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

颜色和材料变化在聚合物的工业加工中非常常见。特别是在连续聚合物挤出时，生产中对时间和材料的投入很高。由于在流动通道的壁处的较低流速，熔融塑料在阻挡层中具有长的阻力时间并且主导转换时间。为了使转换过程更有效，有必要提高对转换过程的理解，包括对流体力学性能以及热流变材料行为的影响。本项目的目的是扩大对热敏材料的热流变材料行为的理解。除了剪切粘度的物理剪切和温度依赖性变化之外，还研究了时间或温度依赖性反应影响等影响量。为了表征材料行为，使用不同的测量方法。这些测量的新结果用于分析模型来描绘剪切粘度的时间依赖性变化。目前，纯粹的热致变化被认为是计算材料性能，现在将详细说明剪切的考虑。此外，流道表面拓扑结构的影响反映了颜色和材料变化过程的研究重点。在此基础上，将前面热流变学研究的知识以及流道表面拓扑结构的影响整合到数值计算方法中。为此，必须在模拟工具中实现材料变化的分析模型。对于CFD模拟的校准，将结果与实际实验进行比较。

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.