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Being in tune with your film extrusion equipment will allow you to identify issues before they start impacting production. What is Your Extruder Trying to Tell You? Extruder wear can cause serious issues in polyethylene film produc- tion, resulting in decreased output rates and increased costs. Some challenges include loss of throughput, poor melt-temperature control, decreased mixing, gel generation, and increased energy usage. Many times, the amount of wear in an extrusion system happens gradually, and often the issues can go unobserved until it is too late. There are certain indicators that plant operations should monitor to determine the onset of extruder wear and possibly when the extruder screw should be replaced. In this article we will take a look at key process- control points and data that could indicate a change in the process due to extruder screw wear. DEVELOP A STANDARD METHOD—BASELINE One key to using your process-control system to identify possible extruder wear is to create a baseline using a standardized method and formulation. Ideally this baseline would be created when the line is new and operating at its maximum efficiency. However, a process baseline can be created at any point in the extruder's life. Creating a baseline of performance is a fairly simple process, and there have been many articles written about how to properly baseline your system. One point that is often overlooked when talking about how to baseline an extrusion system is the need for a standardized formulation. When baselining a system, you should try to minimize any variation when generating your data. One way to do this is to run the same formulation each time you generate the data. The formulation should preferably be simple and not include blends, in the spirit of reducing variation. However, if you choose to use a blend in your standardized formulation for creating your baseline data, it is important to ensure, to the best of your capability, that the blend is exactly the same each time. By Wes Hobson and Mike Rutkowske The Dow Chemical Co. QUESTIONS ABOUT EXTRUSION? Visit the Extrusion and Film Extrusion Zones. As a rule of thumb, it is considered time to replace the screw when the flight clearance increases by 4 times the original clearance. Dow has a full-scale production seven-layer blown film line furnished by Hosokawa Alpine American at the Pack Studios facility in Freeport, Texas. The system is used for customer trials and also by Dow for process optimization and troubleshooting. 66 FEBRUARY 2018 Plastics Technology PTonline.com Tips and Techniques