Unlike the changes that result from exposure to high temperatures, changes brought about by low temperature exposure are generally not permanent and can often be reversed once heat returns. For example, extended exposure to low temperatures will increase an elastomer’s hardness, but the material will soften again when the temperature rises. Perhaps the most important consideration related to low temperatures involves seals which must also work in a low-pressure environment. Unless the selected seal compound is sufficiently soft and resilient, the combination of low temperature (which can cause shrinkage and hardening of the seal) and low service pressure (which will not help hold the seal against the mating surface) can cause leakage and failure.

There are two main tests related to low temperature effects. The first is described in ASTM D 2137 (Method A) as a way to measure the brittleness point, or the lowest temperature at which a sample will not fracture or crack when struck once. The second test is described in ASTM D 1329. More commonly known as a TR-10, this temperature retraction test (see Figure 30) is considered by many within the rubber industry to be the most useful indicator of a material’s low temperature performance.

In a nutshell, the TR-10 measures material resilience. Samples are frozen in a stretched state, then gradually warmed until they lose 10% of this stretch (i.e. retract by 10%). The results of such tests are believed to provide a good basis for evaluating the effects of crystallization and the impact of low temperatures on visco-elastic properties. TR-10 results are generally thought to be consistent with the capabilities of most dynamic seals. Static seals can often function at 15° F / 8° C below the TR-10 temperature.

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