With nine extruders that can be configured to provide numerous stripe and layer combinations, Welex (Blue Bell, PA) says its new five-layer sheet-extrusion system for multicolored food packaging sets a new mark for the number of extruders on one die. Built for a European custom-sheet manufacturer for use in thermoformed yogurt cups, the system has already been shipped and is expected to begin production in April.
The Welex system produces sheet up to 60-inches (1500-mm) wide with thicknesses from 0.020 to 0.060-inch (500 to 1500 µm) and throughput ranging up to 3000 lb/hr (1500 kg/hr). The nine extruders are from 2.5- to 3.5-inches, with a 30:1 LD ratio and vented, air-cooled barrels featuring two-stage screws to run high-impact polystyrene (HIPS) in a range of colors. The five-layer sheet construction includes a crystal PS gloss layer, a five-color custom-configurable stripe layer, a white layer, a scrap foam layer, and a white bottom layer. The scrap foam layer is produced via a proprietary gas-blown foam process. Welex notes that the system can also run polypropylene with no equipment changes.
Each mobile-mounted extruder includes a slide-plate screen changer and gear pump for high-precision output. The machines feed into a valve-distribution block before the multi-manifold and feed-block-equipped die for easy control of the individual component's destinations.
Welex's Sentinel color touch-screen controls are incorporated into each extruder, as well the sheet take-off unit, with each of those controls patched into the Super Sentinel supervisory workstation via Ethernet/IP fieldbus protocol. Sheet profile is monitored by a Scantech x-ray gauging system, which controls the Welex Autoflex thermal expansion bolt-actuated die. Compared to beta-ray systems, Welex says this gauging method has the ability to measure a smaller area for more precise measurement and control.
The sheet extrusion line's Welex Evolution individual roll drive sheet take-off system also has automatic roll-gap controls and a set of water-flow-driven secondary cooling rolls to promote uniform sheet temperature at the end of the line prior to winding onto jumbo rolls. 
