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

在聚合物的工业加工中，颜色和材料的变化是非常常见的。特别是在聚合物连续挤出过程中，对生产时间和材料的要求都很高。由于流道壁面流速较低，熔融塑料在阻挡层中具有较长的阻力时间，并主导着转变时间。为了使转换过程更加有效，有必要提高对该过程的理解，包括对流体力学性能和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。除了剪切粘度随物理剪切和温度的变化外，还研究了时间或温度相关的反应影响等影响量。为了表征材料的行为，使用了不同的测量方法。这些测量的新结果被用于一个分析模型来描述剪切粘度随时间的变化。目前，纯粹的热诱导变化被考虑用于材料行为的计算，现在将详细说明以考虑剪切。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研究的重点，在此基础上，将前人的热流变研究知识以及流道表面拓扑结构的影响融入到数值计算方法中。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了比较。

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.