Influence of Initial Value of Transient Time Step on Numerical Simulation of Blow Molding Balloon

The correlation between the initial time value of transient iterative parameters and the blowing pressure in the numerical simulation process of blowing balloon is investigated by POLYFLOW. The results show that: 1) As the blow molding pressure increases, the boundary value of the iterative time step decreases rapidly at first and then slowly. At the end of the first step of iterative calculation for each boundary value, the balloon parison is in the mold core cavity. 2) If the initial time value of transient iterative parameters is smaller than the boundary value of the iterative time step, the balloon parison is still in the mold core cavity at the end of the first iteration. However, if the iterative calculation continues, the calculation process may be interrupted when the time step is smaller than the initial time value of the transient iterative parameters, which makes the blow molding simulation of balloon unable to continue. 3) It is suggested that the initial time value of transient iterative parameters is one order of magnitude smaller than the boundary value of the iterative time step to complete smoothly the simulation of blow molding balloon.

3层共挤模具交汇夹角对单层厚度及离模胀大的调控机制

聚合物共挤模具结构对制品成型质量有着重要影响,尤其是模具交汇夹角对熔体厚度及离模胀大有着明显的影响。文中采用Carreau黏度模型和Picard迭代计算方法,深入研究了外层为聚十二内酰胺(PA12)、中层为乙烯-醋酸乙烯酯共聚物(EVA)和内层为聚丙烯(PP)的3层微管共挤过程的数值模拟。结果表明,外层熔体交汇夹角增大时,PA12厚度增加,EVA和PP厚度减小,内外径均减小,胀大率增大;中层熔体交汇夹角增大时,EVA厚度增大,PA12和PP厚度减小,内外径均减小,胀大率减小;两处熔体交汇夹角同时增大时,PA12和EVA厚度增大,PP厚度减小,内外径均减小,胀大率增大。3层共挤实验证明了模拟结果的正确性与有效性。该研究结果能够为聚合物多层共挤模具的流道结构设计提供了有价值的参考。