Three-dimensional Modeling of Plastic Transportation in a Single-screw Extruder - Joint Examination of Feed Zone and Melting Zone

在塑料加工中，单螺杆挤出机用于生产型材、管材、板材、薄膜和许多其他产品。单螺杆挤出机是一种连续工作的生产机器。通常，优化的重点是提高吞吐量性能，同时保持产品质量在一个高水平。以前的研究表明，生产量性能一方面受到挤出机进料的限制，另一方面受到熔融性能的限制。在高转速下，螺杆不能从料斗中吸入足够的塑料颗粒以完全填充螺杆通道。同时，插入的塑料颗粒必须在随后的熔化区完全均匀地熔化，以确保高产品质量。因此，模拟方法，特别是三维模型，基本上有助于理解在单螺杆挤出机的进料和熔融段的传输现象。到目前为止，这两个部分必须在现有的模型中单独处理，因为它们的接口处有复杂的物理过程。然而，一个整体的方法是绝对必要的，因为它是不有效的，以提高吞吐量的性能，而不考虑产品质量。该研究项目的目的是通过单一的仿真环境对进料和熔化部分进行集成的三维仿真。本文采用离散元法模拟固体颗粒的输运过程。因此，可以单独考虑插入的塑料颗粒。随后发展的熔体流动将与有限体积法的帮助下计算。两相的耦合，包括相变，将在开源仿真环境CFDEM®耦合中通过一种新的熔化模型实现，该模型将首次在项目中建立和实施。此外，计划利用一个特殊的实验装置来支持模型的开发和验证。通过对光滑料筒和带槽料筒的单螺杆挤出机的研究，说明了该方法的普遍适用性。除了获得的压力和温度数据外，还将进行死停实验，以观察和评估转变点以及挤出机内的熔融行为。然后根据模拟结果对喂料筒和螺杆进行优化设计。该项目计划在一个国际D-A-CH项目中实现。该合作由研究机构Institut für Kunststofftechnik（德国斯图加特大学）和CFDEM研究（林茨，奥地利）组成。在合作范围内，两个研究机构的能力将集中在该项目上。

In plastics processing single-screw extruders are used to produce profiles, pipes, plates, films and many other products. The single-screw extruder is a continuously working production machine. Usually the optimization is focused on an increase of the throughput performance, while keeping the product quality on a high level. Previous investigations show that the throughput performance is limited on the one hand by feeding the extruder, on the other hand by the melting performance. At high rotational speed the screw is not able to draw in enough plastic particles from the hopper to fill the screw channels entirely. Simultaneously the inserted plastic particles have to be melted completely and homogeneously in the following melting zone to ensure a high product quality. Thereby, simulation approaches, especially three-dimensional models, essentially contribute to the under-standing of the transport phenomena in the feed and melting section of single-screw extruders. Until now, both sections had to be handled separately in the existing models due to the complex physical processes at their interface. However, an overall approach is absolutely necessary, because it is not effective to increase the throughput performance without considering the product quality. The aim of this research project is the integrated three-dimensional simulation of the feed and melting section by means of a single simulation environment. The discrete-element method is going to be used for the simulation of the solid particles transportation. Thus, the inserted plastic particles can be considered individually. The subsequently developing melt flow will be calculated with the help of the finite-volume method. The coupling of both phases, including phase transitions, will be realized in the open-source simulation environment CFDEM®coupling by means of a novel melting model, which will be established and implemented within the project for the first time. Moreover, a special experimental set-up is planned to be utilized to support the model development and validation. The general applicability will be shown by means of a study on a single screw extruder with both smooth and grooved feeding barrels. In addition to the obtained pressure and temperature data, dead-stop experiments will be performed to observe and evaluate the transition point as well as the melting behavior inside the extruder. Afterwards the feeding barrel and the screw will be optimized on the basis of the simulation results. The project is planned to be realized within an international D-A-CH-project. The cooperation consists of the research institutes Institut für Kunststofftechnik (University of Stuttgart, Germany) and CFDEMresearch (Linz, Austria). Within the cooperation, the competences of both research institutes will be pooled for the project.