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PROCEEDINGS OF THE FIFTH INTERNATIONAL CONFERENCE ON ENGINEERING COMPUTATIONAL TECHNOLOGY
Edited by: B.H.V. Topping, G. Montero and R. Montenegro
Solving the Twin Screw Extrusion Configuration Problem: A Plasticating Modelling Program
C. Teixeira, R. Faria, J.A. Covas and A. Gaspar-Cunha
Institute for Polymer and Composites, IPC, University of Minho, Guimarães, Portugal
C. Teixeira, R. Faria, J.A. Covas, A. Gaspar-Cunha, "Solving the Twin Screw Extrusion Configuration Problem: A Plasticating Modelling Program", in B.H.V. Topping, G. Montero, R. Montenegro, (Editors), "Proceedings of the Fifth International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 23, 2006. doi:10.4203/ccp.84.23
Keywords: polymer extrusion, compounding, process modelling, twin-screw extruders.
Co-rotating twin-screw extruders are widely used by polymer materials producers and compounders as a result of the number of interesting constructive and functional features. The modular construction of screws and barrels provides great flexibility and adaptability to the particular requirements of each polymer system. Both are built from elements of various available types, thus allowing a good control of dispersive and distributive mixing, residence times, feeding sequence, etc. Therefore, in industrial practice the performance of twin screw extruders is dictated by the proper choice of the operating conditions (screw speed and output, which are controlled independently, and barrel temperature profile) and the screw configuration.
The optimization of such a system is a complex task, which is usually accomplished by experimental trial-and-error procedures (thus, not really ensuring that a true optimum has indeed been obtained). Nevertheless, many studies have contributed to a better understanding of the physical, thermal and rheological phenomena occurring in these machines [1,2,3,4,5,6,7,8,9,10,11]. Some attempts have also been made to develop optimization methodologies, able to define the best screw configuration and, or operating conditions for a given application, which are based on couplings between process modelling and optimization algorithms . Unfortunately, most of these efforts have been compromised by the fact that the available modelling programmes are either too basic to provide precise or complete predictions, or are only capable of covering part of the process (usually melt conveying) [1,3,9].
This paper reports progress on the development of a global modelling program for co-rotating twin-screw extruders accounting for the entire process, i.e., from hopper to die (this is usually denoted as plasticating extrusion). It is organized as follows: initially, the relevant physical phenomena are identified and their mathematical description is presented briefly. Computer implementation is then presented. Finally, cases studies are used to discuss the influence of process parameters on performance measures.
A computer program able to take into account the main phenomena from hopper to die and process parameters of co-rotating twin screw extrusion was developed. In general, the predictions are in accordance with theoretical and experimental evidence, although direct comparison with experiments should be carried out in the next stage of the work.
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