Study On Sealing Performance Of Lip Seals And Hydrodynamic Effects Of Shaft Surface Micro Textures

Lip seals are widely used in rotary machines for its simple structure, reliable performance, easily installation, lower cost, to retain lubricant and exclude contamination, so have been one of the most popular sealing parts. However, the design work of lip seals is mainly dependent on the designer’s current empirics and experiments, caused by the lip seals’ complicated sealing mechanisms and many influencing factors. With the development of modern machinery towards higher temperature, higher speed and higher pressure, it is necessary that lip seals should have zero leakage rate, lower friction force and longer life. The traditional designed methods and lip seal products, in contrast, don’t meet the ever increasing sealing performance requirements, so the lip seals’ research works conducted in this thesis have a significant effect on its practical applications.In order to solve the above problems, the research method of the theoretical analysis, numerical simulation combined with experimental measurements is used to investigate the lip seals static contact performance, sealing performance, and shaft surface micro textures hydrodynamic effects. The research contents and obtained results are as follows:First, the lip seal’s geometric assembly features were analysed, and a two_dimensional axisymmetric mechanics model was presented based on finite element method. The effects of interference fits, rubber-like elastic modules, inner diameter and material constitutional model on the contact pressure, contact width, and radial force, were investigated. The obtained results show that the lip edge contact stress and displacement distribution is the same as the practical values, and the radial force is nearly equal to the theoretical value, it will be beneficial to optimize the lip seals structure and provide more original datas for lip seals theoretical models used for numerical simulation.Second, the sealing and lubricated condition of lip seals was analysed, and a mathematical model based on lip seals lubricated and sealing mechanism, was developed to investigate the sealing performance under steady working condition. The lubrication governing equation, accounting for the JFO(Floberg-Jakobsson-Olsson) cavitation condition in the film and rubber-like lip surface elastic deformation, was constructed and solved by the streamline upwind finite element method. The effects of operating parameters, lip surface roughness parameters and rubber-like material elastic modules on the pump rate, load capacity and frictional force were investigated, and some results were obtained under the certain intial oil film thickness and lip radial force.Third, the shaft surface micro textures were used to improve the lip seals sealing performance, and the the effects of shaft surface micro textures such as diamond-shaped, ellipse-shaped, rectangle-shaped, and triangle-shaped on the lip seals hydrodynamic lubrication were investigated by numerical simulation. The influence of micro texture shapes and geometric parameters on the sealing performance was analysed, and the obtained results show that the rectangle-shaped micro texture is the best one among the investigated shaft surface micro textures, the micro-asperity is better than the micro-cavity.Finally, it is more easily for fabrication of shaft surface micro-cavities than microasperities, so the effects of shaft surface mirco-cavities such as diamond-shaped, ellipse-shaped, rectangle-shaped, triangle-shaped textures on frictional torque of lip seals made from nitrile rubber(NBR) were experimentally investigated and made a preliminary comparison with the numerical simulation results. Furthermore, the effects of the oriental angle, area fraction, depth of rectangle-shape micro-cavity on lip seal’s frictional torque were experimentally measured.The above research works and obtained results are helpful to further the lip seals design theory and methods, it will have an important theoretical and practical impact on improving the lip seals sealing performance and extending service life.