Permanent magnetic material is also called "hard magnetic material". Once magnetized, it can maintain constant magnetism. It has wide hysteresis loop, high coerce and high remanence. In practice, permanent magnetic materials work in the second quadrant demagnetization of the hysteresis loop after depth saturation and magnetization. Common permanent magnetic materials can be divided into al, Ni, Co, Fe, Co, FE, RE and composite permanent magnetic materials. Now they are briefly described as follows:
● Al-Ni-Co is a permanent magnet alloy. With iron, nickel, aluminum elements as the main components, but also contains copper, cobalt, titanium and other elements. With high remanence and low temperature coefficient, magnetic stability. There are two kinds of cast alloy and powder sintered alloy. The material in the 20th century 30 ~ 60 years of application more, now used in the instrumentation industry to manufacture magnetoelectric meters, flowmeters, micro-special motor, relay, etc.
● Ferrochroco-cobalt permanent magnetic alloy. With iron, chromium, cobalt elements as the main components, also contains molybdenum and a small amount of titanium, silicon elements. Its magnetic properties are similar to those of al-Ni-Co permanent magnetic alloy, and can be improved by plastic deformation and heat treatment. Used for manufacturing various small magnet components with small cross sections and complex shapes.
● Permanent magnet ferrite. They are mainly barium ferrite and strontium ferrite with high resistivity and strong coercibility, which can be effectively used in the air gap magnetic circuit, especially suitable for permanent magnets of small generators and motors. The permanent magnet ferrite does not contain precious metals such as nickel and cobalt. It has abundant raw materials, simple technology and low cost. It can replace the al-Ni-Co permanent magnet magnetic separator, magnetic push bearing, loudspeaker and microwave devices, etc. But its maximum magnetic energy product is low, temperature stability is poor, the texture is more fragile, fragile, impact vibration resistance, not suitable for measuring instruments and magnetic devices with precise requirements.
● Rare earth materials. It is mainly rare earth cobalt permanent magnet material and Ndfeb permanent magnet material, which is one of the main production materials of permanent magnet motor. Permanent magnet materials include ferrite permanent magnet, rare earth permanent magnet, aluminum nickel cobalt, iron chromium cobalt, aluminum iron and other materials, among which the most commonly used and the largest amount of ferrite permanent magnet and Ndfeb rare earth permanent magnet. Rare earth permanent magnetic materials are mainly rare earth cobalt permanent magnetic materials and Ndfeb permanent magnetic materials. Rare earth cobalt permanent magnetic material is an intermetallic compound formed by the rare earth elements cerium, praseodymium, lanthanum, neodymium and cobalt. Its magnetic energy can be up to 150 times that of carbon steel, 3 to 5 times that of al-Ni-co permanent magnetic material, and 8 to 10 times that of permanent magnetic ferrite. This permanent magnetic material has low temperature coefficient, stable magnetism, and high forciness. Mainly used for low speed torque motor, starting motor, sensor, magnetic push bearing and other products of the magnetic system. Neodymium-iron-boron permanent magnet is the third generation of rare earth permanent magnet material. It has higher remanence, forced force and maximum magnetic energy product than rare earth cobalt permanent magnet material and is not easily broken. It has good mechanical properties and low alloy density, which is conducive to the light, thin, small and subminiature magnetic components. But its high magnetic temperature coefficient limits its application.
● Composite materials. It is composed of a permanent magnetic powder and a plastic material as a binder. Because it contains a certain proportion of binder, its magnetic properties are significantly lower than the corresponding magnetic materials without binder. Except for metal composite permanent magnetic materials, other composite permanent magnetic materials are limited by the heat resistance of the binder and use at a low temperature, generally not exceeding 150℃. However, the composite permanent magnet material has high dimensional precision, good mechanical properties, good performance uniformity of all parts of the magnet, and is easy to carry out radial orientation and multipole magnetization of the magnet. Mainly used in the manufacture of instruments, communication equipment, rotating machinery, magnetic therapy equipment and sporting goods.
