Preparation And Lubrication Model Of Solid-liquid Two-phase Rolling Emulsion

In order to improve the service life of rolling mill and the surface quality of rolling parts and meet the needs of environmental protection,the use of nano-additives has become an important means to improve the lubricity of rolling fluid.Emulsion has excellent lubrication and cooling properties,while nanoparticles which show good friction reduction characteristics have the characteristics of large surface area,high diffusivity and increased hardness.In this paper,graphene nanoparticles were used as lubricant additives to realize the stable dispersion of nanoparticles in the emulsified solution.On this basis,the tribological properties of the emulsified solution with different content of graphene under different loads and the effect of water content on its lubrication performance were investigated.The wear surface was characterized by scanning electron microscopy(SEM),energy dispersive spectrometer(EDS),3D laser scanner and Raman,and the lubrication mechanism of graphene emulsion was discussed.At the same time,the mixed lubrication model of rolling process was established,which provided a theoretical reference for the optimization of rolling process.Firstly,the preparation of graphene emulsion was completed,and the stability of the emulsion was studied by static experiment.The results showed that the graphene emulsion remained stable without stratification after three months.It was found by four-ball friction and wear tester that the maximum non-sticking bite load(P_B value)of the emulsion was not changed under the low content of graphene(0 wt%-0.08wt%).The results of wettability study show that the wettability angle decreased firstly and then increased with the increase of the content of graphene,and reaches the minimum when the content of graphene is 0.06wt%.Secondly,the tribological properties of graphene emulsion were studied by CFT-1 multifunctional surface performance tester,and the effects of load,the content of graphene and water on the tribological properties of emulsion were investigated.The results showed that the average friction coefficient and the wear area of the lower plate decreased firstly and then increased with the increase of the content of graphene under high load.The average friction coefficient did not change much,and the wear area of the lower plate decreased firstly and then increased with the increase of the content of graphene under low load.For different oil-water ratios,the average friction coefficient decreased firstly and then increased with the increase of the content of water,and the wear area of the lower disc showed a downward trend with the increase of the content of water.Finally,the effects of different rolling conditions on the fluid pressure,contact area ratio and film thickness ratio in the deformation zone are calculated and analyzed by the mixed lubrication model of rolling process.The results showed that the fluid pressure and the contact area ratio increased and the film thickness ratio decreased with the increase of dimensionless velocity and reduction rate.The fluid pressure and the contact area ratio decreased and the film thickness ratio increased with the increase of convex peak angle and emulsion viscosity.The fluid pressure,the contact area ratio and the film thickness ratio in the deformation zone are basically unchanged with the increase of exit velocity ratio.