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Follow these practical examples to improve the feeding efficiency and productivity of your process. Optimize Feeding to Make More Money in Twin-Screw Compounding Every business wants to increase profits. Companies can deploy many strategies to do so that can fall across various areas of the business, such as reducing inventory, negotiating lower prices from suppliers, or increasing mar- keting efforts, to name a few. When it comes to operations, the capital equipment is often already in place and is therefore a sunk cost. Increasing profit- ability in this case usually depends on maximizing productivity of these assets. For twin-screw extrusion processes, this is most easily achieved by increasing throughput rate, thereby spreading operating costs (depreciation, labor, maintenance, etc.) over a greater amount of product produced in the same unit of time. Another option to reduce cost is by increasing energy efficiency in converting raw materials into finished goods. Since energy is relatively inexpensive in the U.S., the dollar amount of these savings tends to be minor compared with productivity increases. But there are other benefits businesses can realize by cutting energy consumption, such as reducing their carbon footprint and enhancing public image. In some cases, though, it is possible to achieve both increased produc- tivity and reduced specific energy consumption. When it comes to increasing throughput, first find out what is causing the current limitations. For twin-screw extrusion processes, limitations can exist anywhere from the feed system through the process section to the downstream equipment. For example, difficult-to-handle materials may stick or flow poorly through feeding equipment, limiting the rate at which they can be discharged into the twin-screw extruder. In the process section, an improperly designed melting section may not be able to fully melt the polymer above a certain throughput rate. By Alex Utracki Coperion Corp. QUESTIONS ABOUT TWIN-SCREW COMPOUNDING? Visit the Twin-Screw Compounding Zone. For materials that tend to bridge, rat hole, or stick to the hopper, agitation is needed to keep the product flowing consistently. Here, a feeder that was experiencing surging during refill was replaced with one better suited for the material. The right-hand column shows the effects of this changes on throughputs and profits. Original Optimized Operating Hours/Yr 6000 6000 Rate, Kg/Hr 2000 2300 Total Kilotons/Yr 12 13.8 Energy Cost*, $/kWh 0.072 0.072 Specific Energy Input, kWh/kg 0.22 0.21 Specific Energy Savings/Kiloton, $ 720 Energy Savings/Yr, $ - 9936 Profit/kg, $ 0.1 0.1 Increased Profit/Y, $ - 180,000 TABLE 1 Effect of Feed-System Performance Optimization on Extruder Throughput (ZSK70MC+) *U.S. Energy Information Administration/August 2016 56 APRIL 2017 Plastics Technology PTonline.com Tips and Techniques