Influence Of Free Water On Lubrication Performance Of Point Contact

In this paper,effects of free water on the point contact lubrication performance is carried out from both experimental and theoretical aspects.Influence of water content on the viscosity of lubricant discussed;Under different oil-supply condition,effects of free water on the lubricating performance of point contact;Under slide-roll condition,influence of free water on the lubricating performance;Analysis of water on the starved elastohydrodynamic lubrication performance.Firstly,the viscosity of the oil-water mixture was measured using a rheometer,Influences of water content,oil product and temperature on the viscosity of the oil-water mixture was analyzed.Based on the experimental date,a new fitting formual of viscosity was obtained considering the effects of water.Results show that,for different oils,the higher the lubricating oil viscosity,the greater the influence of free water.When the water content is within the range of 30% to 90%,effect of the free water on the viscosity of the lubricating oil are obvious.Secondly,using optical interference technology,effects of water on lubrication performance of oil under pure rolling conditions were investigated.Influences of free water on lubricating oil film under different oil supply-conditions were investigated.Results show that,under fully-flooded condition,the shape of the oil film is affected by free water,and the degree of influence is negatively related to the distance from the inlet cavitation boundary to the position of the contact area.In the state of starvation,free water can replenish the oil pool in the contact area,the starved degree reduces and the film thickness increases.Friction and mixing happens for free water and lubricating oil,and “turbulence” phenomenon is generated,so that the boundary of the entrance area becomes dim.Compared to the ceramic ball-glass disk,effects of the film thickness between the steel ball-glass disc are significant by free water.Then,using optical interference technology,the influence of water on the oil lubrication performance under slide-roll conditions was investigated experimentally.Factors of slide-roll ratio,water content,etc.are considered,and effects free water on the lubrication performance of point contact were provided.The results show that,the free water can significantly increase the friction coefficient under slide-roll conditions.As the water content increases,the free water washes off the lubricating oil,and results in a slight increase in the friction coefficient.With different slide-roll ratios,the oil film thickness decreases significantly due to addition of free water.The film thickness decreases slightly as the water content increases.When the slide-roll ratio increases,the influence of free water on the lubricating oil film increases.The larger the slide-roll ratio,the large the variation in the shape of the oil film,and the greater the degree of fluctuation of the film thickness.Finally,a starved isothermal point contact elastohydrodynamic lubrication model considering the influence of water was established.Effects of water content,entrainment speed and oil-supply conditions on the film thickness,the pressure and fractional oil film ratio were analyzed.The results show that,free water reduces the viscosity of the lubricating oil,resulting in a decrease in the film thickness.When the water content is too high,the oil film pressure decreases,and the secondary pressure peak decreases or even disappears.Free water increases the pressure of the film and the range of the bearing area under starved lubrication.As the entrainment speed increases,the influence of free water on the film thickness increases under fully-flooded condition.The film thickness increases firstly,and then remains unchanged under starved condition as the entrainment speed increases,and the influence of free water on the film thickness can be ignored.The viscosity model has a greater influence on the film thickness,and the fitting viscosity model is more sensitive to free water content.Under the starved condition,the free water mainly has an infulence on the film thickness and pressure,and the effect of free water on the contact pair of steel ball-glass disc is greater than that of ceramic ball-glass disc contact pair,and this is consistent with the test results.