LOW EXPANSION METALS L019
It is important in high temperature metal bellows applications that you choose a metal face holder component with an expansion rate similar to carbon-graphite or the seal face can fall out during high temperature operation.
Two metals are commonly used, but neither of them has very good corrosion resistance.
- Invar 36. Mostly iron with 36% nickel and small amounts of impurities of carbon, manganese and silicone
- Carpenter 42 (42% nickel).
Other low expansion metals include:
- NiSpan C
- Elinvar Extra
Elinvar is noted for its constant modulus of elasticity over a wide temperature range. Because of their titanium content, NiSpan C and Elinvar Extra can be solution heat treated and aged to very high strength levels. Tensile yield strengths to 180,000 psi (1241 Mpa) with a corresponding Rockwell C hardness of Rc 42 have been attained.
As a comparison, a Rockwell C hardness of 40-50 Rc is common in mechanical seal hard faces.