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Induction Heat Treating
Surface Hardening
The 'case depth' depends on applied power density, operating frequency, quench delay, quench duration, velocity, temperature and quench medium, besides material properties.
The jobs can be hardened by 'single-shot' or 'progressive-hardening' methods. In single-shot mode, the entire surface to be hardened is heated at a time and quenched thereafter. This permits good control over the case pattern, and the cycle time is short. However, this requires a high-power source.
In progressive hardening (also known as traverse hardening or scan hardening), the inductor heats only a small periphery at a time. The job or the inductor is moved progressively with respect to the other. A quench ring follows the heating inductor. Thus the desired length of the job is progressively heated and quenched.
This requires a lower power compared to the single shot process. Cycle time is longer. Being economical, progressive hardening is common.
'Through' Hardening
'Through hardening' by induction is limited to jobs of small diameters. As the heat is generated only on a thin layer below the surface, the power density (thereby the rate of heating) has to be low and the heating time has to be large. Thus the core of the job reaches the desired temperature by thermal conduction. 'On-off' cycling of power is employed sometimes. For jobs of large sections, the hardness at the core depends on the quenchability of the material.
Click here for Application Variants
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