应力集中效应对熔体挤出流动不稳定性的影响

用双毛细管流变仪研究了线型低密度聚乙烯、低密度聚乙烯及其共混物在较宽速率范围内的流变行为,通过分析流场中应力集中效应与不稳定流动的关系,从而控制不稳定流动现象。结果表明:挤出物在口模入口处的应力集中占总压力的15%以上时,一般导致毛细管人口压力降的无规振荡及挤出物的整体无规则波动和破裂;整条毛细管上的挤出压力发生振荡,挤出物外观发生光滑段和粗糙段交替出现的有规畸变。

Relation between stress concentration and unstable flow of melt in extrusion process

This paper studied rheological behaviour of low density polyethylene (LDPE),linear low density polyethylene (LLDPE) and the blends thereof by double-capillary rheometer in a wide flowrate range.The relation between the stress concentration in flow field and instability in flowability of the resin melt was analyzed for the sake of controlling the phenomenon of the unstable flow.The results show that oscillation in pressure drop at inlet of the capillary and the vibration and rupture of the whole extrudate could occur when the stress concentration of the extrudate at entrance of the die accounted for over 15% of the total pressure. In such a case,the extrusion pressure throughout the whole capillary oscillated;smooth and rough surface regions formed alternatively in the appearance of the extrudate