Integrated 3-D Model of Plastic Transportation in Extruders

The research institutes Institut für Kunststofftechnik (IKT, University of Stuttgart) under the direction of Prof. Dr.-Ing. C. Bonten and CFDEMresearch (Linz) under the direction of Dr. C. Kloss and Dr. C. Goniva are working on a novel integrated research approach for the increase of the throughput performance of a single-screw extruder with consideration of the product quality. In plastics processing single-screw extruders are used to produce profiles, pipes, plates, films, cables and many other products providing them e.g. for packaging, electrical, construction and automotive industry. 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. Pure experimental trials of process optimization are related to extensive costs. This is why the realization of novel ideas is restricted considerably. In contrast, simulation models contribute substantially to an increase of efficiency. Thus, e.g. the feeding behavior of a single-screw extruder can be improved by means of three-dimensional simulation methods in such a way that the throughput performance increases remarkably. However, these currently available simulation approaches cant be unconditionally transferred to practical application. Increasing only the throughput does not guarantee a high product quality. In the subsequent section the inserted granules have to be melted completely and homogenized. Currently, an integrated approach for modelling the feed section combined with the melting section does not exist. 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 fact that in the feed section discrete solid particles are present, while in the subsequent section a mixture of solid particles and molten plastic is transported, represents a high challenge to the model development. The coupling of both phases will be realized in the open-source simulation environment CFDEMcoupling by means of a novel melting model, which will be established and implemented within the project for the first time. Therefore, numerical methods have to be applied to reproduce the complex processes inside the extruder. The general validity of the novel simulation method is planned to be demonstrated on one hand by means of a special experimental set-up, on the other hand two extruder types are planned to be utilized for this purpose. Once the novel simulation method is ready to use, the efficiency of design optimization of a single-screw extruder including the feed section and the screw will be substantially improved. Also, this could enhance the process itself in such a way that a raise of the throughput is achieved, while ensuring a high product quality and a compact extruder design.

Goal of the DACH Cooperation project with FWF project number I 3202 between Prof. Christian Bonten (Institut für Kunstofftechnik at the University of Stuttgart) and Dr. Christoph Kloss (DCS Computing GmbH) was the development and the experimental validation of a new CFD-DEM (Computational Fluid Dynamics - Discrete Element Method) model for the computer simulation of the plastic melting in a single-screw extruder. While CFD-DEM modelling finds already application in a wide range of fields, it is still less established in the CAE (Computer Aided Engineering) of plastic extrusion due to the inherent complexity of the phenomena involved, namely the melting of solid plastic granules and the dynamic interaction between two immiscible fluids (molten plastic and air) and the solid plastic granules themselves. In light of these requirements, a series of cutting-edge features have been included in the CFD-DEM model, like the physical interaction between three phases (air, solid and molten particles) via a coupled VOF (Volume of Fluid) solver, the heterogeneous temperature distribution within a particle and the particle melting representation. The model was implemented in the simulation environment CFDEMcoupling and calibrated/validated using the experimental results from the project partners at IKT. The close correspondence between the experimental and the simulation melting rate proved the suitability of the CFD-DEM approach for studying the plastic melting in a single-screw extruder and paves the way to future developments in this field.