【摘要】 根据中空型材的结构特点,利用三维等温微分黏弹有限元方法,对中空"回"型截面型材的4种聚合物熔体挤出方式(无气辅、内/外壁单气辅和内外壁双气辅挤出)在口模内外的流动场进行数值模拟,得到4种挤出方式的离模膨胀率、压力场、速度场、剪切速率和法向应力场分布情况。研究结果表明:对于内/外壁单气辅挤出,由于内/外壁面的压力、速度、剪切速率和应力场分布不对称,使得挤出熔体容易出现突出的膨胀/收缩现象;虽然无气辅挤出的各种物理场数值相对较大,但由于内外壁面产生的物理场均存在相互反作用,离模膨胀效应却不是特别严重;而内外壁双气辅挤出,由于熔体内外壁均满足完全滑移条件,使得压力、法向速度、剪切速率和应力场均为0,离模膨胀效应得到有效消除。更多还原

【Abstract】 According to the structural feature of hollow profile, by using three dimensional isothermal differential viscoelastic finite element method, four kinds of different extrusion methods(i.e., traditional without gas-assisted extrusion(TWGE), inner wall alone gas-assisted extrusion(IAGE), outer wall alone gas-assisted extrusion(OAGE), and internal and external double wall gas-assisted extrusion(IEDGE)) of the hollow back-typed section profile’s melt flow field inside and outside the die were numerically simulated. The die swell ratio, pressure, velocity, shear rate and normal stress field distributions of four extrusion methods were obtained. The results show that the phenomenon of die swell and shrink are easily generated due to the non-uniformed distribution of the pressure, velocity, shear rate and normal stress field for the IAGE and OAGE methods. Although the TWGE’s physical field values are the largest, the die swell effect is not very serious due to the interaction force existed between the outer wall and inner wall. But for the IEDGE method, the pressure, normal velocity of X and Y direction, shear rate and stress fields are equal to zero inside and outside the die, and the die swell effect is greatly removed because the full slip condition inside of the die is satisfied by using the double gas-assisted extrusion method.更多还原