Surface hardening of steel

Induction heating surface hardening

Basic principle of induction heating

This is a schematic diagram of induction heating surface quenching. Put the workpiece into the inductor (coil) wound by hollow copper tube. When the coil is connected with alternating current, alternating magnetic field will be generated immediately. Then the induction current with the same frequency and opposite direction will be generated in the workpiece. The induced current will form a circuit in the workpiece, which is called "eddy current". The current density is not distributed on the workpiece surface Under the action of the basic resistance of the workpiece, the surface layer is heated rapidly to the quenching temperature while the center part is still close to the room temperature. After the water spray cooling immediately, the surface quenching is achieved.

Selection of induction heating frequency

1. High frequency induction heating

The frequency is 200-300khz, and the depth of hardening layer is 0.5-2mm. It is mainly used for small and medium parts with thin hardening layer. Such as: small module gear, medium and small shaft surface hardening.

2. Medium frequency induction heating

The frequency is 500-10000hz, and the depth of the hardened layer is 2-8mm. It is mainly used for processing the parts with deeper requirements of the hardened layer. For example: the shaft with larger diameter and the gear with larger module.

3. Power frequency induction heating

The frequency is 50Hz, and the depth of hardening layer can reach 10-15mm. Large diameter parts with deep hardening layer, such as roller and train wheel, are required.

4. Over frequency induction heating

Frequency 20-40hz, such as: medium and small module gear, spline shaft, sprocket.

Surface quenching by flame heating

Flame heating surface quenching is a kind of surface quenching method with high temperature flame as heat source. The flame is acetylene oxygen flame, with a maximum temperature of 3200 ° C. In addition, there is gas oxygen flame, with a maximum temperature of 2000 ° C. It is used to rapidly heat the workpiece to the quenching temperature, and then spray water for cooling to obtain the required surface hardness and hardening layer hardness.