Surface quality of PVC fittings based on the design of the sprue

The prediction of the surface quality of injection parts supposes a great advantage, because it can avoid the optimization of the product by trial-and-error methods, i.e., by the modification of the mould and the process parameters, both expensive and time-consuming. In the injection of polyvinyl chloride (PVC) fittings, a blush around the gate appears; this defect is produced by the design of the feeding system as much as the injection conditions. To improve the overall quality of PVC injection moulded components, the influence of the feeding system is analyzed through the design of two different sprues. Since it is important to analytically predict the blush produced by each sprue, computer-aided engineering (CAE) simulation and experimental injection tests have been performed. The correlation between the variables obtained by both methods, such as flow temperature and shear stress, allows to determine which factors are responsible for the surface defect and to choose the right sprue. The procedure followed can be applied to analytically check the suitability of other gate injection designs.