Abstract: 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.

Key words: coextrusion blow molding, melt extrusion velocity, viscoelasticity, die swell, mechanism, numerical simulation