Effect of air change rate on rubber accelerated ageing tests in hot air. Part 1. Preliminary study

Using a multi-cell ageing oven an NR compound was aged for 168 h at 70 °C in air with 3, 8, 10 and 15 air changes per hour. Ageing was evaluated by values of stress at 300% elongation (M 300), tensile strength (TS), elongation at break (EB) and hardness (IRHD). Simultaneously, a similar ageing treatment but in a normal oven at much lower air change rate was carried out. The statistical analysis of results showed that there are significant differences in M300 and TS after ageing among the various air-flows and also in M300 and EB between the results obtained in the normal oven and in the block oven at 3 air changes per hour. There were no significant differences among the cells in the oven nor (except in hardness test prices) in the material subjected to ageing, although it was prepared in several curing operations.