Power frequency induction heating

Industrial frequency induction heating is often used to relieve stress on large parts. However, practical experience shows that medium frequency induction heating is often more desirable due to its higher power density, despite the slightly higher investment cost.

Power frequency induction

The lower current in the medium frequency induction coil allows the use of thinner cables, which are easier to maintain and easier to lay on the heating equipment. For example, the stress relief of heat exchangers used in nuclear power plants uses medium frequency power.

The heat exchanger is made by welding several steel cylindrical cylinders to each other and finally welding hemispherical heads on both ends of the cylinder. Before welding, the edges of the welded part can be induction preheated and at the end of welding, the entire heat affected zone can be heated to the temperature required for stress relief by induction heating.

Industrial frequency induction furnace

The outside of the heated part is covered with insulation material, and a specially constructed flexible cable is placed in an appropriate position according to the shape of the inductor. The outer insulation material is fixed with non-ferrous metal sheets clamped on the cylinder.

The same insulation layer is used inside the part to be heated. The cable ends pass through the housing into the base plate and are connected to the busbars there. The busbars are powered by a 200 kW, 2500 Hz generator. The application of induction heating for stress relief and annealing is not limited to large-scale heating.

It can also be applied to small parts, such as local stress relief treatment of tractor pins that have been previously hardened in a heating furnace. A device for this purpose has a set of pin continuous conveyor chain mechanism with a production rate of 720 pins/hour.