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ABOUT THE AUTHOR: Alex Utracki is director of process technology for Coperion's Compounding and Extrusion division. His group is responsible for trials in Coperion's twin-screw extrusion process lab in Pitman, N.J. as well as providing technical support for process development, new machine sales, and existing customers. Contact: (856) 256-3019; alex.utracki@ coperion.com; coperion.com. the conveying efficiency. The secondary effect is to remove some of the entrained air from the powder, reducing its volume. The magnitude of the effect of FET is not the same for all powders, and depends on attributes such as bulk density and particle size. For talc, it has been proven to increase throughput rate by over 250%, while for calcium carbonate, the increase in throughput is mostly negligible. The limitation is that FET can only be used in zones where only dry, unmelted powders are present. Wet or molten materials will plug the filter; and large, solid particles such as pellets will damage it. For compounding processes, this technology is typically applied to the side- feeder barrel, though it is also available in the main extruder barrels as well. To calculate the profitability of installing FET, consider an example of a 45-mm twin-screw extruder compounding poly- propylene with 40% talc for an automotive application (Table 2). For this process, the throughput is limited by the volume of talc that can be fed. At rates higher than 600 kg/hr, the side feeder starts to back up, and the extruder is able to use only 54% of its total motor power. By installing FET, the conveying efficiency of the side feeder is greatly increased, and the throughput can be increased until the motor power becomes the limitation at 1100 kg/hr. As a result of increasing the throughput rate at the same screw speed, the specific mechanical energy input to the material also decreases, and less power is used per kilogram of material. With a profit margin of 20¢/kg, the 500 kg/hr increase in rate could mean an increased profit of $600,000 annually, offsetting the cost of FET several times over. The specific energy requirements are reduced by 4% or 33 MWh annually. The examples offered highlight just a few common limita- tions in feeding twin-screw extrusion processes. There are many more areas where limitations can occur. The principle of first identifying the limitation, understanding it, and implementing a solution, then repeating for the next limitation, can be applied for those limitations not discussed in this article. Factors such as energy cost, profit, and ability to sell excess production should be evaluated for your specific business. These calculations can provide the framework to justify taking on these optimization projects. As always, your twin-screw extruder manufacturer is a good first point of contact for process-optimization advice. Need Help? IMS to the Find these great products and many more at imscompany.com IMS Screw Handler Feed Screw Transporter SAFESEAL Rust Preventive UNIVEST ® Barrel Insulation IMS ResQ Station Versatile Work Table IMS ResQ Cart * Mobile Utility Cart IMS Select Hoist Ring Rack * IMS Select Line Conveyors *other items sold seperately @plastechmag 61 Plastics Technology T W I N - S C R E W C O M P O U N D I N G