挤管用螺旋芯模机头内熔体流动分析

本文以B.Procter的简化模型(方法Ⅰ)为基础,考虑流动指数与剪切速率的关系(方法Ⅱ)和垂直于轴的截面上的压力平衡(方法Ⅲ),用迭代法分配计算单元的轴向和沿螺旋流道方向的体积流率。编制了模拟螺旋芯模机头内熔体流量、压力降和剪切速率分布的计算机程序。模拟结果表明,根据漏流分布曲线的特性选择几何参数的螺旋芯模机头对熔体的分配效果不受更换物料和改变机头温度及挤出速率的影响。用高密度聚乙烯进行挤管实验时测定的机头压力降和管材壁厚偏差介于用方法Ⅱ和方法Ⅲ模拟结果之间,实验测定结果与用方法Ⅰ模拟结果的差别最大。高密度聚乙烯管的内、外表层的结晶不同,其差别随挤管时的牵引速度的提高而降低。

FLOW ANALYSIS IN SPIRAL MANDREL PIPE DIES

On the basis of the earlier work of B. Procter (mode I ) ,the division of flow volume of a element into spiral channel flow and axial flow was carried out by means of flow behavior index on apparent shear rate (mode I )and pressure balance of adjacent elements (mode I ). Computer programs for lay-out of the spiral mandrel dies were developed according to the modes. The measured pressure loss in the test die and the deviation of the wall thickness of produced pipe using the die lie between the values calculated with mode I and that with mode 0 . The difference between measured value and calculated one with mode I is larger than the others. It was shown ,that a spiral mandrel die with the geometry optimized according to the specifications of the leaksteam profile can keep precise melt distribution in the circumference during raw material change as well as alteration of output rate and melt temperature.