The principle of high-frequency quenching: placing the workpiece in an inductor wound with a hollow copper tube, and after introducing high-frequency alternating current, forming an induced current of the same frequency on the surface of the workpiece, rapidly heating the surface or part of the part (in seconds) It can be heated to 800 ~ 1000 ° C, the heart is still close to room temperature. After a few seconds, immediately spray (dip) water cooling (or spray oil cooling) to complete the immersion work, so that the workpiece surface or local to meet the corresponding hardness requirements.
The equipment for induction heating and heat treatment is mainly composed of power supply equipment, quenching machine and inductor. The main function of the power supply device is to output an alternating current with a suitable frequency. The high-frequency current power supply device has two types of tube high-frequency generators and thyristor inverters. The intermediate frequency current power supply unit is a generator set. Generally, the power supply device can only output current of one frequency. Some devices can change the current frequency, or can directly use the 50 Hz power frequency current for induction heating.
The choice of power supply unit is related to the depth of the heating layer required for the workpiece. For workpieces with deep layer heating, power supply equipment with lower current frequency should be used; for workpieces with shallow heating layer, power supply equipment with higher current frequency should be used. Another condition for selecting a power device is device power. As the heating surface area increases, the required power supply increases accordingly. When the heating surface area is too large or the power supply is insufficient, a continuous heating method may be employed to relatively move the workpiece and the inductor, the front side is heated, and the rear side is cooled. However, it is best to heat the entire heated surface once. In this way, the hardened surface layer can be tempered by utilizing the residual heat of the workpiece core, thereby simplifying the process and saving energy.
The depth of the hardened layer of the induction hardened surface layer depends on the frequency of the alternating current. Generally, the frequency is high and the heating depth is shallow, and the depth of the hardened layer is shallow. The relationship between the frequency f and the heating depth δ has the following empirical formula: δ = 20 / √ f (20 ° C); δ = 500 / √ f (800 ° C).
Where: f is the frequency, the unit is Hz; δ is the heating depth, the unit is millimeter (mm).
Induction heating surface quenching has the advantages of good surface quality, small brittleness, hard oxidative decarburization and small deformation of quenched surface, so induction heating equipment has been widely used in metal surface heat treatment.