Plastics Technology

JAN 2019

Plastics Technology - Dedicated to improving Plastics Processing.

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Page 34 of 60 E X T R U S I O N K now How 32 JANUARY 2019 Plastics Technology ABOUT THE AUTHOR: Jim Frankland is a mechanical engineer who has been involved in all types of extrusion processing for more than 40 years. He is now president of Frankland Plastics Consulting, LLC. Contact or (724)651-9196. h is the channel depth. It's clear, then, that the use of the same channel depth with an increase in screw size will produce a much different shear rate and result in differing melt quality and melt temperature. It's also clear that there is more consistency between the square of the diameter ratio to 0.7 power than the 0.5 power, compared with the first power of the diameter used in calculating the shear rate. Maddock and others determined that the 0.7 power of the ratio of the screw diameters was a better factor for determining channel depth then the square root of the ratio of the screw diameters, as it takes more fully into account the heat-transfer distances, increased shear heating over the flights due to higher peripheral speed, flight- length ratio, and increased leakage flow over the flights due to the SUPER G ® HighSPEED ™ EXTRUSION SYSTEMS ENERGY EFFICIENT (PP 6-7+ PPH/HP, 2.7-3.2+ KG/HR/HP) HIGH MACHINE THROUGHPUTS (2,500+ PPH, 1135 KG/HR) ULTRA COMPACT FOOTPRINT ULTRA HIGH REGRIND RECOVERY RATES (+80%) EXCELLENT MELT QUALITY AVAILABLE WITH ALL PTI ROLL STAND CONFIGURATIONS Continuous Filtration Delivers • Months of non-stop operation. No hot breaker plates and dirty screen packs • Closer tolerances. Uniform gauge control. Consistent process pressure & melt temperature The Leader in Continuous Melt Filtration Since 1969 • Highest level of process integration with smallest footprint • Automatically maintains constant differential pressure across the screen • Unconditionally guaranteed not to leak NO MOVING PARTS. NO HYDRAULICS. NO LEAKS. Made in the USA larger flight clearances as the diameter is scaled up. Additionally, heat removal through barrel cooling is reduced because of the ratio of barrel area to output. The use of (D1/D2)0 . 7 generates a greater channel depth in the scale-up and reduced shear rate to counter those effects. In conclusion, the use of (D1/D2)0 . 7 as a scale-up factor for the metering depth of screws with similar geometry and L/D has been found to be a very satisfactory general approach. C.I. Chung, in his 2000 book, Extrusion of Polymers, arrived at the same scale-up factor as a "balanced" basis for overall scale-up.

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