PROCESSING | SCREWS AND BARRELS
Schematic showing Comac’s three piece ‘sandwich’ barrel construction, which eliminates internal sleeves
to start a major experimental testing programme in August with a view to launching the new screw element later this year.
Simpler selection The company believes screw selection has become too demanding, with many types of screw element with complex geometries currently on the market from manufacturers for various applications. “In our experience, when screw geometry gets too complex it gets increasingly difficult to understand the performance and behaviour of it - good or bad,” says Daigo Saga, Extrusion Process Supervisor. “Without doubt the easiest and most popular screw element for compounding currently is the standard kneading element, with combinations of left-handed, neutral and right- handed elements. Our newly developed V-Kneading element is a kneading element in appearance, except that it has a unique V-shaped screw tip. Overall it shows quite similar conveying and resistance behaviour to standard kneading elements, except that it provides a boost to apply extra shear stress to the polymer,” he says.
“We developed this screw element initially for
Cellulose-Nanofibre (CNF) compounding applications. These are currently getting increasingly popular in Japan, although not so much in the European and US markets yet because CNF compounding requires high shear-stress mixing,” he explains. “With this development proceeding, we are now planning to expand the range of applications of the V-Kneading element in forthcoming trials in August.” Feddem says it has optimised the mixing performance of its extruders through combinations of its type FME mixing elements with the benefit of extended lifetimes of barrels and screws. The company says the goal is to expand the application range of its screw geometries to a wider variety of materials and reduce the need for exchanging screws and reducing down time of the compounding line.
Right: Feddem’s extruder temperature regulation system with heating cartridges shown in red and water cooling
channels in blue 60 COMPOUNDING WORLD | August 2020
Cooling gains In addition, the company is making improvements to its extruder cooling systems. “Cooling borings perpendicular to the process direction provide the best combination of cooling efficiency and ease of access when cleaning of the cooling system is required,” says Klaus Hojer, Business Development Manager. “We have worked on expanding the maintenance intervals on the extruder’s cooling system and increasing the service life of its components. We have optimised the selection of materials for piping, fittings, solenoid valves and circulation pump in the cooling loop of the extruders to work in combina- tion with the steel casings of the extruder barrels. With appropriate cooling water specifications and periodical monitoring of the composition of the circulating water, maintenance intervals can be expanded, substantially,” Hojer says. “Over time scaling may occur in the cooling
www.compoundingworld.com
IMAGE: COMAC
IMAGE: FEDDEM
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