Thermo-rheological phenomena at wall boundary layers during color and material changes in plastics extrusion

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Colour and material changes are very common in industrial processing of polymers. Especially at continuous polymer extrusion, the efforts in production for time and material are high. As a result of the lower flow velocity at the wall of the flow channel, the molten plastic has a long resistance time in the barrier layer and dominates the changeover time. To make the changeover process more efficient, it is necessary to achieve an improved understanding of the process, concerning the influences on fluid-mechanical properties as well as the thermo-rheological material behavior.The aim of this project is to expand the understanding of the thermal-rheological material behavior of thermal sensitive materials. In addition to the physical shear- and temperature dependent changes of the shear viscosity, the influence quantiies like time or temperature dependent reactive influences are investigated. To characterize the material behavior, different measuring methods are used. The new results of these measurements are used for an analytical model to depict the time dependent changes of the shear viscosity. Currently, a purely thermally induced change is considered for the calculation of the material behavior and will now be elaborated for a consideration of shear. Furthermore, the influence of the surface topology of the flow channel surface reflects the focus of the study of color and material change processes.After that, the knowledge of the preceding thermo-rheological investigation as well as the influence of the flow channel surface topology, are integrated into a numerical calculation method. For this purpose, the analytical model for the material change must be implemented in the simulation tool. For the calibration of CFD simulations, the results are compared with practical experiments.