Abstract:

Based on the characteristics of gas compressibility, the concept of compressible gas-assisted extrusion was proposed. To verify the effect of compressible gas on polymer extrusion molding, the two-phase flow model polymer melt phase and compressible gas phase was established by means of finite element method, the non-isothermal viscoelastic numerical simulation of the compressible gas-assisted CG extrusion molding and the traditional without gas-assisted TWG extrusion method were performed. The density distribution of gas-assisted extrusion was not a constant value, but was different with the space distribution of pressure and temperature. Compared with the results of two kinds of extrusion methods, when the interaction of gas on polymer melts and gas compressibility were considered, all physical field distributions of CG extrusion method were obviously different from the TWG method. Shrinkage degree was more prominent when inlet pressure of gas phase increased, which was consistent with the results of experiments. These results and factors could not be reflected in the TWG extrusion simulation method.

Key words: polymer processing, gas-assisted extrusion, two-phase flow, compressibility, computational fluid dynamics, numerical analysis

摘要：

基于气体具有可压缩性特点提出了可压缩气辅挤出概念,为探明气辅挤出中可压缩气体对聚合物熔体挤出成型的影响建立了熔体和压缩气体两相流模型,利用有限元计算方法对可压缩气辅的聚合物挤出成型进行了非等温黏弹数值模拟,并对比分析了传统无气辅和可压缩气辅挤出的物理场分布情况。研究表明,气辅挤出中的气体密度分布不是恒定值,而是随压力和温度空间分布变化,并且在引入气体层以及气体可压缩性后,可压缩气辅挤出与传统无气辅挤出方法相比在各物理场分布上存在较大的差异,当可压缩气体入口压力逐渐增大时熔体挤出收缩程度明显增大。该结果与实验一致,这些是传统无气辅挤出模拟无法体现出来的。

关键词: 聚合物加工, 气辅挤出, 两相流, 可压缩, 计算流体力学, 数值分析