Indirect Core Type Induction Furnace: Construction & Working Principle

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Induction Heating Furnace

An electrical furnace in which the heat is produced by induction heating of metal, is called the induction heating furnace. The induction heating furnaces have the capacities range from less than 1 kg to 100 tons and are used to melt various metals like iron, copper, aluminium, etc.

Indirect Core Type Induction Furnace

The indirect core type induction furnace works on the principle of Faraday’s law of electromagnetic induction (mutual inductance). The schematic of an indirect core type induction furnace is shown in the figure below.

In this type of induction furnace, a heating element is heated by induction, which transfers the heat to the charge, to be heated, by radiation.

The indirect core type induction furnace consists of a primary winding through which an alternating current is passed. The secondary winding consists of a metal container which forms the walls of the furnace proper. The primary winding is magnetically coupled to the secondary winding by an iron core.

When the primary winding is connected to the AC supply, the secondary current is induced in the metal container by transformer action which heats up the container. The heat produced due to induced current is transmitted from the metal container to the charge to be heated by radiation.

The part AB of the magnetic circuit situated inside the furnace chamber consists of a special alloy which losses its magnetic properties at a particular temperature (called critical temperature) and regains them when cooled back to the same temperature. The part AB of the magnetic circuit is detachable and can be replaced by other part having different critical temperature, between 400 °C to 1000 °C. As soon as the furnace chamber attains the critical temperature, the reluctance of the magnetic circuit increases greatly thereby cutting off the supply of the heat.

The main advantage of the indirect core type induction furnace is that its temperature can be automatically controlled without the use of any external equipment.