Theory of Thermoelastic Instability of Rotating Rings in Sliding Contact With Wear

Abstract

The instability of two rings in rotating, sliding contact is examined. The configuration is typical of that of a mechanical face seal. Circumferentially varying friction heating at the seal interface may lead to an unstable thermoelastic distortion of the ring and uneven wear. Heat transfer equations are developed which include the effects of contact conductance and unsteady state heat transfer in one of the rings. Deflection equations, which include both thermal and mechanical loading, are developed and combined with a wear equation to form a mathematical model that predicts the limits for stable operation. It is shown that contact conductance, ring stiffness, thermal coefficient of expansion, sliding speed, friction, thermal conductivïty, and geometry are important parameters in relation to stability. Stability conditions are established for several cases. The harmonic content of the uneven wear resulting from instability depends on the initial waviness of the ring and point of operation in the region of instability. It is shown that some seals are stable at all harmonics.