Viscoelastic Modelling of Polymer Melts and Rubber Compounds
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Thermoplastic melts and rubber compounds are viscoelastic fluids. They show a complex flow behavior, which is influenced by various factors such as polymer type, molar mass distribution, recipe, filler-filler network and in some cases wall slippage. Most of the state-of-the-art simulation software packages use viscous material models for the calculation of the flow field as well as pressure and temperature distribution, neglecting the viscoelastic nature of polymers. This simplification may lead to an underestimated pressure demand in injection molding simulation.
This contribution presents how to correctly measure viscosity data (shear and extensional viscosity) for thermoplastics and rubber compounds taking into account the pressure dependency of the viscosity and the influence of viscous dissipation in capillary rheometry at higher shear rates. Moreover, a guideline on how to best fit rheological data with the viscoelastic K-BKZ/Wagner model is outlined. Comparing CFD simulation results to experimental data, only the K-BKZ/Wagner model is able to correctly predict pressure losses of contraction flow dominated geometries. Examples will be given for NBR and PP-PNC.
KeywordsPolymer melt Viscoelasticity K-BKZ/Wagner model Injection pressure
This research work was supported by the Austrian Research Promotion Agency (FFG) as part of the “RubExject II” project (corresponding project number 855873) and the company partners SKF Sealing Solutions Austria GmbH, Judenburg, Austria, IB Steiner, Spielberg, Austria and ELMET Elastomere Produktions- und Dienstleistungs-GmbH, Oftering, Austria. The authors further thank company PKT Praezisions-kunststofftechnik Buertlmair Gesellschaft m.b.H. and Prof. T. Lucyshyn, Dr. Ivica Duretek, MSc Stephan Schuschnigg and Dr. Matthias Haselmann for their respective contributions.
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