Simulation Study Of Material Movement Under The Action Of "liquid Medium + Small Load Impact

Mechanical galvanizing process is a green surface treatment process that has arisen in recent years.Because of its advantages of simple process operation,no pollution,no hydrogen embritzability of the coating and uniform coating organization,it is widely paid attention to by industrial developed countries.However,there are many influencing factors in the forming process of mechanical galvanizing layer,and the external conditions such as the cross section shape of the cylinder,the rotating speed of the cylinder and the particle size of the impact medium play a key role in the formation of the coating and the density and appearance quality of the coating.The current mechanical plating equipment has many limitations.It can not directly observe and analyze the collision,force and energy transfer of materials in the plating cylinder during the formation of the mechanical galvanizing layer.It can only observe the surface quality after the coating is formed.The bonding strength and porosity of the coating were measured and the surface and cross section morphology of the coating were characterized by scanning electron microscopy to determine the quality of the coating.Therefore,this paper selected this as the entry point,based on discrete element method and computational fluid dynamic method,simulated the mechanical galvanizing process,analyzed the movement process of materials in the plating cylinder under different process parameters from the collision frequency,collision frequency,collision energy,collision contact force and velocity cloud diagram of fluid phase,and prepared the corresponding galvanized layer samples.Scanning electron microscope,electron probe X-ray microanalyzer,X-ray diffractometer and high frame rate industrial camera were used to characterize the microstructure and phase composition of galvanized layer,so as to provide reliability basis for further improvement of mechanical plating process:(1)The inert zone of the material(impact medium and substrate)in the cylinder is small when the cylinder speed is 50 rpm or 60 rpm;When the rotating speed of the cylinder was 40 rpm and 50 rpm,the number of collisions between the impact medium and the substrate in the cylinder changed more regularly,and the small load impact provided by the impact medium was more conducive to the shape and thickening of the coating.When the rotating speed of the cylinder is 60 rpm,the impact force(positive impact and friction)brought by the impact medium is too large,which is easy to make scratches on the surface of the coating;By analyzing the velocity nephogram of the fluid phase,it is shown that the motion region and velocity of the fluid domain in the cylinder are consistent with that of the solid particles when the rotating speed of the cylinder is 40 rpm and 50 rpm.(2)In the EDEM simulation of the material movement in the cylinder,the effective collision frequency of the material in the cylinder is higher when the section shape of the cylinder is octagon and round;in the EDEM-Fluent coupling simulation,the effective collision frequency of the material in the cylinder is higher when the section shape of the cylinder is hexagon and octagon;The impact contact force between the impact medium and the substrate in the octagon cylinder fluctuates evenly and there is no abnormal increase of the contact force.By comparing the velocity nebulogram of the material when the cross-section shape of the cylinder is quadrilateral,hexagonal,octagonal and circular,it can be concluded that the fluid phase in the octagonal cylinder has a higher velocity,and the moving region of the fluid phase is consistent with that of the solid particles.(3)When the impact medium particle size is 4 mm,5 mm,6 mm,the inert zone of material movement in the plating cylinder is small;When the particle size is 2 mm,3 mm,4 mm,the effective collision frequency of the material is higher;When it is 3mm,4 mm and 5 mm,the kinetic energy of collision between materials fluctuates evenly.At 5 mm,the motion velocity of the fluid phase is higher,and the movement area is mainly concentrated in the lower right part,so that the solid phase and the liquid phase can be coupled.When it is 4 mm and 5 mm,the contact force changes regularly,and the contact force strength is higher than zinc yield strength.The obtained particle size ratio(Group 2)is: 2 mm 23%,3 mm 23%,4 mm 23%,5 mm27%,6 mm 4%.Compared with the mixed impact medium with five particle sizes accounting for 20%(group 1),in the simulation test of the second group of mixed particle size,the collision frequency between materials is higher and the collision regularity is strong,and the abnormal increase of the contact force between materials is less.In the second group of simulation tests,the regularity and homogenization of the impact medium of 5 mm made the velocity of the fluid field more stable and uniform.(4)Galvanized samples with different cylinder speeds and two groups of mixed particle sizes were prepared.Through comparative analysis,it was found that the average thickness and relative density of galvanized layer prepared at the cylinder speed of 50 rpm were higher,and the average deviation of coating was small.In addition,most of the zinc powder particles in the coating had undergone extrusion plastic deformation and were in the shape of mutual embedding,with dense accumulation between particles.With this particle size ratio(Group 2): The galvanized samples prepared on the basis of 2 mm 23%,3 mm 23%,4 mm 23%,5mm 27% and 6 mm 4% have higher average thickness and relative density than the galvanized samples in the first group(the five particle sizes all account for 20%),and the surface of the galvanized layer in the second group has a large area of compact plate,and there is a small gap between the zinc powder particles.Most of the zinc powder particles have plastic deformation,deposited on the surface of the substrate under the impact and friction of glass beads,and the coating gradually from loose to compact.