Bimetal(redirected from Tri-metal)
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a metallic material consisting of two layers of heterogeneous metals or alloys (such as steel and aluminum, steel and niobium, aluminum and titanium, titanium and molybdenum). Bimetals are used to increase the strength or heat resistance of structures, to reduce their bulk while economizing on expensive or scarce materials, and to obtain materials with special characteristics when required. For example, in electrical and radio engineering, bimetals are widely used because the density of an alternating current is greater at the periphery of the conductor than at its core, and therefore it is sometimes expedient to coat the surface of a conductor made of cheaper material (steel or aluminum) with good conductive material (copper or silver). In instrument-making, the differences in temperature coefficients of expansion of the different metals in bimetallic plates are utilized. In machine-building, certain parts of machinery, such as bush bearings, are made of bimetals.
Bimetals are made primarily by simultaneous rolling or pressing of two slabs of different metals or alloys. The casting of a fusible metal onto a refractory one and the immersion of a refractory metal in a molten fusible one are also common. In electroplating, the layer of the more precious metal is applied electrolytically. The expensive and scarce harder alloys are applied to steel by electric heating (in the production of cutting tools, dies, and the like).