MACHINERY | TWIN SCREW EXTRUDERS


A MAS conical twin screw extruder paired with a single screw unit in an “ES” compounding configuration


good for compounding mineral fillers, in powder and pellet form, as well as fluff. In addition to the feeding capacity, the two


and high processing tempera- tures (some 100°C higher than normal for such a material). In a recent presentation at a Society of Plastics Engineers event, Martin also described how twin-screw extruders can be used for process- ing polyolefinic post-consumer reclaim. Highlight- ing again the need for removing metals and also the need to eliminate moisture picked up during washing, he added that it may be preferable to use a single-screw extruder to melt and pump the PCR feedstock through a screen changer prior to mixing the fillers in the twin-screw unit. A gear pump would then be mated to the exit of


the screen changer to meter melt. “The TSE can now use a shorter L/D and smaller horsepower motor because of the upstream melting and filtration unit operations being performed before the melt enters the TSE,” he said. “The continued expansion of TSE technology as


part of atypical extrusion systems will help improve manufacturing efficiencies in a wide variety of new applications that benefit from the consistent TSE in-line mixing process,” says Martin.


Right: Ren- Com’s Renol lignin-based compound is produced on a Coperion ZSK twin screw extruder


Conical niche Recycling also comes up in discussions with machinery maker MAS. This Austrian company has an unusual take on twin-screw extruder design with its conical co-rotating system. Conical counter- rotating extruders are, of course, well known in the PVC industry, but MAS applies its technology in a niche of its own. Most of its units are used for plastics recycling, particularly PET recycling, but some are also employed for compounding virgin materials. A key point with the design, says the company’s


General Sales Manager Stefan Lehner, is that they can accept exceptionally large volumes at the input zone. This characteristic is ideal for regrind, especially for flakes, but also for any material with a low bulk density. So Lehner says MAS extruders are


18 COMPOUNDING WORLD | March 2021 www.compoundingworld.com


screws, which taper to the melting/compression zone, support the use of high torque. This trans- lates into high throughput with low screw speed, and also a very low shear rate. “The high screw filling rate of the MAS stands for high specific throughput,” says Lehner. “That is the reason why MAS can extrude a wide range of polymers with very low melt temperatures.” The MAS extruder can be combined with the company’s single screw TA series venting extruder downstream to improve degassing performance and to increase output. Another variant is the “ES” compound line, in which a single-screw extruder directly feeds polymer melt to the MAS extruder where fillers and/or fibres are fed into the MAS hopper. The company recently sold a line of this type with an output of around 1000kg/h to a company in Indonesia. It is scheduled for delivery this month. MAS produces several models in its conical


counter rotating twin screw line, ranging from the MAS 45 (with 1,190mm long screws that have a diameter of 100mm in the feed area and taper to 45mm) through to the MAS 93 (with 2,680mm long screws that taper from 186mm diameter down to 93mm).


Energy benefits The MAS extruders are also particularly energy- efficient, according to Lehner. He says the short processing unit means residence times are low and so the installed extruder heating power required is also low. “As a result, the MAS extruder requires significantly lower specific energy than parallel twin-screw extruders,” he says. An energy saving of up to 20% is said to be possible. A further advantage of the design is that screw


IMAGE: MAS


IMAGE: COPERION


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