Eddy current couplings and brakes
In contrast to the drive and brake elements described previously, the torque in eddy current clutches and brakes (fig.4) is only produced by a relative speed between drive and driven sides.
Thus the transferable moment increases with the relative rpm. Fig. 10 shows the torque gradient for two different air gaps. In practice rings or segments in permanent magnet material e.g. HF 24/20 are magnetised on one side with several poles and on the other hand we find a copper disc 2-5 mm thick, which for magnetic reasons has a soft iron backing of 2-6 mm thickness. Table 4 compares the torques, which can be achieved by eddy current clutches and brakes for 3 different relative rpm. and various air gaps.
The given values relate to room temperature which was set by measurements of corresponding cooling of the copper discs. In eddy current clutches and brakes the temperature coefficient of the copper is considered along with the temperature coefficient of the magnet. Eddy current clutches and brakes heat up considerably due to the development of eddy currents with increasing rpm.; with temperature increase the value of the torque attainable decreases considerably. If cooling is not provided, temperatures up to 200°C at relative rpm of 1000/min can occur on the copper disc whereby the torque decreases by 50%. The losses thereby incurred are partly irreversible. They can only be recovered by remagnetisation. If the temperature is kept below 50°C, the decrease in torque is only about 10%.
In certain rpm ranges eddy current clutches show a roughly proportional or constant torque – rpm. – characteristic. This means, eddy current clutches are suitable for use in coil machines where constant band tension and constant band speed are required. For details please refer to special literature.
Please find below an extract of our product range. Further types on request. We also develop solutions according to your special requirements.
 Eddy current clutches and brakes in HF 24/20, SmCo and Cu/Fe |
 Diagrammatic representation of torque of hysteresis and eddy current clutches dependent on relative speed |
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