in the In previous columns, I have written about table below. reducing the amount of dysprosium we use in our sintered NdFeB magnets and optimizing Grade Pressing Typical Typical Method Br (kG) (BH) max our designs to reduce waste. These are steps (MGOe) in the right direction. However, lowering the 633 AP Axial 12.6 38 Dy content may not always be possible. 633 TP Transverse 13.2 42 In the fall of 2011, I spoke to some people who had given up on sintered NdFeB in favor 633 HR Isostatic 13.5 44 of SmCo. They may have since changed their opinion; however, at that time, some grades Pressing methods used to make sintered magnets. Note that in isostatic pressing, the The same general behavior is found with of SmCo were less expensive than sintered part is aligned in a separate processing step, nearly all grades and producers. In this case, NdFeB, especially the higher Dy-containing prior to pressing. Source: Vacuumschmelze catalog there is about a 7 percent increase in B from grades of NdFeB. That is a price situation r that I thought I would never see! Of course, axial to isostatic and a 5 percent increase switching to SmCo means becoming vulnerable to cobalt price from axial to transverse. Note that these increases take place fluctuations; but for the time being, that does not appear to be an with no change in the chemical composition of the magnet and issue.1 But we do need to be careful not to overreact to the price that most of the other magnetic properties are unaffected by the increases, because they do not appear to be permanent. Funda- pressing method used. A major exception is energy product, mentally we need to be prudent; our action needs to be propor- which increases about twice as much as Br. tional to the problem. Would a 5 to 7 percent increase in flux without a change in maIn some cases, I have seen designs with both NdFeB and SmCo terial be helpful? It seems like it would be. It could be used either options. Similarly, it makes sense to look at both bonded and sin- to increase the amount of available flux, to decrease the amount tered NdFeB solutions. This kind of flexibility seems very wise of material needed (again in the 5 to 7 percent range depending on to me, since it gives users the ability to buy the least expensive the application) or even some combination of the two. magnet material at any point in time in the future. So the first order of business, if you don’t know already, is to In this column, I want to focus on a small change that gives a find out how your sintered NdFeB magnets are pressed. If they tangible benefit with a relatively small amount of engineering. are axially pressed, ask if you have other options. It is a discusBut first some background information on magnet processing. sion worth having with your supplier. And while you’re at it, be Sintered NdFeB magnets are pressed in three distinct ways, sure to do the necessary engineering to assure that what I have which lead to slightly different products. These methods include claimed abstractly actually applies to your specific situation. axial, transverse and isostatic pressing, as shown in the figure. Does this mark the end of axial pressing? It seems highly unFor those not familiar with the names, they describe the rela- likely to me given that some configurations are very difficult to tionship between the pressing axis and the alignment axis. Axial do any other way. However, we do need to exploit every possible pressing means the pressing and alignment axes are the same. way to use magnets more effectively, and this is one of many Transverse pressing means the pressing axis is perpendicular to ideas to consider. the alignment axis. And isostatic pressing means the pressure is applied equally in all directions. In addition, isostatically pressed [1] Caveat emptor. I made a similar pronouncement about samarium in my fall 2010 column and its price immediately shot upward. Dr. Stan Trout has more than 30 years experience in the permanent magnet and rare earth industries. Dr. Trout has a B.S. in Physics from Lafayette College and a Ph.D. in Metallurgy and Materials Science from the University of Pennsylvania. Stan is a contributing columnist for Magnetics Business and Technology magazine and the Director of the Magnet Business for Molycorp Minerals, LLC. Spontaneous Materials, his consultancy, specializes in technical training on magnetics. He can be reached at strout@ieee.org. 30 Magnetics Business & Technology • Summer 2012 www.MagneticsMagazine.com http://www.MagneticsMagazine.com

Table of Contents for the Digital Edition of Magnetics Business & Technology - Summer 2012

Magnetics Business & Technology - Summer 2012
Editor's Choice
Injection Molded Magnets for Electrical Machines
The Process of Developing and Testing a New Transformer
Rare Earths & Corporate Social Responsibility
Research & Development
RE-use, RE-duce, RE-cycle, RE-place
Magnets • Materials • Measurement
Application • Component Developments
Industry News
Rare Earth Crisis Dissected: Securing the Future
Marketplace
Advertising Index
Spontaneous Thoughts: The End of Axial Pressing?

Magnetics Business & Technology - Summer 2012