Study Of Correction Coefficient Of Rheology Of Polypropylene In Injection Moulding

The rheology theory of polymer melt plays important roles in injection moulding; it’s the guidance for choosing polymer and apparatus, designing mould structure and optimizing moulding process. Rheological behavior of the polymer involves complex mass and heat transfer process; it’s determined by the polymer properties as well as the injection moulding conditions. In the injection moulding process, there is solidified layer formed on the mould inner surface because the temperature difference between the polymer melt and mould, but the influence of solidified layer has been overlooked during study of polymer rheological behavior.In this study, we investigated the rheological behavior of PP by Archimedes helix "online" measurement system, and studied the influence of the solidified layer by giving a correction coefficient. The details are as follow:1) Developed and improved the Archimedes helix "online" measurement system, including designing and processing mould, installing and setting temperature and pressure transmitters, establishing model to analyze the rheological parameters.2) Investigated the forming process of the solidified layer and its effects on the polymer rheological property. Established the even-distributed solidified layer model and derived theoretical formula for the effects of solidified layer to polymer rheological property.3) Designed and conducted experiments to investigate the rheological property of PP polymer and the rheological parameters such as apparent shear viscosity was obtained by the Archimedes helix "online" measurement system. Two different rheological curves of PP polymer were obtained when considering and overlooking the influence of solidified layer. The correction coefficient was derived by analyzing and comparing the two rheological curves; and the influences of melt temperature and injection pressure to correction coefficient were investigated.4) With applying the correction coefficient to testing rheological property of PP polymer, we investigated the relation between injection moulding parameters(injection temperature, mould temperature and melt temperature) and the rheological property and obtained the rheological curve. We also studied the effects of injection molding process on the melt filling length with mould cavity pressure as a benchmark.