The Principle of Surface Quenching

1）Basic Principle: the workpiece in the wind with the hollow copper pipe in sensors, access to intermediate frequency or high frequency alternating current (ac), formed in the surface with the frequency of the induced current, the workpiece surface or local rapid heating (a few seconds to temperatures of 800 ~ 1000 ℃, the heart is still close to room temperature) immediately after several seconds quickly spray (dip) water cooling (or spray oil immersion cooling) complete immersion fire work, make the hardness of workpiece surface or local corresponding requirements.

2) Heating Frequency: at room temperature, the relationship between the depth (mm) of the induced current flowing into the surface of the workpiece and the current frequency f (HZ) is as follows: frequency increases, current penetration depth decreases, and the quenching layer decreases.

The current frequencies commonly used for high frequency quenching of science and technology are:

1. High-frequency heating: 100 ~ 500KHZ, commonly used 200 ~ 300KHZ, for electronic tube high-frequency heating, hardened layer depth of 0.5 ~ 2.5mm, suitable for small and medium-sized parts.

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

3. Power frequency heating: the current frequency is 50HZ.The mechanical power supply with power frequency heating is adopted, and the hardened layer is up to 10 ~ 20mm, suitable for surface quenching of large diameter workpiece.

(iii) application of High frequency induction heating machine heating surface quenching: compared with ordinary heating quenching,

1. The heating speed is very fast, which can expand the transformation temperature range of body A and shorten the transformation time.

2. After quenching, the surface of the workpiece can obtain extremely fine cryptocrystalline martensite with slightly higher hardness (2 ~ 3HRC).Low brittleness and high fatigue strength.

3. The workpieces processed by this process are not easy to be oxidized and decarbonized, and some workpieces can even be directly assembled and used after processing.

4. The hardened layer is deep, easy to control and operate, easy to realize mechanization and automation.

5. flame surface heating and quenching: suitable for medium carbon steel 35, 45 steel and medium carbon alloy structural steel 40Cr and 65Mn, gray cast iron, alloy cast iron flame surface quenching.The workpiece is rapidly heated by a jet of flame burning a mixture of acetylene and oxygen or gas and oxygen.After the surface of the workpiece reaches the quenching temperature, immediately water cooling.The depth of the hardened layer is 2 ~ 6mm, otherwise the surface of the workpiece will cause serious overheating and deformation and cracking.