Study On The Mechanism Laser Surface Texturing And Tribological Performance Of Textured Hydrodynamic Journal Bearing

The existence of friction will reduce the efficiency of equipment,and the failure of mechanical equipment is mostly caused by friction and wear.Therefore,to control friction,reduce wear,and improve lubrication has become an important measure to save energy and extend the service life of equipment.Laser surface texturing(LST)is an effective means to reduce friction and wear,improve lubrication performance and service life of equipment.In this paper,hydrodynamical journal bearing was taken as the research object and aimed at reducing friction and wear.The effects of laser on physical properties and geometric morphology of bearing surface,as well as the tribological properties of LST bearing were systematically analyzed.To solve the technical problems of surface texture preparation by studying the forming mechanism,and further explored scientific issues such as the friction and wear mechanism of LST hydrodynamic journal bearing.In this work,hydrodynamical journal bearing made of brass was taken as the object.Combined with theoretical analysis of forming process,ANSYS simulation,Scanning Electron Microscope(SEM)and Energy Dispersive Spectrometer(EDS),LST forming process and its mechanism were expounded as well as the geometric morphology of surface texture were analyzed.The results showed that laser machining has outstanding process stability,which laid a foundation for the study of the influence of LST forming process.According to this,the forming mechanism of surface texture is essentially the distribution of electrons obtained and lost in the combined form of matrix material,which presents thermal ablation and recasting in a macroscopic view.In order to control the process parameters to obtained the ideal surface texture,the significance of the process parameters that affecting micro-texture formation,as well as the effects of process parameters on the surface physical properties and geometric morphology were systematically studied by surface texture test and Minitab software simulation.It showed that diameter and depth increased with the increase of energy,the expansion of micro pits presented ablation saturation under a certain repetition times(>5 times)and laser frequency hardly affected on the expansion of micro pits.In addition,the higher the energy at the same place,the higher the hardness,and the hardness gradually decreased along the micro pits wall from surface to bottom.The process parameters that significantly affect micro pit diameter are energy and pulse width,while the significantly affect micro pit deep forming are energy,pulse width,repetition times and interaction between energy and pulse width.Thus,the energy and width pulse should be controlled on the first available to achieve ideal surface texture.A mathematical model for evaluating the lubrication performance of textured bearing was established to analyse lubrication characteristics of textured bearing.The tribological properties of textured bearing were analyzed by tribological properties test and the correctness of mathematical model was further verified.The results showed that oil film pressure of textured bearing was approximately parabolic at lower eccentricity,and oil film force increased with the increase of eccentricity.However,the eccentricity decreased gradually as the process of the capacity Sommerfeld number from 0.001 to 10.The decreasing eccentricity had no obvious effect on the dynamic characteristics of textured hydrodynamic journal bearing.In LST hydrodynamic journal bearing tribological performance test,the wear capacity and friction coefficient decreased first and then increased,as well as the optimal surface texture area ratio and aspect ratio were 20% and 0.12 respectively.The friction and wear means were three body friction,running in wear and abrasive wear,and its antifriction mechanism was to store abrasive particles and formed secondary dynamic pressure lubrication.In the research,the lubrication properties of hydrodynamic journal bearings with various arrangements were different,and diagonal consistent square lattice surface texture could transfer to hydrodynamic lubrication state under larger loads or lower rotational speeds.The optimal tribological properties of hydrodynamic journal bearings with various arrangements was obtained when the clearance was 0.1 mm,and friction torque of bearings with different working conditions increased first and then decreased to a stable state with time.The wear capacity and temperature of hydrodynamic journal bearings under the same arrangement increased with the increase of rotational speeds and loads.In many various surface texture arrangement ways,the diagonal consistent square lattice texture could not only reduce oil film failure caused by excessive temperature rise,but also reduced friction and improved the service life.In the t-test,the wear capacity of diagonal consistent square lattice texture could be predicted accurately by using Grey-Markov prediction model.The behaviors of surface textured bearing during the test were described based on M-B fractal theory.In the running-in wear stage,wear rate increased with the increase of surface parameters(characteristic scale coefficient,fractal dimension and material characteristic coefficient)under the same contact area,and the wear rate increased with the increase of actual area when the surface parameters were constant.In the stage of abrasive wear,the wear rate was the smallest when the fractal dimension was1.6.The wear rate increased with the increase of contact area under the same characteristic scale coefficient,while the wear rate decreased with the increase of characteristic scale coefficient under the same contact area,as well as the smaller the material constant and the larger the probability constant,the higher the wear rate.