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Tuyere is a metallurgical term referring to an opening through which oxygen or air is delivered to the inside of a furnace, hearth or forge, helping increase the temperature in order to smelt, or melt, various types of metal. This device is often shaped like a tube or nozzle that sticks into the furnace from the outside, and is usually made from copper or cast iron. Commonly a set of bellows or a blast engine is connected to the tuyere, forcing air or oxygen through it and into the smelting device. Older types of furnaces often had only one tuyere, while modern industrial furnaces can have more than 40, helping make higher temperatures possible. The word tuyere is ultimately derived from the ancient Germanic word tuyau, meaning pipe, and this device can also be called a tu-iron, twyer or twire-pipe.
Smelting of iron and other metals such as tin and copper has been practiced by humans for thousands of years. The earliest type of smelter capable of melting iron was the so-called bloomery. A bloomery usually consisted of a pit or chimney structure, with a metal or clay tuyere piping air into it through a sidewall. These smelters produced a so-called bloom, meaning a mass consisting of slag and iron which could be forged into wrought iron.
Bloomery-style furnaces were eventually replaced by blast furnaces, which are usually used to smelt iron ore. The ability to produce better furnace fittings, such as cast iron tuyeres, was one factor in the development of blast furnaces. A blast furnace usually has several tuyeres located at the bottom of the structure. Each tuyere blows air or oxygen into the furnace, while ore and fuel, such as coal, is put into the furnace from the top. A blast furnace is capable of higher temperatures than a bloomery, and is usually used to produce pig iron which can then be made into other types of iron or used for steelmaking.
Most tuyeres that pipe air or oxygen into furnaces are cooled by water in order to withstand the high temperatures. In some cases, tuyeres can be used to insert devices for measuring the temperature inside the furnace, or to add various materials to the metal being smelted. A blacksmith's hearth can also be equipped with a tuyere. In this case, the tuyere is often attached to a hand or foot operated bellows that supplies the air keeping the hearth hot enough for the blacksmith to work the metal.