Zhou Guo-fa

Numerical Investigation on the Influence of Melt Viscoelasticity on Die Swelling of Polymer Co-extrusion Process

It is very important to study the mechanism of co-extrusion die swell for laying the scientific theoretical foundation of a die design method.The influencing rule and mechanism of viscoelastic rheological parameter on polymer co-extrusion die swell are modeled by the stable numerical algorithm established.Research results show that the co-extrusion die swell is caused by the viscoelastic melt secondary flow,and depends on the direction and strength of melt secondary flow.The direction of melt secondary flow depends on the sign of secondary normal stress difference,and the strength of melt secondary flow is proportional to the absolute value of secondary normal stress difference.When the secondary normal stress difference of core and skin melt is negative,core and skin melt will produce die swell,the ratio of die swell increases with increasing of secondary normal stress difference.When the secondary normal stress difference of core and skin melt is positive,core and skin melt will produce die shrinkage,the ratio of die shrinkage increases with increasing of the absolute value of secondary normal stress difference.Moreover,research results show that core,skin melt and holistic die swell decrease with increasing of skin melt relaxation time,but increase with increasing of core melt relaxation time.