Sliding Friction and Heat Generation in Pressurized U-Cup Seals Under Low-Speed Reciprocating Conditions

Abstract

A test apparatus was designed and constructed to investigate the friction and heat generation characteristics of sliding polymeric U-cup seals used in high-pressure nitrogen gas springs. Tests were run at three speeds; and friction and temperature data were obtained. Seal specimens were examined under a scanning electron microscope before and after each test. Evidence of degradation and thermal softening of the seal material was found for the highest relative speed tests where elevated temperatures were measured. In addition, a semi-empirical transient finite-difference thermal analysis of the rod and the high-pressure chamber in the test apparatus was also developed. Numerical simulations of the three tests were performed using measured friction force data, and temperature predictions from the model were compared with those measured at different locations in the test apparatus. Predicted values exhibited reasonable agreement with the measured values, particularly under steady-state conditions. The variations observed for certain transient conditions appeared to be due to overestimated convective heat transfer coefficients at lower speeds, and due to the transient nature of thermal resistances between the seal cartridge and the high-pressure chamber, which may vary with a change in temperature.