熔体粘弹性对聚合物多层共挤成形离模膨胀影响的数值分析

研究共挤成形离模膨胀的产生机理对于奠定其口模设计方法的科学理论基础具有重要的意义。通过建立的稳态有限元数值算法,系统模拟粘弹性流变性能参数对共挤成形离模膨胀的影响规律,并揭示离模膨胀的机理。结果表明,多层共挤成形芯壳层熔体的离模膨胀是由粘弹性熔体的二次流动引起,主要取决于芯壳层熔体二次流动的方向与强度。熔体二次流动的方向与第二法向应力差的正负号有关,而熔体二次流动的强度则与第二法向应力差绝对值的大小成正比。当口模出口处芯壳层熔体的第二法向应力差为负,芯壳层熔体产生离模膨胀,其离模膨胀比随第二法向应力差的增大而增加。当口模出口处芯壳层熔体的第二法向应力差为正,芯壳层熔体产生离模收缩,其离模收缩比随第二法向应力差绝对值的增大而增加。研究还表明芯、壳层熔体及口模整体的离模膨胀随着壳层熔体松弛时间的增大而减小,而随着芯层熔体松弛时间的增大而增加。

Numerical Investigation on the Influence of Melt Viscoelasticity on Die Swelling of Polymer Co-extrusion Process

It is very important to study the mechanism of co-extrusion die swell for laying the scientific theoretical foundation of a die design method.The influencing rule and mechanism of viscoelastic rheological parameter on polymer co-extrusion die swell are modeled by the stable numerical algorithm established.Research results show that the co-extrusion die swell is caused by the viscoelastic melt secondary flow,and depends on the direction and strength of melt secondary flow.The direction of melt secondary flow...