螺杆加工塑料时熔体流动的数值模拟

Study on Simulation of Molten Polymer Flow in the Screw Groove

为了解螺杆加工塑料时多因素交变作用下熔融塑料在螺槽中的流动状况,结合塑化时熔融塑料在螺槽中的受力、运动情况建立物理模型,推导基于时间过程的控制熔融塑料流动的偏微分方程,包括连续性方程、动量方程、本构方程。利用有限差分法离散偏微分方程得到代数方程组,通过数值计算方法,求解得到加工低密度聚乙烯(Low density polyethylene,LDPE)时熔融塑料在螺槽中流动的速度分布、切应力分布、压力分布。以工程中实际应用的螺杆参数为例计算,分析计算结果发现以下规律:在螺槽左下角和右下角部位熔融塑料流动速度和切应力基本为0;熔融塑料在螺槽中作螺旋形的总体运动,并受不同方向的交变切应力、压力作用。这些规律为改善设备性能和提高塑料加工质量提供指导作用。

The status of molten polymer flow needs to be made clear when it is processed in the screw groove with action of various factors.The time based partial differential equations,includes continuity equation,momentum conservation equations and constitutive equation of molten polymer flow are deduced from physics principles of fluid movement.And physical model is established for screw processing considering the situation of force,movement of molten polymer flow.The partial differential equations are discretized to form algebraic equation set by finite difference method.On the basis of the equations and the physical model,the velocity isoline,velocity vector distribution,share stress distribution and pressure distribution of molten polymer flow in engineering practice are solved by applying the numerical calculation methods.The analysis of the results which worked out according to the actual screw parameters in industry reveals the rules of molten polymer flow in the screw groove.The rules includes： The velocity and shear stress are close to zero in the corner of left bottom and right bottom;The molten polymer move in a spiral track as a whole,and is acted by alterative shear stress and press.These rules are helpful for improving quality of plastic products and facility performance.