采用Phan-Thien and Tanner(PTT)本构方程,建立了矩形截面共挤口模内外两种聚合物熔体流动的三维粘弹数值模型,有限元模拟了聚丙烯/聚苯乙烯(PP/PS)共挤过程中的挤出胀大现象,并用实验验证了模拟结果.研究表明:当入口体积流量相同时,两熔体挤出口模后会朝向黏度较高的PS熔体一侧偏转,型材截面呈非对称畸变.两熔体在垂直挤出方向上的速度分布导致了挤出胀大过程中熔体的偏转流动,而口模出口处的剪切速率分布基本决定了共挤型材截面的形状.实验结果与模拟结果基本相符,模拟所得挤出胀大率比实际值太8.6%.等温假设是影响共挤出胀大数值模拟准确度的主要因素.
A three-dimensional viscoelastic numerical model with Phan-Thien and Tanner (PTT) constitutive equation was established for the flow of two polymer melts inside and outside a coextrusion die with rectangular shaped cross-section, the die swell of the polypropylene/polystyrene(PP/PS) melts were simulated through finite element method, and the results were verified by experiments. The study shows that the melts with same inlet volume flow rates flow with a deflection towards the PS side and the cross-section presents an asymmetrical distortion when they were extruded from the coextrusion die. The velocity distribution in the direction perpendicular to the extrusion direction determines the deflexion flow, and the shape of the coextrusion profile basically depends on the shear rate distribution at the die exit. The experimental results are in accordance with the simulated results, the simulated die swell ratio is 8.6% higher than the experimental value. The isothermal assumption affects the simulation accuracy.
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