聚合物熔体在任意长径比圆锥口模的挤出胀大唯象研究

Phenomenological Studies on Extrusion Swell of Polymer Melt through Conical Dies with Different L/D Ratios

深入讨论了聚合物熔体在不同长径比、不同角度圆锥口模的挤出胀大现象及机理。对口模长径比较小的挤出胀大,由于熔体入口拉伸弹性变形来不及松弛,产生较大的挤出胀大;对长径比较大的口模,熔体在平直流道内停留时间较长,入口弹性形变逐渐松弛,这时主要是流动剪切应变引起的弹性变形,产生较弱的挤出胀大,比长径比小的挤出胀大来得小,并且聚合物熔体的挤出胀大随着长径比的增大而趋向一恒定值。结果还表明:聚合物熔体在圆锥口模的挤出胀大受到挤出口模入口角影响。当L/D较小时,挤出胀大与口模入口角有关;当L/D较大时,口模入口角对挤出胀大影响较小。

Discussed thoroughly the extrusion swell phenomenon and mechanism of polymer melts in conical die with different entrance angles and different ratios of length to diameter. The extrusion swell of short die is bigger than long die, because ratio of length to diameter of dies is shorter and short stay time of polymer melt at straight channels is found and elastic form of melt on entry extensional effect relaxes too late and the extrusion swell of long die is mainly caused by elastic reversion of shear deformation. Withal the extrusion swell of polymer melt tends to a fixed value along with the ratio of length to diameter augmenting. Results indicate that die entrance angle influences extrusion swell at conical dies. When L/D is small,die swell relates to entrance angles,and when L/D is quite great,the influence of die entrance angle for die swell is less.