processing feature | Kneaders Knittel says X-Compound kneaders are ideal for
processing rigid and flexible PVC in calendering lines producing very thin clear rigid foils. “They are very good when you need high quality material that is very clear, which has very few particulates, and which has no yellowness,” says Knittel. Major producers such as Klöckner Pentaplast, Bilcare and others all favour this technology, he claims. Knittel also highlights growth in interest in kneaders
X-Compound’s new CK 240 kneader is
being used by a major PVC flooring producer in the USA
it further. “Three-flight technology is not old-fash- ioned!” he says. All kneaders, whatever the number of flights, are
available in various versions, according to the applica- tion. A fundamental characteristic of all stand-alone kneaders is that they do not build up high pressure. “The machine is designed to treat material sensitively,” says Knittel. “High pressure would work against this aim, and any pressure that does build up is fluctuating because of the oscillating movement of the screw. “For all pressure-consuming processes downstream
from the kneader, you need a discharge on the kneader. Only on calendering lines, where the material exits directly from the kneader onto the calender, is a discharge unit not required. You always need a second stage if you need to carry out filtering, or pelletizing, for example.” For such applications, the kneader is configured in a
cascade arrangement with a single-screw extruder mounted in-line (mainly for PVC) or in a T-configuration. This latter cross-head configuration is more appropri- ate for stickier, higher viscosity materials. For less sensitive materials, an in-line arrangement with a melt pump flanged directly onto the kneader is more appropriate. X-Compound makes its own single-screw extruders, but sources melt pumps externally.
for PVC flooring. “There is a revival in interest in PVC flooring, but this application has always presented problems for kneaders because the equipment was too small,” he says. “You need equipment with very high output capacities.” This has led X-Compound to develop – and deliver – its biggest kneaders ever. Earlier this year, it delivered two systems based on
its new CK 240 unit to a major PVC flooring producer in the USA. This unit has a maximum output of 10 tonnes/ hour of PVC, which is almost twice as much as the company’s next-biggest model, the CK 200. The customer also took delivery of two CK 200s. The machinery supplier says one version is being used in a direct cascade arrangement with a calender, and the other is fitted with a pelletizer. “PVC flooring was a market off-limits for us in the
past, but now we think prospects are good,” says Knittel. He points out that this type of flooring often has a middle layer that is highly filled with calcium carbon- ate that provides wear problems for planetary extruders and twin-screws, but not for kneaders. Knittel says 2014 was a record year for the company, when it sold 12 lines. He says that new synergies with parent company Troester should enable X-Compound to build on this, especially in cable compound applications.
Extra oscillations Possibly the most interesting innovation in the recent past in the kneading field is the TriVolution, first unveiled by B&P Process Equipment (whose roots are in Baker Perkins) at K 2010 in prototype form. The TriVolution is so-named because for each revolution of
Images from X-Compound show how the melt (in yellow) is simultaneously sheared and compressed by flights on the screw (four are shown here, the longer elements) and the pins on the barrel (two shorter elements). In the diagram, the screw appears to be static and the barrel pins are moving. In reality, it is the screw that moves.
40 COMPOUNDING WORLD | August 2015
www.compoundingworld.com
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