Bimetal refers to an object that is composed of two separatemetals joined together. Instead of being amixture of two or more metals, likealloys, bimetallic objects consist of layers of different metals. Trimetal and tetrametal refer to objects composed of three and four separate metals respectively. A bimetal bar is usually made of brass and iron.
Bimetallic strips and disks, which convert a temperature change into mechanical displacement,[1] are the most recognized bimetallic objects due to their name. However, there are other common bimetallic objects. For example,tin cans consist ofsteel covered withtin.[2] The tin prevents the can fromrusting. To cut costs and prevent people from melting them down for their metal,coins are often composed of a cheap metal covered with a more expensive metal. For example, theUnited States penny was changed from 95%copper to 95%zinc, with a thin copperplating to retain itsappearance. A common type of trimetallic object (before the all-aluminium can) was a tin-plated steel can with analuminum lid with a pull tab. Making the lid out of aluminum allowed it to be pulled off by hand instead of using acan opener, but these cans proved difficult torecycle owing to their mix of metals.
Blades forbandsaws andreciprocating saws are often made with bimetal construction. The teeth, made ofhigh-speed steel, are bonded (by various methods, for example,electron beam welding orlaser beam welding) to the softer high-carbon steel base. Such construction makes for blades with a better combination of cutting speed and durability than shown by non-bimetal blades, because the advantages and disadvantages of each of the metals are applied in the best locations: the teeth areharder (and thus cut better), but therefore alsobrittler; meanwhile, the body area of the band is softer (which would make for poorer teeth), but also less brittle, and thus more resistant to cracking and breaking (which is desirable in the body area).
