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C-20 DeDuster® – removes dust and streamers Better systems for brilliant products and higher margins. Learn more: www.pelletroncorp.com Better systems for brilliant products and higher margins. streamers Better systems for brilliant products and higher margins. No dust + No streamers = Reduced scrap rate and production costs www.pelletroncorp.com www.pelletroncorp.com and production costs The research literature is full of papers that discuss the ability of DSC to detect minor transitions in a material that can provide information on the thermal history of a molded part. Semi-crystalline polymers, when exposed to elevated application temperatures, will develop a new population of crystals that will melt at a temperature slightly above the temperature at which they were formed. Therefore, these inflections not only tell us that the material had been exposed to elevated temperatures, they also give us a good approximation of that temperature. In this case the temperature of the secondary transition was in good agreement with the summertime temperature inside the warehouse where these parts were stored for extended periods of time. It is also known that with an increased degree of crystallinity, the strength and stiffness of a semi-crystalline polymer will increase while the ductility will decrease. The DSC results that we noted had been evident in an earlier analysis. But because the tests had only been performed on failed parts, the significance was missed and the inflections were accounted for by a different mechanism that turned out to be incorrect. It should be evident that this elevated temperature exposure was not the cause of the failures. Hundreds of thousands if not millions of these parts went through storage at these summertime conditions. Only those parts that had experienced this treatment and exhibited particularly poor color homogeneity and had been damaged by the high-speed automated assembly machinery and were assembled from parts at the extremes of the toler- ance range displayed failure. This last factor is particularly impor- tant. None of the parts in the assembly were out of print. But when a part molded to the high end of its outer diameter was inserted into a part with a mating inner diameter that was on the low end of the tolerance, this created the high-stress condition needed to tip the scales. Too often when a dimensional analysis is performed, parts are checked to determine if they meet the print and if they do then this factor is set aside as not worth considering. Before we leave this subject of specialization, there is one more feature of our modern organization struc- ture that we need to address. And that involves the division of labor within the analytical laboratory. That will be the subject of my next column. ABOUT THE AUTHOR Mike Sepe is an indepen- dent, global materials and processing consultant whose company, Michael P. Sepe, LLC, is based in Sedona, Ariz. He has more than 40 years of expe- rience in the plastics industry and assists clients with material selection, designing for manufac- turability, process optimization, troubleshooting, and failure analysis. Contact: (928) 203-0408 • mike@thematerialanalyst.com. APRIL 2017 26 Plastics Technology PTonline.com M AT E R I A L S K now How