Indirect Arc Furnace – Construction, Working, and Applications

Indirect Arc Furnace

An electric arc furnace in which the heat is produced by striking the arc between two electrodes and then transferred to the charge to be heated is called an indirect arc furnace.

In an indirect electric arc furnace, the electric arc does not come in contact with the charge but heat is transferred through radiation from the electric arc to the top surface of the charge and through conduction from the top surface to the bottom layer in the charge.

Construction and Working

The construction of the indirect arc furnace is shown in the figure. The figure shows a rocking arc furnace which working on the principle of indirect arc heating. The furnace is made of steel shell of cylindrical shape. The inner surface of the steel shell has to be lined with some refractory material. It has two carbon electrodes supplied from a single-phase AC supply for striking the arc.

In the indirect arc furnace, the low voltage 1-phase AC supply is applied across the electrodes and the arc is struck by short-circuiting the electrodes manually or automatically for a moment and withdrawing these apart.

The heat from the arc is transferred to the top layer of the charge and to the refractory lining through radiation and the heat from the top layer of the charge to the other parts of the charge is transferred through conduction.

Since the arc does not come in contact with the charge, to be heated, so the automatic stirring action is not present in the indirect arc furnace. Therefore, the indirect arc furnace needs to be equipped with automatic rocking equipment. Hence, to distribute the heat properly, the indirect arc furnace has to be rocked continuously exposing further layers of the charge, not only to transfer the heat from the arc, but also from the exposed lining, results in the prolonged life of the lining.

As the indirect arc furnace is working on a 1-phase AC supply, it may cause the following two problems −

• It will result in a great load unbalance on the supply system, if the proper furnace transformer is not used.

• This furnace is not supported to handle melting beyond 1 tonne.

The indirect arc furnace unit works quite efficiently due to totally enclosed construction and the carbon electrodes further improve the quality of ferrous melts. The power factor of the indirect arc furnace varies from 0.7 to 0.8.

Applications of Indirect Arc Furnace

Indirect arc furnaces are mainly used for melting non-ferrous metals. Also, they are used in iron foundries where small quantities of iron are required frequently.