Bimetal refers to an object that is composed of two separate

metal A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...

s joined together. Instead of being a

mixture In chemistry, a mixture is a material made up of two or more different chemical substances which are not chemically bonded. A mixture is the physical combination of two or more substances in which the identities are retained and are mixed in the ...

of two or more metals, like

alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...

s, 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 stripe

Bimetallic strip A bimetallic strip is used to convert a temperature change into mechanical displacement. The strip consists of two strips of different metals which expand at different rates as they are heated. The different expansions force the flat strip to be ...

s and disks, which convert a temperature change into mechanical displacement, are the most recognized bimetallic objects due to their name. However, there are other common bimetallic objects. For example,

tin can A steel can, tin can, tin (especially in British English, Australian English, Canadian English and South African English), steel packaging, or can is a container for the distribution or storage of goods, made of thin metal. Many cans ...

s consist of

steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...

covered with tin. The tin prevents the can from

rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO( ...

ing. To cut costs and prevent people from melting them down for their metal,

coin A coin is a small, flat (usually depending on the country or value), round piece of metal or plastic used primarily as a medium of exchange or legal tender. They are standardized in weight, and produced in large quantities at a mint in order ...

s are often composed of a cheap metal covered with a more expensive metal. For example, the

United States penny The cent, the United States one-cent coin (symbol: ¢), often called the "penny", is a unit of currency equaling one one-hundredth of a United States dollar. It has been the lowest face-value physical unit of U.S. currency since the abolition ...

was changed from 95%

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...

to 95%

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

, with a thin copper

plating Plating is a surface covering in which a metal is deposited on a conductive surface. Plating has been done for hundreds of years; it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to impro ...

to retain its

appearance Appearance may refer to: * Visual appearance, the way in which objects reflect and transmit light * Human physical appearance, what someone looks like * ''Appearances'' (film), a 1921 film directed by Donald Crisp * Appearance (philosophy), or p ...

. A common type of trimetallic object (before the all-aluminium can) was a tin-plated steel can with an

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

lid with a pull tab. Making the lid out of aluminum allowed it to be pulled off by hand instead of using a

can opener A can opener (in North American English and Australian English) or tin opener (used in British English) is a mechanical device used to open tin cans (metal cans). Although preservation of food using tin cans had been practiced since at leas ...

, but these cans proved difficult to

recycle Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...

owing to their mix of metals. Blades for

bandsaw A bandsaw (also written band saw) is a power saw with a long, sharp blade consisting of a continuous band of toothed metal stretched between two or more wheels to cut material. They are used principally in woodworking, metalworking, and lu ...

s and

reciprocating saw A reciprocating saw is a type of machine-powered saw in which the cutting action is achieved through a push-and-pull ("reciprocating") motion of the blade. The original trade name Sawzall is often used in the United States, where Milwaukee Elec ...

s are often made with bimetal construction. The teeth, made of

high-speed steel High-speed steel (HSS or HS) is a subset of tool steels, commonly used as cutting tool material. It is often used in power-saw blades and drill bits. It is superior to the older high-carbon steel tools used extensively through the 1940s in tha ...

, are bonded (by various methods, for example,

electron beam welding Electron-beam welding (EBW) is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined. The workpieces melt and flow together as the kinetic energy of the electrons is transformed into heat u ...

laser beam welding Laser beam welding (LBW) is a welding technique used to join pieces of metal or thermoplastics through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequen ...

) 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 are harder (and thus cut better), but therefore also brittler; 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).

See also

References

Further reading