Extrusion International USA 5-2019

39 Extrusion International 5/2019 lication [HB18] for the design specifications and the exact procedure. Based on this plug, the plug wall angles and the radii at the plug edge are systematically varied from the side wall to the side bottom. The 4° wall angle and the 3 mm radius correspond to the specifications of the design guideline and are based on the geometric dimen- sions of the negative mould and thus of the investigated cup geometry. The selected cup has an opening diameter of 60 mm, a draft angle of 4° and a depth of 40 mm. The used plug material is a syntactic foam (type: Hytac W, manufacturer: CMT Europe BV, Waalwijk/Netherlands). The selected plug geometries are shown in Figure 1. In addition to the systematic variation of the wall angle and the radius, plugs are investigated which have larger wall angles and change tangentially to radii at the bottom of the plug. In this case flat plugs become pointed plugs. In the following plugs which have a flat area at the bottom are referred to as “flat” plugs. The other plugs are referred to as “pointed” plugs. Besides these geometrically easy de- scribable plugs (wall angle/radius), more complex plugs are also investigated, which can no longer be described by two simple geometric properties. These so-called “warts” have an undercut which can help prevent the film from adher- ing to the plug. Less contact area between film and plug offer the possibility to minimise quench marks. Preliminary tests to determine the process parameters and evaluation methodology In order to investigate the influence of pre-stretch plugs in thermoforming, preliminary tests are carried out to determine the corresponding process parameters that enable the production of rotationally symmetrical cups. The tests are carried out on the single-station moulding machine Kiefel KD 20/25, Kiefel GmbH, Freilassing. The Figure 2:Measuringpositions on the cupand representationof a polystyrene cup formedonlywith compressedair (filmthickness 0.8mm, filmtemperature 120 °C) Working for a better future www.ngr-world.com Customized recycling technology for the plastics converting industry. It will not only satisfy, but also inspire. MEMBER OF NEXT GENERATION GROUP S:GRAN SHREDDER-FEEDER-EXTRUDER COMBINATION K 2019 16.–23.10.2019 Düsseldorf . Hall 9, Booth B38