Extrusion International 3-2023

31 Extrusion International 3/2023 New Enhancements Help Processors Maximize Efficiency and Boost Screen Changer Performance  Faced with surging manufactur- ing demands, processors can employ a range of new options to boost productivity and enhance screen changer performance, according to PSI-Polymer Systems (PSI), a leading global supplier of high-performance gear pumps, screen changers, cus- tom auxiliaries, and rebuilds for the polymer, adhesive, chemical, and food processing industries. With heightened capacity de- mands and extended lead times for production equipment including extruders, processors are looking to maximize efficiency and dial-in cer - tain enhancements to improve the overall manufacturing process, says Don Macnamara, general manager of PSI-Polymer Systems. “Processors are using every avail- able resource and thinking creatively to manage increased backlogs and retain customers,” said Macnamara. “To get more out of the process, there are a range of tried-and-tested enhancements that will give proces- sors a leg up in meeting their day-to- day manufacturing demands.” Processors can wring out greater efficiencies by using Super Plate, Oval Screen Pocket, and LowDelta P Breaker Plate options. Super Plates add efficiency and life to screen packs by allowing better utilization of the surface area. Doing so reduc- es screen replacement frequency and cost, according to the company. The gain is achieved by lifting the screen pack away from the flat, solid surface of the breaker plate. Conven- tional breaker plate open area is typ- ically 50% to 55%. This means 45% to 50% of the screen rests on a solid surface. As a result, screen life dimin- ishes rapidly as the small correspond- ing area over the breaker plate holes is blinded and the material must laterally traverse less clogged areas of the wire cloth to reach a through hole. This can be observed on spent screen packs as dense pockets of fil - tered contaminants over the breaker plate holes and lesser concentrations over the solid part of the breaker plate, according to PSI. Use of a Super Plate fully ex- poses up to 95%+ of the screen to through-flow of the melt stream. This can yield a gain of 30 to 55% in effective filtration area over a con - ventional design. The Super Plate is a precision- manufactured grid of stainless- steel diamond-shaped blades, cross welded to provide superior strength and support. The screen pack rests on the edge of the blades. Spacing and support of the blades often al- lows the cost-saving elimination of a 20-mesh or higher support screen. The Super Plate also eliminates the risk of screen blow-through and resulting contaminants in the end product that can occur if the delta-P exceeds the tensile strength of the wire cloth sitting directly above a breaker plate hole. Meanwhile, Low Delta P Breaker plate design can significantly im - pact production run times between screen changes. Every process has a high-pressure limit defined either by the extruder or the yield strength of the screen pack. Starting (clean screen) pressure drop defines the low end of the process pressure win- dow. Since screen micron rating and related wire diameters are generally standardized, when working with a defined filtration level, the remain - ing variable for reducing pressure drop is the diameter of the holes in the breaker plate. Efficient breaker plate design bal - ances open area and yield strength to minimize pressure drop. For most polymers and adhesives processed through screen changers, the indus- try standard (Class 2) breaker plate hole size works well. However, for high viscosity, fractional melt mate- rials, the typical hole diameter gen- erates a high-pressure drop. This reduces the pressure window and corresponding run time available for a given screen pack and results in more frequent screen changes, according to the company. To reduce pressure-drop for these materials and add run time between screen changes, PSI offers Class 3 and Class 4 breaker plates, each hav- ing successively larger holes than the standard Class 2 plate. The Class 2 holes are ideally sized to support a 20-mesh screen. The larger diameter of the Class 3 and 4 holes use a Super Plate or a 10-mesh support screen for the finer filter screens. Breaker-Plate-Class 2-4 Oval and standard breaker plate