Neue Wave- Schneckenkonzepte in High-Speed Extrudern.
Zusammenfassung der Projektergebnisse
The aim of the research project was to develop strategies for the targeted design of wave-dispersion screws in single-screw extrusion. In the course of this research project, mathematical formulations for wave-dispersion screws were developed in two core areas: the description of the pressure/throughput behaviour with the network theory extended by a hybrid approach and the analytical description of disperse melting. In a first step, the flow was fundamentally investigated by means of a wave rheometer, which represents an unwound channel of a double-wave screw. This method offered the advantage that the pressure flow could be considered without the influxes of the drag flow. In addition, the pressure throughput behaviour calculated with the method of network theory could be verified by means of the wave rheometer. Here good agreement between network theory and laboratory tests was found. Furthermore, CFD simulations of the wave rheometer were carried out, which also corresponded with the network theory and the laboratory investigations. Not only the pressures determined were in agreement, but also the flow propagation was described by the CFD simulations according to the laboratory investigations, whereby a further use of CFD simulations for the investigations of wave-dispersion screws is conceivable. Furthermore, a mathematical model for the description of viscosity changes caused by solid particles in the melt was validated. This model describes the viscosity change as a function of the solid content and the solid particle size in the melt. This is essential in order to be able to describe the melting behaviour correctly in the following. In order to validate the model, various contents of fine glass beads were added to the plastic melt. Afterwards this compound was measured in a high-pressure capillary rheometer. The viscosities determined corresponded to the viscosities calculated from the model, which makes it possible to determine the viscosity of a solid-melt mixture by means of the data on melt viscosity, solids content and solids diameter. In order to determine at which point in the process the solid bed breaks up, a test rig was developed and set up with which solid bed samples could be produced under different boundary conditions. The samples were tested for tensile strength by means of a tensile test. Subsequently, regressions were formed which describe the solid bed strength. The strength of the solid bed was consistently in a relatively low range, which is why it can be assumed that the wave geometries of a wave-dispersion screw will fundamentally break the solid bed as long as a sufficient amount of melt is available. The modelling of the disperse melting behaviour was purely analytical. The basic idea is the heat conduction of the surrounding melt into the particles. In addition, the temperature increase in the melt due to shear dissipation using the increased viscosity of the solid-melt mixture as well as the cooling of the melt due to the heat flow into the particles is taken into account. Validation tests using the dead-stop method showed that, especially in the areas of lower solid content, melting is simulated to be too slow. Here the analytic approach reaches its limits, since effects such as expanding solid particles in combination with high shear at the offset flights are not considered. The former leads to an increased surface to volume ratio, which favors melting, while the latter generally leads to a further energy input in addition to pure heat conduction. By means of the developed model, effects of geometry and process parameters and their tendencies can be shown, but for a safe dimensioning, further investigations should be carried out by means of CFD simulations, which also take melting into account. In this way, the complex flow processes can be represented more accurately and transferred into a mathematical regression by means of statistical experimental design. The modelling of the pressure/throughput-behaviour was done using the network-theory and a novel hybrid approach. A semi-numerical simulation procedure based on network theory was developed to predict the down-channel and cross-channel flows in wave-dispersion screws. To further improve the melt-conveying models for wave-dispersion-screws, a hybrid modeling approach was developed, which build an analytical regression models from a large number of numerical solutions. Both models were successfully validated. All the experimental investigations of wave-dispersion screws on smooth barrel and grooved barrel extruders have shown that wave-dispersion screws achieve significantly better homogeneity in terms of both thermal and material mixing quality without the need for additional mixing parts. It has also been shown that higher throughputs can be achieved with satisfactory melt quality using wave-dispersion screws and the associated disperse melting behaviour, also causing higher efficiency. Furthermore, the screws can show their advantages also at conventional speeds, which makes them interesting for a large number of plastics processors. All in all, it has been shown that wave-dispersion screws can be an innovation in the field of single-screw extrusion. Models for the pressure-/throughput behaviour as well as the melting behaviour were developed. In order to further improve the models, more in-depth research in the field of wave-dispersion screws with current simulation possibilities such as CFD simulation is to be aimed for.
Projektbezogene Publikationen (Auswahl)
- A Network-Theory-Based Comparative Study of Melt-Conveying Models in Single-Screw Extrusion: A. Isothermal Flow, Polymers, 10, 2018, 929
Marschik, C.; Roland, W.; Miethlinger, J.
(Siehe online unter https://doi.org/10.3390/polym10080929) - An Experimental Validation of a Heuristic Melt-Conveying Model for Single-Screw Extruders, Conference Proceedings ANTEC 2019, Detroit
Marschik, C.; Roland, W.; Löw-Baselli, B.; Miethlinger, J.
- Application of Network Analysis to Flow Systems with Alternating Wave Channels: Part A (Pressure Flows), Polymers, 11, 2019, 1488
Marschik, C.; Dörner, M.; Roland, W.; Miethlinger, J.; Steinbichler, G.; Schöppner, V.
(Siehe online unter https://doi.org/10.3390/polym11091488) - Comparison of the Conventional and the Disperse Melting Model regarding different Process Parameters, Conference Proceedings ANTEC 2019, Detroit
Dörner, M.; Schöppner, V.
- Extended Regression Models for Predicting the Pumping Capability and Viscous Dissipation of Two-Dimensional Flows in Single-Screw Extrusion, Polymers, 11, 2019, 334
Roland, W.; Kommenda, M.; Marschik, C.; Miethlinger, J.
(Siehe online unter https://doi.org/10.3390/polym11020334) - Symbolic regression models for predicting viscous dissipation of three-dimensional non-Newtonian flows in single-screw extruders, JNNFM, 268, 2019, 12-29
Roland, W.; Marschik, C.; Krieger, M.; Löw-Baselli, B.; Miethlinger, J.
(Siehe online unter https://doi.org/10.1016/j.jnnfm.2019.04.006) - Analysis of the Advantageous Process and Mixing Behaviour of Wave-Dispersion Screws in Single Screw Extruder, Conference Proceedings ANTEC 2020, San Antonio
Dörner, M.; Marschik, C.; Schöppner, V.
- Development of an Analytical Mathematical Modelling Approach for a More Precise Description of Dispersed Melting in Solid Bed Breaking Screw Concepts, 36th International Conference of the Polymer Processing Society, 2020, Montreal
Dörner, M.; Schöppner, V.
