Screenchangers | machinery feature
The need to boost product quality has led to improvements in screenchangers and melt filtration – such as higher operating efficiency and faster changeover. Lou Reade reports
All change: advances in melt filtration and screenchangers
The increased use of recyclate in polymer processing can raise problems. Processors must take care to remove impurities during processing – in order to raise product quality, and ensure that the materials process properly. This can be ensured through material testing, and by
incorporating efficient melt filtration. At the recent K2016 exhibition, a number of exhibitors showcased their latest developments to help film and sheet extruders process a range of polymers more effectively.
High contamination Nordson has developed a new melt filtration system for recycling highly contaminated plastics – saying it provides greater productivity than comparable ma- chines while maintaining constant melt pressure and product consistency. The BKG HiCon R-Type 250 transforms contami-
nated polyolefin or styrenic plastics into clean, high- quality material, and exhibits less melt loss than traditional backflush systems, says Nordson PPS business unit director, Sven Conrad. The system uses a cylindrical ‘separating head’ –
with knives arranged on its surface in a helical pattern – to move contaminant particles forward as the head rotates. Enclosing the head is a stationary filter element called a ‘strainer tube’. When contaminated melt from an entry port flows into the cylindrical space between the rotating head and the strainer tube, the knives capture the contaminant while the contaminant-free melt moves through the strainer into flow channels that lead to an exit port. At the same time, the rotating head turns a screw that guides the contaminated material through cooling sections and finally to where it is
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discharged into collecting bins. “This cleans much more efficiently than commercial
available filtration systems for highly contaminated polymers,” said Conrad. “The special design makes possible a uniform load on the strainer tube during the cleaning process, providing an extended lifetime for the filter and scrapers and increasing the overall efficiency of the system at far less melt loss.” The system operates at a maximum pressure of 350 bar and maximum temperature of 320°C. Throughput can range from 500 to 1,500kg/h, depending on factors such as polymer viscosity, filtration fineness and levels of contamination. As it exits the system, filtered
Nordson’s HiCon R-Type
250 transforms contaminated polyolefin or styrenic
plastics into clean, high- quality
material
December 2016 | FILM & SHEET EXTRUSION 13
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