Strength changes of moulded polyamide composite caused by thermal oxidation

Rolling-bearing cages (separators) which were made by injection moulding fr om polyamide 66 filled with short glass fibres were tested before and after exposures in hot air at temperatures 120, 140, 160, and 180 degrees C at v arious times ranging from a few hours to three weeks. The cages were loaded in tension and the changes of maximum force corresponding to ultimate tens ile stress were studied. A very simple degradation mechanism containing the main features of the real degradation processes was proposed and its kinet ic equations were derived. On the basis of the assumption that the changes of properties during ageing are proportional to the changes of chemical com position and structure a regression function was proposed. It was used for the fitting of the measured results and for the construction of predictive curves which describe the temporal and temperature dependence of strength f or working temperatures and long times. (C) 1999 Kluwer Academic Publishers .