Injection Molding of Reinforced Thermosets

Abstract

Abstract The orientation of glass fibers (initial length 20 mm) and the mold filling of reinforced unsaturated polyester compounds have been studied. Observations of the fiber orientation have been made in three molds where shear and elongational flows occur in variable ways. A part of the fibers are split and broken into filaments. Reinforcement can be more or less buckled. A thin skin layer without fibers is observed. The great thickness of a core region with an orientation perpendicular to the flow direction shows the importance of negative elongational flows. Efficiency of positive elongational flows to suppress buckling and to give a well flow aligned orientation is also observed. On the contrary the efficiency of shear flows is limited compared to elongational flows. The incidence of injection conditions on the pressure inside a rectangular plaque has been studied both experimentally and theoretically. Experimental difficulties due to the material heterogeneity leads to measure viscosity data of the uncured material on a special capillary rheometer and rheological kinetic data on a simplified compound. Numerical results are in good agreement with experimental measurements. For instance the effect of crosslinking which leads to a pressure rise at low flow rate or high mold temperature is well predicted.