Main properties of permanent magnet materials commonly used in motors

Main properties of permanent magnet materials commonly used in motors

Permanent magnet materials commonly used in motors include sintered magnets and bonded magnets. The main types are AlNiCo, ferrite, samarium cobalt and neodymium iron boron.

　　 Al-Ni-Co materials were used more before the 1980s. It has the advantages of excellent temperature stability, time stability and application of ultra-high temperature environment conditions. It is only used in some special applications such as high temperature requirements and very good magnetic stability. Military or instrumentation and other special use environments. .

　　 Ferrite material is a non-metallic permanent magnet material, and the price is low. It is mainly used in economical series of micro-motor products that do not require high performance and volume, and have a large quantity and a wide range. Such as toy motors, household electrical appliances motors, audio and video motors, office equipment and general instrument motors, automotive and motorcycle motors, and industrial low-power drive motors.

　　Samarium-cobalt material is a permanent magnet material with excellent magnetic properties that emerged in the mid-1960s, and its performance is very stable. Samarium cobalt is particularly suitable for manufacturing motors in terms of magnetic properties, but due to its high price, it is mainly used for research and development of military motors such as aviation, aerospace, weapons and high-performance motors in high-tech fields where price is not the main factor. NdFeB material is called the third-generation high-performance permanent magnet material that appeared in the 1980s. It has higher magnetic properties than samarium cobalt, poor thermal stability, and is easy to rust. It must be surface protected, but it is cheap , So it is quickly promoted and applied. With the continuous update of NdFeB materials, the temperature performance continues to improve, especially since the 1990s, low temperature coefficient, high temperature resistant NdFeB materials have been successfully developed, and the working temperature of high-performance heat-resistant NdFeB can reach 200℃, and the price is constantly decreasing, so that most of the industrial and civil motors use neodymium iron boron materials, and will replace most of the original ferrite materials and be used in low-cost economical motors.

The bonded permanent magnetic material is a composite permanent magnetic material made by the method of compression, injection or extrusion molding after mixing the binder and the permanent magnetic material, including bonded ferrite, bonded alnico, adhesive Samarium cobalt and bonded neodymium iron boron. Among them, bonded NdFeB is currently the best bonded permanent magnet material. Compared with sintered permanent magnet materials, it has the advantages of good machining performance, easy forming, can be made into various complicated shapes, good uniformity and consistency of magnetic properties, and easy multi-pole magnetization. However, the magnetic properties of bonded permanent magnet materials are lower than that of sintered magnets of the same type, and the magnetic energy product is about 40% to 70% of that of sintered magnets of the same material. Among bonded permanent magnet materials, bonded NdFeB has the best prospects. If bonded NdFeB solves the process problems and improves the quality, it will become the most widely used permanent magnet material. It is currently mainly used in precision micromotors such as small brushless DC motors and stepper motors.