Rubber Testing & control Thermal testing
Thermal testing
Temperatures affect the properties of polymeric materials much more significantly than metals and ceramics. This is evident not only in property changes when the temperature changes, but also in critical temperatures being reached relatively early.
TR testing
TR testing is the most common method in Sweden when it comes to cold testing. TR stands for "Temperature Retraction"; in Swedish, we refer to the method as "elastic recovery after freezing." The test is conducted by stretching the test specimens, typically 50%, and then cooling them to -70°C for 10 minutes. Most rubber materials become completely rigid at this temperature. The clamps holding the test specimens are released, and the specimens are then heated at a rate of 1°C per minute while their recovery is monitored.
Standard for TR testing of rubber is ISO 2921.
Brittleness
Brittleness point is a method where hammer blows are applied to test bars cooled in a cold bath. The brittleness point is the temperature at which the samples just do not break from a single strike.
Standard for brittleness point testing of rubber is ISO 812.
Stiffness
During a torsional test, the relative torsional stiffness between 23°C and lower temperatures is usually determined. If the dimensions of the test specimen are known, the torsion modulus can also be calculated.
The test procedure involves mounting a test rod in series with a calibrated steel wire. When determining the torsional stiffness of the rubber sample, both the rubber and the steel wire are twisted 180°. The 180° twist is distributed between the steel wire and the rubber sample in proportion to their torsional stiffness, and the torsional angle of the rubber sample is then determined. The test is subsequently performed at different temperatures to enable the calculation of torsional stiffness.
Standard for brittleness point testing of rubber is ISO 1432.
Dynamic Mechanical Analysis
If you want to determine the modulus as a function of temperature, you can advantageously use modern DMA equipment for this, Dynamic Mechanical Analysis. With DMA testing, the viscous and elastic modulus are measured along with damping over a temperature range. The test is performed dynamically in either bending, tensile, compression, or shear. This test can replace most other low-temperature testing.
The standard for DMA analysis of rubber is ISO 4664.
Compression set
To determine the rubber's ability to recover after compression, a compression set test is performed at a specified temperature. The test specimens are compressed for a given time, and then the residual deformation is measured after recovery.
The testing can be performed at room temperature and elevated temperatures, where both physical and chemical changes affect the result, as well as at low temperature where both measurement and recovery occur in the cold.
The standard for compression set testing of rubber is ISO 815.