Screenchangers & melt fi ltration | machinery feature
The screen changer is a key factor in ensuring pristine polymer fl ow, to guarantee that products meet suitable quality standards. Lou Reade reports
Keeping it clean: melt fi ltration and screen changers
Screen changers play a vital role in improving melt quality and performance. As well as protecting downstream equipment from damage, they can help to improve product appearance and prevent mechanical failure of fi nished parts. With the increased prevalence of material re-use, they can also help to add value to recycled material and contaminated melt sources. At last year’s Fakuma exhibition in
Germany, Ettlinger showcased its expertise in continuous melt fi ltration with its ERF 500 model – a new addition to its ERF melt fi lter series. ERF 500, designed for a maximum
throughput of 5000kg/hour, rounds off the company‘s series of high end fi lters for recycling post-consumer and post-industrial plastic waste. The earlier ERF 200 and ERF 250 models achieve throughputs of 1.5 tonnes/ hour and 2.5 tonnes/hour, respectively. ERF 500 has the same compact design and, like its predecessors, is durable – and capable of handling contamination amounts of up to 18% by weight. The high fi ltration effi ciency assures a both high product quality and minimal melt loss. The central component of the ERF 500 is a rotating,
cylindrical fi lter screen with millions of conical holes that can be supplied with a wide variety of fi ltration levels. When melt fl ows through the fi lter, contami- nants are retained on the outside of the screen. This includes not only solid contaminants like wood or paper particles, but also the high-molecular and cross-linked fractions that arise due to high temperature stresses. The cleaned melt on the inside of the drum is
supplied to the downstream mould via a system of fl ow channels. The rotary motion of the fi lter drum simulta- neously supports the blending effect and ensures
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optimally homogeneous conditions in the melt. With every revolution the servo-drive fi lter screen is
cleaned by a scraper. Particles removed from the surface are continuously fed to an exit screw driven by a second servo motor, which discharges the contami- nants from the fi lter system. In automatic mode the melt losses due to the continuously discharged contaminants are only minimal because these contami- nants are highly enriched (up to 70%) at the exit. Keeping the screen of the ERF fi lter open throughout
the production phase leads to reliable and stable processing, says Ettlinger: the melt pressure downstre- am of the fi lter remains constant, as does the melt throughput.
Preventing leakage PSI-Polymer Systems has introduced a new seal, applicable to any of its bolt type screenchangers and divert valves, which prevents material leakage on very
January/February 2015 | PIPE & PROFILE EXTRUSION 17
Gneuss has developed a
new variant of its RSFgenius, for processing highly contami- nated materials
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