Magnequench ProcessingMr. Mitchell Spencer
Magnequench Corp., Anderson, IN
When the oil valve was turned off by the OPEC cartel in the mid 1970's, there was a strong incentive for weight reduction in automobiles. General Motors discovered that NdFeB (Neodymium-Iron-Boron) provides much superior magnetic force for weight. Out of this discovery, in 1986 GM opened Magnequench as a production facility for the new magnets to be used in cranking motors.
Unfortunately, early NdFeB magnets did not receive much acceptance in the automotive industry, so in 1995 GM spun off the company, which by then had found many new markets for its products, most importantly small motor magnets in devices like floppy drives, hard disk dries, and read/write motor control in the computer industry and stepper motors in other equipment.
Currently NdFeB magnets comprise about 33% of the entire magnet market. This is expected to rise to 50% by 2005. The largest market share belongs to Japan, followed by China, and then the USA (primarily Magnequench).
Magnequench magnets can be made in complex net shapes, and with thin walls if necessary. The best grade of NdFeB magnets can be as much as 40 megagauss-oersted (which is about 10 time that of ferrite magnets and about 4 times that of platinum-cobalt, the next best magnetic material). Magnetism is maintained up to about 600F in NdFeB magnets, however binders used to form the shapes are susceptible to failure at lower temperatures.
Magnequench uses three processes to make its magnets:
All three processes begin with the reduction and separation of Nb from a neodymium oxide / calcium / calcium oxide mixture with calcium in the molten state. The raw neodymium is then alloyed with iron in about a 20/80 eutectic ratio, and refined in a vacuum induction furnace prior to casting an ingot. This alloy is then remelted in a melt spinner and undergoes rapid solidification on a quenching wheel to form a ribbon which is ground to become the primary source material.
The MQ1 process makes the most versatile, and least expensive magnets. The raw material is mixed with a thermoset epoxy and molded into any shape needed. The last step is magnetization (usually performed by the customer) which involved the discharge of a large capacitor bank such that the flux field intersects the parts to be magnetized. The magnets are (of themselves) isotropic.
The MQ2 process produces a stronger magnet and no binder of adhesives are added to the magnet material. Instead they are hot compacted under controlled conditions to form isotropic parts.
The MQ3 process is a continuation of the MQ2 process, in that hot compacted billets are directionally forged in order to obtain a specific alignment of grains. These materials are anisotropic, but also have the highest magnetic densities of any material known.
Magnequench hopes to open a plant in China in the next few years to avoid the transportation costs for the neodymium, most of which is produced in China anyway.