壁面条件对异向锥形双螺杆挤出硬质聚氯乙烯过程的影响

 数值模拟了壁面条件对异向锥形双螺杆挤出硬质聚氯乙烯（RPVC）过程的影响。由Navier线性滑移定律确定螺杆壁面熔体所受的剪切应力与熔体滑移速度的关系，在不同壁面条件下，使用Polyflow软件的Eolution法，数值计算了异向锥形双螺杆计量段流道内RPVC熔体的体积流量和三维等温流场。结果表明，熔体在螺杆壁面无滑移时，螺杆流道内熔体速度大，速度梯度大，剪切速率等值线形状不规则，分布杂乱。当滑移系数小于104Pa·s/m时，锥形双螺杆流道内熔体的体积流量不变。当滑移系数大于104Pa·s/m时，随着滑移系数的减小，锥形双螺杆流道内熔体的体积流量增大，速度梯度减小，压力和剪切速率梯度减小，参考线上熔体压力波动减小。因此，改善壁面条件有利于提高聚合物螺杆挤出过程的稳定性，降低制品的残余应力，提高制品质量。

Effect of Wall Conditions on Counter-Rotating Conical Twin Screw Extrusion of Rigid Polyvinylchloride

The effect of wall conditions on the counter-rotating conical twin screw extrusion of Rigid Polyvinylchloride (RPVC) is studied. The relationship between the screw wall shear stress and the slip velocity of the flowing melt follows the Navier linear law. The volumetric flow rate and 3D isothermal flow fields of RPVC are calculated under different wall slip conditions in the metering section of a counter-rotating conical twin screw extruder by the use of the evolution technique in Polyflow. The results show that the melt velocity and the velocity gradient are high when there is no slip. The shape of the shear rate isolines is irregular with the distribution in disarray. When the slip coefficient is smaller than 104Pa·s/m, the volumetric flow rate of melt is constant and it is in the full slip condition. When the slip coefficient is greater than 104Pa·s/m, with the decrease of the slip coefficient, the volumetric flow rate increases, the gradients of velocity, pressure and shear rate decrease, and the fluctuation of the pressure along the reference line decreases. The residual stress of the product is thus decreased. As a result, the improvement of the wall condition is beneficial to the stability of polymer extrusion process and the improvement of the product quality.