Extrusion International 3-2021

49 Extrusion International 3/2021 silo to the extruder consists of the above-mentioned components PE (grass blades), PP (base fabric) and latex/PU (adhesive layer), as well as marginal residual amounts of rub- ber granulate. For the further processing of this input material MAS has developed an extrusion cascade consisting of a conical twin-screw extruder with degassing unit, a subsequent con- tinuous melt fi lter, a single-screw extruder and a granulating station (Picture 6). The advantage of the conical MAS-extruder is the system- speci fi c large cross-section of the feed opening. This makes it particu- larly suitable for materials with a low bulk density, such as synthetic lawn fi ber fl akes. The co-rotating MAS-twin-screw- principle is characterized by a plas- ticization at a comparatively lower mean pressure and level of shear and a highly uniform melt fl ow with excellent homogenization. The lat- ter is particularly important for re- cycling applications. This is because it is the prerequisite for the release of undesired plastic fractions in gas form and fi ltering. The plastic melt is conveyed from the MAS extruder through a CDF(Continuous Disc Filter)-melt- fi l- ter-unit, developed and patented by MAS for recycling applications. The core component of all CDF- fi lters is a fi ltration disk rotating in the incom- ingmelt fl ow. It holds back the impu- rities, in the speci fi c case remaining rubber particles or unmolten plastic particles. The fi lter discs are made of hardened steel and, depending on the application, are available with fi ltration fi neness from 90 μ m to 1,000 μ m. The impurities are wiped off from the rotating fi lter-disc by a stationary scraper in the fi lter housing. From there a screw con- veyor conveys them together with a minimum amount of plastic to the outside. The melt- fi lter-series is MAS Maschinen- und Anlagenbau Schulz GmbH A-4055 Pucking, Austria www.mas-austria.com matched to the MAS-extruders and for throughputs of up to 2 t/h. From the CDF fi lter, the melt fl ows via a special distributor block into the subsequent single-screw extrud- er, equipped with a second degas- sing-station. This offers a procedural innovation. It is the patented divi- sion of the melt fl ow into a series of individual fl ows (Picture 7). This di- vision ensures that the pre-cleaned polymer-mixture can consequently be degassed in the single-screw- extruder more ef fi ciently due to the increased melt surface. From the single-screw extruder, the melt is ei- ther fed to a pelletizer or processed further in-line. The outcome is a high-quality-PE/PP- granulate for a variety of different quality products, e.g. fi lms, as could be documented by a series of plasti- cizing tests (Picture 8). This opens up the potential for one or more “rein- carnations” of worn arti fi cial grass in other applications or products. Author: Reinhard Bauer - TECHNOKOMM of fi ce@technokomm.at Picture 7: Section through the “multi-channel melt feed block”, in which the melt fl ow coming from the melt fi lter is divided into individual melt fl ows (Picture: MAS) Feed section of the MAS-single screw extruder Melt feed from fi lter unit Melt distribution in multiple melt fl ows Picture 8: End product of the arti fi cial grass recycling - a high-quality raw material for new quality products (Photo: MAS)