In-Line Visualisation of Polymer Plastication in an Injection Moulding Screw

• Published in: Key engineering materials 2013-06, Vol.554-557, p.1683-1691
• Main Authors: Balcaen, J., Bereaux, Yves, Charmeau, J.Y., Pham, T.L.
• Format: Article
• Language: English
• Subjects: Barrels (extruders); Compacting; Conduction heating; Injection molding; Lasers; Mathematical models; Melt pools; Screws
• ISSN: 1013-9826; 1662-9795; 1662-9795
• DOI: 10.4028/www.scientific.net/KEM.554-557.1683

In injection moulding or in extrusion, plastication is the step during which polymer pellets are melted by the means of mechanical dissipation provided by a rotating screw and by thermal conduction coming from a heated metallic barrel. This step is crucial for melt thermal homogeneity, charge dispersion and fibre length preservation. Although there have been a large number of theoretical and experimental studies of plastication during the past decades, mostly on extrusion and mostly using the screw extraction technique, extremely few of them have dealt with trying to visualise plastication, let alone measuring the plastication profile in real-time. As a matter of fact, designing such an equipment is an arduous task. We designed an industry-sized metallic barrel, featuring 3 optical glass windows, each window possessing 3 plane faces itself to allow for visualisation and record by synchronised cameras and lightening by lasers. The laser can be used in a laser induced fluorescence or in a particle imaging velocity measurement framework. The images recorded can be further analysed by digital image processing. Preliminary results confirm the plastication theory and show a compacted solid bed and a melt pool side by side. The total plastication length is a direct function of screw rotation frequency as it is obvious from results on the melt pool width, which increases when the screw rotation frequency decreases. However, some evidence of solid bed breakage has been recorded, whereby the solid bed does not diminish continuously along the screw but is fractured in the compression zone These experimental findings are compared to predictions by a one-dimensional model of plastication