Tips for Improving Extrusion Efficiency and Preventing Problems

Adjust feed throat temperature. When processing polyolefins, the feed throat should be warm to the touch. It improves processing by enhancing solids conveying, and reduces energy by not displacing heat through the feed throat water discharge.  

Maintain a consistent regrind form. Maintaining a consistent shape promotes bulk density, improves flow in the feed hopper, and a gives a consistent conveyance in the screw's feed section. All of these factors influence the screw's output stability.  

 Cool screws when processing polymers to minimize degradation. This is important when using polymers that have a tendency to stick to the root of the screw in the feed section. The cooling bore should stop before the end of the section. Extending the bore beyond this point could cause the screw to become unstable. Use a full-length bore to process thermally sensitive materials like rigid PVC.  

Return to: Proper Machine Selection + Setup = Success for Medical Extruders

 When starting an extruder with an empty screw, start turning the screw slowly and then introduce the resin by opening the feed throat slide gate. This gradual action allows the polymer to slowly work down the screw and melt, providing a lubricant between the screw flights and barrel. The lubrication prevents the possibility of damaging the screw flight hard surface and the barrel lining. Opening the slide gate after the screw is turning will help reduce the possibility of a melt block forming on the screw.   

 Use only treated water in your closed-loop, water-cooled barrel system (commonly found on larger sized extruders). Water that is high in minerals will foul the water passages in the system’s heater passage, heat exchanger, and other components. Adding glycol to the system can reduce its effectiveness to cool because the glycol changes the flash point of the water.  

 Align extruder barrels as part of the maintenance procedure. Be sure an experienced firm does the alignment. This should be done every six months or once a year so you have a history of the condition of the equipment. It also needs to be done each time a barrel, feed throat, or gearbox is mounted to the extruder and when an extruder is being relocated. A properly performed barrel alignment reduces the risk these components failing.  

 Choose a screw supplier with an extrusion lab where you can bring in trials. That allows extruders to customize and change screws more quickly especially when working with new materials.  

 Have the capability to run a variety of resins and tubing sizes. Extruders may have multiple screw designs for one machine because there’s no such thing as a “one screw fits all” scenario.