There are the following methods of electric heating:
- Resistance heating.
(i) Direct heating. (ii) Indirect heating.
- Induction heating.
(i) Direct heating. (ii) Indirect heating.
- Dielectric heating.
- Electric arc heating.
Core less induction type furnace.
This type of furnace is suitable on high frequencies 500 — 3000 Hz, mains. In this case the body (charge) to be melted is made the secondary of the transformer. The primary winding is wound over a crucible ‘A’ itself and separated from it by a thin layer of heat insulating material. The coil ‘C’ which acts as primary winding of a two winding transformer, is energised by a high frequency supply. It produces the eddy currents in the charge which is made as the secondary as shown in Fig. 8.2. The eddy currents induced in the charge, heat it and melts. An automatic stirring due to electro-dynamic force is obtained in this process.
Fig. 8.2. Core loss instiation typo
The frequency employed usually depends upon the size of the furnaces. Even 3000 Hz supply is supplied for lower size of machine and 500 Hz for higher sizes i.e. 100 kW The melting capacity range from 50 kg to 20 tonnes.
