The workpiece is placed in an inductor wound with a hollow copper tube, and after the medium-frequency or high-frequency alternating current is applied, an induced current with the same frequency is formed on the surface of the workpiece, so that the surface or part of the workpiece is rapidly heated (the temperature can rise to 800 ~ 1000℃ in a few seconds, and the core is still close to room temperature) for a few seconds, and then the workpiece is quickly and immediately cooled by water spraying (soaking) (or oil spraying) to complete the fire soaking work, so that the surface or part of the workpiece is rapidly heated. ?

chief method

Induction heating surface quenching (high frequency, medium frequency and power frequency), flame heating surface quenching, electric contact heating surface quenching, electrolyte heating surface quenching, laser heating surface quenching and electron beam heating surface quenching.

The combination of rapid heating and rapid quenching and cooling. ?

By rapid heating, the surface of the steel to be processed reaches the quenching temperature, and it is cooled quickly before the heat reaches the center, so that only the surface layer is hardened into martensite, and the center is still the original annealed (or normalized) structure, which has good plasticity and toughness.

select frequency

At room temperature, the relationship between the depth δ(mm) of induced current flowing into the workpiece surface and the current frequency f(HZ) is as follows: the frequency increases, the current penetration depth decreases, and the hardened layer decreases.

Commonly used current frequencies are:

1, high-frequency heating: 100 ~ 500 kHz, commonly used 200 ~ 300 kHz, high-frequency heating by electron tube, and the depth of hardened layer is 0.5 ~ 2.5 mm, which is suitable for small and medium-sized parts.

2. Intermediate frequency heating: the current frequency is 500 ~ 500~ 10000HZ, commonly used 2500~8000HZ, and the power supply equipment is mechanical intermediate frequency heating device or thyristor intermediate frequency generator. The depth of hardened layer is 2 ~10mm. Suitable for large diameter shafts, large gears, etc.

3. Power frequency heating: the current frequency is 50HZ. The depth of hardened layer can reach 10 ~ 20 mm by using mechanical power frequency heating power supply equipment, which is suitable for surface quenching of large diameter workpieces.