Experimental And Theoretical Studies On Hydrodynamic Lubrication Under LLS

Due to environmental and energy problems,quantities of lubricants used are now attracting more and more concerns of researchers in the tribology community.It is expected to realize lubrication with limited lubricant supply(LLS),or to obtain efficient and accurate lubrication with very small amounts of lubricant.In the present project an old test rig for film thickness measurement of a slider bearing was updated,and has been used to study the hydrodynamic lubrication in flat-on-flat contact under LLS.The work finished mainly includes:(1)A new unit for real-time control and monitoring of speeds.A precision circular grating was adopted for speed measurement of the disc.A program was written in C# to give accurate speed as a function of time,and as well the monitoring and storage of the real-time speed during the experiment.(2)Construction of friction measurement unit.The unit was designed in such a way that the friction force was enlarged by using an air bearing and the load lever to facilitate the friction measurement.A double-point positioning scheme was proposed and the unstable slider swaying during the old measurement system was significantly suppressed.(3)Experimental studies under LLS.PAOs with different viscosities were tested in different lubricant supply quantities,speeds,loads,reflow time by the new measurement system.With LLS the interferogram is characterized by an inlet starvation area with fragmented/rippled fringes.The starvation area shows a meniscus shape at small and mild starvation.The capillary effect is found to give more lubricant supply at the boundary of starvation area within the contact,and contribute the formation of the side ridges of the lubricant layer on the running track.With increasing speeds,the film thickness increases at first and then remains nearly unchanged due to enlargement of the starvation.A relative film thickness is defined and used to evaluate the decrease of load-carrying capacity caused by LLS.When starvation grows the relative film thickness decreases.Results showed that the lubricant viscosity and the reflow time between two slide-overs can markedly affect the film building.Under the condition of LLS,the friction increased slightly,which is beneficial to lubrication.(4)Two-dimensional numerical calculation program for hydrodynamic lubricaiton.The finite difference method was used to solve the Reynolds equation and a computation program has been written in FORTRAN.The film thickness and friction under different working conditions were calculated and compared with the experimental data,and the accuracy of the experimental system was verified.(5)Calculation of load-carrying capacity under LLS.According to the shape of the starvation area,the load-carrying capacity of the starvation area and full film area is calculated.Comparison between experiments and numerical calculations showed that the starvation area can bear some of the load.At present it is thought that the local tiny full film fragments/oil bridges may be responsible for the load.