Magnetic coupling at elevated temperatures

Magnetic couplings are used in many applications within pump, chemical, pharmaceutical, process and safety industries. They are typically used with the purpose of reducing wear, sealing of liquids from the environment, cleanliness needs or as a safety factor to brake over if torque suddenly rises.

The most common magnetic couplings are made with an outer and inner drive, both build up with Neodymium magnets in order to get the highest torque density as possible. By optimizing the diameter, air gap, magnet size, number of poles and choice of magnet grade, it is possible to design a magnetic coupling that suits any application in the range from few millinewton meter up to several hundred newton meters.

When only optimizing for high torque, the designers often tend to forget considering the influence of temperature. If the designer refers to the Curie point of the individual magnets, he will claim that a Neodymium magnet would fulfill the requirements up to more than 300°C. Concurrently, it is important to include the temperature dependencies on the remanence, which is seen as a reversible loss – typically around 0,11% per degree Celsius the temperature rises.

Furthermore, a neodymium magnet is under pressure during operation of the magnetic coupling. This means that irreversible demagnetization will occur long before the Curie point has been reached, which typically limits the use of Neodymium-based magnetic coupling to temperatures below 150°C.

If higher temperatures are required, magnetic couplings made of Samarium Cobalt magnets (SmCo) are typically used. SmCo is not as strong as Neodymium magnets but can work up to 350°C. Furthermore, the temperature coefficient of SmCo is only 0,04% per degree Celsius which means that it can be used in applications where performance stability is needed over a larger temperature interval.

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