Milling Principle
Magnetic powder is constituted by lots of basic neodymium iron boron particles and the gaps between particles. Powder is material between solid and colloid. Solid material, under 0.1μm is called colloid, while ones, exceeding 1μm are dense body or solid. There are many poles between neodymium magnet powders with small connecting surface, so, unlike dense bodies, powder does not have fixed shape, which is similar to fluidity of the fluid. In dense bodies, there are no macro pores, so it is bound by atoms.
Commonly, powder metallurgical process is adopted in rare earth permanent magnet alloy preparation process. NdFeB magnetic powder is classified into coarse, medium and fine process technology, granularity is require to be between 3-5μm. Neodymium rare earth magnets are easy to oxidize and these oxide powder spontaneously combusts in the air. With the interaction between magnetism, powder become secondary particles, the group of thousands of particles formed by the interaction between Van der Waal force, London force and magnetism. So, powder of rare earth permanent magnetic alloys has poor fluidity, which increases difficulties to the next step, magnetic field orientation.
Requirement of Neodymium Magnetic Powder Particle
Granularity of strong neodymium magnetic powder should be measured by particle size measurement instrument. The sizes of magnetic powder particle are 3-5μm. Distribution of magnetic particles should be also measured by particle size measurement. Particles of sizes of 3-5μm should cover 80%-90%. Particles with size under 1μm should be less than 15% during production. Particles with sizes bigger than 5μm should be as less as possible. When powder is made by jet mill, it should be smaller than 50ppm.
The powder particles should be like ball or similar to ball. Crystal imperfection should be as less as possible. The above all requirements are basic for sintered neodymium permanent magnets .
China Rare Earth Magnet Limited manufactures sintered neodymium permanent magnets.
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