Low temperature performance is one of the most overlooked properties in seal performance. Exposure to low temperature can contract elastomeric materials, resulting in decreased compression and possible leakage. When seal materials are exposed to a lower temperature than their designed limit, seals become less flexible and brittle. Seals can fail by two modes under low temperature:

  1. The seal material will harden when the low temperature limit is reached and resist deformation to pressure causing leak paths.
  2. The seal will undergo a compression set, so when heated above the low temperature, this allows for leak. Material selection is key for the low temperature seal performance.

Low Temperature Testing

Three standard low temperature tests are performed to measure material performance. Brittleness (ASTM D2137) measures the ability of a material to withstand breaking when bent at a given temperature for a period of time. Temperature Retraction (ASTM D1329) measures the temperature at which a material returns from an elongated state. Torsional Stiffness Ratio (ASTM D1053) measures the ratio from when a material is twisted, first at room temperature and then at a given low temperature. These tests give some idea of low temperature performance but have limited value for seal applications. One example is that a material might not break at -40°C, but the material could be stiff enough to allow leak paths.

A good indicator for seal performance is Compression Set at Low Temperature (ASTM D1229). This test measures set at 3 min. after exposure to a given temperature and at 30 min. This gives a clear indication of what will happen to a material when exposed to low temperature and allowed to return to higher temperatures. A quick indicator is the Glass Transition Temperature (Tg). This shows the temperature at which the material becomes hard.

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