Solidification Criterion on Shrinkage Predictions for Semi-Crystalline Injection Moulded Samples

The phenomenon of shrinkage in injection moulding is particularly evident in semi-crystalline polymers. During cooling, these materials experience a transition from a completely amorphous to a partially crystalline status, which results in a severe change of all material characteristics, including volumetric parameters. In this study an iPP was injection moulded in a rectangular impression (120 mm x 30 mm x 2 mm) with a 1.5 mm thick line gate. The influence of holding pressure and time, and geometry constraints on linear shrinkage was explored. In-mould shrinkage was measured by means of a recent method based on strain gauges. Experimental results are compared with predictions for shrinkage obtained by C-Mold and a code developed at the University of Salerno, which takes into account crystallisation kinetics. The solidification criterion resulted to be extremely relevant for shrinkage predictions