Study On Seal Tribological Properties Using A Bi-gaussian Stratified Surface Theory

Dry gas seal is a typical non-contacting mechanical face seal,and is widely applied in the fields of energy,petrochemistry and aviation,serving as the key component in rotating machinery.Friction-wear mechanism is a fundamental issue to achieve the sealing demands on stability,efficiency and long lifespan.From the bi-Gaussian stratified viewpoint,the surface characterization and simulation technology is improved as a basic tool.The performance of lubrication and contact,the mechanism of friction and wear,and the evolution law of sealing performance are investigated.The dissertation proposes a deeper knowledge of surface,contact,friction and wear,and seal-performance deterioration with respect to dry gas seals,providing references to the related fields.A continuous separation method is proposed by establishing a surface combination theory to obtain the continuous form of the probability material ratio curve.A truncated separation method is proposed based on the direct truncation of the upper Gaussian component that replaces the typical curve fitting of the probability material ratio curve.The two separation methods as well as the existing ISO segmented separation method are applied to characterize real worn sealing surfaces,finding that the new methods own proper physical idea,high efficiency,perfect fluctuation resistance and roughness-scale independence.Moving average time series model with Fast Fourier Transform is used to establish the superposition-principle-based bi-Gaussian surface simulation approach.An iterative algorithm is used to cover the shortage of identifying component correlation lengths.In contrast with the existing non-Gaussian surface simulation approach,the modified bi-Gaussian approach is much closer to a real worn situation: can generate stratified surfaces,breaking through the limitation of single-stratum surface;can satisfy the target skewness and kurtosis simultaneously;has flexible autocorrelation functions.Finite difference method with relaxation coefficients is used to establish the deterministic model with respect to dry gas seals and water-film mechanical face seals.The influence of surface topography on lubrication and contact performance is analyzed,finding that the bi-Gaussian stratified characteristic is much closer to a real worn situation than the non-Gaussian feature.Meanwhile,the existing segmented stratified asperity statistic contact model between worn surfaces is revised,and a new continuous stratified statistic contact model is developed.Both two stratified statistic contact models are demonstrated by the deterministic contact model,thus releasing the dependence of previous statistic contact models on a Gaussian distribution assumption.A surface-surface dry sliding wear of silicon-carbide and carbon-graphite discs is conducted on a Plint rotational standard tribological tester to investigate the evolution of surface parameters especially the bi-Gaussian surface parameters in a wear process.Bi-Gaussian surface parameter evolution models are established.From the surface topography viewpoint,the evolution models reveal the essence of the running-in and stable periods in a sliding wear process.By using a dry gas seal test rig,the experiment focusing on a spiral groove dry gas seal under a low-speed condition is performed.The bi-Gaussian surface parameter evolution of the sealing rings is found to identify the face contact,adhesive wear and deep scratches.The surface-topography evolution exhibits a high correlation with the recorded indexes including leakage rate,torque and acoustic emission signal,which is helpful in exploring the deterioration mechanism of sealing performance.