The Requirement Of Different Type Of Motors For Magnetic Material

Different types of motors have different needs for magnets due to their different requirements and environments. The following is divided into three parts: focus on the 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 that they have different requirements for magnetization. In the magnetization waveform, the quality of 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 magnetization or magnet 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. Under the same extreme value, its size determines the output of the motor. However, the larger it is, the greater the positioning torque of the motor will be, and it will not feel good when rotating. Generally, in DC motors, the large output is required, so the duty cycle is relatively large; while brush-less motors require stable rotation. It has an indicator-torque fluctuation, especially at low speeds, the smaller the torque fluctuation, the magnetizing waveform is required The closer to the sine wave. This means that we require that the rising edge of the magnetizing waveform rises steadily and slowly.

Let us first talk about the types of magnetization:

a. The external charging of the magnetic ring-that is, the magnetic pole is charged on the outer surface of the magnetic ring, which is generally used for the rotor of the motor;

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

c. Oblique charging of the magnetic ring—that is, the magnetic poles charged on the surface of the rotor form an angle less than 90° with the two ends of the magnetic ring;

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

⑴ Axial 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;

⑵Axial single-sided multi-pole magnetization-the main product is a magnetic sheet, that is, more than 2 magnetic poles are charged on one surface of the magnetic part;

⑶ Axial double-sided multi-pole magnetization-that is, more than 2 magnetic poles are charged on both sides of the magnetic part, and the polarity is opposite.

For axial single-sided or double-sided multi-pole magnetization, the surface magnetism of single-sided magnetization is higher than that of double-sided magnetization, but the surface magnetization of the other surface of single-sided magnetization is very low. The addition of is the same.

e. Radial magnetization-as the name implies, radial magnetization means that the magnetizing magnetic field radiates from the center of the circle to the surroundings. For the magnetic ring, the inner surface of the inner circle after magnetization has one polarity, and the outer surface has the same polarity; for the magnet tile, the effect of radial magnetization is better than that of ordinary magnetization. It can make Each point on the inner arc of the magnet tile has similar magnetic properties.

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, some of which have 4 poles; while the magnetic rings used in stepper motors, brushless motors, and synchronous motors have even-numbered poles such as 4, 6, 8, 10...

Judge its application from the shape and number of poles of the magnet

Their performance is increasing, and the price is the same, which determines their respective applications. Injection magnets are divided into injection-molded ferrite and injection-molded NdFeB. The binders include nylon 6, 12, and PPS. Nylon is slightly cheaper than PPS, but the surface finish, strength, and temperature resistance of the magnetic parts are worse than PPS. Their common feature is that they can be injection molded with various parts or shafts to ensure product quality. Injection-molded ferrite magnets are divided into isotropic (isotropic) and anisotropic (anisotropic). The isotropic magnetic energy product is low, about 1.5 MGOe, and the anisotropic magnetic energy product is about 2.1 MGOe. It is mainly used for products with a large quantity and a wide range, such as toy motors, stepping motors for air conditioners, and fans. The highest magnetic energy product of injection-molded NdFeB is around 6.0MGOe. If imported raw materials are used, it can reach 6.5MGOe, but the price is higher. At present, the application of injection-molded NdFeB is not extensive, mainly because it is not well known to everyone. In fact, it can replace more low-energy product bonded NdFeB magnetic parts, especially in stepper motors and rotors with shaft injection molding.

Bonded NdFeB is the most widely used in high-performance products. The upper part can enter the sintered NdFeB product, and the lower part can enter the ferrite product. This is mainly because its performance is between the two, and it is isotropic. Suitable for various magnetizing methods. Its disadvantage is poor temperature resistance, the highest is 150 ℃, which also determines its suitability for small motors and control motors, depending on the specific situation of the drive motor.

Sintered NdFeB is widely used because of its higher performance, but it is currently mainly used for driving motors. Among the motors we are talking about, they are mainly brushless motors and AC servo motors, and are mainly tile-shaped. Because the current sintered NdFeB is mainly unidirectional, that is, the magnet can only be magnetized in one direction, so it is It cannot be made into a magnetic ring for magnetizing more than 2 poles. The radial orientation sintered NdFeB developed now can do this. The difference between the two is that the orientation direction during pressing is different, but the mold for radial products is more complicated, and there is a mold fee for the magnetic parts. The radially oriented sintered NdFeB magnetic ring will first be used in brushless motors and AC servo motors, which is determined by their prices. The radial orientation is very beneficial even for the magnetic tiles, and the waveform after magnetization is close to a rectangular wave instead of a saddle shape.

Possibility and result of the interchange

Generally speaking, in the same kind of material, it is easier to replace the high and low performance, and the replacement of different materials, although the performance is different, there are great differences, the structure of the motor must be changed, otherwise, the use of high performance Substituting the low-performance materials for the low-performance materials can not get good performance. Generally, high substitutes low, the structure becomes smaller, low substitutes high, and vice versa.

How to judge the pros and cons of magnetic materials from the operating results of the motor

Motor Torque   

Generally speaking, the motor torque is large, the magnetic steel performance is high, and the small is low. In small motors, the positioning torque is expected to be small, that is, the moment the torque of the motor from standstill to rotating is mainly determined by the magnetizing waveform and the iron core groove shape.

The Speed Of the Motor

The speed of the motor includes no-load speed and load speed. When discussing the relationship between the speed and the performance of the magnet, the influence of other resistance torques of the motor should be excluded. High no-load speed, low magnetic performance, conversely, high magnetic performance; high load speed, high magnetic performance, conversely, low magnetic performance.

Motor Current

The current of the motor also has no-load current and load current. When discussing the relationship between the current and the performance of the magnet, the influence of other resistance torques of the motor should also be excluded. The no-load current is large, the magnetic performance is low, on the contrary, the magnetic performance is high, but this is not obvious in the motor. The size of the no-load current is more related to the resistance of the winding; the load current is large, the magnetic performance is low, and vice versa, the magnetic performance high.

The above relationship can be illustrated by the following table:

In fact, the three are interrelated, and comprehensive consideration should be given to changes in magnetic properties.