Modelling of friction and wear for cryogenic valve seals of rocket engines

Based on the experimental results, earlier work presented a first attempt at the statistical modelling of the friction and wear valves and seals of rocket engines must withstand. Available friction coefficients and wear rates (as defined in Archard's equation) were fitted against two independent variables. sliding speed and contact pressure. The computations yielded second-degree polynomials and the corresponding response surfaces. However, it was felt that a statistical design of experiments to reduce the test activities and maximise result quality was needed. A detailed analysis led to the choice of Doehlert's approach, with a contribution of the general equiradial design. Testing was performed with a pin-on-disk tribometer capable of working at room temperature (RT) and under liquid nitrogen (at 77 K). The results pertaining to two examples are discussed. Statistical as well as practical aspects of the work performed and consequences of the results are covered : based on correlation factors and other mathematical indicators, on the general profile of the response surfaces and on requirements for use, the tribological properties of the considered materials are illustrated, leading to their eventual usefulness in cryotechnic equipment and space applications.