NdFeB permanent magnet material is known as "magneto". It was discovered in 1983 and began industrialization in Japan, China, Europe and America in 1985. It has gone through 35 years. In the past 35 years, the global Nd-Fe-B permanent magnet material industry has been booming, the magnetic properties are constantly breaking records, the varieties and brands of materials are increasing, the industrial technology innovation is changing with each passing day, and the output of materials is increasing rapidly.
Nd-Fe-B permanent magnet is a tetragonal crystal formed by Nd, Fe and B. according to different production processes, it can be divided into sintered Nd-Fe-B, bonded Nd-Fe-B and hot pressed Nd-Fe-B. due to different production processes, they have great differences in magnetic properties, post-processing and application of products.
Sintered Nd-Fe-B is the largest and most widely used product in the Nd-Fe-B family. It is produced by powder metallurgy. According to the coercivity of the products, it can be divided into seven series: n, m, h, SH, uh, eh and th. The remanence and intrinsic coercivity of sintered NdFeB are up to 1.45t and 2786ka / m respectively, and the working temperature is 80 ℃ °~ two hundred ° between. Sintered NdFeB is easy to be oxidized and corroded, so it needs surface treatment. According to the different requirements of the use environment, phosphating, electroplating, electroless plating, electrophoresis, vapor deposition and other surface treatment methods can be used, such as zinc, nickel, nickel copper nickel, epoxy resin and so on.
Sintered NdFeB is difficult to be precisely processed into a special shape, and it is easy to crack, damage, difficult to assemble and other problems in the process of processing. In order to solve these problems, people try to crush the permanent magnet and mix it with adhesive, and then press it into shape in the magnetic field, so bonded NdFeB comes out. It has the advantages of low cost, high dimensional accuracy, large degree of freedom of shape, good mechanical strength and light specific gravity, and has been widely used in the market.
At present, there are four molding processes of bonded NdFeB: calendering, injection molding, extrusion molding and molding, of which calendering and injection molding are the most popular. The density of bonded NdFeB magnets is only 80% of the theoretical density due to a large amount of binder, so the magnetic properties of bonded NdFeB magnets are weaker than that of sintered NdFeB magnets. Bonded Nd-Fe-B magnets are isotropic magnets with the same magnetism in all directions, so it is convenient to make multi pole or even multi pole magnets（ Bonded NdFeB can also be made into anisotropic magnets
Hot pressed NdFeB
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. However, its mechanical properties are not good. Due to patent monopoly and high processing cost, only a few companies have achieved mass production of hot pressed NdFeB products in the market.
Due to the limitation of molding technology, hot pressed NdFeB can only be made into ring, and its application scope is limited to a certain extent. At present, it is mainly used in automobile EPS motor and other fields. The magnetic properties of the hot pressed NdFeB magnet are high, and the maximum radial magnetic energy product of the magnetic ring can reach 240-360kj / m3. The magnetic ring is oriented along the radial direction, and the radial magnetic performance is uniform, which can make the motor run quiet and the torque output smooth. At the same time, it also has high heat resistance, the use temperature can reach 180 ℃ - 200 ℃.
Three kinds of NdFeB permanent magnets have their own merits
Due to the great differences in magnetic properties and molding, bonded Nd-Fe-B and sintered Nd-Fe-B are not widely used. Bonded Nd-Fe-B is mainly used in hard disk drive spindle motor and low-power micro motor and other fields, while sintered Nd-Fe-B is more used in high-power drive motor and other fields. Due to the limitation of shape, hot pressed NdFeB is only used in Automotive EPS.