Study On Elastohydrodynamic Friction Properties Of Grease At High Shear Rate Under Full Supply Of Grease

In this study,a Mini-Traction Machine(MTM)has been used to studies the friction characteristics and lubrication mechanism of grease under sufficient grease supply condition.The influence of single factor on grease lubrication is explored under controlled conditions.The grease is evaluated and studied correctly under the actual operation conditions of bearings.Greases with different components were prepared according to the experimental requirements.Lithium grease and polyurea grease were prepared with PAO,ester oil and paraffin mineral oil.Scanning electron microscopy(SEM)showed that the three-dimensional structure of greases made from different base oils and thickeners were different.The fibre structure of lithium grease with ester oil is coarse and the gap between fibre structures is large.However,the fiber structure of lithium grease with PAO is finer,and the gap between the fiber structures is smaller.Viscosity-temperature characteristics of grease base oil were studied.Walther-ASTM viscosity-temperature models of PAO,ester oil and paraffin-based mineral oil were established.A new dynamic viscosity-temperature model was also presented,and its prediction accuracy was high.The effect of operation conditions on the friction characteristics of grease was investigated.The experimental results show that the friction coefficient of grease decreases with the temperature and rolling speed,increase with load and slide-roll ratio.The slide-roll ratio and friction coefficient curve approximate logarithmic function.The first-order fitting formula of friction coefficient and slip-roll ratio is established.A quadratic fitting formula for predicting the friction coefficient of lubricating grease was established by using the coefficient of the first fitting formula under different operation conditions.The curve of friction coefficient varying with slip-to-roll ratio can be obtained by inputting the operation conditions in quadratic fitting formula.The effects of base oil,thickener,consistency and mechanical degrade on the friction characteristics of grease were investigated.The experimental results show that the friction coefficient of lithium grease with polyol ester oil is higher than lithium grease with PAO under the same operation conditions.When mineral oil is used as base oil,the friction coefficient of lithium-based grease made by adding lithium-based thickener is less than polyurea-based grease made by adding polyurea-based thickener.At the same time,the lubrication film thickness of the two greases on the ball raceway was photographed by micro-traction tester.It was found that the lubrication film thickness of lithium grease was larger than polyurea grease.Under different temperatures,the effects of grease consistency and mechanical degrade on the friction characteristics of urea grease are different.The friction coefficients of greases with different cone penetration and mechanical degrade are basically the same at room temperature and differences with the increase of temperature.