Analysis Of Transport Flow Field And Screw Wear Of Single Screw Extruder

Single screw extruder is a commonly used equipment for plastic modification.Plastic modification requires adding filler particles with certain hardness into the master batch.Due to the addition of higher hardness filler particles,the modified plastics have higher hardness.During the reprocessing of these high hardness plastics,the single screw extruder is susceptible to abrasive wear of the plastic particles in the solid conveying section and erosion wear of the filler particles released by the melting of the plastic particles in the melt conveying section.Both kinds of wear will lead to premature screw failure.Therefore,the analysis of abrasive wear and erosion wear of single screw extruder can predict the failure rule of single screw and clarify the influence of process parameters on screw wear,which is of great significance to reduce screw wear.Using numerical simulation method and EDEM software,the abrasive wear behavior of low density polyethylene particles on the solid conveying section of single screw extruder was studied,and the influence of different factors on the abrasive wear of the section of screw was analyzed.Fluent software was used to study the erosion wear behavior of filler particles Si O₂ on the screw in melt conveying section,and the related influencing factors were analyzed.The specific content is as follows:（1）The discrete element model of the transport of plastic particles was established,and the transport process of plastic particles in the solid transport section was simulated.Based on the Archard Wear model and Relative Wear model,the abrasive Wear behavior of the screw caused by plastic particles was analyzed,and the influence of screw speed and particle size on the abrasive Wear of the screw was studied.The results show that the wear degree of the screw decreases with the increase of the axial distance from the thrust plane.The distribution of tangential accumulated force and tangential accumulated energy corresponds to the distribution of wear morphology,which indicates that the abrasive wear of screw is mainly caused by the tangential friction of particles.Screw wear increases with the increase of rotating speed and the decrease of plastic particle size.（2）Analysis of the force of the melt conveying section of the filler particles,the particle motion equation is established to determine the interaction between particles and boundary of the model,using DPM model to simulate the flow of the melt conveying section of the solid liquid two phase flow,determines the method for calculating the rotating flow field,simulates the Si O2 filled low density polyethylene melt extrusion flow field.The results show that the pressure in the flow field increases gradually from the inlet to the outlet on the whole,and the pressure in the same spiral groove decreases along the direction of extrusion.The velocity of the flow field decreases gradually from the surface of the screw groove to the inner wall of the cylinder,and reflux occurs at the clearance of the top of the screw groove.In the clearance at the top of the spiral edge,the movement direction of some particles is opposite to the extrusion direction.（3）Based on the Oka erosion model,the erosion behavior of the screw by the filler particles in the melt conveying section was studied,and the effects of screw speed,filler particle size and filler mass fraction on the maximum erosion rate of the screw were analyzed.The results show that the top of the thrust surface and the top of the back of the screw are the erosion concentration areas of the screw,and the analysis results are consistent with the actual erosion morphology of the screw.The maximum erosion rate of screw increases with the increase of screw speed,packing particle size and packing mass fraction.