Low Expansion Alloy Strip

LOW-EXPANSION ALLOYS include various binary iron-nickel alloys and several ternary alloys of iron combined with nickel-chromium, nickel-cobalt, or cobalt-chromium alloying. Many of the low-expansion alloys are identified by trade names: Invar, which is a 64%Fe-36%Ni alloy with the lowest thermal expansion coefficient of iron-nickel alloys Kovar, which is a 54%Fe-29%Ni-17%Co alloy with coefficients of expansion closely matching those of standard types of hard (borosilicate) glass Elinvar, which is a 52%Fe-36%Ni-12%Cr alloy with a zero thermoelastic coefficient (that is, an invariable modulus of elasticity over a wide temperature range) Super Invar, which is a 63%Fe-32%Ni-5%Co alloy with an expansion coefficient smaller than Invar but over a narrower temperature range Besides these common trade names, alloy compositions are also selected to have appropriate expansion characteristics for a particular application. Low-expansion alloys are used in applications such as: Rods and tapes for geodetic surveying Compensating pendulums and balance wheels for clocks and watches Moving parts that require control of expansion, such as pistons for some internal-combustion engines Bimetal strip Glass-to-metal seals Thermostatic strip Vessels and piping for storage and transportation of liquefied natural gas Superconducting systems in power transmissions Integrated-circuit lead frames Components for radios and other electronic devices Structural components in optical and laser measuring systems Low-expansion alloys are also used with high-expansion alloys (65%Fe-27%Ni-5%Mo, or 53%Fe-42%Ni-5%Mo) to produce movements in thermoswitches and other temperature-regulating devices.