Furnace

Furnace, insulated structure in which high temperatures can be produced and controlled. In most furnaces the heat is produced by burning a fuel such as coal, oil, or gas, though some use the heating effect of electricity. In the so-called atomic furnaces (nuclear reactors), the heat comes from the splitting or fission of atoms and is used to generate electricity. In solar furnaces the heat is produced by concentrating the rays of the sun. Simple furnaces are used in the home to heat water for the heating system. Much larger ones are used in industry to heat, melt, and vaporize all kinds of materials. Metallurgical furnaces, massive structures that produce temperatures of thousands of degrees, are lined with refractory (heat-resistant) bricks that may also be water-cooled. In blast furnaces, used for reducing iron from its ore, fuel (coke) is burned in a blast of hot air inside a vertical cylindrical furnace. In the open hearth, or reverberatory furnace, the heating flame passes over the charge to be melted, and heat reflected from the low roof melts the charge; since there is no contact with the fuel, the charge does not receive any impurities. In the converter type of furnace, such as the Bessemer converter, which is used for refining pig iron, air or oxygen is blown through molten metal to burn out impurities; no fuel is necessary since the “blow” itself generates heat. The electric furnace heats the charge externally and so does not contaminate the product.