聚合物气体辅助挤出中气体流动对熔体截面的影响

摘要

将聚合物熔体和低速热空气均视作不可压流体,针对一聚苯乙烯(PS)片材的全气体辅助挤出,建立了描述其气体-熔体两相分层流动的三维有限元模型,采用黏弹应力分离法(EVSS)和非协调流线迎风法(SU)等有限元方法,利用PolyFlow求解器对气体辅助流道中气体和熔体流动进行了计算,分析了熔体截面变化的规律及原因.研究结果表明:气体辅助流道内,气体对熔体有拖曳作用;沿挤出方向,熔体速度逐渐增大,而截面积逐渐减小,都在口模出口面上达到极值,同时截面形状有微小改变;口模出口面上熔体沿挤出方向的速度随入口气体体积流率的增大而近似线性增大,熔体截面积则近似线性减小.%For the fully gas-assisted extrusion of a polystyrene sheet,a 3D finite element model which described the gas-melt stratified flow was established with the polymer melt and low speed heated air both being considered as incompressible fluid.Numerical computations of the flows in gasassisted channel were performed by PolyFlow solver with some FEMs such as elastic-viscous-splitstress method (EVSS),streamline-upwind (SU) method etc.The effect laws of gas flow on melt cross sections were analyzed.The results show that in the gas-assisted channels the melt is towed by gas layer.Along the gas-assisted channels,the melt velocity in extrusion direction increases,and the melt sectional area decreases,both with flow distance and gradually reach an extreme value at die exit.On the outlet plane,the melt velocity in extrusion direction increases,and the melt sectional area decreases,both with gas volume inflow rate and in an approximately linear way.