Multi-objective Optimization Of Lubrication And Leakage Properties For Textured Mechanical Seals

With the rapid development of large-scale,high-efficiency and high-reliability of mechanical equipment,the working condition of mechanical seals is becoming more severe.Mechanical seals are required to be stable under severe working conditions such as high speed,high pressure,high temperature and complex medium.Thus,the innovative research and technological improvements in the mechanical seal industry have received lot of attentions.Among them,designing surface texture on seal face is an important approach.However,some studies found that it is difficult to improve the lubrication and leakage characteristics of mechanical seals simultaneously by surface texture.In view of this,this paper applied the multi-objective optimization to optimize the surface texture on the sealing end face for improving the combination performance of mechanical seals.Firstly,the influence of surface texture on the lubrication and leakage characteristics of mechanical seals are investigated by theoretical calculation and experimental methods.Both studies have found that the surface texture designed for improving the load-carrying capacity,the film stiffness and reducing the friction coefficient of mechanical seals is often accompanied by a higher leakage rate.Similarly,the friction reduction effect of the surface texture with a lower leakage rate is also not well.The results show the conflict between the lubrication and the leakage characteristics of the textured mechanical seal.Based on the conflict relationship between the lubrication and leakage characteristics of textured mechanical seal,the basic theory and algorithms of multi-objective optimization are introduced.The method of multi-objective optimization of surface texture on mechanical seals is first proposed.And taken spiral groove as an example,the algorithm NSGA-II is used to optimize the parameters of the spiral grooves.Compared with the spiral grooves of non-optimal parameters,the optimal spiral groove structures obtained by multi-objective optimization can provide higher load-carrying capacity at the same leakage rate,and similarly,they can provide lower leakage under the same load-carrying capacity.Then,the optimal parameters of spiral grooves are analyzed by collinearity diagnostics,which provides a method to simplify the multi-objective optimization procedure.Because the groove is prone to cutting,the dimple model with higher shape freedom is established in this paper and the dimple shape is optimized by multi-objective optimization method.Then,the surface textures are processed by lithography electrolysis technology,and the high-speed seal friction tester is used to conduct experiments to verify the calculation results.It is found that the optimal ’freeform’ shapes always show an asymmetric ’V’ feature for different lubrication conditions.Compared with optimal circular,elliptical,square and triangular shapes,the asymmetric ’V’ shape texture can obtain higher load-carrying capacity at the same leakage rate,which is about 23.5% higher than the regular shape texture,and similarly,they can obtain a lower leakage rate at the same load-carrying capacity.The experimental results and the calculation results show a high agreement.In experiments,the asymmetric ’V’ shape texture has a lower coefficient of friction than the optimal circular texture and smooth specimen in most cases,although it has a slightly higher leakage rate than the smooth sample,but it reduces the friction coefficient greatly.It can be considered as an excellent choice in situations where the leakage rate requirement is not very critical.This paper proposes a multi-objective method to design the surface texture that aims to improve the combination performance of mechanical seals.And the asymmetric ’V’ shape textures with a better combination performance are obtained basing on this method.The research results can further promote the application of surface texture technology on mechanical seals.