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Rack and Pinion Actuator for Mold Side-Pull Disclosure Number: IPCOM000004752D
Original Publication Date: 2001-Apr-30
Included in the Prior Art Database: 2001-Apr-30
Document File: 2 page(s) / 258K

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Eric Haupt: AUTHOR


Rack and Pinion Actuator for Mold Side-Pull

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Rack and Pinion Actuator for Mold Side-Pull

Eric Haupt

Plastic Injection Molds for Motorola Personal Communications Sector hand-held devices tend to be highly complex machines. Often there are side holes in the covers for these devices that require cavity, or appearance side side-pulls. These must be actuated prior to the opening of the main parting line of the mold to avoid damaging the part and/or mold, as the part stays with the other half of the mold before ejection.

Actuation of the cavity-side side-pulls can be hydraulic, pneumatic or mechanical. Use of hydraulic or pneumatic cylinders increases the likelihood of mold and/or part damage, as the sequence of events during the cycling of the mold can be (incorrectly) altered. When a mechanical system is properly timed, the sequence is automatically repeated. This enhances mold safety.

The traditional method of mechanical actuation for a side-pull on the cavity half utilizes an angled pin on the "A"-half coupled with a floating plate arrangement. When the floating plate splits from the stationary plate the side-pull moves. This arrangement is best used when the runner system does not use a hot-tip or hot manifold, as these are subject to thermal expansion and contraction that would cause binding, galling and subsequent leakage of plastic throughout the mold.

Another common actuation method is an angle pin used with a floating "B"-side plate. In order for this to be mechanically feasible, the stroke of the side-pull must be small. Otherwise the angle and length of the pin become too great, and either the pin is not strong enough to actuate the side pull or the system will bind.

During a tooling program at Motorola PCS one of the tools had recurring issues with steel breakage caused by improper set-up and timing of a hydraulic cylinder. The cylinder had initially been chosen because of the length of pull and the presence of a hot-runner system. A mechanical lockout system was put in place with an established set-up procedure to eliminate the breakage. This system was not straight forward, and required special training for all personnel handling the tool.

A new tool was built for increased production capacity. Due to the poor maintenance history of the original tool, and the ongoing dependence on human intervention to prevent breakage, a decision was made to redesign the new tool for mechanical actuation. Use of a cam pin was inadvisable for the reasons cited above, due to the long stroke (1.0") needed for one of the side-pulls.

The mold maker had had extensive experience using rack-and-pinion systems to actuate unscrewing mechanisms. It would be a very simple mechanical system to use a drive rack, a pinion (gear) and a passive rack attached to the slide. All that would remain would be to design the system so that the drive rack would always engage the gear in the proper timing, and so that the locking mechanis...