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New hot-runner source.

A new supplier of hot-runner systems, Marathon Plastics Inc. of Wayside, N.J., has come to market with a full complement of conventional and miniature designs. The company also makes specialty systems for PET bottle preforms, two of which have already been sold.

Paul Brown, formerly mold research manager at Husky Injection Molding Systems and now a principal in Marathon, supervises all the design work for the new supplier while an undisclosed moldmaker actually builds the systems in the northeastern U.S.

Miniature designs aside, Marathon's product line encompasses standard sizes with both edge and valve gating as well as thermal shut-off. The company also sells its own line of heater bands.

Marathon's smallest hot-runner components reflect a current trend to miniaturization in this field. Its hot-tip nozzles measure only 0.75 in. across, allowing center-to-center spacing of 0.78 in. The diameter for valve-gate nozzle is 1.0 in. for pitches as small as 1.06 in.

Diminutive size isn't all these units have to offer. Brown says he has addressed some of "the known maintenance problems" associated with valve gates. All designs feature a removable back plate to give access to the piston assembly without splitting the mold. O-rings can be changed with the mold still hanging in the press. The same holds true for the company's standard systems.

Also, because the mold need not be split open as often, the metal-to-metal seals remain intact. "When you disturb the seals, you always run the danger of creating leaks," Brown asserts. He adds that Marathon has also moved the valve-gate pneumatics to a cooler part of the mold to reduce the thermal degradation of the air piston O-rings.


For PET preform molding, Marathon has systems that preserve the easy-maintenance features of its other valve-gate nozzles. The PET systems, however, also feature adjustable valve stems to optimize thermal conditions at the gate and minimize crystallization, Brown says. Comparing the Marathon system with competing ones, Brown says he uses larger flow channels throughout to reduce pressure drop, shear heating, and residence time. He has also beefed up the insulation around the valve bushing to minimize heat loss to the plates, which he believes to be another cause of crystallinity.

Marathon's PET preform systems are now used in Japan, where a four-cavity and a 48-cavity mold are up and running.

Lastly, the company builds systems for injection-blow molding that rely on valve-gating and a proprietary "bridge manifold." These features allow the system to deliver balanced melt flow and fill the cavities uniformly for improved bottle quality. A three-cavity model is currently being built.
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Title Annotation:Marathon Plastics Inc.'s miniature designs
Author:Ogando, Joseph
Publication:Plastics Technology
Date:Aug 1, 1992
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