machinery feature | Screenchangers “We were so certain of the seal design that we
demonstrated leak-free performance for a major OEM by filling the screenchanger with hydraulic oil in place of polymer,” said Don Macnamara, general manager of PSI. “Not once, during the three days, did the seals leak or seep. This is the first slide-plate screenchanger I’ve experienced that can perform truly leak-free under these extreme conditions.” The screenchangers are available with standard
metallurgy or in stainless steel for processing extrusion coating polymers with corrosive properties.
A patented seal is at the heart of PSI’s leak-free screenchanger for extrusion coating applications
At the same time, the company has developed its
latest generation of PLC touchscreen control system that can adapt to varying conditions. Optional param- eters are configured via an automation algorithm, which detects real time processing conditions and adjusts the operations of the screenchanger accordingly. “These innovations deliver major enhancements with
respect to performance, integration, reliability and ease of use,” said Aline Alroy, vice president of sales for Hitech.
Cutting leaks PSI-Polymer Systems has developed and tested a leak-free screenchanger for extrusion coating applica- tions – which have traditionally presented a challenge in terms of leakage due to the low viscosity of the polymer melt.
Screenchanger mechanical seals use clearances Fimic has
developed the Era filter,
which filters twice in sequence
between the seal and body (typically 0.001-0.0015in radial) to allow removal and replacement. In typical process applications, polymer viscosities are too stiff to pass through these clearances, and the machines run without trouble. However, extrusion coating typically runs at 330°C or higher. The resulting low viscosity polymer can leak through clearances as tight as 0.0005in. At the same time, positioning the screen- changer above the die means that any leak will compro- mise the web or – even worse – drip onto the hot die. This means that most extrusion coating operations
rely on a hard-to-access cartridge block filter – which must be changed manually in a labour-intensive operation. PSI has overcome this by redesigning its lifetime
pressure activated seal. The device now incorporates a conformable seal component – which is heat-resistant to 650°C – that prevents low viscosity polymers from migrating around the seal. PSI was recently granted a US patent on the seal. One customer in Asia is already using a five-layer
version of the system, where maximum operating temperatures for the LDPE is typically 630°C. The screenchangers have experienced no leakage.
16 FILM & SHEET EXTRUSION | December 2016
www.filmandsheet.com
Filtering PVC Fimic has developed a new filter that is aimed specifi- cally at PVC processing. Its RAS technology is based on collecting a high level
of contamination inside a hollow blade holder, and discharging it based on a pre-set pressure. It has been modified to recycle PVC electrical cables, which are difficult to recycle and contain high levels of copper, aluminium, rubber and other plastics. Because of the level of contamination – usually
above 20% – the machine is set in continuous mode. This allows the blade holder to keep slowly scraping the stainless steel screen and gradually accumulate the removed contamination. Thanks to the 150 micron laser screen and its high
open area, this plastic material – usually considered unmanageable – has been successfully processed by four separate end users. The modified Fimic filter still features fast cover opening and a rapid changeover times of between 15 (for the RAS400) and 50 minutes (for RAS700) – compared to a typical 90 minutes for competing technologies. “This is important if you consider that the screen
could need changing every three days, and that the line stops reduce overall production,” said the company. For this reason, Fimic has installed a line that
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