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Polymers 2018, 10(8), 823; https://doi.org/10.3390/polym10080823

Vortical Fountain Flows in Plasticating Screws

1
Department of Plastics Engineering, University of Massachusetts Lowell, 220 Pawtucket St., Lowell, MA 01854, USA
2
Fachbereich Maschinenbau und Kunststofftechnik, Hochschule Darmstadt, Gebäude C10, Schöfferstraße 3, Darmstadt 64295, Germany
*
Author to whom correspondence should be addressed.
Received: 23 June 2018 / Revised: 13 July 2018 / Accepted: 18 July 2018 / Published: 26 July 2018
(This article belongs to the Special Issue Model-Based Polymer Processing)
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Abstract

Variances in polymers processed by single-screw extrusion are investigated. While vortical flows are well known in the fluids community and fountain flows are well known to be caused by the frozen layers in injection molding, our empirical evidence and process modeling suggests the presence of vortical fountain flows in the melt channels of plasticating screws adjacent to a slower-moving solids bed. The empirical evidence includes screw freezing experiments with cross-sections of processed high-impact polystyrene (HIPS) blended with varying colorants. Non-isothermal, non-Newtonian process simulations indicate that the underlying causality is increased flow conductance in the melt pool caused by higher temperatures and shear rates in the recirculating melt pool. The results indicate the development of persistent, coiled sheet morphologies in both general purpose and barrier screw designs. The behavior differs significantly from prior melting and plastication models with the net effect of broader residence time distributions. The process models guide potential strategies for the remediation of the processing variances as well as potential opportunities to achieve improved dispersion as well as complex micro and nanostructures in polymer processing. View Full-Text
Keywords: single-screw extrusion; fountain flow; residence time distribution; polymer process simulation and modeling single-screw extrusion; fountain flow; residence time distribution; polymer process simulation and modeling
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Kazmer, D.O.; Grosskopf, C.M.; Venoor, V. Vortical Fountain Flows in Plasticating Screws. Polymers 2018, 10, 823.

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