螺棱梯形底角和凹槽半径对反应挤出机流场的影响

利用Polyflow计算机软件,在相同温度的条件下,通过最大剪切速率、最大剪切应力、最大混合指数和累计停留时间这4个指标,研究螺杆螺棱截面形状为梯形时其梯形底角角度和凹槽半径两个变量对聚乙烯在单螺杆反应挤出机中流场的影响。结果表明,当螺杆螺棱截面梯形底角角度为60°时,螺杆提供的最大剪切速率、最大剪切应力、最大混合指数均较底角为30°和45°的高,粒子累积停留时间则居中;在底角为60°的梯形螺棱上开半径为1.5 mm的半圆凹槽时,该结构所提供的最大剪切速率、最大剪切应力和最大混合指数均较不开槽(凹槽半径0 mm)和凹槽半径为2 mm的高,粒子累积停留时间相对最短。当螺杆螺棱截面梯形底角角度为60°且凹槽半径为1.5 mm时,可使物料获得的剪切效果最好且使其在流道中的停留时间最短,从而为大规模生产加工节约了时间。

Effects of Screw Arris Trapezoid Base Angle and Radius of Groove on Flow Field of Reactive Extruder

Based on the Polyflow software and under isothermal condition,when the screw arris section is trapezoidal shape, through four aspects of maximum shear rate,maximum shear stress,maximum mixing index and particle cumulative residence time, the effects of two variables :trapezoid base angle of screw arris section and radius of groove in the screw arris on the flow field of polyethylene in single screw reactive extruder were studied. The results show that when the trapezoid base angle is 60°,the maxi-mum shear rate,maximum shear stress and maximum mixing index provided by the screw are better than those of 30° and 45°,the cumulative residence time is in the middle. When the trapezoid screw arris with 60° base angle is slotted with semicircle groove on radius of 1.5 mm,the maximum shear rate,maximum shear stress and maximum mixing index are better than those of the groove on radius of 0 mm and 2 mm,the cumulative residence time is relative shortest . Therefore,when the trapezoid base angle of screw ar-ris section is 60° and the radius of groove in the screw arris is 1.5 mm,the materials can gain the best shear effects and has the short-est residence time in runner,which saves time for the massive production and processing.