1Requirements of different types of motors for magnetic materials

Different types of motors must have different requirements for magnets due to their different requirements and environments. The following is described in three parts: focusing on the different requirements of DC motors and brushless motors for magnets.

Both DC motors and brushless motors use magnetic tiles or magnetic rings, but the main difference between the two is the different requirements for their magnetization. In the magnetization waveform, the quality of the magnetization can be judged mainly by observing several parameters in the waveform: average extreme value, extreme difference and area (or duty cycle). The average extreme value indicates whether the performance of the magnetization or the magnetic steel meets the requirements of the product; the extreme difference indicates the uniformity of the magnetization; the area (or duty cycle) indicates the size of the magnetization waveform. The size determines the output of the motor, but the larger it is, the greater the positioning torque of the motor, and the feel of rotation is not good. Generally, in a DC motor, a large output is required, so the duty ratio is large; while a brushless motor requires stable rotation, it has an index - torque fluctuation, especially at low speed, the smaller the torque fluctuation, the magnetization waveform is required closer to a sine wave. This means that we require the rising edge of the magnetization waveform to rise steadily and slowly.

2、Requirements for the number of poles of different types of motors for magnetization

Here we first talk about the types of magnetizations:

a. The outer filling of the magnetic ring - that is, the outer surface of the magnetic ring is filled with magnetic poles, which are generally used for the rotor of the motor;

b. The inner filling of the magnetic ring - that is, the inner surface of the magnetic ring is filled with magnetic poles, generally used for the stator or outer rotor of the motor;

c. The oblique filling of the magnetic ring - that is, the magnetic pole charged on the surface of the rotor forms an angle less than 90° with the two ends of the magnetic ring;

d. Axial magnetization—that is, magnetization up and down along the axis of the magnetic ring and magnetic sheet, which can be divided into:

⑴Axial 2-pole magnetization—that is, one end of the magnet is N pole and the other end is S pole, which is the simplest magnetization;

⑵ Axial single-sided multi-pole magnetization - the main product is a magnetic piece, that is, one surface of the magnetic piece is filled with more than 2 magnetic poles;

(3) Axial double-sided multi-pole magnetization—that is, more than 2 magnetic poles are charged on both sides of the magnetic part, and the polarities are opposite. For axial single-sided or double-sided multi-pole magnetization, the surface magnetism of one side is higher than that of double-sided, but the surface magnetism of the other side of single-side magnetization is very low. The addition of is the same.

e. Radial magnetization——As the name suggests, radial

magnetization means that the magnetizing magnetic field radiates from the center of the circle to the surroundings. For the magnetic ring, after magnetization, the inner surface of the circle is all of one polarity, and the outer surface of the outer circle is of the same polarity; and for the magnetic tile, the effect of magnetization from the radial direction is better than that of ordinary magnetization, which can make the surface magnetism of each point on the inner arc surface of the magnetic tile is relatively similar. Generally speaking, the number of poles refers to the multi-pole magnetization of the motor. For magnetic rings, 2-pole magnetic rings are mostly used in small DC motors, and some have 4 poles; while stepping motors, brushless motors, and synchronous motors use magnetic rings with even-numbered poles such as 4, 6, 8, 10, etc. 

3Judging the application occasions from the shape and number of poles of the magnet

For magnetic tiles, they are generally used in DC motors and brushless motors, and in DC motors, most of them are 2-pole and 4-pole, which can be judged according to their central angle, as mentioned earlier. When the brushless motor uses the magnetic tile as the stator, it generally exceeds 6 poles, so its central angle is much smaller than the magnetic tile used in the DC motor; but when the magnetic tile is used as the rotor of the brushless motor, it can have more than 4 or 6 poles , for 4 poles, the outer surface of the rotor is magnetized, and because it needs to be assembled into a circle, its central angle is close to 90°, which can be distinguished from DC motors. If it is a magnetic ring, it is mainly to distinguish stepper motors, brushless motors and synchronous motors. The outer diameter of the magnetic ring used in the stepping motor is small, most of which are around 20, rarely more than 30, and its wall thickness is relatively thin, between 1.0-1.5; the number of poles is large, above 10 poles, there are up to 50 poles. The diameter of the magnetic ring of the brushless motor is generally greater than 20, the number of poles is between 4-12 poles, and its wall thickness is mostly between 1.5-5.0. The magnetic ring of the small synchronous motor is between 20-40, the number of poles is 8-16 poles, and the wall thickness is 1.0-3.0.

 Differences between injection molded magnets, bonded NdFeB, and sintered NdFeB and their general applications Injection magnet, bonded NdFeB, and sintered NdFeB are commonly used in small motors, especially the first two. These three materials have their own characteristics, which are only briefly summarized here.




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