Magnet is a kind of material with wide hysteresis loop, high coercive force and high remanence. Once magnetized, it can keep constant magnetism. It is also called hard magnetic material. In practice, permanent magnet materials work in the second quadrant demagnetization part of deep magnetic saturation and hysteresis loop after magnetization. Commonly used permanent magnet materials are divided into aluminum nickel cobalt system permanent magnet alloy, iron chromium cobalt system permanent magnet alloy, permanent ferrite, rare earth permanent magnet material and composite permanent magnet material. What are the materials?
Alnico permanent magnet alloy: with iron, nickel and aluminum as the main components, it also contains copper, cobalt, titanium and other elements. With high remanence and low temperature coefficient, the magnetic property is not disordered. It can be divided into forging alloy and powder sintered alloy. It was widely used in the 1930s-1960s. Now it is mostly used in the manufacturing of magnetoelectric instruments, flow meters, micro special motors, relays, etc. in the instrument industry.
FeCrCO system permanent magnet alloy: with Fe, Cr and CO as the main components, it also contains Mo and a small amount of Ti and Si. The magnetic properties of the alloy are similar to those of Al Ni Co permanent magnet alloy, and can be improved by plastic deformation and heat treatment. It is used to manufacture various small magnet elements with small cross section and complex shape.
Permanent ferrite: mainly barium ferrite and strontium ferrite, with high resistivity and high coercive force, can be effectively used in the air gap magnetic circuit, especially suitable for small generators and permanent magnets of electric thoughts. 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 al Ni Co permanent magnet system to make magnetic separator, magnetic thrust bearing, loudspeaker, microwave device, etc. However, its maximum magnetic energy product is low, its temperature is not disorderly, its texture is brittle and fragile, and it is not resistant to impact vibration, so it is not suitable for measuring instruments and magnetic devices with precise requirements.
Rare earth permanent magnet materials: mainly rare earth cobalt permanent magnet materials and neodymium iron boron permanent magnet materials. The former is an intermetallic compound formed by rare earth elements such as cerium, praseodymium, lanthanum, neodymium and cobalt. Its magnetic energy product is 150 times of that of carbon steel, 3-5 times of that of aluminum nickel cobalt permanent magnet, 8-10 times of that of permanent ferrite. Its temperature coefficient is low, its magnetism is not disordered, and its coercive force is as high as 800 Ka / m. It is mainly used in the magnetic system of low-speed torque motor, starting motor, sensor, magnetic thrust bearing, etc. Neodymium iron boron permanent magnetic material is the third generation of rare earth permanent magnetic material. Its remanence, coercive force and maximum magnetic energy product are higher than the former. It is not fragile, has better mechanical function, and has low alloy density, which is conducive to the lightness, thinness, miniaturization and ultra miniaturization of magnetic components. However, its high magnetic temperature coefficient limits its partial application.
Composite permanent magnet material: it is composed of permanent magnet powder and plastic material as binder. Because it contains a certain proportion of binder, its magnetic function is significantly lower than the corresponding magnetic materials without binder. In addition to metal composite permanent magnet materials, other composite permanent magnet materials are limited by the heat resistance of the binder, and the service temperature is relatively low, generally no more than 150 ℃. However, the composite permanent magnet material has high dimensional accuracy, good mechanical function, good functional average of all parts of the magnet, and it is easy to conduct radial orientation and multipole magnetization of the magnet. It is mainly used in the manufacture of instruments, communication equipment, rotating machinery, magnetic therapy equipment and sporting goods.
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