Magnetic Materials in Permanent Magnet Motors

Permanent magnet motors use permanent magnets to generate the magnetic field of the motor. It does not require an excitation coil or excitation current. It is a good energy-saving motor because of its high efficiency and simple structure. With the rapid development of various motors and the invention of current magnetizers, people have conducted in-depth research on the mechanism, composition and manufacturing technology of permanent magnet materials. A variety of permanent magnet materials such as carbon steel, tungsten steel, and cobalt steel have been discovered one after another. The magnetic material used in permanent magnet are neodymium iron boron, samarium cobalt and ferrite.

The neodymium iron boron permanent magnet materials are called the "magnet king", and it was discovered in 1983. It has been 37 years since China and Europe and the United States simultaneously started industrialization in Japan in 1985. NdFeB permanent magnets are tetragonal crystals formed of neodymium, iron, and boron. According to different production processes, they can be divided into sintered NdFeB, bonded NdFeB and hot-pressed NdFeB. Due to different production processes, they have big differences in magnetic properties of product, post-processing and applications.

Samarium cobalt permanent magnet material is a kind of rare earth permanent magnet, which is made of rare earth elements samarium, cobalt and other elements after proportioning. It has a high magnetic energy product and a very low temperature coefficient, with a maximum operating temperature of 350°C. Compared with neodymium iron boron, samarium cobalt permanent magnets are more suitable for working in high temperature environments. It can still maintain good temperature stability and chemical stability above 180°C. At the same time, it has strong corrosion and oxidation resistance. Therefore, it is widely used in aerospace, defense and military industry, microwave devices, communications, medical equipment, various magnetic transmission devices, sensors, magnetic processors, motors, magnetic cranes and so on.

Ferrite permanent magnet materials are also called hard ferrites. This material has high coercivity and is not easy to demagnetize after magnetization. The raw materials for the preparation of permanent ferrites are mainly strontium oxide or barium oxide and iron trioxide (other chemical components such as cobalt (Co) and lanthanum (La) will be added to some specific high grades to improve their magnetic properties). Permanent ferrite is generally a magneto plumbite structure, which is mainly used for speakers, earphones, motors and various instruments.

The use of injection molded ferrite, injection molded NdFeB and other injection molded magnetic materials in permanent magnet motors has gradually increased. It has been widely used in sensors, motor magnets and other fields, providing new design solutions for motor design, especially in the field of small and micro motors.