Magnetic couplings at elevated temperature are used in many applications within the pump, chemical, pharmaceutical, energy, Power-to-X, process and safety industries. They are typically used with the following purposes:
- Reducing wear
- Improving the sealing of liquids from the environment
- Safely closing high-pressure systems
- Meeting cleanliness needs
- Providing a safety factor for torque limiting if the torque suddenly rises
The neodymium magnets that are typically used in magnetic couplings, are strongly affected by higher temperatures, therefore, other solutions must be found.
At Sintex we have two different solutions for high temperature applications.
Standard Samarium Cobalt magnetic couplings:
Standard Samarium Cobalt (SmCo) magnets can work at temperatures of up to 350 °C. When these magnets are used in magnetic couplings the systems can typically run under stable conditions at 300 °C with a good safety margin.
When only optimizing for high torque, the designers often forget to consider the influence of temperature. When referring to the Curie point of the individual magnets, it is often claimed that a Neodymium magnet will fulfil the requirements up to more than 300 °C. Furthermore, even though the maximum working temperature of the magnet is of use, one most be careful due to the relatively low magnetic load. Therefore, 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 magnetically loaded 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 couplings to temperatures below 150 °C.
If higher temperatures are required, magnetic couplings made of samarium-cobalt magnets (SmCo) are typically used. Samarium-cobalt magnets are not as strong as Neodymium magnets, but can work up to 350 °C. Furthermore, the temperature coefficient of samarium-cobalt 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.
New magnetic coupling generation – R&D project
Challenged by strong partners, a new generation of magnetic couplings has been developed by Sintex.
The purpose of this project was to develop a magnetic coupling that could expand the working temperature range to reach temperatures of molten salts at around 600 °C. By exchanging the inner drive with a soft magnetic material with a higher Curie point and boosting the magnetic field of the outer drive with special magnetic designs, we have developed a magnetic coupling that started at a lower torque level at room temperature, with only a minor reduction in torque level as a result of temperature change. This results in superior performance above 160 °C, both measured against neodymium- or samarium-cobalt-based system. As shown on the graph below, the torque level of the High Hot drives has been tested in temperatures up to 590 °C on the inner drive with a torque reduction of 15-20% compared to room temperature.
The graph also shows that the temperature coefficient of the High Hot coupling is even lower than for the samarium-cobalt system. This opens a lower temperature market where performance stability is more important than a larger temperature interval.
