The largest application field of rare earth permanent magnets is permanent magnet motors. Motors are commonly known as motors. Motors in a broad sense include motors that convert electrical energy into mechanical energy, and generators that convert mechanical energy into electrical energy. Whether they are motors or generators, they all use The law of electromagnetic induction or the law of electromagnetic force serves as the underlying principle for electrical equipment. The air gap magnetic field is the premise of the working principle of the motor. The air gap magnetic field generated by electric excitation is called an induction motor, and the air gap magnetic field generated by permanent magnets is called a permanent magnet motor.
The air gap magnetic field in the permanent magnet motor is generated by permanent magnets. There is no need to apply additional electric energy or add additional windings. Therefore, the biggest advantages of permanent magnet motors compared to induction motors are high efficiency, energy saving, small size, and simple structure. Therefore, permanent magnet motors The application of magnetos, especially in various types of small micromotors, is very wide.
The picture below is a simple working principle model of a permanent magnet DC motor. Two permanent magnets generate a magnetic field at the central coil. The coil is passed through current, and the electromagnetic force (left-hand rule) is generated by the magnetic field, which then rotates. The motor The rotating part is called the rotor, and the non-moving part is called the stator. The permanent magnet in the picture below belongs to the stator, and the coil belongs to the rotor.
For rotating electrical machines, when the permanent magnet is the stator, the shape of the tile-shaped magnet is usually an outer arc surface-mounted type and is attached to the casing. When the permanent magnet is the rotor, the shape is usually an inner-arc surface-mounted tile-shaped magnet that is attached to the rotor core. , or embedded in the rotor core in a square shape.
For linear motors, the permanent magnets are mainly square and parallelogram. Cylindrical linear motors also use axially magnetized ring magnets.
Permanent magnet motor magnets have the following characteristics:
1. The shapes are not too complicated (except for some micromotors, such as VCM motors), and are mostly rectangular, tile-shaped, sector-shaped, and bread-shaped. Especially under the premise of reducing the cost of motor design, many will use embedded square magnets. steel;
2. Magnetization is relatively simple, basically unipolar magnetization and a multi-pole magnetic circuit is formed after assembly. If the entire ring is made, such as bonding a NdFeB magnetic ring or a hot-pressed magnetic ring, multi-pole radiation magnetization is generally used;
3. The core technical requirements are mainly high-temperature stability, magnetic flux consistency, and adaptability. Surface-mounted rotor magnets will require good glue affinity. Linear motor magnets will have relatively strict requirements for salt spray. Wind power electromagnetic steel will require The requirements for salt spray will be more stringent, and the drive motor magnets will require very good high-temperature stability;
4. Magnetic energy products are used in both medium and low grades, but the coercivity is mostly at the mid-to-high level. At present, the magnetic steel grades of drive motors of electric vehicles are mainly high magnetic energy products and high coercive forces, such as 45UH, 48UH, 50UH, and 42EH. , 45EH, etc., mature diffusion technology is essential;
5. Segmented bonded magnets have been widely used in the field of high-temperature motors. The purpose is to improve the segmented insulation of the magnets and reduce the eddy current loss of the magnets when the motor is running. Some magnets will also appear on the surface. Add an epoxy coating to increase its insulation.
Key testing items for motor magnets:
1. High temperature stability. Some customers will require open-circuit magnetic attenuation measurement, and some customers will require semi-open-circuit magnetic attenuation measurement. When the motor is running, the magnets must not only withstand high temperatures but also withstand alternating reverse magnetic fields, so the finished product's magnetic attenuation and base material high-temperature demagnetization curves must be tested and monitored;
2. Magnetic flux consistency. Magnetic steel is the magnetic field source of the motor rotor or stator. If there is a consistency difference, it will cause motor vibration and power reduction, which will affect the overall motor function. Therefore, motor magnets generally have requirements for magnetic flux consistency, and some require 5%. Within, some require 3% or even 2%. Factors affecting the consistency of the magnetic flux must be taken into consideration, such as the consistency of the residual magnetism, the consistency of the tolerance, and the consistency of the chamfer coating, etc.
3. Adaptability. Surface-mounted magnets are mostly in the shape of tiles. Conventional two-dimensional testing methods for angles and radians have large errors or are difficult to test. At this time, its adaptability needs to be considered. Some closely arranged magnets require To control the accumulated gap, and some dovetail groove surface-mounted magnets need to consider the tightness of the assembly. It is best to make a self-made profiling jig according to the user's assembly method to test the suitability of the magnets.
Procurement personnel need to focus on the following points:
1. Rare earth market. Magnets, as the largest single-cost component in motors, have always been the main source of motor cost reduction. Since the shape of motor magnets is relatively simple, the material cost accounts for the largest proportion. Procurement personnel need to pay attention to the rare earth metals at all times. Market conditions to understand the price trend of motor magnets;
2. Performance indicators. The shape of magnet steel is relatively simple, and the material cost accounts for a large proportion. Therefore, the level of performance indicators will directly affect the amount of heavy rare earths in the magnet steel, thereby directly affecting the cost of the magnet steel;
3. Quantity. Most motor magnets are relatively large, with lengths ranging from 10 mm to more than 100 mm. The number of pieces produced from one blank is not large, so when the demand is not large, there will be a large waste of stock blanks, and the production of fixed molds requires The problem of apportioning mold fees results in higher costs.