New postby Peter Blunsdon » Tue Oct 07, 2008 9:02 pm

Invar , an alloy of principally iron and about 36% of nickel, discovered by Dr Guillaume. Other combinations of alloys exist. In its early years a difficult material to make to give repeatable results. Nowadays far better.
Low coefficient of expansion, one twentieth that of steel. Frequently used in pendulums and hairsprings. The very best clocks still employ compensation though. Expensive and said to be difficult to machine
Hamilton produced Elinvar, their answer to Invar.
Guillaume got a Nobel prize for his contribution.

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Re: Invar

New postby Fortunat Mueller-Maerki » Wed Oct 08, 2008 12:36 pm

Invar is a highly specialized metal alloy, whose main components are iron and nickel. It gets its name from 'invariable', because the dimensions of a piece of invar (e.g. the length of a pendulum rod) changes less per degree of temperature change than virtually any other metal.

It's designation is FeNi36 (64FeNi in the US)

it is notable for its uniquely low coefficient of thermal expansion . It was invented in 1896 by Swiss scientist Charles Édouard Guillaume. He received the Nobel Prize in Physics in 1920 for this discovery, which shows the importance of this alloy in scientific instruments.

Invar® today is a registered trademark of ArcelorMittal - Stainless & Nickel Alloys, formerly known as Imphy Alloys (US Trademark #63970). Like other nickel/iron compositions, Invar® is a solid solution; that is, it is a single-phase alloy — similar to a dilution of common table salt mixed into water.

Elinvar is a completly different alloy, it was designed to keep the elasticity componet 'invariable'. It is used for balance springs because when using Elinvar the variabilty of the elasticity of the metal as a function of temperature changes is minimized. The name is a contraction of the French 'Elasticité invariable'. It was invented around the 1920s by Charles Édouard Guillaume, a Swiss physicist who also invented Invar (not by Hamilton as implied in the above post). Elinvar consists of 59% iron (as oposed to Invars 64%), 36% nickel, and 5% chromium. It is almost nonmagnetic and corrosion resistant.
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