An arc furnace (AF) is one which uses an electric arc to generate heat which is applied on materials until they reach their melting point, mostly metals. It works by passing electrical current through the material via some electrodes. The material being melted is also referred to as the “charge”. Heat generated by passing current combines with the arcing on the charge hence heating and melting the material. They are mostly installed dental prosthesis labs, cast iron industries, steel plants and research facilities. Their capacity can vary from small sizes to big ones that can handle as much as 400 tons of material.
The structure of an AF can be pictured as one containing a shell with side walls. At the bottom is a hollow bowl and at the top is a cover with a rectangular roof that acts as the entry point for graphite electrodes to cover the furnace. The bowl part of the shell has a lining of hard material referred to as hearth. It also has a tap whose function is to drain out molten material. The tap is either situated at the bottom or at the sides. The shape of the electrodes is generally round but made up of threaded parts to enable more of new electrodes to be added to replace burnt ones.
A Resistance furnace (RF) on the other hand is mostly used in homes to generate heat and warm the house. It is also called an electric resistance furnace. The heat develops when current is passed through a suitable material with a certain amount of internal resistance. The heat warms up air which is then circulated througout the house by use of a blower through various designated ducts.
There isn’t any form of combustion that takes place in an RF. They run on electricity and are generally easier to maintain in comparison to gas or oil ones. In most cases they are attached to a thermostat which is then attached to relays inside the RF. This allows one to vary the amount of heat needed.
The thermostat is able to switch heat on and off automatically depending on the temperature in the house. It also contains an air circulation switch which enables the user to run the blower continuously thus allowing constant flow of air. The switch can either be on the furnace itself or on a thermostat.