Exploring the mechanisms critical to the operation of metal face seals through modeling and experiments

Abstract

This thesis aims to explore operation mechanisms of a special type of mechanical face seals: the flexible metal-to-metal face seal (FMMFS). Unique features of the FMMFS include much more flexibility in the circumferential than in the radial direction, identical rotating and stationary seal rings, and a loading mechanism using elastomeric O-rings. Two versions of the numerical models have been developed to evaluate seal performance under various operating conditions. Both models consider interactions among surface deformations due to thermo-mechanical twists, unsteady lubrication in the sealing band, and heat transfer in the seal pair simultaneously. Outputs include contact pressures, oil film thickness, cavitation zone, partial film density, friction coefficients, dynamic oil transport, and seal temperature distributions. In the meantime, experimental efforts have been made to measure the friction coefficients and seal temperatures during different operations. The model predictions were then compared with the experiment results through the two above-mentioned quantities. The comparisons show that the numerical simulations consistently overestimate the friction by 15%-20%. However, overall trend of friction variation with speed and even some details of the friction can be captured, indicating that the current models are able to properly predict some underlying physics of seal operations. The numerical models were then used to evaluate scoring and leakage failures of the FMMFS through three important variables: surface temperature, contact wetness, and oil exchange. Some surface geometric features, which contribute to differences of scoring and leakage behaviors, are identified. In order to achieve higher scoring resistance and minimum leakage, the sealing surface should have the following features: (1) random or dispersed asperity distributions, (2) relatively large surface roughness, and (3) combination of concave and half-concave- half-convex radial profiles.