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Electric Arc Furnaces

Electric arc furnaces may be categorised as direct arc or indirect arc. Both types of units are suited for the melting of high melting point alloys such as steels. They may be lined with acid or basic refractories.

Direct arc furnaces

Direct arc furnaces are very popular for the melting of alloy steels and range in size from a few kilograms, for laboratory units, to in excess of 100 tonnes per batch. Typically units found in foundries are in the range of 1 to 10 tonnes. The furnace generally consists of a cylindrical steel shell which is lined with acid or basic refractories. The roof which can normally swing away to facilitate charging, generally contains three carbon electrodes operating on a high tension three-phase power supply. These electrodes protrude vertically through the roof and an electric current passes directly through them and into the metal bath. The distance between the electrodes and the metal bath is automatically controlled and determines the power input into the bath.

These furnaces generally have a door at the back for alloying, oxygen lancing and slag removal purposes, and a pouring spout at the front. The entire unit is capable of being tilted for discharge of the melt through the pouring spout.

Some of the advantages of direct arc furnaces include high melt rates, high pouring temperatures and excellent control of melt chemistry.

Indirect arc furnaces

Generally consist of a horizontal barrel shape steel shell lined with refractories. Meltin is effected by the arcing between two horizontally opposed carbon electrodes. Heating is via radiation from the arc to the charge. The barrel shaped shell is designed to rotate and reverse through approximately 180°C in order to avoid excessive heating of the refractories above the melt level and to increase the melting efficiency of the unit.

Indirect arc furnaces are suitable for melting a wide range of alloys but are particularly popular for the production of copper base alloys. The units operate on a single-phase power supply and hence the size is usually limited to relatively small units.

References

Fundamentals of Foundry Technology - PD Webster, Portcullis Press 1980
A Century of Melting and Pouring Improvements - R Joe Planson, Foundry Managment and Technology, Sept 1992
Induction Melting for the Smaller Foundry - Chris Buck, Inductotherm Aust Pty Ltd., AFI Convention Proceedings 1994

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