Influence of injection parameters on the formation of blush in injection moulding of PVC

This paper presents results of the study of influence of injection parameters of PVC fittings moulding on the formation of blush. The aim was to determine the cause of the blush and predict its evolution in relation to the injection rate and melt temperature, based on Finite Element (FE) moulding software. The computation model was fitted by means of experimental tests carried out with a prototype fitting mould. Once the cavity pressure was verified, the analysis of results provided by the software such as the shear stress distribution around the gate and the flow front temperature enabled the identification of the injection rate as the principal reason for the flaw, the melt temperature being a secondary factor.