Single Coil Dual Frequency: Gear Hardening pt. 4

The gear is induction preheated to a temperature determined by the process features, typically being 350 to 100°C below the critical temperature Ac1. The pre- heat temperature depends on the type and size of the gear, tooth shape, prior mi- crostructure, required hardness pattern, acceptable distortion, and the available power source. Usually, preheating is ac- complished by using medium frequency (3 to 10 kHz). Lower frequency results in greater eddy current penetration depths, which lead to more “in-depth” preheating effect. A high frequency (30 to 450 kHz) and high power density are applied during the final heating stage.

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