Low Temperature Effects
Low temperature testing is imperative to ensuring sufficient seal performance in industries where low temperature operating conditions are common. Low temperature cause an increase in brittleness of the compound which leads to cracking, breaking and failure of the O-ring. There are multiple methods of testing including ASTM D2137 (crack resistance) and ASTM D3418 (Glass transition). Parker tests compounds at low temperatures using ASTM D1329, also called the TR-10 method.
For O-rings and other compression seals, the TR-10 value per ASTM D1329 provides a better means of approximating the low temperature capability of an elastomer compared to methods used in the past. The low temperature sealing limit is generally about 8°C (15°F) below the TR-10 value. This guideline has been used, with a few exceptions, to establish the recommended low temperature limits for Parker compounds.
TR-10 is the temperature at which the compound loses resiliency and transitions from rubber behavior to soft plastic behavior. In this method, the compound is clamped, then stretched 50% in a temperature controlled chamber, and frozen to a temperature below what the material can recover from. At this point one end of the specimen is unclamped, and because the temperature is colder than the material’s flexibility, the specimen stays elongated. Gradually the chamber temperature is increased, and when the material regains flexibility, it begins to retract. The temperature at which the specimen retracts 10% of its elongated length is defined as TR-10 temperature. The O-ring industry defines a material’s low temperature rating by taking the TR-10 measurement in Fahrenheit, and subtracting 10-15 degrees. Application experience has proven that an O-ring elastomer will seal statically 10 to 15 degrees below the TR-10 temperature, and in dynamic applications, O-rings perform well at and above TR-10.