A Furnace is a device used for heating. The term furnace is used exclusively to mean industrial furnaces which are used for many things, such as the extraction of metal from ore (smelting) or in oil refineries and other chemical plants, for example as the heat source for fractional distillation columns.
An Induction Furnace is an electrical furnace in which the heat is applied by induction heating of a conductive medium (usually a metal) in a crucible placed in a water-cooled alternating current solenoid coil. The advantage of the induction furnace is a clean, energy-efficient and well-controllable melting process compared to most other means of metal melting. Most modern foundries use this type of furnace and now also more iron foundries are replacing cupolas with induction furnaces to melt cast iron, as the former emit lots of dust and other pollutants. Induction Furnace capacities range from less than one kilogram to one hundred tonnes capacity, and are used to melt iron and steel, copper, aluminium, and precious metals.
Operating frequencies range from utility frequency (50 or 60 Hz) to 400 kHz or higher, usually depending on the material being melted, the capacity (volume) of the furnace and the melting speed required. Generally the smaller the volume of the melts the higher the frequency of the furnace used; this is due to the skin depth which is a measure of the distance an alternating current can penetrate beneath the surface of a conductor. For the same conductivity the higher frequencies have a shallow skin depth – that is less penetration into the melt. Lower frequencies can generate stirring or turbulence in the metal.
There are two types of induction furnaces. The first is coreless and the second is called channel. The coreless induction furnace has copper coils that are protected by a steel and magnetic shield and kept cool by water circulating from a special cooling tower. A layer of refractory, or difficult to melt material, is placed above the coils and heated to the desired temperature. A crucible, which is a melting pot made of heat resistant material, is above the refractory. The metal to be melted is placed inside the crucible and the heat produced by the electromagnetic charge melts the scrap. The channel induction furnace can also be called a core induction furnace. It functions very similarly to the coreless furnace, except for the addition of a heated core. Channel furnaces were originally used as molten metal holders, but have been found useful in the melting of lower melt temperature metals.