Stabilization & Calibration

Magnetic Stabilization

Permanent magnets suffer extremely low loss except when driven beyond certain critical parameters at which point we say they have "irreversible loss." If re-magnetization restores all of the original magnetic output, then they have not suffered irrecoverable or structural loss. When only irreversable loss is present and it results in unacceptable differences between initial and subsequeent operation, it is almost always possible to "precondition" the magnets so that little to no additional loss is observed in operation. (This assumes that the optimal material has been selected and extraordinary methods must be applied).

If the loss (during use) is expected to come from elevated temperature, then a Thermal Stabilization is recommended. If the loss is due to demagnetizing stress, then a Magnetic Stabilization should be performed.

Magnetic Calibration

Variation in magnetic output (flux output) is unavoidable. Most applications are can tolerate normal variations in flux output. For those that require extremely tight tolerances, magnets can be "calibrated" to a set output by partial knockdown. This is usually a magnetic calibration procedure, though occasionally thermal calibration is used - - where uniformity at elevated temperature is essential.

Arnold has extensive experience in performing both thermal and magnetic procedures. For example, one consideration is that thermal conditioning can be performed either in open circuit or fixed load line.

For applications requiring stable output over a wide temperature range, customers are urged to consider Recoma™ STAB, a grade of SmCo with less than 50 ppm change in output per ºC from -40 to 200 ºC.

A paper discussing magnetic and thermal knockdown is: NdFeB for High Temperature Motor Applications. Additional papers on related subjects can be found in the Publications section of the Technology Center.