Christian Kneidinger,
"Solids Conveying, Melting and Melt Conveying in Single Screw Extruders and Extrusion Dies"
, 3-2021
Original Titel:
Solids Conveying, Melting and Melt Conveying in Single Screw Extruders and Extrusion Dies
Sprache des Titels:
Englisch
Original Kurzfassung:
Plastics have become indispensable in today's world. Single-screw extruders occupy a special
position in plastics processing. Due to their reliability and their good price/performance ratio, they
are used wherever possible. To optimize these machines, the individual operations in the extrusion
process are modelled. Good models not only reproduce the real behavior, but also allow further
insight into the process to better understand it.
The main goal of this work is the development of sub-models, which are required to model the
processes that take place in the solids conveying zone, the delay zone, the melting zone, and the
extrusion die. With respect to the solids conveying zone, a new model to describe the pressure
and temperature dependent bulk density in the screw channel was developed. This new model is
significantly better than the existing models. Furthermore, it was shown that the external friction
coefficient is not only dependent on pressure and temperature, as previously known, but also on
the shape of the pellets and the frictional distance. The pellet shape also has a significant influence
on the bulk density. Regarding the delay zone and the melting zone, the melting process via the
so-called "drag induced melt removal" was investigated. Here, too, a dependence on the pellet
shape and pressure was found. Both factors are not considered in classical models. A further
important aspect of this work is the modeling and the experimental determination of the melting
behavior of mixed polymers. These show a significantly reduced melting behavior compared to
pure materials. A method is presented herein, which calculates the theoretically achievable values
of shear stress and melting rate, while on the other hand, applying experimentally determined
synergy factors. Thereby, the experimentally determined data of the pure materials are used,
because the existing calculation models can only partially describe the experimentally determined
behavior well. The synergy factors describe the differences between the theoretically achievable
values of mixtures and the experimentally determined data. Furthermore, a new method for the
calculation of one-dimensional flows is shown. This method enables difficult viscosity models,
multilayer flows, wall slip, interfacial slip between the layers and asymmetrical velocity profiles as
well as moving boundary conditions to be to applied. For this purpose, a numerical integration
method is employed. The method is classified between analytical calculations and CFD solutions.
The developed models consider the underlying physical principles and can therefore be easily
extrapolated. The developed models and methods and the knowledge gained from the model
experiments contribute to a better understanding of single-screw extrusion allowing further
optimization.(Evaluators: Univ-.Prof. DI Dr.mont Jürgen Miethlinger, Univ-.Prof. DI Dr.mont Clemens Holzer, Univ-.Prof. DI Dr.mont. Gernot Zitzenbacher)