Numerical Analysis of Viscoelastic Welding Flow. Part 2. Effect of Temperature on Molecular Orientation.

Abstract

In the polymer processing operations of extrusion and blow molding, weld-lines often occur on the product, especially on the parison made by extruding polymer melts.This is because the polymer molecules near the weld-line highly orient owing to the elongational flow and the molecular orientation does not relax.In the present paper, the nonisothermal viscoelastic welding flow in the channel with a spider that supports a mandrel was numerically calculated for analyzing the molecular orientation in the weld-line region.The single-mode Giesekus model was used as a constitutive equation.The effect of the temperature on the velocity, the stress and the molecular orientation in the stress relaxation process at the weld-line was analyzed.The calculations were carried out for the channel wall temperatures Tw=190, 195, 200, and 205°C at the inlet temperature T1=190°CThe numerical results showed that the overshoot of the velocity along the centerline downstream of the spider was large when the channel wall temperature was high.For a fluid with remarkable shear-thinning property, the spider with a large rear-end-angle suppressed the overshoot in the case of Tw=205°C When the wall temperature was high, the distance necessary for relaxation of molecular orientation were short, thus little anisotropy remained in the weld region after solidification.