Plastics Technology

AUG 2016

Plastics Technology - Dedicated to improving Plastics Processing.

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ABOUT THE AUTHOR Mike Sepe is an independent, global materials and processing consultant whose company, Michael P. Sepe, LLC, is based in Sedona, Ariz. He has more than 35 years of experience in the plastics industry and assists clients with material selection, designing for manu- facturability, process optimization, troubleshooting, and failure analysis. Contact: (928) 203-0408 • mike@thematerialanalyst.com. WHICH ELBOW PROBLEM DO YOU NEED TO SOLVE? PROBLEM CAUSE SOLUTION Formation of streamers, ers, Formation of streamers, angel hair and snake skins when conveying plastic pellets Plastic pellets skidding against the outside radius of conventional elbows create friction and heat, melting pellet surfaces. Smart Elbow ® replacements from HammerTek eliminate these problems by eliminating impact li by eliminating impact i by eliminating impact ti by eliminating impact impact Unlike Unlike conventional "impact" elbows and conventional "impact" elbows and "plugged-tee" "plugged-tee" elbows that rely on material elbows that rely on material impact to change direction, HammerTek's mpact impact to change direction, HammerTek's to change direction, HammerTek's Smart Smart Elbow Elbow ® design features a spherical chamber that protrudes partially beyond hamber that protrudes partially beyond the desired 90º or 45º pathway, which he the desired 90º or 45º pathway, which desired 90º or 45º pathway, which causes a ball of pellets suspended in air auses a ball of pellets suspended in air to rotate, gently deflecting incoming o to rotate, gently deflecting incoming rotate, gently deflecting incoming pellets pellets around the bend. around the bend. No No impact means no wear and no fines and impact means no wear and no fines and no no streamers, angel hair or snake skins. streamers, angel hair or snake skins. Wear and failure when conveying glass-filled, mineral-filled or other abrasive pellets Abrasive pellets hit the outside radius of conventional impact elbows at high speed, continually wearing through the elbow wall. EE-0299 Free, No-Risk Trial Offer See how Smart Elbow® deflection elbows eliminate conventional and plugged-tee impact elbow problems—at no cost or obligation. 1-610-814-2273 sales@HammerTek.com www.HammerTek.com 45° and 90° elbows available in diameters ranging from 1.25 to 18 inch Impact testing is another way of assessing ductility using a higher spectrum of strain rates. Figures 2 and 3 show the results of instrumented impact tests performed on a PVC material at room temperature using two different velocities: 15 ft/sec and 5 ft/sec, respectively. The purple line represents the load on the sample while the blue line gives the energy collected in the process of producing the failure. The high-velocity test in Fig. 2 shows a rapid increase in the load in a period of about 3 millisec. As soon as the test achieves a maximum value, the load drops off very quickly, signaling the occurrence of a brittle failure. Almost all the energy that was required to produce the failure, a total of 21 joules, was expended in the process of initi- ating the failure and very little additional work was required to produce final failure. The lower-velocity test shown in Fig. 3 looks like it was performed on a different and much tougher material. The load builds up more gradually, partly due to the lower speed of the initial impact. But the most important difference can be observed when the peak load is reached. Instead of failing immediately, the material continues to manage the energy of the event, extending the time frame of the test to more than 20 millisec, an eternity when it comes to impact tests. The total energy required to cause complete failure increases by approximately 50% to 32 joules. But most importantly, the mode of failure changes from brittle to ductile simply because of the change in the impact velocity. Both of the changes illustrated here, in the tensile tests on PP and the impact tests on PVC, could also have been created by keeping the strain rate the same and changing the temperature at which the test was performed. Reducing the temperature would have the same effect as increasing the strain rate, while increasing the temperature would have the same effect as decreasing the strain rate. If you were not told how the tests were performed, you would have no way of knowing which change was selected. And that is the point—neither can the plastic. Impact testing is another way of assessing ductility using a higher spectrum of strain rates. @plastechmag 29 Plastics Technology M AT E R I A L S

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