The Practical Processor: June 2010

Your processing questions answered

Q. I have several jobs using different materials, and I need to run them on the same machine. Is there a way to get good performance without changing screws every time I change materials?


A. Many processors wish there could be a universal or general-purpose screw. In reality it’s very difficult to design a screw that will provide optimum performance on more than one material. You can’t run PVC on a screw that was designed for PE, for example, because they have very different melting properties and require very different screw geometry. It may be possible to develop a design that will work acceptably on similar materials—PE and PP, for instance—but it will still be a compromise. Product quality may be acceptable, but you may not be able to achieve the same throughput with both materials. The best you can do is tell your screw supplier which materials you plan to run and let him suggest the best compromise. Usually that will mean designing for best performance on the one material you run most often and acceptable results on one or two other materials you use less frequently.

Jeff Kuhman, v.p. of engineering
Glycon Corp., Tecumseh, Mich.
(800) 255-9969 •