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Self-contained hot edge-gate system converts existing molds.

Self-Contained Hot Edge-Gate System Converts Existing Molds

A hot edge-gate system that is said to permit economical conversion from cold-runner to runnerless molding has been developed by Polyshot Corp., Rochester, N.Y. The system, which is called the E-100, was designed for Efson Corp., a molder in Wilmington, N.C., which was able to eliminate cold runners from its molding process and automate downstream operations.


Resin enters the E-100 system from the nozzle of the molding machine into the nozzle cap. It flows through the center feed zone into the threaded-in, replaceable spreader assembly. Once inside the spreader, the resin flows in a straight path and then is diverted about 80 degrees, where it is distributed into individual flow channels that feed each gate into the parts. Efson uses eight gates to feed one part, a pulley of 33% glass-reinforced nylon.

The feature that distinguishes this hot edge-gate system from others on the market, says Polyshot president Douglas Hepler, is that it is a self-contained unit. Gates are actually integrated into the hot edge system by placing a 1/2-in. edge-gate cap around the end of the unit. The resin flows from the spreader across a narrow air gap and through a reverse-taper hole in the gate cap before proceeding directly into the part.


The integration of the edge-gate cap is the key that allowed Efson to retrofit 100% of its molds that were using conventional cold sprue bushings. Previously, Efson could not automatically separate the runner from the part, and had to do so manually in a secondary operation.

According to plant manager Charles Speaker, Efson decided to eliminate runners entirely rather than figure out a way to separate runners and parts. To that end, Polyshot replaced the conventional sprue bushing in each mold with the E-100 edge-gate system. To convert to the new system, Efson required only one edge-gate system for each of its molding machines, plus a colar retrofittable to each mold. This arrangement permitted the molder, which stocks about 175 molds and adds five new molds per month, to economically convert to runnerless molding, says Speaker. He adds that the retrofit was accomplished easily, requiring only minor dimensional changes to the core after removal of the sprue bushing from the mold.

The retrofit has eliminated the entire secondary handling problem of separating parts from runners, and permitted Efson to automate its downstream operations. It is now installing several automated systems in which molded parts are conveyed to a box filling station where molded parts are counted and packed and new boxes are indexed into place as prior ones are filled.

The retrofit has also allowed Efson to virtually eliminate in-plant scrap from its process. Previously, the molder ground up its runners and fed up to 15% back into the process, which made holding tight tolerances somewhat difficult, says Speaker. So far, Efson has reported good results using glass-reinforced nylon, a somewhat tricky material to mold, because it freezes off quickly and burns easily.

The Polyshot Hot Edge-Gate System can be used individually or integrated into a Polyshot manifold system to feed a larger number of parts individually. It can be supplied with or without the edge-gate cap. Other features of the system include stainless-steel replaceable collars to allow easy "A" length changes; hardened steel body; and a heat-conducting gap to allow access to the four cartridge heaters and single thermocouple. The thermocouple position is as close as possible to the end of the assembly, which is said to provide excellent control of temperature conditions at the resin spreader area.

The E-100 system will be available to molders this spring at a cost of about $2900; additional blank collars cost about $120.

PHOTO : Self-contained Polyshot E-100 Hot Edge-Gate System integrates gates by placing an edge-gate cap around the end of the unit. It's said to permit economical conversion from cold-runner to runnerless molding.
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Copyright 1992, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Author:De Gaspari, John
Publication:Plastics Technology
Date:Jan 1, 1992
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