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  

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

作　　者：周文彦[1] 周国发[1] 

机构地区：[1]南昌大学环境科学与工程学院,南昌330031

出　　处：《机械工程学报》2010年第6期111-119,共9页Journal of Mechanical Engineering

基　　金：国家自然科学基金(20274016);江西省教育厅科技攻关(s00123)资助项目

摘　　要：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。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 depends on the sign of secondary normal stress difference, and the strength of melt secondary flow is proportional to the absolute value of secondary normal stress difference. When the secondary normal stress difference of core and skin melt is negative, core and skin melt will produce die swell, the ratio of die swell increases with increasing of secondary normal stress difference. When the secondary normal stress difference of core and skin melt is positive, core and skin melt will produce die shrinkage, the ratio of die shrinkage increases with increasing of the absolute value of secondary normal stress difference. Moreover, research results show that core, skin melt and holistic die swell decrease with increasing of skin melt relaxation time, but increase with increasing of core melt relaxation time.

关 键 词：粘弹性 共挤成形 数值模拟 离模膨胀 机理 

分 类 号：TQ320[化学工程—合成树脂塑料工业]