What are the stages of the development of rare earth permanent magnet materials?
The development of permanent magnet motor is closely related to the development of permanent magnetic material. China is the world's first found that the magnetic properties of permanent magnet materials and apply it to the practice of the country, two thousand years ago, China's use of the magnetic properties of permanent magnet materials made of the compass, played a huge role in navigation, military and other fields, has become one of the four great inventions of ancient china.
With the rapid development of the needs of all kinds of motor current and magnetizing apparatus of the invention, composition and manufacturing technology are deeply studied people and mechanism of permanent magnetic materials, have been found in carbon steel, tungsten steel (the maximum energy product of about 2.7 kJ/m3), cobalt (maximum energy product of about 7.2 kJ/m3) and other permanent magnetic materials. Especially the alnico permanent magnet appeared in 1930s (the maximum energy product of up to 85 kJ/m3) and ferrite permanent magnet appeared in 50s (the maximum energy product of up to 40 kJ/m3), the magnetic properties have been greatly improved, but also have a variety of micro and small motor using permanent magnet. Permanent magnet motor power from milliwatts, to tens of kilowatts, has been widely used in industrial and agricultural production and daily life, military, production increased dramatically. Accordingly, this period in permanent magnet motor design theory, calculation method, magnetization and manufacturing technology and so on have also made a breakthrough, formed by the permanent magnet graphic method is represented by a set of analysis methods.
The first motor in the world in 1820s was a permanent magnet motor with an exciting magnetic field generated by a permanent magnet. But the permanent magnetic material used at that time was a natural magnetite ore (Fe3O4), and its magnetic energy density was very low. The motor made of it was bulky and was replaced by electric excitation motor.
