Research On Heat Transfer Characteristics Of Graphene Additive Lubricants For Si₃N₄-GCr₁₅ Friction Pair

Under the condition of high speed,the electric spindle bearing of CNC machine tools,due to the frictional heat of the bearing and the heating of the stator coil of the electric spindle,cause a large amount of heat to be deposited inside the bearing.Long-term overheating work,bearing life and precision of motorized spindle are seriously affected.Compared with pure lubricants,nano-fluid lubricants in recent years have the advantages of good thermal conductivity,excellent heat exchange,and improved lubrication performance.Whether graphene is used as a lubricating oil additive,while improving the lubrication performance,it has not been studied whether it is beneficial to the heat transfer in the bearing cavity.Using a combination of molecular dynamics simulation and experimental research to analyze the heat transfer characteristics of graphene in Si₃N₄-GCr₁₅friction pairs has important research significance.Based on molecular dynamics and heat transfer,a molecular dynamics model of graphene additive lubricant was established to analyze the effect of graphene additive amount and temperature on the thermal conductivity of graphene lubricant.The simulation results show that within the research temperature range?298 K?532 K?,at the same temperature,as the amount of graphene added increases,the thermal conductivity increases first and then decreases.There is an optimal graphene addition at each temperature The amount makes the graphene lubricant the best thermal conductivity.When the same amount of graphene is added,the thermal conductivity of graphene lubricating oil increases first and then decreases with increasing temperature.There is an optimal temperature for the highest thermal conductivity of graphene lubricating oil.An experimental scheme was designed to study the heat transfer performance of graphene lubricants,and the effect of the amount of graphene addition on the heat transfer performance of graphene lubricants was experimentally studied.The experimental results show that the addition of appropriate amount of graphene helps to improve the convective heat transfer between the lubricating oil and the test piece,but with the increase of the amount of graphene,the viscosity of the mixed oil increases,which reduces the interaction between the fluid and the wall.The convective heat transfer coefficient decreases accordingly.A model of graphene-attached GCr₁₅bearing steel structure was established to analyze the effect of graphene on the surface heat conduction of GCr15 bearing steel,and the effect of temperature on the thermal conductivity of graphene-attached GCr₁₅bearing steel structure was studied.The simulation results show that the graphene adhesion layer can improve the surface thermal conductivity of GCr₁₅bearing steel,and the temperature has little effect on the thermal conductivity of the graphene adhesion GCr₁₅bearing steel structure.Aiming at graphene to enhance the surface heat conduction performance of GCr₁₅bearing steel,the friction experiment and thermal diffusion experiment of graphene-attached GCr₁₅bearing steel were designed.The effect of graphene on the surface heat conduction of GCr₁₅bearing steel was experimentally studied.The experimental results show that the graphene adhesion layer can improve the surface thermal conductivity of GCr₁₅bearing steel and reduce the heat entering the GCr₁₅bearing steel.The research in this paper shows that the graphene-lubricant nanofluids also have a cooling effect while generating lubrication.The cooling effect is mainly manifested in the following parts.First,the addition of graphene to the lubricating oil improves the heat transfer and heat exchange performance of the lubricating oil.The graphene lubricating oil is distributed on the inner wall surface of the bearing cavity,which accelerates the heat conduction.Second,graphene enters between the friction pairs with the lubricating oil,and graphene adheres to the surroundings of the friction parts,which accelerates the conduction of heat from the friction position to the surroundings.