Plastics Technology

NOV 2018

Plastics Technology - Dedicated to improving Plastics Processing.

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ABOUT THE AUTHOR Mike Sepe is an inde- pendent, global materials and processing consultant whose company, Michael P. Sepe, LLC, is based in Sedona, Ariz. He has more than 40 years of experience in the plastics industry and assists clients with material selection, designing for manufacturability, process optimization, troubleshooting, and failure analysis. Contact: (928) 203-0408 • Finally, if regrind is being used, the fibers in the reground material are shorter than those in the virgin material, even if the process conditions are optimal. The amount of regrind should be carefully controlled to keep the properties from progressively declining as the material is continually recycled. The higher the regrind percentage, the more second-, third-, and fourth-generation reclaim becomes part of the molded article. I once visited a processor who was producing parts in a 30% glass-fiber rein- forced PBT polyester that were consistently brittle. We discovered that 85% of the shot was in the runner, and the runner was being reground and put immediately back into the drying hopper. With very little virgin material being added to the mix, it was not long before at least half the material in the hopper was at least fourth-genera- tion regrind and the glass fibers were little more than powder. One last example is worth including: There is an increase in the need for polymers that can shield electromagnetic and radio-frequency interference (EMI/ RFI). This is achieved by using conductive fillers, and among the choices are long fibers of stainless steel. Levels of this fiber as low as 6-10% can produce the desired results. But effective shielding relies on an overlapping network of fibers through the wall of the molded part. This, in turn, is ensured by keeping the fibers long. It has been shown that excessive length reduction of the stainless-steel fibers degrades the shielding properties. So far in this series, we have reviewed four aspects of material composition that the processor has a role in preserving or optimizing: molecular weight, crystal structure (if it is expected), molded-in stress, and fiber length in those materials where fibers are used. We have one more to review, the additive package. We will address this topic in our next column. The amount of regrind should be carefully controlled to keep the properties from progressively declining as the material is continually recycled Tel: 412 459 0450 A Full Range of Robots One Unique Control Sepro offers the industry's widest choice of 3, 5 and 6 axis robots for machines from 20 to 5000 tons, plus advanced connectivity and new control developments to improve your molding efficiency. With Sepro, the Future is Open 4.0 3-Axis 6-Axis 5-Axis 22 NOVEMBER 2018 Plastics Technology M AT E R I A L S K now How

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