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The Developmental Course Of Permanent Magnet Motor
May 20, 2017

The development of permanent magnet motor is closely related to the development of permanent magnet material. China is the world's first found that the magnetic properties of permanent magnet material and put it into practice. More than two thousand years ago, China uses the magnetic properties of permanent magnetic material made compass, in the maritime, military and other fields play a huge role , has become one of the four great inventions of ancient china.

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In 1920s, the world's first motor was a permanent magnet motor that produced an exciting magnetic field from permanent magnet.But the permanent magnet material used at that time was natural magnetite (Fe3O4), the magnetic energy density was very low, and the motor made of it was bulky and was soon replaced by the electric field motor.

With the rapid development of various motors and the invention of the current magnetizer, people on the permanent magnet material mechanism, composition and manufacturing technology carried out in-depth study, have found a carbon steel, tungsten steel (large magnetic energy product of about 2.7 kJ / m3 ), Cobalt steel (large magnetic energy product of about 7.2 kJ / m3) and other permanent magnetic materials. In particular, the aluminum nickel cobalt permanent magnet (large magnetic energy product of up to 85 kJ / m3) and the ferrite permanent magnet (large magnetic energy product of up to 40 kJ / m3) appearing in the 1950s, the magnetic properties have been greatly improved, a variety of micro and small motor and have used permanent magnet excitation. Permanent magnet motor power as small as several milliwatts, as large as tens of kilowatts, in the military, industrial and agricultural production and daily life has been widely used, the output increased dramatically. Correspondingly, this period has made breakthrough progress in the design theory, calculation method, magnetization and manufacturing technology of permanent magnet motor, and formed a set of analytical research methods represented by permanent magnet diagram.

However, the coercivity of alnico permanent magnet is low (36 ~ 160 kA / m), and the remanence density of ferrite permanent magnet is not high (0.2 ~ 0.44 T), which limits their application range in motors. Until the 1960s and 1980s, rare earth cobalt permanent magnet and NdFeB permanent magnet (both referred to as rare earth permanent magnet) have come out, their high remanence density, high coercivity, high magnetic energy product and linear demagnetization curve Of the excellent magnetic properties are particularly suitable for the manufacture of motors, so that the development of permanent magnet motor into a a new historical period.

The development of rare earth permanent magnet materials is broadly divided into three stages. In 1967, the United States KJStrnat professor found that the samarium cobalt permanent magnet for the first generation of rare earth permanent magnet, its chemical formula can be expressed as RCo5. In 1973, the second generation of rare earth permanent magnets with better magnetic properties appeared. The chemical formula was R2Co17. 1983 Japan's Sumitomo Specialty Metal Company and the United States General Motors Corporation successfully developed NdFeB permanent magnet, known as the third generation of rare earth permanent magnet. As the magnetic properties of NdFeB permanent magnet is higher than that of other permanent magnetic materials, the price is lower than that of rare earth cobalt permanent magnet material. The content of neodymium in rare earth ore is ten times of that of samarium, and it does not contain the strategic substance - cobalt Has aroused great concern at home and abroad the magnetic sector and the electrical sector, have invested a lot of manpower and resources for research and development. Is currently studying the new higher performance permanent magnet materials, such as samarium iron nitrogen permanent magnet, nano-composite rare earth permanent magnet, hoping to have a new and greater breakthrough.

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