机头流道压缩段过渡形状对管材挤出成型的影响

Effects of Transition Geometry of Flow Channel Compression Section in Pipe Extrusion

在分析了塑料熔体经过机头流道的流动过程与流变学特性基础上,将机头流道压缩段的过渡形状设计为直线型和圆弧型。利用Ployfow软件对直线型和圆弧型过渡压缩段的机头流道进行数值模拟,分析不同压缩段过渡形状对流道压力场、速度场和剪切速率场的影响。结果表明,流道压缩段过渡形状设计为圆弧型后,增大了熔体在成型段内的压力降、流动速度几流道出口速度均匀性,提高了管材的密实度、壁厚均匀性和力学强度,减少了熔体在流道内的停留时间。改进后的流道成型段最大壁面剪切速率从99.6 s^(-1)降低至76.3 s^(-1),远低于硬质聚氯乙烯(PVC-U)管材表面出现鲨鱼皮现象的临界剪切速率,流道出口壁面剪切速率均匀性与管材表面质量均得到显著提高。

Based on analysis of flowing process and rheologicl properties of plastic melt passing through the die flow channel,the transition geometry of compression section was designed as straight line and circular arcs type.Numerical simulation was carried out on flow channel of straight line and circular arcs type compression die by Polyflow.The effects of different compression section geometry on the pressure field,velocity field,and shear rate field was analyzed.The result showed that,after compression section geometry was designed as circular arcs type,pressure drop,flow velocity and outlet velocity uniformity of melt flowing in forming section were increased.The compactness,wall thickness uniformity and mechnical strength of pipe were improved,and residence time of melt flowing in channel was reduced.Maximum wall shear rate of the improved channel forming section decreased from 99.6 s^(-1) to 76.3 s^(-1),which was far lower than the critical shear rate of shark skin of PVC-U pipe.Uniformity of wall shear rate at the outlet of channel and surface quality of pipe were significantlyimproved.