Solids Conveying, Melting and Melt Conveying in Single Screw Extruders and Extrusion Dies

Research output: Types of ThesesDoctoral Thesis


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.
Original languageEnglish (American)
QualificationDr. techn.
Awarding Institution
  • Johannes Kepler University Linz
Award date17 Jun 2021
Publication statusPublished - 17 Jun 2021


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