Transient Rheological Properties And Model Prediction Of Lithium-based Grease

Friction and wear is one of the natural phenomena that are common in nature.According to statistics,about one-third of the world’s energy consumption is caused by friction and wear.Among the various lubricants,the unique lubricating properties of the grease make it an important position.So the grease has been valued by researchers all over the world.Based on the study of the rheological properties of grease,this study studies the transient rheological properties of grease at low speed.Lithium-based greases on the market are very different in terms of composition materials etc.,and expecting to prepare lithium-based greases for testing.Firstly,we compared the thickener and base oil required for the preparation of grease in the laboratory,and used 12-hydroxystearic acid,stearic acid and light refined naphthenic base oil as raw materials for the preparation of grease samples;the double-layer glass reactor and YSP hydraulic three-roll mill was used as the grease preparation equipment to determine the preparation process;the physical and chemical properties of the prepared grease samples were determined;the rheological property test instrument was selected and used as the experimental tool for grease rheology experiments.The transient rheological properties of lithium-based greases were studied.The stress overshoot behavior of lithium-based greases under low-speed shear conditions was mainly investigated.The shear rate,thickener content and base oil viscosity were analyzed for the influence of rheological properties.The structure of the lithium-based grease determines its viscoelastic properties at low speeds,and the stress overshoot process include three stages of rapid rise,decay and smoothness.The different thickener content of the grease is at the same shear rate,the greater the thickener content shows the more obvious stress overshoot process.Under the same shear rate conditions,the greater the viscosity of the base oil is,the more obvious the stress overshoot process is.The greater the shear rate is,the smaller the time to reach the maximum shear stress is and the greater the maximum shear stress is.The rheological model was used to quantitatively describe its transient rheological properties.The relationship between stress overshoot characteristics and shear rate,thickener content and base oil viscosity were analyzed.The Leider-Bird model has its own limitations on the stress curve fitting of lithium-based greases.The first stage of the curve fits well,while the second stage is poor.From the characteristics of the stress curve segmentation,the fitting analysis was performed by the piecewise polynomial model.A four-parameter polynomial model fit was used before the maximum shear stress;a fiveparameter polynomial model fit was used after the maximum shear stress.The fitting results are significantly better than the fitting results of the Leider-Bird model.We Calculated the shear yield energy density and analyzed the relationship between shear rate,thickener content,base oil viscosity and yield energy density.