Knowing in advance how a rubber part will behave over 10 or 20 years of real-world service is critical information for both manufacturers and customers. Testing that length of time in real time, however, is simply not practical. This is why the rubber industry relies on accelerated aging tests at elevated temperatures to estimate service life within a reasonable testing period. This article covers how these tests work and their limitations.
Oven Aging Tests
Defined in standards such as ASTM D573 and ISO 188, oven aging involves heating rubber samples in a controlled oven at a specific elevated temperature — typically between 70°C and 100°C — for set durations, such as 24, 72, or 168 hours. Properties measured before and after the test are compared to evaluate the material’s resistance to thermal aging.
Predicting Service Life with the Arrhenius Approach
To translate high-temperature test results into real service-temperature predictions, the Arrhenius equation is used. This approach is based on the principle that chemical reaction rates increase exponentially with temperature: as a general rule of thumb, the rate of an aging reaction roughly doubles for every 10°C increase in temperature. This allows results obtained in a few days at 100°C to be mathematically extrapolated to what would happen over years at, say, 25°C in service.
Properties Tracked
Aging tests typically track changes in the following mechanical properties:
- Loss of tensile strength.
- Decrease in elongation at break.
- Increase in hardness (Shore value) — aged rubber generally becomes harder and more brittle.
- Visual indicators such as surface cracking, discoloration, or tackiness.
Limitations of Accelerated Testing
Arrhenius-based predictions provide a useful roadmap, but they are not an absolute guarantee. At high temperatures, different degradation mechanisms that don’t occur under real service conditions can come into play — for example, the early evaporation of certain additives. For this reason, accelerated tests should be evaluated alongside real-world field data and application-specific validation testing.
At Alpin Rubber & Plastic Technologies, we follow evaluation approaches aligned with the relevant test standards so that our customers can set accurate expectations about the long-term performance of the rubber parts we manufacture.