19/02/2015

www.gupta-verlag.de/rubber

Twin-screw extruders for shear- and temperature-sensitive WPCs

[image_0]According to the company, wood plastic composites have become very popular in Europe for indoor and outdoor applications, due to their favorable properties, convenient price, and high environmental compatibility, showing annual growth rates of up to 25 %.[image_1_right] "WPC decking profiles in particular are in high demand,” reports Kai Schwedthelm, responsible for process engineering development in compounding and processing of bio-plastics at KraussMaffei Berstorff. "The perfectly adapted modular screw and barrel system make co-rotating twin-screw extruders the ideal solution for processing shear- and temperature-sensitive WPCs.” The KraussMaffei Berstorff engineers have now succeeded in implementing numerous optimized features along the processing section to meet the specific material requirements of WPCs. As a special highlight, Schwedthelm notes the combination of kneading and multi-process elements in the plasticizing zone that reduces the melt temperature by about 10 % while the melting efficiency remains identical with that of standard screws. In addition, the company has also succeeded in adapting the screw configuration in the fiber feed area to achieve better results. The same applies to the mixing section where the multi-process elements reduce the temperature by about 10 %, which additionally contributes to improved material quality. Further process benefits in WPC processing are achieved by the 6D-long combined barrel elements, which are typical features of ZE extruders: these elements allow the wood proportions to be efficiently incorporated and the air trapped during the process to be removed at an adequate distance in process engineering terms. For degassing the 12 % residual moisture content in the natural fibers in particular, the degassing openings, 6D long, ensure high process reliability at low gas velocities. The hold-down systems that are frequently needed in these applications are not required with this configuration. Finally, the extruder is equipped with a ZSFE side feeder with special Ultra Feed vacuum technology that gives higher output rates by increasing the apparent density of light filler materials.

www.gupta-verlag.de/rubber