Theoretical And Experimental Study On Lubrication State Transformation And Lubrication Characteristics Of Sliding Bearing Under Heavy Load

When the sliding bearing works in heavy load conditions,there is often a large fluctuation of the load,resulting in a significant change in the oil film thickness.As the load increases,the eccentric becomes lower and lower,it is easy to cause oil film thickness and bearing surface roughness peak height in the same order of magnitude in the sub-overload(high eccentric)range of sliding bearings.Bearing lubrication will change from complete fluid lubrication to mixed lubrication which is included asperity contacts.At the same time,the influence of solid elastic deformation and lubricating oil properties cannot be ignored.The research on the transformation process of lubrication state and the bearing characteristics under different lubrication states will provide certain significance for the design of heavy load sliding bearing.This paper takes the journal sliding bearing as the research object.Firstly,the lubrication state and the transformation process of lubrication state under different conditions are analyzed,then the elastohydrodynamic lubrication model considering journal misalignment,bearing deformation and viscosity-pressure relationship and the mixed lubrication model considering surface roughness are established respectively.The governing equations of different models are discretized by finite difference method and solved numerically by C++ program.The oil film pressure distribution,loadcarrying capacity,friction coefficient,dimensionless fluid film stiffness and damping coefficient and threshold speed are obtained under different lubrication states.Finally,on the basis of theoretical analysis,the running-in and friction-wear tests of friction pair specimens were carried out by using M2000 friction and wear tester,and the test data of friction force,friction torque and temperature rise of lubricating oil were obtained,so as to verify the theoretical results.Theoretical calculation results show that with the increase of load or the decrease of spindle speed,the lubrication state will transform from complete fluid lubrication state to elastohydrodynamic lubrication state.The higher the surface roughness of bearing and spindle is,the easier it is for the bearing to enter the mixed lubrication state with rough peak contact.Under the elastohydrodynamic lubrication state,the axial inclination angle increases the maximum oil film pressure and causes stress concentration,load-carrying capacity and threshold speed decrease.Under the mixed lubrication state,the load-carrying capacity increases with the increase of surface roughness,and the attitude angle decreases.At the same time,the friction force and the temperature rise of lubricating oil increase rapidly,which is easy to cause the bearing surface wear and is not conducive to lubrication.The experimental results show that with the increase of load,the lubrication state of friction pair is transformed from the fluid lubrication state to the mixed lubrication state with rough peak contact,resulting in a sharp increase in the temperature rise of lubricating oil and obvious scratch damage on the surface of the specimen,and the greater the surface roughness,the more significant the change.The experimental results are consistent with the theoretical results of the mixed lubrication model.