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

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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.