Automated Optimization of Spiral Shearing and Mixing Elements for Single-screw Extruders

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During the processing of polymers in various extrusion lines, more and more single-screw extruders with a grooved feed section are being used. This is due to their constant conveying characteristics which aren’t being influenced by the extrusion die. Because of the highly specific throughputs of these high-speed extruders, mixing units are applied at the end of the screw to ensure thermal and material homogeneity of the melt. A great challenge here is the design of these mixing units under consideration of varying requirements, which are interacting with each other. Therefore, a pure experimental evaluation of mixing elements is very time-consuming and cost-intensive. Also, the experimental setup does not allow a detailed insight into the mixing processes. In that case, the mixing unit represents a black-box which responds incalculably to any changes in the process or to modifications to the processed material properties. The computational fluid dynamics simulation is an alternative to the pure experimental design of mixing units. Regrettably, the existing methods for the prediction of the mixing quality have substantial shortcomings, which make the virtual design impossible. This fact has been verified in the literature as well as in own preliminary studies. In recent years, further research has been carried out at the applicant's research institute on the current state of the art, so that new and verified simulation models are now available that allow a holistic view of the mixing process in terms of distributive and dispersive mixing capability.The objective of this research project is to provide a tool which automatically optimizes a mixing geometry in regard to the distributive and dispersive mixing performance within a profitable time frame. Beside the mixing performance, flow and thermal properties such as pressure drop, residence time and melt temperature will be influencing the optimization as well. During an extensive validation of the optimization tool within a particular experimental setup, the validity of the simulation tool will be verified under different conditions. This experimental setup additionally enables a local evaluation of the mixing quality inside the mixing unit. Finally, this new approach will be compared to conventional alternatives and its advantages and disadvantages will be worked out.