New extrusion technology from Welex Inc., Blue Bell, Pa., gives processors another option to extrude PET and PLA sheet without needing to predry or crystallize the material. The Welex Converge CTS Sheet Line is based on conical twin screws rather than the parallel designs offered by other suppliers, notes Jim Nissel, Welex director of sales for Europe, Middle East, Africa, and Asia-Pacific.
Welex has worked for several years with Austrian machine builder MAS GmbH to design and test components for the system. Compared with parallel twins, the conical design offers “better feeding characteristics for low bulk densities, higher pressure capability due to larger thrust bearings, more torque capability due to larger screw diameter and shorter machine length, the lowest possible melt temperature, reduced footprint, low shear and outstanding IV retention, and significant energy savings,” Nissel states. In the case of melt temperature, Nissel says trials on PLA have been run at 184 C, about 30° less than is typical for the material. The system reportedly can process undried material with moisture content up to 2500 ppm. Systems are available in throughputs from 1100 lb/hr to more than 4400 lb/hr.
Because of a generously sized feed opening, the system also permits talc, calcium carbonate, and other fillers to be incorporated without need for side feeders, Nissel states. A swiveling barrel design facilitates screw removal.
Welex has already sold one system to an undisclosed North American sheet processor. It will be integrated with a Welex Evolution sheet takeoff and Sentinel Intelligent Process Control system. It will run in line with a thermoformer. The line will ship in September and is expected to be in production in the fourth quarter, says David Schroeder, Welex president & CEO.