CONTROL & INSTRUMENTATION | MACHINERY


Close control: boosting the extrusion process


Specialist software and measurement equipment can help to maintain precision in the extrusion process. Lou Reade reports


Computer control – and modelling – of the extru- sion process can help to squeeze out extra perfor- mance and throughput. Researchers from the University of Duisburg-


Essen in Germany have used computer modeling to boost the output on a blown film line by around 10% – without affecting film quality. The researchers said that the limiting factor in boosting output is usually the air cooling ring – which must be substituted or modified in order to increase throughput. This is time- and cost-inten- sive, they said – and the outcome is also uncertain. “Not all thermodynamic and fluidic phenomena caused by the changing cooling configuration – and their impact on the formation of the bubble – are predictable in advance,” said Benedikt Neubert, of the Institute of Product Engineering, in


www.filmandsheet.com


a presentation at Antec last year. This research adapts the well-established


Process Model, and applies it to high capacity blown film lines with a throughput of more than 750kg/h. It uses Computational Fluid Dynamics (CFD) to optimise the design of cooling devices that work both inside and outside the bubble. Generating an accurate simulation requires various input data: the biaxial stretching of the film – and subsequent stress on it – must be adequately modelled, for instance. Other data includes frost line height and film velocity. The calculation is split into two modules: one uses Matlab to calculate film contours and thickness profiles; the second uses CFD to calculate the film’s temperature profile and streaming velocity of the cooling air. “The goal lies in modifying the oncoming flow


Main image: Researchers have used CDF to boost blown film line output


March 2018 | FILM & SHEET EXTRUSION 33


PHOTO: SHUTTERSTOCK


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