NatureWorks and Welex sheet line yield high output at lower costs

THE FIRST Welex Converge CTS sheet line is now being used by a leading manufacturer of food service disposable ware. This was announced by Graham Engineering, owner of the Welex brand.  

The sheet line, which directly feeds an inline thermoforming process, enables running of Ingeo PLA  resin from NatureWorks LLC at a rate of 3,500 lb. (1,590 kg) per hour and a temperature of 200°C. Welex Converge CTS runs at a temperature 25 to 50°C less than what has experienced with Ingeo at these outputs with other processing technologies, said Jim Nangeroni, senior applications development engineer for NatureWorks.

 With the lower temperatures, Welex Converge CTS system lead to a reduction in molecular weight degradation, which in turn results not only in higher quality first-pass parts but also in sustained quality with post-industrial regrind. Processing with conventional technology, even under ideal conditions often results in around 4% molecular weight loss per pass, comparable to polystyrene. But the trial of the Welex system shows virtually no loss of molecular weight through eight passes. This technology, combined with Ingeo pricing of $0.80-$1/lb. for standard extrusion/thermoforming grades can make for a very competitive package.

Based on co-rotating conical twin screw technology, the Welex Converge CTS sheet line processes PET and PLA with moisture content up to 2,500 ppm while eliminating need to crystallize or pre-dry the material. Surface moisture is removed by means of a low vacuum applied at the feed area. After the material is plasticized in the first stage of the extruder, there is a decompression section where a high vacuum is applied through a large vent to complete moisture removal.

Large thrust bearings enable Welex Converge CTS system to produce higher pressure, and a large screw diameter generates greater torque. As a result, the Converge CTS line processes PET and PLA effectively at the lowest possible melt temperature, according to Jim Nissel, Welex sales director. Benefits of a lower melt temperature include energy savings, higher melt strength, less monomer reformation, and color preservation.

In addition to the processing benefits, mechanical and operating advantages cited by the company for the Welex Converge CTS system include: reduction of overall line length by about 20%, chiefly because the screws are half the length and weight of conventional parallel twin screws; faster screw removal, with almost no added clearance required, made possible by a pivoting barrel; and a large feed throat opening, providing the ability to add fillers without the added cost and complexity of side feeders.