On The Dynamic Evolution Of Lubrication Films In Greased Rolling Contacts

A majority of rolling bearing in use are grease lubricated due to the easy of use of greases.However,the rheology and the lubrication mechanisms determined by the constitution of greases,are complicated.Although considerable researches were conducted to explore the lubrication behaviours of grease,the underlying mechanisms of grease lubrication,as yet,are not fully revealed.Therefore,the development of new grease formulations and design for rolling bearings are implicated.This thesis focus on the investigations of the dynamic evolution of grease films with revolutions in pure rolling ball-and-disc contacts.Some parameters e.g.speed,grease structure,load and grease supplying conditions on the lubricating film evolution were experimentally observed.Combing with the analysis of the patterns of final track,the dominant mechanisms that contributes to the film formation were explored.The main work can be summarize as:(1)The improvement of optical ball-and-disc film thickness measurement apparatus.To meet the requirements of present experiments,an encoder was supplemented to capture the speed and count the rotation cycles.(2)Experimentally and theoretically studies on the transitions of lubrication regimes.Under fully and restricted lubricant supply conditions,the speed,load,lubricant viscosity and lubricant amount on the lubrication transitions were experimentally investigations.Theoretical analysis were carried out to qualitatively determine the extend of influence of the factors.Thus,the effects of elastic deformation and pressure-viscosity on the film formation were explored.(3)Experimental investigations of the grease film evolution.Given a running condition,the variations of grease films with rotating cycles were conducted.The speed,grease structure and load on the dynamic process of film evolution were observed.The film formation induced by the underlying mechanisms of the grease under different running phase,were revealed.(4)Experimental investigations of the grease film evolution under different grease supplying conditions.The grease single charging amount,the initial grease layer with and the multi-charging effect on the film evolution were observed.The results show the influence of initial grease distributions on the film evolution and the existence of the optimal grease charging amount.This work provides some fundamental knowledge for the understandings of grease lubrication.And it may be beneficial for grease selection and grease development.