Neodymium Magnets

Magnetic material based on rare earth

It was in the nineteen seventies when the first magnetic materials based on rare earth became available to the industry. The main raw material used for these magnets, the so-called rare earth, according to the periodic system of elements, belongs to the lanthanide series. This is the collective name of the elements with atom numbers between 57 and 71, from lanthanum to lutetium. The atom numbers (Z) provide the number of protons (positively charged elementary particles) found in the atomic nucleus of the element in question. For magnetic materials an alloy of different elements is always used, the most important elements being neodymium (Nd), Z 60 and samarium (Sm), Z 62. The manufacturing process of magnetic materials based on rare earth is extremely complex. The raw materials needed for the alloy have to be very accurately mixed in a vacuum or under a mixture of inert gases. The raw material particles are then ground until the mixture meets the exact tolerances required. The products are then pressed.

In addition a strong magnetic field is implemented to align the metal particles. Finally the parts are sintered in special vacuum ovens. As the end product is extremely hard. further work has to be carried out by spark erosion machines or by machines fitted with diamond tools. In addition special cooling methods are applied. Magnetic materials based on rare earth are samarium • Cobalt (SmCo, and Sm,Co11) and Neodymium (Nd,F”B). To prevent undesired oxidation processes, the Neodymium finished products are coated with a zine-, nickel-, tin- or epoxy layer. These high-grade magnetic materials are used in places where an extremely strong magnetic force is required (NdFeB is by far the strongest magnetic material currently available). These materials are successfully used in places where, in spite of limited space, a strong magnetic field is required (miniaturization). NdFeB magnets have the same amount of strength as hard ferrite magnets but require up to five times less space. On the other hand is of course also applicable that, with constant dimensions, a five to ten times greater energy product can be attained. NdFeB and SmCo magnets can also be used for low temperature projects.

Plastic bonded magnetic materials based on rare earth. For magnetic components that need to be slightly flexible or completely dimensionally stable, the base material can be mixed with a thermoplastic raw material such as polyamide. NdFeB-material plastic bonded is significantly more corrosion-resistant then sintered material, thanks to the relatively high amount of plastic (up to 20%), which protects the neodymium parts. Any possible surface corrosion will not penetrate the material quickly and usually therefore no special surface treatment is required. With the aid of compression (BM 9 Np, 10 Np, 12 Np) or injection (BM 4 Np, 7 Np, 8 Np) moulding techniques, magnetic materials plastic bonded are ideal for the manufacture of large numbers of magnetic products.

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