Types of Magnets Used in Motors, Generators and Actuators

Rare earth magnets (samarium cobalt and neodymium) or ferrite (ceramic) magnets can be used in magneto and automotive magnet applications. Rare earth magnets are usually 2 to 3 times stronger than ferrite or ceramic permanent magnets. In motors, this enables smaller and lighter motors with higher performance. Correspondingly, rare earth magnets are also more expensive than ferrite (ceramic) magnets.



Samarium Cobalt Magnet

Samarium Cobalt (SMCO) magnets were produced in the 1970s. Before NdFeB magnets, one of the advantages of using SmCo is that they are not easy to corrode and have better temperature resistance. This means that it can maintain its magnetic properties at extremely high or low temperatures. It is a good choice for applications with abnormally high or low temperatures. However, their power is slightly weaker than neodymium magnets. Its high magnetic strength, excellent temperature resistance and reliable performance without oxidation protection are ideal for high-temperature motor applications. Samarium cobalt magnets are a relatively powerful type.

Corrosion resistance: Samarium cobalt magnets have excellent corrosion resistance (neodymium magnets do not have), and most applications do not require electroplating or surface coating, which makes them beneficial for medical applications.

Temperature stability: Samarium-cobalt magnets can withstand higher temperatures than neodymium magnets. The maximum operating temperature of samarium-cobalt magnets is 250-550°C, and the Curie temperature range is 700-800°C.

Neodymium iron boron magnet

Neodymium magnets are often called the simplest permanent magnets, but their magnetic force is usually the strongest. Neodymium magnets are widely used in the automotive industry. The choice of samarium cobalt or neodymium as automotive magnets is usually based on the operating temperature and/or corrosion resistance.

Operating temperature: If a low-coercivity neodymium magnet is heated above 80°C, it may start to lose strength. High-coercivity neodymium magnets have been developed to work at temperatures up to 220°C, with very little irreversible loss. The need for low temperature coefficients in neodymium magnet applications has triggered several levels of development to meet specific operating requirements.

Corrosion: Neodymium magnets are prone to corrosion, especially along the grain boundaries of sintered magnets. This type of corrosion can cause severe degradation, such as crushing magnets into small magnetic powders. This loophole can be solved by adding a thin film coating to prevent exposure to the atmosphere, such as nickel coating or a double-layer copper-nickel coating, or other metal or polymer and paint protective coatings can be used.

Ferrite or ceramic magnet

Compared with rare earth magnets, although ferrite magnets have lower energy consumption, they have been widely accepted due to their strong demagnetization resistance, strong corrosion-resistance, and low price. They are the most commonly used magnets in most types of DC motors. They are not as powerful as neodymium magnets, but they are a cost-effective choice for basic crafts, refrigerator magnets, or storage of lightweight items.

Working temperature: The maximum working temperature of the ceramic magnet is 250°C. Although it will experience magnetic loss when operating at high temperatures, the loss will recover when the material drops to normal ambient temperature. Working at very cold temperatures (-20°C) may cause permanent loss of magnetic strength unless the circuit is designed for this extreme situation.

Corrosion: Ceramic magnets have good corrosion resistance and generally do not require coating or electroplating.

Conclusion

There are several different types of magnets mentioned above, each of which has its own characteristics. Using magnets and understanding the differences between magnets is important for choosing the best magnet for your project. A motor is generally composed of a part of permanent magnets and electromagnets. The electromagnet needs a power source that can be turned on or off, while the permanent magnet maintains its magnetism.


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