Permanent magnets for motors are the topic we’ll talk about. The primary application for permanent magnets is the permanent magnet motors.
The performance of an electric motor is based on the air gap magnetic field. The air gap magnetic field of permanent magnet motors is produced by permanent magnets. There is no need for any extra electrical energy. The advantages of permanent magnet motors include higher efficiency, energy savings, compact size, and simple structure. For instance, compact size and space-saving make the permanent magnet motors widely used in small micro-motors.
Image Source: World oil
The working principle of a motor is easy to understand. A permanent magnet DC motor is made of two parts. The rotating part of the motor is the rotor. The non-rotating part is called the stator. For example, two permanent magnets are set in the center of a coil and generate a magnetic field. When current is passed through the coil, an electromagnetic force is produced and forces the rotor to rotate.
For rotary motors, if the permanent magnets for motors apply to the stators, they are typically arc-shaped magnets attached to the casing. When the permanent magnets for motors act as the rotors, they are generally tile magnets affixed to the rotor cores or embedded in the rotor cores in the shape of a square.
The permanent magnets used in the linear motors are primarily square-shaped or parallelogram-shaped. Axially magnetized ring magnets are also employed in cylindrical linear motors.
Common Knowledge of Permanent Magnets for Motors:
Shape: Usually, Their shapes are not very complicated. For functional reasons, some micromotors, such as VCM motors, are exceptions. Main shapes include rectangular, tile-shaped, fan-shaped, or bread-shaped. In motor designs aimed at cost reduction, many embedded square magnets are used.
Magnetization: The magnetization of permanent magnets for motors is relatively simple, essentially single-pole magnetization, assembled to form a multi-pole magnetic circuit. If the whole ring is used, such as NdFeB magnet ring or other permanent magnet ring for motors, the main option is more multi-pole radial magnetization.
Technical Standard: Considering the operating environments and demagnetization, the main design requirements are high-temperature stability, magnetic flux consistency, and adaptability. Moreover, some special requirements are applied to different magnets. Good adhesion is very crucial to surface-mounted rotor magnets. Salt spray resistance is an important pillar of some motors, such as linear motor magnets and wind turbine magnets. To avoid influencing the performance of motors, drive motor magnets require excellent high-temperature stability.
Option for magnets: Magnets with different magnetic energy products are used in different motors. Besides magnetic energy products, medium and high coercive forces are essential. Currently, high magnetic energy products and high coercive force, such as 45UH, 48UH, 50UH, 42EH, and 45EH, are widely used in the drive motors of electric vehicles.
Eddy Current: To enhance the segmented insulation and decrease the effect of eddy current when the motor operates, more and more segmented magnets are being used in high-temperature motors. For the same reason, some magnets with epoxy coatings to enhance their insulation properties.
Key Standards of Permanent Magnets for Motors:
High-temperature stability. Depending on clients’ specific and different requirements, an open circuit magnetic decay test or semi-open circuit magnetic decay test is an option. Being stable under high temperatures, it’s crucial to test and monitor the magnetic decay of the end product and the high-temperature demagnetization curve of the permanent magnets for motors.
Magnetic flux consistency. As to permanent magnets for motors, their magnetic flux must remain consistent. Otherwise, the variations could cause vibration and power loss, impacting the overall performance of motors. So, the standard of magnetic flux consistency is 5% or less. For some high-end clients, it will be 3%, 2%, or less. At the same time, the consistency in residual magnetism, dimensional tolerance, and chamfering should also be well examined.
Adaptability. It’s essential to consider the adaptability. We must take the assembly tightness into account. Ideally, it would be best to make test fixtures according to the client’s assembly method to test the adaptability of the permanent magnets for motors.