The Application and Behavior of Elastomers at Cryogenic Temperatures
Elastomers offer the cryogenic engineer a dramatic demonstration of how the properties of some materials change radically when cooled to cryogenic temperatures. These materials have room-temperature properties of high extensibility and forcible quick retraction but, without exception, become hard and glass-like when sufficiently cooled, and thereafter behave like crystalline solids. Around this so-called glass-transition temperature, the modulus of elasticity may increase by a factor of 400 to 1000, and the coefficient of expansion may decrease by a factor of three or more . Because of these changes, elastomers are not commonly used at cryogenic temperatures to solve problems for which they would be used at room temperature. Where an elastomer O-ring would perform the function of astatic seal at room temperature, countless designs are now being used to seal cryogen transfer lines, fuel and oxidizer missile components, experimental apparatus, and so on. However, none of these alternatives has met with universal approval, and all exhibit at least one of the disadvantages of high cost, poor performance, or complexity.
KeywordsLeak Rate Cryogenic Temperature Leak Detector Helium Pressure Bolt Hole
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