【摘要】 实验发现气辅挤出中气体压力对熔体挤出影响较显著,为了探明气体压力对熔体挤出成型的影响机理,建立气体/熔体两相流气辅挤出模型,通过有限元方法对气辅挤出成型进行了非等温黏弹数值模拟,得到不同气体压力下,熔体的挤出形貌、流速、压力、法向应力差分布等变化规律。模拟结果表明:气体压力对熔体挤出流场分布及成型形貌具有较大影响,在气体压力相对较小且能形成稳定的气体层时,熔体速度场分布均匀,压力、法向应力差较小,挤出无形变;随着气体压力增大,熔体的速度、压力、法向应力差和形貌收缩程度等均显著增大。研究表明,由于气体的作用,在气体/熔体入口交界面处产生的第一法向应力差是引发熔体挤出形变和流场分布变化的主要原因。更多还原

【Abstract】 Experiments found that the influence of gas pressure on the melt extrusion was very significant in gas-assisted extrusion( GAE). In order to ascertain the influence mechanism of the gas pressure on the melt extrusion,a gas/melt two phase fluid model was established,the non-isothermal viscoelastic numerical simulation of the GAE was performed using finite element method,the change discipline of melt extrudate profile,flow velocities,pressure drop and first normal stress difference etc were obtained under different gas pressures. Simulation results demonstrated that gas pressure has a significant effect on the flow distributions and extrudate profile of melt. When the gas pressure is little and stable gas layer can be formed,the flow velocities is uniform,pressure drop and first normal stress difference is little,and no extrudate deformation appears. But with the increase of gas pressure,the flow velocities,pressure drop,first normal stress difference,and the extrudate shrinkage degree of melt all evidently increase. It was demonstrated that the first normal stress difference at the entrance of the gas / melt interface is the main reason for triggering the extrudate deformation and flow distributions changes due to the influence of gas.更多还原