Study On The Mechanism Of PE Pipe Based On Embedded And Spouted-accumulated Forming

The application of large-diameter PE pipes is getting more and more extensive.Extrusion molding and winding fusion molding are currently the main molding methods at present.However,extrusion molding has some disadvantages of complicated molds,difficulty in molding with larger diameters,difficulty in flexible molding and so on.Winding fusion molding has the disadvantages of complex processes,obvious weld mark,and difficulty in continuous production.Considering the above,this paper proposed a new flexible molding technology of large-diameter plastic pipe based on additive manufacturing and calendaring without mold.The research of this technology has a great academic and practical engineering significance.This article first introduced the application of large-diameter plastic pipes,the development status and existing problems of conventional extrusion,winding fusion molding and other molding methods domestically and abroad.The technology of forming PE pipe based on embedded and spouted-accumulated forming technology and its characteristics were presented.The so-called spouted-accumulated forming technology is that a plastic melt at a certain temperature and pressure is ejected from a nozzle which has been embedded in upper layer of tube embryos.After calendaring and sizing,the newly ejected melt is re-welded with the upper tube embryo by using the heat of itself in a certain space which is constrained by the block plate and calendaring roll,finally a continuous large diameter plastic tube is formed after cooling.A physics-mathematical model was established to study the molding process based on the embedded and spouted-accumulated forming.According to the assumptions and boundary conditions,the simultaneous equations,equations of motion,energy equations and constitutive equations were solved.The distribution of velocity field and temperature field of the melt in the processing were obtained;the main process parameters that can influence the forming process and the performance of the pipeline structure were revealed,including extruder speed,cooling temperature,traction speed,and calendering speed.The mechanism of embedded and spoutedaccumulated forming process was explored,which provided important theoretical guidance for the optimization of process parameters and the improvement of the performance of the pipeline structure.Through continuous optimization of process parameters,the HDPE pipeline with a diameter of 800 mm and a wall thickness of 20 mm was successfully formed for the first time by using a spouted-accumulated device and then mechanical properties(including ring stiffness,tensile strength,and impact strength)and microstructures(including DSC and SEM)of the pipes were successfully tested.The effect of main process parameters on the structural properties of the pipe was analyzed,and the experimental results are basically consistent with the theoretical analysis.Comparing the spouted-accumulated pipe with conventional extruded pipe of the same specification,it can be found that the ring stiffness of the the spoutedaccumulated pipe is 1.72 times that of conventional extruded pipe,which exceeds the standard SN2 level by 42% or more;The hoop and axial impact strengths are 1.95 and 1.53 times that of conventional extrusion molding,respectively.Finally,this article made a summary and outlook,and gave some suggestions for the improvement of the spouted-accumulated forming technology and the early realization of industrial production made recommendations.