People have been casting metal since at least 3000 B.C.E. Over time, the practice became more and more sophisticated as our understanding of metal and its properties became clearer. There are different types of melting furnaces, some of which are of varying degrees of technology.
One of the oldest style of melting furnaces, the cupola furnace, has a tall, cylindrical shape. The insides of these furnaces are lined with clay, blocks or bricks which protect the furnace's interior from heat, abrasion and oxidation. To melt the metal in the furnace, workers add layers of metal such as ferro alloys, limestone and coke. The limestone reacts with the metal, making the impurities float up to the surface of the melting metal.
Induction furnaces use alternating currents to create the necessary heat with which to melt the metal. The refractories, or the lining, of these are made from materials such as alumina, silica and magnesia. These furnaces work well for melting metal such as iron as well as metals that are nonferrous. Inside the induction furnaces are copper coils which are cooled with water.
These furnaces are often used in steel mills as well as foundries. Metal and additives are poured into the furnace. The additives help to separate the impurities present in the metal. The furnace melts the metal through the use of granite or carbon electrodes which create an electric arc.
A hearth furnace works well for melting small quantities of nonferrous metal. These furnaces use natural gas or electricity to produce heat by which to melt the metal.