Heat aging testing allows manufacturers to predict exactly how a rubber product or material— such as conveyer belts, shoe soles, erasers, rubber hoses, vibration dampers, and gaskets—ages over time when exposed to heat. Long-term heat exposure can cause oxidation and thermal aging of rubber, contributing to deteriorated and weakened performance of rubber products and components. Consequently, accelerated aging and heat resistance test like those specified in ISO 188:2023—Rubber, Vulcanized Or Thermoplastic – Accelerated Ageing And Heat Resistance Tests are critical in determining the effects of high-heat service environments on rubber products and materials.
Accelerated Aging or Heat Resistance Tests
Heat aging testing, also called oven aging or accelerated aging, uses heat to accelerate the aging process to determine the service temperatures for a product or material. It stimulates real-time aging and shelf life by using elevated temperatures to speed up the aging process. Accelerated aging and heat resistance tests are further used to determine the change of defined properties of rubber and thermoplastic elastomers over a specified period. These properties are compared before and after these two tests.
- Accelerated Ageing Tests: Test pieces are subjected to a higher temperature than the rubber would experience in its intended application to simulate the effects of natural ageing in a shorter time
- Heat Resistance Tests: Test pieces are subjected to the temperature they would experience in their intended application to gain information about their service performance
ISO 1817:2022: Rubber, Vulcanized Or Thermoplastic defines volcanized and thermoplastic rubber as well as methods to evaluate the resistance of these rubbers to the action of liquids.
What Is ISO 188:2023?
ISO 188:2023 specifies accelerated ageing or heat resistance tests on vulcanized or thermoplastic rubbers/thermoplastic elastomers. In these tests, test pieces are exposed to air at a given elevated temperature and at atmospheric pressure with controlled conditions of air circulation. Physical properties are measured before and after exposure and the results compared. The change of physical properties depends on the temperature and air speed. This means that even tests at the same temperature but different air speed (different ovens) may give different results. ISO 188:2023 specifies the use of two types of ovens: cell ovens and cabinet ovens.
Moreover, in the absence of any indication of these physical properties, the standard recommends that tensile strength, stress at intermediate elongation, elongation at break (in accordance with ISO 37), and hardness (in accordance with ISO 48-2) are measured.
Accelerated Ageing or Heat resistance Methods
ISO 188:2023 specifies that there are four methods to conduct accelerated ageing or heat resistance tests on vulcanized and/or thermoplastic elastomers:
- Method A: Using a cell or cabinet oven with low air speed, laminar flow of air past the stationary test pieces and air exchange rate between 3 and 10 changes per hour.
- Method B: Using a cabinet oven with high air speed, laminar flow of air past the test pieces and air exchange rate between 3 and 10 changes per hour.
- Method C: Using a cabinet oven with high air speed, turbulent flow of air past the test pieces, rotation of the test piece carrier and air exchange rate between 3 and 10 changes per hour.
- Method D: Using a cabinet oven with high air speed, turbulent flow of air past the stationary test pieces and air exchange rate greater than 30 changes per hour
For method A, B and method C, provision should be made for a slow flow of air through the oven of not less than three and not more than ten air changes per hour. For method D, an air flow between 0,25 to 3,0 m/s is necessary as well as an air exchange rate above 30 changes per hour.
ISO 188:2023—Rubber, Vulcanized Or Thermoplastic – Accelerated Ageing And Heat Resistance Tests is available on the ANSI Webstore.