PSI-Polymer Systems

PSI-Polymer Systems, Inc. Leak-Free Screen Changer for Extrusion Coating Applications Conover, NC (August 29, 2016)

PSI-Polymer Systems has developed and successfully field tested a true leak-free screen changer seal for high temperature, low viscosity extrusion coating applications.

For decades, high temperature extrusion coating applications have presented a difficult challenge to slide plate screen changer seal technology for leak-free operation.  Screen changer mechanical seals utilize clearances between the seal and body (typ. 0.001” to 0.0015” radial) to accommodate removal and replacement. For typical process applications, polymer viscosities are too stiff to pass through these clearances and the machines run trouble-free.  Extrusion coating applications, however, often process polymers at temperatures at 630 deg. F (332 deg. C) and higher.  These elevated temperatures result in extremely low viscosities which can flow through radial clearances as tight as 0.0005”. Compounding this problem is the typical placement of the screen changer above the die. Any polymer leak from this position will compromise the web or, worse, drip onto the hot die.

Because of this problem, most extrusion coating operations default to a cartridge block filter that requires manual change out, is difficult to access and is labor intensive.

PSI has successfully resolved slide place screen changer leakage problems for extrusion coating through a proprietary upgrade of its patented, lifetime pressure activated seal.  The change introduces a conformable, heat-resistant (1200 deg. F / 650 deg. C) annular seal component that stops polymers with extreme low viscosities from migrating around the OD of the seal. 

The first five-layer system was sold in 2015 to a major international engineering firm and started operation in Asia.  Typical maximum operating temperature for the LDPE is 630 deg. F (332 deg. C).  Since installation, the screen changers have performed with zero leakage.  “We were so certain of the seal design,” reports Don Macnamara, General Manager for PSI, “that we demonstrated leak free performance for a major OEM by filling the screen changer with hydraulic oil in place of polymer.  Not once, during the three day test, did the seals leak or seep.  I’ve been involved with screen changers since 1983.  This is the first slide plate screen changer I’ve experienced that can perform truly leak-free under these extreme conditions.”

To date, PSI has supplied close to two dozen more screen changers for high temperature extrusion coating, all of which are running without seal leakage.  The screen changers are available with standard metallurgy or in stainless steel for processing extrusion coating polymers with corrosive properties.