Study On The Characteristics Of Lubrication In Conformal Contact Under Limited Lubricant Supply

Nowadays energy problems and environmental concerns necessitate lubricant consumption as little as possible.Limited lubricant supply(LLS)lubrication,which means to achieve effective lubrication when only limited amount of lubricant is provided,requires systematic studies and comprehensive investigations to understand the mechanism therein.Until now knowledges about film building under LLS are mostly concentrated on starved elastohydrodynamic lubrication(EHL)in no-conformal point contact.However conformal contacts are not uncommon in industrial practices,and unfortunately related researches are not enough to solve their lubrication for limited lubricant supply.With a custom-made test rig for measuring lubricating film in conformal slider-on-disc contact,this work delivers experimental and theoretical studies on characterizing lubrication film generation under conditions of limited lubricant supply.The main studies and contributions in this dissertation are as follows:(1)The film thickness with LLS has been measured experimentally,and its variations were characterized under different working parameters.The mechanism of film building with LLS was analyzed through the interferograms captured.In the experiments,the lubricated contact consisited of a stationary slider plane and a rotating transparent glass disc.The film thickness was measured of different viscosities,different loads,different speeds under different lubricant supply quantities.The results showed that a small quantity of lubricant can spread readily on the lubrication track of the rotating disc,and continuous lubrication behavior is then observed.The interferograms showed when only a small quantity of lubricant is supplied,lubrication film cannot be generated in the whole contact region,and some air/lubricant mixture film appears at the inlet area.It is interesting to find that under limited lubricant supply lubricant of higher viscosity cannot always give higher the film thicknes,which is quite different from that higher viscosity always presents thicker lubrication film under fully flooded lubricant supply.With limited lubricant supply,the film thickness decreaseswith increase in load;The film thickness increases with increasing speeds at first and then remains nearly constant under limited lubricant supply.(2)The influence of surface wettability on the LLS lubrication has been studied.The results showed that lubricant could spread well and give continuous layer on the disc surface of high wettability,and film thickness increases with increasing lubricant quantities.High surface wettability leads to strong spread of lubricant,which is not beneficial to the lubricant replenishment on the lubricantion track and lubricant supply to the contact,resulting in lower lubricant film thickness.(3)It has been found that dewetting could influence LLS lubrication as a new influencing factor.When the surface energy of the glass plate is low and the wettability is poor,lubricant stays in the form of discrete oil drops due to dewetting on the lubrication track.Compared to the continuous lubricant layer on the lubrication track,the discrete oil drops here can produce better lubricant replenishment on the lubrication track,and form local load-bearing films in the oil-gas two-phase zone at the entrance,and consequently high lubricant film thickness is produced.In the meaningtime,it was found that when the lubricant quantity is larger,the size of discrete lubricant droplets on the glass disc is larger,and the surface area to volume ratio is smaller,and then the resistance to inertia force is small.(4)The effect of ionic liquid as additive on the lubrication under limited lubricant supply has been studied,and the new role of ionic liquids was revealed.It showed that an adsorption film,which is formed after the experiment,can reduce the surface energy to give dewetting.Therefore the film thickness increases under limited lubricant supply.(5)The behavior of the lubricating film under limited lubricant supply in conformal contacts were studied by numerical simulation.In view of the continuous and discrete distribution of lubricant on the lubrication track,two simplified lubricant supply models were proposed.The numerical simulations and the experimental results of the building of the hydrodynamic film results are correlated.In particular,the numerical simulation results show the local load-bearing capacity generated by the discrete lubricant droplets in the inlet area,confirming the conjecture of the influence mechanism of dewetting.