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End cap assembly for heat- and shear-sensitive materials.

A new end-cap assembly that is said to help aid injection molding of heat- and shear-sensitive materials was jointly developed by EMI Corp. of Jackson Center, Ohio, and BFGoodrich Co.'s Application Engineering and Design Laboratory in Avon Lake, Ohio. Called the Unrestricted, Free Flow End Cap, the new assembly reportedly minimizes the possibility of shear-burning problems when processing higher flow grades of materials such newer PVC compounds, ABS or polycarbonate. EMI says field use has demonstrated that the new design produces a more uniform melt, more consistent shot sizes, and helps to avoid sudden pressure drops.

EMI has built several of the end-cap assemblies for BFGoodrich. According to Carl Toensing, manager of BFG's Molding Technical Service, conventional "smear-head" screw tips used for more viscous materials could not prevent backflow, leading to shear burning and inadequately packed mold cavities. In developing its new end-cap assembly, EMI modified its 100% Free Flow sliding check-ring valve, which is said to give the resin a completely unrestricted flow path. The narrow, tapered channel between the ring valve and end cap smoothly directs the flow of the melt during injection, discouraging shear burning and carbonized plastic build-up. The longer taper continues through the nozzle adapter and tip, minimizing sudden pressure drops.

EMI offers a choice of hardened tool steels or stainless steels for the assembly. Cost of the assembly varies according to application. A 2-in. Free Flow End Cap assembly would typically list at around $1460. This includes the end cap, ring valve, nozzle adapter, and nozzle tip.
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Title Annotation:Technology News
Author:De Gaspari, John
Publication:Plastics Technology
Date:Jan 1, 1993
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