Bimetal refers to an object that is composed of two separate

metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

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 can be separated by physical method. It is an impure substance made up of 2 or more elements or compounds mechanically mixed together in any proporti ...

of two or more metals, like

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

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 or bimetal strip is a strip that consists of two strips of different metals which expand at different rates as they are heated. The different expansion rates cause the strip to bend one way if heated, and in the opposite dire ...

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), or can is a container made of thin metal, for distribution or storage of goods. Some cans are opened by removing the to ...

s consist of

steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

covered with

tin Tin is a chemical element; it has symbol Sn () and atomic number 50. A silvery-colored metal, tin is soft enough to be cut with little force, and a bar of tin can be bent by hand with little effort. When bent, a bar of tin makes a sound, the ...

. 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(OH) ...

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

coin A coin is a small object, usually round and flat, 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 to facilitate trade. They are most often issued by ...

s are often composed of a cheap metal covered with a more expensive metal. For example, the United States penny was changed from 95%

copper Copper is a chemical element; it has symbol Cu (from Latin ) 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 pinkish-orang ...

to 95%

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It 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 periodic tabl ...

, with a thin copper

plating Plating is a finishing process in which a metal is deposited on a 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 improve solderab ...

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 ...

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

aluminum Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

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 (North American and Australian English) or tin opener (British English) is a mechanical device used to open metal tin cans. Although preservation of food using tin cans had been practiced since at least 1772 in the Netherlands, the ...

, but these cans proved difficult to

recycle ReCycle is a music loop editor designed and developed by Sweden, Swedish software developers Propellerhead Software. It runs on Microsoft Windows and Apple Macintosh based Personal Computer, PCs. The software debuted in 1994. The principal idea ...

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 lum ...

s and

reciprocating saw A reciprocating saw is a type of handheld, small, machine-powered saw, in which the cutting action is achieved through a push-and-pull ("reciprocating") or back-and-forth motion of the blade. The original trade name, Sawzall, is often used in th ...

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. Compared to high- carbon steel tools, high-speed steels can withstand higher temperatures without losing their temper (hardness), allowing use of ...

, are bonded (by various methods, for example,

electron beam welding Electron-beam welding (EBW) is a fusion welding process in which a charged-particle beam, 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 ...

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 freque ...

) 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