Optical Interference Experiment Research Of Pin-bush Pair Based In Industrial Chain Transmission

This thesis takes the industrial chain drive as the research background.The pin-bush contact pair in the industrial chain is a typical finite line contact of higher pair.During the rotation of the chain,when the roller enters into engagement with the sprocket,the bush makes a reciprocating sliding motion relative to the pin,which form a finite sliding frictional line contact pair.Due to the extremely atrocious conditions of the chain,and the supplying lubricating oil is difficult into the pin-bush pair under restricted clearance conditions,the wear of the pin and bush is the main cause of chain elongation.The authors observe the variations of oil film shape and thickness by means of optical interference experiments,to investigate the lubrication behaviour occurring in the pin-bush pairs and its lubrication mechanism by combining the relevant tribology theories.(1)In order to simulate the lubrication behaviour occurring between different types of pin-bush pairs in industrial chain drives,the authors have carried out experimental and theoretical studies respectively.The contact between roller with different size and glass disc to simulates the pin-bush contact in industrial chains.The oil film thickness and shape variation of pin-bush finite line contact pairs with different sizes are obtained through optical interference experiments;numerical simulations of the finite line contact are carried out through a multiple mesh algorithm.The results show that the mid-sectional film thickness increases with the increase of the roller diameter.(2)The straightness error of pins removed from industrial roller chain are measured.The custom-made pins with less straightness error form an EHL line contact pair with the glass disc.The straightness error and the surface roughness error are used to characterise the pin surface precision.The 4 pins with different straightness errors and roughness errors were designed to form two control experiments.The effect of straightness error and roughness error on the lubrication behaviour of industrial chains was investigated under steady state,unsteady state,adequate oil supply and rare oil supply conditions.It was found that either for steady-state or reciprocating motion,better surface precision leads to better lubrication state and thicker film thickness.Due to the characteristic of reciprocating motion,the caviation zone in the outlet area of one stroke turns to be the inlet starvation zone in the next stroke,under rare oil supply condition,even for the best surface precision,direct contact happens after long working cycles.The time of effective lubrication turns to be shorter for pins with lower surface precision.Favourable lubrication is difficult to maintain in real chain drives because the parts are made with much lower surface precision as well as with poor oil supply condition.Thus,wear and as a result of surface wear,chain elongation and failure may take place very easilty.(3)The complete contact area of the pin-bush pair was photographed by an optical interference testing machine.The 4 generatrices of the same pin form the long elliptical contact pair and finite line contact pair respectively with the glass disc.Under adequate oil supply conditions,the film thickness at the end of Generatrix pair is thinner than that of the long elliptical contact pair,and the film thickness at the middle region is thicker than that of the long elliptical contact pair.With the same working period,the longer the stroke length,the thicker the oil film formed.Under modest oil oil supply conditions,oil starvation occurs more rapidly in long elliptical contact than in finite line contact.The "edge effect" and the "close effect" significantly reduce the film thickness at the edges of the finite line contact,which is detrimental to lubrication.However,the "close effect" also reduces the end leak of the lubricant,which slows down the rate of oil starvation profitably.Therefore,the design of the generatrix profile of pin or bush in such a way that an effective lubricant film is formed at the contact edge,while also can reduce end leakage,will have a positive impact on the pin-bush lubrication.