熔体粘弹性流变性能参数对聚合物共挤成型离模膨胀影响的数值分析

共挤成型中,聚合物粘弹特性与过程参数波动的耦合作用会产生波动的挤出胀大,使得根据共挤制品的形状设计相应的共挤定型口模在工程上仍是一项技术挑战,文章基于这一技术问题,建立了全三维稳态等温粘弹性共挤成型的理论模型,并通过DEVSS/SU,Mini-Element法和罚函数法等稳态有限元技术,建立了与该模型相适应的快速收敛的稳态有限元数值算法,并通过有限元数值模拟,系统研究了粘弹性流变性能参数对共挤成型离模膨胀的影响规律,通过理论分析,揭示了其离模膨胀机理。研究表明,共挤口模芯壳层熔体离模膨胀是由于口模出口处的二次流动引起,口模出口处的芯壳层熔体的第一、第二法向应力差随着芯壳层熔体松弛时间增加而增加,其口模出口处的二次流动增强,从而导致共挤口模芯壳层熔体离模膨胀随着芯壳层熔体松弛时间的增加而增加。

Numerical analysis of influence of melt viscoelastic rheological parameters on co-extrusion die swell for viscoelastic polymer

In co-extrusion,interaction between the polymer melt viscoelastic nature and unavoidable fluctuations of the operating conditions results in fluctuating die swell which makes the design of co-extrusion die according to the shape of productions a technology challenge.Based on the technology difficult,The full three dimension isothermal viscoelastic theory model describing co-extrusion process was established in this paper,and based on the stable finite element techniques of the DEVSS/SU method,Mini-Element method and penalty function method ect.,the corresponding stable numerical algorithm with fast convergent was established.The affecting law of melt viscoelastic rheological parameters on the co-extrusion die swell was studied by the finite element numerical simulation,and the influencing mechanism of the co-extrusion die swell was disclosed by theoretical analysis.Research showed that the co-extrusion die swell is caused by secondary flow near die exit,and the core,skin first and secondary normal stress difference near die exit increase with core and skin melt relaxation increasing which results in increasing of secondary flow,therefore,the co-extrusion die swell increase with core and skin melt relaxation increasing.