Significance and Test Method
The mechanical and elastic properties of elastomers change with temperature. Depending on the type of elastomer and the formulation, a threshold is reached sooner or later when temperatures fall, at which the material becomes brittle and hard, which means it approaches more and more the glassy state.
The TR10 value (Temperature Retraction) describes the resilience of elastomers in cold conditions. It indicates the temperature at which a frozen, stretched elastomer sample has recovered by 10% when slowly heated.
Significance for Application Technology
This makes the TR10 value one of the most informative characteristic values for the mechanical behaviour of elastomers at low temperatures in terms of application technology.
This low-temperature guide value allows to evaluate the sealing capacity of seals at low temperatures and represents a rather conservative low-temperature limit.
Experience shows that seals that are dynamically loaded or pressurised are effective up to the TR10 value. With static use and ambient pressure, they even remain technically tight down to temperatures of 10-15 °C below their TR10 value, depending on the material.
The TR10 Test
The standards ISO 2921 and ASTM D 1329 describe the testing of the TR10 value on elastomers. For the test, an elastomer sample is stretched by either 25% or 50% and frozen in the stretched state. The frozen, unloaded sample defrosts by controlled heating. During defrosting, the restoring path is recorded as a function of temperature and the temperature is determined at which the sample has recovered by 10%. This temperature is called the TR10 value.
The TR10 value is usually determined on standard specimens, but we can also measure directly on O-rings with cord thicknesses of up to max. 4 – 5 mm and with an inner diameter of at least approx. 8 mm. Optionally, from an inner diameter of approx. 20 mm, also on cords (cut O-rings).
