When choosing a material, it is important to consider the temperature range in which it will be operating as rubbers can be very sensitive to extreme temperatures. Some rubber compounds have more resistance to temperature than others, each compound must be tested to determine the specific operating temperature of the material. At very low temperatures, rubbers can become stiff. This loss of flexibility can cause cracking in the rubber which will remain in the material forever, even after it has been reheated.
On the other hand, high temperatures can cause ageing and deterioration of rubber. Initial exposure to high temperature can cause the material to soften. This change will reverse once the temperature drops again. However, if a rubber is held at a high temperature for a long period of time, chemical changes begin to occur within the rubber polymer. These changes can lead to an increase in material hardness as well as changes in the tensile strength and the elongation of the material. These chemical changes are irreversible.
The maximum operating temperature of a rubber compound is based on the long-term function service of the material. The material should be able to perform reliably even after being held at this temperature constantly for 1000 hours.
Material selection is extremely important when choosing a rubber for a high temperature application. For example, rubbers used in a steam or gas turbine may be exposed to high temperatures. Rubber compounds such as silicone or Fluorocarbon are good choices in these cases as they offer excellent heat resistance.
Unlike in other materials, rubber contracts in heat and expands in cold temperatures. This is because when the long chains get hotter and vibrate, they shorten, causing the material to contract. When the chains cool down, they relax and stretch out and cause the material to expand.