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machinery feature | Melt filtration A Maag


Automatik CSC before and


after retrofit to increase its filter area


ery, which have been part of the same group of companies for five years, finally completed a merger to form Maag Automatik at the beginning of June. The combined company offers tailor-made combinations of melt pumps, screen-changers and pelletizers. “This of course has had a wide


influence to the screen-changer technology, as increasing melt pump and pelletizer throughput capacities needs larger filtration surfaces to match the required filter fineness and flux rate data,” says Harald Pohl, polymer screen-changer product manager.


Increasing filter area “The target of our screen-changer development for compounding applications was to supply an enlarged filter surface inside a very much smaller filter housing than usual,” he explains. The result is the CSC-R continuous large-area filter, and its shorter brother, the CSC-RS. They are both derived from the CSC-P, which has been on the market for several years. This uses “arched screen” technology with pre-formed screens, for throughput rates up to a massive 750 tonnes/day. The new models have more modest output capabilities, ranging from around 700 kg/h all the way up to just under 19,000 kg/h, or around 450 tonnes/day. The large-area screen-changers are based on a


sturdy double-piston design. The curved screen plate provides four times more active screen area than a conventional screen-changer with circular screen cavities, Maag Automatik says. It claims that the very compact size permits higher throughput rates and filtration grades, reduces pressure loss and multiplies the screen lifetime. Operation is leak-free, without the need for additional sealing elements. The patent-pending cavity design is claimed to


Maag Automa- tik’s CSC-R has an extended arched screen cavity to provides four times more filter surface


provide rheologically optimized melt flow channels without dead zones. “The screen cost and its reliable handling were the


most important part and main focus of the develop- ment,” Pohl says. While pre-formed screens are used for large-scale applications, an all-new screen design and handling procedure was necessary for applications with much lower throughput rates and screen dwell times of a few hours or days. Maag Automatik offers potential customers two


choices: either an existing CSC unit with a conventional circular screen can be upgraded to a CSC-R/S (the screen-changer remains in the line, and only the piston needs to be replaced: the filter handling and venting procedure will remain the same). This provides a 2.5-times enlargement of the filter surface. Alterna- tively, a new CSC-R, with its extended arched screen cavity, provides a filter surface that is four times larger.


Improved sealing Econ has a new sealing technology on its screen- changers that was first applied to models with four pistons and an automatic backflush function. It has subsequently been applied to all models – with one, two or four pistons in both continuous and discontinuous configurations, either with or without backflush. Magdalena Deisl, in sales administration and marketing, says that the seal technology offers advantages particularly for very low-viscosity


plastic melts such as polyamides and PET. “At the same time the potential for blockages with highly viscous materials, such as PC or highly


filled compounds, or polymers that are prone to thermal degradation followed by depositions in the


extrusion system, can be reduced significantly.” A characteristic feature of the new design is the high


proportion of the free-flow area of the screen: 75% is permanently open for the melt stream while the rest is being backwashed. Two meshes are located next to one another in each of the two displacement piston units, a


62 COMPOUNDING WORLD | July 2015 www.compoundingworld.com


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