A fully predictive computer model SSEM (Single-Screw Extrusion Model) has been developed for the single-screw plasticating extruders (with conventional and mixing screws). The model takes into account five zones of the extruder (hopper, solids conveying, delay zone, melting zone, and melt conveying) and the die, and it describes an operation of the extruder-die system, making it possible to predict the mass flow rate of the polymer, the pressure and temperature profiles along the screw channel and in the die, the solid-bed profile, and power consumption. Moreover, the mixing degree, the temperature fluctuation, and the viscoelastic characteristic of the polymer are evaluated. The model also makes it possible to predict the morphological changes of the polymer blend during the compounding process in the single-screw extruder. The simulation parameters are the material and rheological properties of the polymer, the screw, hopper, and die geometry, and the operating conditions (screw speed and barre...

Chemomechanical Systems: Study of Contraction and Mechanical Work of Poly(Acrylonitrile) Gel Fibers

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Prozessnahes Qualitätsmanagement beim Spritzgießen

When it comes to the design of extrusion line components such as single-screw extruders and extrusion dies, no one has yet succeeded in developing a well-functioning concept for wall-splipping materials. This article examines the fundamental influences of the wall slippage effect on flow behavior in the extrusion die and plastification unit. New and extended methods of calculation for describing this flow phenomenon are presented for both these extrusion line components, and the general possibilities for linking the two approaches are discussed.

Global Concept for Describing and Investigation of Wall Slip Effects in the Extrusion Process

A novel computer optimization system for flood fed/starve fed single screw extrusion of polymeric materials has been developed. This coupled system allows us to optimize single screw extrusion both flood fed and starve fed. Optimization is based on process simulation which is performed using global extrusion model GSEM (Global Screw Extrusion Model). The process is optimized with the use of GASEO (Genetic Algorithms Screw Extrusion Optimization) procedures which were developed using Genetic Algorithms. An example of optimization of extrusion process parameters has been presented to maximize extrusion output and minimize specific energy consumption. Optimization has been performed in a unique and original way in a coupled manner when both modes of feeding were allowed. The studies have shown that the optimal process is extrusion with starving. In this case, the global objective function reached the highest value, and extrusion throughput was relatively high and specific energy consumption was minimal.

https://www.mdpi.com/2073-4360/12/1/149/pdf

Optimization for Starve Fed/Flood Fed Single Screw Extrusion of Polymeric Materials.

A review paper is presented on optimization and scale-up for polymer extrusion, both single screw and twin screw extrusion. Optimization consists in obtaining a multidimensional space of process output variables (response surface) on the basis of an appropriate set of input data and searching for extreme values in this space. Scaling consists in changing the scale of the process according to specific criteria, that is, changing the process while maintaining the scaling parameters at a level that is as close to the reference process parameters as possible. It consists in minimizing the differences between the parameters characterizing the reference process and the resulting process. This may be obtained by using optimization techniques leading to the minimization of discrepancies between the parameters of scaled processes. In the paper, it was stated that optimization and scale-up based on process simulation are more effective than those based on experimentation which is time consuming and expensive. The state-of-the-art on extrusion process modeling which is the basis of optimization and scale-up has been presented. Various optimization techniques have been discussed, and the Genetic Algorithms have been identified as powerful and very efficient. Optimization and scale-up based on the process simulation using Genetic Algorithms have been broadly reviewed and discussed. It was concluded that, up to date, there is a lack of optimization studies on the counter-rotating twin screw extrusion, although the global models of this process are known. There is also a lack of process simulation-based scaling-up studies, both on the counter-rotating twin screw extrusion and on the starve fed single screw extrusion. Finally, development perspectives in this field have been discussed.

https://www.mdpi.com/2073-4360/13/10/1547/pdf

Optimization and Scale-Up for Polymer Extrusion

The analysis of polymer flow processes in extruder screws is usually based on the wall-sticking behaviour of these materials. There are however some materials, among them the ultra high molecular HOPE and the polyvinylchloride (PVC), which may be wall-slipping plastics under certain conditions. The existing theories for the flow calculation of these materials are difficult to apply in screw design, due to the highly sophisticated material data to determine the slipping velocity at the wall. This paper therefore tries to suggest a solution which will consider the slip condition of polymer melt, avoiding additional and lengthy determinations of material data from the user's side. The target is not to do research work in the detailed analysis of wall-slipping, but to introduce this kind of material behaviour in the normal flow analysis for screw design. The theory in this paper needs only the results of measuring the temperature and shear-rate dependent viscosity. It is assumed that the critical wall shear stress that marks the beginning of wall-slipping is only a function of the temperature and not related to the flow channel geometry. Equations are performed for the throughput and temperature behaviour. They were included in the software package REX for the computer-aided simulation of single-screw extrusion processes. The experimental verification was done by comparing the theoretical results with experimental data from a 45 mm single screw extruder processing various PE-HD. The results show a satisfying accuracy, taking into account the target of the work. The process behaviour of wall-slipping materials can be determined with the same accuracy as that of wall-sticking materials.

V. Schoppner

Papers

Successful Simulation of Wall-Slipping Plastics

Optimierung mit hilfe statistischer modelle