ASTM D454 test is used to determine the physical properties of vulcanized rubber under accelerated conditions of elevated temperature and at high air pressure. The physical properties of rubber and other rubber products may deteriorate with time due to oxidation and thermal aging. This test may not provide the required correlation with service performance in some cases as the performance conditions differ in a wide range. But this test helps evaluate rubber compounds on a laboratory comparison basis.
For ASTM D454, the samples are preheated to the operating temperature of 125≠1°C (257≠1.8 °F). Then, the samples are suspended for exposure vertically in the pressure chamber.
During the exposure periods, the air pressures should be maintained at 550≠14 kPa (80≠2.0 psi). If possible, the simultaneous exposure of a varied group of different compounds is avoided. The samples are placed in the heated chamber for a particular exposure period. After that, the chamber is closed immediately, and air pressure is applied. The whole operation should be completed within 3 minutes. However, the time interval elapsing from the starting time is recorded until the temperature of the chamber reaches 125 °C (257 °F). Then, appropriate exposure periods are selected based upon the rate of deterioration of the specific material being tested.
The time intervals used are 3, 5, 8, 12, 20, and 30 hours. The air pressure is released gradually at the end of the exposure period. The samples are removed from the pressure chamber immediately within 5 minutes to avoid porosity formation in the samples. Then, the samples are cooled to room temperature on a fate surface and allowed to rest between 16-96 hours before evaluating the physical properties. Finally, gage lines are applied for determining elongations to the samples.
The standard samples for ASTM D454 are dumbbell-shaped, as described in ASTM D412. The most typical tested shape is a die-cut C dumbbell sample with an overall length of 115 mm (gauge length of 25 mm), a width of 6 mm, and a thickness of 3 mm. The thickness of the sample is measured three times, and the median value is taken.
The results of the air pressure heat test results for each exposure period in each physical property are expressed as a percentage change.
P= percentage change in property,
O= original value, and
A= value after aging or exposure.