Numerical Simulation Study Of The UHMWPE Gas-assisted Extrusion

The ultra high molecular weigh polyethylene (UHMWPE) is a new type of engineering plastics with outstanding properties, so it is used widely. Because of its melt characters there have several shortcomings such as die swell, melt fracture, high die pressure drop and very low productive efficiency in the molding of UHMWPE.In order to solve some of the problems in UHMWPE processing, a new technique—the gas-assisted extrusion was introduced. It provides a gas layer between the melt and die wall, so the flow between the die and extruded melt fall into full slip and the friction in the extrusion is greatly reduced. Because the study we did before shows that the gas-assisted extrusion is effective for solving the problems in the traditional extrusion, like die swell, large extrusion pressure drop and melt fracture when the extrusion speed exceeds the limit.The main work finished in the paper is listed below:(1) Based on the technique characteristics of gas-assisted extrusion and theories of polymer rheology, hydrokinetics etc. viscoelastic theoretical model of UHMWPE gas-assisted extrusion was established by means of reasonable assumption.(2) The simulation of UHMWPE extrusion was conducted by means of the CFD numerical analysis software POLYFLOW and the velocity field, pressure field and shear-rate in the gas- assisted extrusion die was analyzed with the comparison of normal extrusion.(3) The influence of characters of polymer and parameters of process on the distribution of various fields have also been studied.