Coil Failures: Coils for Internal Surfaces pt. 12

In contrast to inductors used to heat external surfaces or outside diameters, the effectiveness of an internal coil depends to a much greater extent on the coil-to-workpiece gap. Electrical efficiency of internal coils rapidly decreases with an increase in the coil-to-workpiece coupling gap, particularly when heating nonmagnetic metals or carbon steels above Curie temperature.

Click here for more information.