The NdFeB permanent magnet material is called "Magnetic King". It was discovered in 1983 and industrialized in Japan, China, Europe and the United States at the same time in 1985, and it has gone through 35 years. In the past 35 years, the global neodymium iron boron permanent magnet material industry has developed vigorously. Its magnetic properties have continuously set new records, material varieties and grades have been continuously increased, industrial technology innovation has been changing rapidly, and the output of materials has increased rapidly.
NdFeB permanent magnets are tetragonal crystals formed of neodymium, iron and boron. According to the different production processes, they can be divided into three types: sintered neodymium iron boron, bonded neodymium iron boron and hot-pressed neodymium iron boron. Due to the different production processes, They have big differences in product magnetic properties, post-processing and applications.
Sintered Neodymium Magnet
Sintered NdFeB is the product with the largest output and the most widely used in the NdFeB family. It is produced by powder metallurgy, and is divided into N, M, H, SH, UH, EH and TH according to the different coercivity of the product. Series. The sintered NdFeB that has been commercially produced has a remanence of up to 1.45T and an intrinsic coercivity of up to 2786kA/m. The operating temperature is between 80° and 200° depending on the coercivity. Sintered NdFeB is easy to be oxidized and corroded, so surface treatment is required. According to different requirements of the use environment, surface treatment methods such as phosphating, electroplating, electroless plating, electrophoresis, and vapor deposition can be used. Common coatings such as zinc, nickel, Nickel copper nickel, epoxy resin, etc.
Bonded Neodymium Magnet
Sintered neodymium iron boron is difficult to precisely process into special shapes, and it is easy to crack, break, and be difficult to assemble during the process. To solve these problems, people try to crush the permanent magnets and mix them with adhesives and press them in a magnetic field. , Bonded NdFeB has just come out. It has the advantages of low cost, high dimensional accuracy, large degree of freedom of shape, good mechanical strength, light specific gravity, etc., and has been widely used in the market.
There are currently 4 processes for forming bonded neodymium iron boron: calendering, injection molding, extrusion and compression molding, of which calendering and injection are more mainstream. Bonded NdFeB magnets are generally only 80% of theoretical density due to the addition of a large amount of adhesive, so they are weaker than sintered NdFeB magnets in terms of magnetic properties. Bonded neodymium iron boron is an isotropic magnet with the same magnetism in all directions, so it is convenient to manufacture multi-pole or even countless monolithic magnets. (Bonded NdFeB can also be made into anisotropic magnets)
Hot-pressed Neodymium Magnet
Hot-pressed NdFeB can achieve magnetic properties similar to sintered NdFeB without adding heavy rare earth elements. It has the advantages of high density, high orientation, good corrosion resistance, and high coercivity, but the mechanical properties are not good. , And due to patent monopoly and high processing costs, currently only a few companies on the market have achieved mass production of hot-pressed NdFeB products.
Due to the limitation of the molding technology, the current hot-pressed NdFeB can only be made into a ring shape, and the application range is limited to a certain extent. At present, it is mainly used in the fields of automobile EPS motors. The hot-pressed NdFeB magnet has high magnetic performance, and the maximum radial energy product of the magnetic ring can reach 240～360kJ/m3. The magnetic ring is oriented in the radial direction, and the radial magnetic performance is uniform, which can make the motor run quietly and the torque output is smooth. At the same time, it has high heat resistance, and the use temperature can reach 180℃-200℃.
