Injection Molding without Packing

Abstract

Abstract By injection molding two kinds of frozen-in orientation will arise: During the filling phase the outer layers of the molding will be sheared and simultaneously cooled. This results in highly oriented layers at the outside of the molding (orientation by filling). During the packing phase the melt, forced into the cavity, gives rise to low rates of deformation in the molding, but since the viscosity has become high by cooling, high stresses and frozen-in orientation will also result (orientation by packing). This last kind of orientation can be avoided by high pressures in the filling phase, followed by immediate mechanical sealing of the cavity (injection molding without packing), and hereby a better quality of the moldings can be achieved. Some results with moldings of PS and PP are given.