Hans-Jürgen Luger,
"High-Performance Extrusion under Consideration of Extensional and Wedge Flows"
, 2-2020
Original Titel:
High-Performance Extrusion under Consideration of Extensional and Wedge Flows
Sprache des Titels:
Englisch
Original Kurzfassung:
The aim of the present work is to improve the performance of plastication in extrusion lines by
employing extensional and wedge flows. Extensional flows occur in many process steps of
polymer processing, such as fiber spinning, production of blown films or stretching of flat films or
flows through extrusion dies. Extensional and wedge flows are essential in the conveying and
mixing processes of single and multi-screw extruders. The steady growth of the polymer
processing industry and the competition between machine suppliers has driven the development
and efficiency increase of extruders, i.e. the increase of output whilst ensuring or improving
material quality. A thorough understanding of the physical transport processes, accurate
calculation models and valid process measurement techniques are crucial for the design
process of machine parts, process optimization and quality control.
In the first part of this thesis, an on-line rheometer for simultaneously measuring the extensional
and shear viscosity of polymer melts and filled compounds during processing is developed.
Extensional viscosity determination is realized by means of the converging flow method in a
novel and patented hyperbolic slit contraction that enables constant extensional rates along the
contraction. Due to the unique design, pressure transducers can be incorporated directly into the
two slit sections, which prevents material from accumulating in pressure holes. The results
obtained with the developed rheometer are validated by well-established measurement
methods, such as plate-plate rheometry, high-pressure capillary rheometry and the SER
(Sentmanat Extensional Rheometer). Furthermore, the applicability for condition monitoring is
demonstrated based on several examples. By measuring the extensional viscosity, material
effects and behavior are observed which cannot solely be detected by means of shear
rheometry.
In the second part, the thesis focusses on modeling and experimental investigation of doublewave
and energy-transfer screws. In general, wave or wave dispersion screws exhibit wave-like
channel depth profiles (sequences of compression and decompression in channel depth) and
flight undercuts. The main purpose of the wave screw design is to induce solid bed break-up,
dispersion of solid agglomerates and enhance dispersive mixing by creating extensional and
wedge flows in the tapered screw channels and flight undercuts. The main objective is to model
the non-isothermal pressure-throughput behavior of wave zones by means of network analysis.
To this end, heuristic melt conveying and dissipation models, which describe the pressurethroughput
relation for isothermal, three-dimensional flow of shear-thinning fluids in rectangular
screw channels, are used. In addition, melt conveying models considering the effect of flight
undercuts in wave screw channels are developed by means of symbolic regression based on
heuristic methods. In further consequence, experimental data are validated against CFD
simulations. Experimental investigations demonstrate the potential of wave screws to increase
extrusion performance compared to barrier screws.
Forschungs-