In the polymer processing, weld-lines often occur and cause the degradation of the mechanical and optical properties of products. These properties are degraded when the polymer molecules near the weld-line highly orient owing to the elongational flow and the orientation is fixed by solidification of the polymer melts before it returns to a random condition. In the present paper, the viscoelastic welding flow was numerically calculated for analyzing the molecular orientation in the weld-line region. The numerical simulation of the flow around a spider supporting a mandrel was carried out using the single-mode Giesekus model as a constitutive equation. The effects of the spider shape and viscoelastic properties of polymer melts on the anisotropy of the molecular orientation at the weld-line were analyzed. The calculation was carried out for three spider shapes, i.e. the spider-rear-end-angle suppressed the elongational rate, the stress, and the maximum value of the degree of the molecular orientation near the spider rear end, where the weld-line occurred. When the Weissenberg number is large and the influence of shear-thinning is great, the maximum value of the elongational rate wasEspecially at large Weissenberg number (=2.4), the elongational stress was reduced more effectively using the spider of the case
Weld-lines degrade the mechanical and optical properties of products. This is because the polymer molecules near the weld-line highly orient owing to the elongational flow and the molecular orientation is fixed by solidification of the polymer melts before it returns to a random condition. Birefringence experiments were, therefore, carried out for welding flows of a low density polyethylene (LDPE) past a spider supporting a mandrel. The die used in the present study has a glass window to observe the birefringence pattern. The birefringence in the polymer melts was measured by the photoelastic method. The purpose of the present study is to elucidate the effect of the die temperature, spider shapes and a viscoelastic property of polymer melts on the anisotropy of the molecular orientation in the stress relaxation process downstream of the spider. The birefringence pattern in the welding flow of LDPE was measured at the die temperature T190, 205 °C and the polymer melts temperature 719O °C for flow rates of 0.7, 1.0, 2.2, 2.9, 4.6 cm3ls. The results showed that complete relaxation of birefringence depended on the flow rate. For high die temperature (205 °C), the distance necessary for the relaxation of molecular orientation was short. Moreover, the birefringence pattern in the welding flow was numerically calculated using the single-mode Giesekus model as a constitutive equation, and the results were compared with the experimental data. The numerical predictions agreed with the experimental results.
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 non-isothermal 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 T190, 195, 200, and 205 °C at the inlet temperature T190 °C. The 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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.