Gas-assisted Polymer Extrusion Process And Numerical Simulation

Extrusion is one of the basic methods in polymer poreessing. However, in normal extrusion, several problems appear. Firstly, due to the high viscosity and viscoelasticty of polymer melts, appears in extrusion the die swell which makes it more difficult to enhance the precision of extruded products. The next is the lagre pressure drop which leads to high energy consumption and the third is the appearing of surface disfigurement, which astricts the efficiency of extrusion. Gas-assited 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.Firstly, this paper, summarizes the gas-assisted extrusion mechanism and the basic principles of process design 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 viscoe theoretical model of describing gas-assisted extrusion molding proeess is established.Secondly, by UG, GAMBIT and other three-dimensional modeling software for geometric modeling and meshing. Taking the boundary condition of non shear stress as the effect of the gas layer, optimizing the free surface with three dimensional lattice method, the gas-assisted extrusion process numerical simulation of I-type die extrusion and steel framed polyethylene plastic pipe extrusion die was performed by using the POLYFLOW, a kind of CFD finite element software. The velocity field, pressure field and shear rate distributions inside and outside the die were worked out and compared with those simulation results worked out for the conventional extrusion. 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 molding paves the way to implement the high speed produetion.