Extrusion International 6-2019

31 Extrusion International 6/2019 disc filter system on the way to the subsequent cascade extruder with degassing unit. At the end of the processing line, the recyclate reaches the granulation unit after an overall shorter throughput time and with a much lower melt temperature of 160 to 210 °C. A quantitative comparison between the traditional recycling systems and the MAS cascade extrusion tech- nique results for the specific Kaska- da application that the MAS system processes PE-film-flakes with a much lower specific energy expenditure than the other existing recycling- lines (just 0.34 kW/kg at a through- put of 650 kg/h) and converts them into granulates with higher quality levels (Picture 6). The overall lower shear and temper- ature load leads to a comparatively higher quality level, which is substan- tiated by the determination of the mechanical characteristic values. In addition, the most obvious features are the better transparency, the lower yellowing and the lower odor emission, as well as the significantly higher tensile and puncture resis- tance, clearly demonstrated by the Kaskada boss (Picture 7). MAS recycling concept pays off Investing in MAS equipment tech- nology has been financially reward- ing for Kaskada. For example, the recycled HD and LDPE-granulates produced for customers who are pre- dominantly in Germany, France, Aus- tria and Spain can be marketed with surpluses of 50 to 80 EUR/tonne, as company MAS (Maschinen- und An- lagenbau Schulz GmbH). It features a cascade extrusion plant based on the MAS-specific conical twin-screw extruder with co-rotating screws fol- lowed by a MAS disc melt-filter-unit and a single-screw degassing ex- truder and a pelletizing unit. About two years ago, we ventured into this fundamentally different system tech- nology.” (Picture 5) With this system, there is no need for a cutter compactor feeding the film flakes to the extruder. The conical twin-screw extruder, with its system- typical large-area feed opening, of- fers good conditions for the efficient intake of materials with a low bulk density without having to agglomer- ate them beforehand. Before feed- ing the regrind flakes, coming from the washing line, into the extruder, they pass, if required, a MAS drying centrifuge (DRD dry cleaner) where they are dried in a stream of hot air and then conveyed into the extruder via a gravimetric dosing system. Due to the conical layout the plasti- cizing section of the MAS extruder is significantly shorter compared with a single-screw extruder and the plasti- cizing process due to the geometry of the co-rotating twin-screws particu- larly gentle and less exposed to shear- stress. The shorter melt-path offers in addition to the lower temperature ex- posure additionally the beneficial side effect of an significantly lower energy consumption for the plasticization. After the conical twin-screw extruder, the melt passes through the likewise MAS-specific, continuously operating the Kaskada boss confirms and adds: “Through selective mixing of input materials whose quality potentials our employees now know very well, we can achieve even higher qual- ity levels. This enables us to raise the quality of the final product to a certain level. This may be even the quality level of virgin material. This is our contribution to increasing the acceptance of recycled materials that would otherwise end up in incinera- tion or landfill.” Working together on the future of recycling Since proven plant technology also offers room for improvement, an ex- change of ideas between MAS and the Kaskada technicians takes place at regular intervals, during which the experiences and wishes from produc- tion are incorporated into the ma- chine development (Picture 8). Seen in this way Plovdiv 2019 was not only the European Capital of Culture, but also a “hot spot” of recycling tech- nology. Author: Reinhard Bauer – TECHNOKOMM office@technokomm.at MAS Maschinen- und Anlagenbau Schulz GmbH A-4055 Pucking, Austria www.mas-austria.com Kaskada Ltd BG 4204 Tsaratzovo, Bulgaria www.kaskada-bg.com Picture 8: MAS Managing Director Dipl.-Ing. Martin Schnabl, MAS Sales and Application Engineer Eng. Stefan Lehner, MAS-regional sales manager Daniel Pashev, Kaskada- owner and managing director Daniel Nedev and Valeria Nedeva, Kaskada-purchasing officer are working on further increasing the qualities of the recycling machines