Study On Rheological Properties And Lubrication Mechanism Of Grease Under Full Supply Of Grease

As a lubricating material,grease has many advantages,such as long service life,strong bearing capacity and good sealing performance.It is widely used in relative moving parts of bearings and mechanical equipment.The rheological properties of grease refers to its ability to flow and deformation under external force,which plays a decisive role in the bearing and lubrication properties of the grease.Lubricating grease is a non Newtonian fluid,and its rheological property has a great dependence on the shear rate.At present,the conclusion of the rheological property under low shear rate is not necessarily applicable to the bearing grease under high shear rate.Especially for some high speed bearing grease worked at special parts,such as wind power bearing,aeroengine bearing and so on,the lubrication effect of grease directly affects the operation of the whole equipment.The friction performance determined by rheological properties is an important index to evaluate the lubrication performance of lubricating materials,which is of great significance for the optimization of grease formulation,the selection of grease and the development of lubrication theory.In order to obtain the friction coefficient of the grease under the actual working condition,a high shear rate friction test bench was built to simulate the actual working conditions of the bearing.The test bed is mainly composed of driving system,hydraulic system,loading system,cooling system,data acquisition system,automatic fat supply system and ball disc test parts.The test-bed can simulate the working condition of grease in wide range of working conditions(shear rate,load and speed),and measure its friction characteristic under different working conditions.According to the most widely used lithium grease and urea based grease,5 kinds of lubricating grease were prepared by the combination of PAO base oil,polyol ester oil,paraffin base mineral oil and twelve hydroxyl lithium thickener and urea compound thickener.The friction coefficient of the 5 kinds of grease under different working conditions was measured by the built friction test bench.The skeleton structure of different lubricating grease and the soap fiber structure of lithium grease under different working conditions were observed by SEM.The experimental results show that lithium based grease and urea based grease have different skeleton structures,resulting in different frictional properties.Under scanning electron microscope,the structure of the soap fiber of lithium base grease is obvious,and each other cross-linking to form a three-dimensional structure skeleton.However,the structure of urea base grease is relatively short,and the degree of crosslinking is relatively low,and the skeleton structure of urea base grease is transparent tube,which is filled with base oil.The friction coefficient of lithium grease increased rapidly at low shear rate.With the increase of slip ratio,the increase trend of friction coefficient slowed down and the friction coefficient reached the maximum value.Then,with the continue increase of slip/roll ratio,the friction coefficient remained constant or began to decrease.While the friction coefficient of urea grease increases approximately linearly with the increase of slip/roll ratio at slip/roll ratio.The friction coefficient increases slowly with the increase of slip/roll ratio.The combination of different base oils and thickeners has different properties.In this paper,the rheological properties and lubrication mechanism of grease under different working conditions are studied based on the viscosity of base oil,the friction coefficient and the structure of lubricating grease.It provides a basis for a better understanding of the change of the fluid state and the structural change during the use of grease,and provides a direction for the research and application of grease.