Ferrite block magnet is a kind of non-metallic permanent magnet material. There are two kinds of ferrite commonly used in motor, barium ferrite and strontium ferrite. Their magnetic properties are similar, and the Hc value of strontium ferrite is slightly higher than that of barium ferrite, which is more suitable for use in motors.
It is cheap and does not contain rare earth elements, cobalt, nickel and other precious metals; The manufacturing process of the ferrite block magnets is relatively simple; The coercive force is relatively large, its Hc is 128~320kA/m, and the anti-demagnetization ability is relatively strong; Its density is small, only 4~5.2g/cm³, and the mass is lighter; The demagnetization curve is close to a straight line, or a large part of the demagnetization curve is close to a straight line, and the recovery line basically coincides with the straight-line part of the demagnetization curve, so there is no need to perform magnetization stabilization like AlNiCo permanent magnets. It is the most widely used in motors and is currently the largest permanent magnet material in motors.
The remanence density is not high, Br is only 0.2~0.44T, and the maximum magnetic energy product (BH) max is only 6.4~40kJ/m³. Therefore, it is necessary to increase the cross-sectional area for providing magnetic flux, so that the volume of the motor is increased, and the environmental temperature has a great influence on the magnetic performance. The temperature coefficient of the coercive force of ferrite permanent magnet is positive, and its coercive force increases with increasing temperature and decreases with decreasing temperature, which is different from several other commonly used permanent magnetic materials. When ferrite permanent magnets are used, the maximum demagnetization operating point at the lowest ambient temperature should be checked and calculated to prevent irreversible demagnetization at low temperatures.
Ferrite block magnets are hard and brittle, and cannot be electrically processed, which can only be sliced and subjected to a small amount of grinding. Usually, a soft grinding wheel is used, preferably R3 silicon carbide grinding wheel, and the grinding speed should be appropriate. During grinding, water should be sufficiently cooled, so that the grinding speed can be accelerated without the permanent magnets being worn.
