熔体挤出速度对共挤吹塑型坯离模膨胀影响的数值模拟

基于三维非等温黏弹性熔体多相分层流动有限元数值模拟技术，模拟研究了熔体挤出速度对多层共挤吹塑成型环坯离模膨胀和初始温度场的影响规律，揭示了型坯离模膨胀的产生机理。结果表明，多层共挤吹塑成型环坯离模膨胀是由熔体的二次流动诱发而产生，与熔体流出机头进入自由膨胀段的二次流动强度成正比，而其二次流动强度随着熔体挤出速度的增大而增强，因而导致环坯离模膨胀随着熔体挤出速度的增加而增大；多层共挤吹塑成型熔体的二次流动强度与其第二法向应力差成正比关联关系，这与Debbaut的试验研究结论完全吻合，表明二次流动是由第二法向应力差驱动而产生。

Numerical Simulation of the Influence of Melt Extrusion Velocity on the Parison Die Swell of Coextrusion-blow-molded Parisons

Based on the finite element numerical simulation technology of three dimensional non isothermal viscoelastic melt multiphase stratified flow, the influence of melt extrusion velocity on the die swell of multilayer coextrusion blow molded parisons and initial temperature distribution were studied. The mechanism of the parison die swell was revealed by theoretical analysis. It showed that the die swell during the multi layer co extrusion blow molding was induced by the secondary flow of the melt, which was proportional to the secondary flow strength in which polymer melt flowed from head into free swell segment. The secondary flow strength increased with increasing melt extrusion velocity, therefore the parison die swell increased with increasing melt extrusion velocity. It was also found that secondary flow strength was proportional to the second normal stress difference. The result of numerical simulation was fully consistent with B. Debbaut’s experimental conclusion which showed that the secondary flow was driven by second normal stress difference.