气体压力对气辅共挤成型界面的影响

Effect of Air Pressure on Interface Profile in Gas-Assisted Coextrusion Process

将气体简化为广义牛顿流体,并作为单独一层,针对矩形气辅共挤口模,建立了三维粘弹有限元模型,对理论模型进行了数值计算,研究了气体压力对气辅共挤成型界面形貌的影响及形成稳定气垫层所需最小气体压力与气垫层厚度和熔体流率的关系。研究表明,当稳定气垫层形成后,随着气压力或气垫层厚度的增大,共挤制品挤出胀大率减小,粘性包围程度增大;形成稳定气垫层所需的最小气体压力随气垫层厚度的增大而减小,随着熔体流率的增大而增大。

A three-dimensional viscoelastic numerical simulation was developed for gas-assisted coextrusion through a rectangular channel using the finite element method. The Phan-Thien and Tanner （PTT） model was considered as viscoelastic constitutive equations and the gas was simplified as a generalized Newtonian fluid. The effect of gas pressure on interface profile in gas assisted coextrusion processes was examined. The relationships of the minimum gas pressure to establish a stable gas layer at a die/molten polymer interface and gas layer thickness and polymer melt flow rate were analyzed. Numerical results show that the die swell decreases and encapsulation phenomena increases with increasing gas pressure after the stable gas layer is established. The minimum gas pressure to found a stable gas layer decreases as the gas layer thickness increases and increases as the polymer melt flow rate increases.