Theoretical And Experimental Study On Polymer Melt Flow Within The Die In Plastic Profile Gas-assisted Extrusion

Gas-assisted extrusion is a new type of technology on polymer extrusion. It provides a gas layer between the melt and die wall, so the flow boundary of extruded melt changes to full slip in the die and the friction between the melt and die wall is thereby reduced greatly. The advanced extrusion is effective for solving the problems in the traditional extrusion, just like die swell, large extrusion pressure drop and the appearing of unstable flow("Sharkskin" and extrusion distort)when the extrusion speed exceeds the limit. On the basis of the former studies, the experimental study and numerical simulation of gas-assisted extrusion on plastic profile have been conducted in this paper. The main work is listed below:1,Based on the process and characteristics of gas-assisted full slip extrusion molding and the theories of rheology and hydrokinetics etc., under reasonable assumptions, a full three dimension steady isothermal viscoelastic theoretical model of describing gas-assisted extrusion molding process is established.2,Considering the non-convergence and unstable problem of solving the equation due to the coupling of the viscoelasticity and the tracing of the swell free surface and control equation, simulations on traditional extrusion and gas-assisted extrusion were carried out on the basis of the stable finite element discrete techniques of Galerkin method, Evolution method, and DEVSS/SU method etc.,3,The gas-assisted full slip extrusion molding mechanism is studied by means of direct finite element numerical simulation, and all kinds of the several flow fields under different processing conditions and parameters have been obtained. The influencing rules of the viscoelasticity property parameters and process parameters on the die swell of the gas-assisted full slip extrusion molding are analyzed. Through the analysis of simulated results, the proper length of gas-assisted die has been determinated. In addition, the quantitative comparisons between the gas-assisted full slip extrusion molding process and traditional extrusion molding process are implemented. In this case, the influencing rules of the viscoelasticity property parameters and process parameters on the die swell of the profile extrusion molding in the two processes were studied systematically.4,Compared the two processes, the research results showed that the gas-assisted full slip extrusion molding process can almost eliminate extrusion die swell and distort. Therefore, the gas-assisted full slip extrusion molding process can not only implement the automatic and accurate control of production dimention., but also can save energy. And the gas-assisted full slip extrusion moldng paves the way to implement the high speed production5,Design the gas-assisted extrusion die of profile and carry on the experiments. By the experiments, the gas-assisted extrusion on plastic profile could be realised. The impact on die swell and extrusion pressure drop in gas-assisted extrusion under various conditions has been investigated also.