Gardner Business Media

Hot Runner Technology OCT 2017

Gardner Research

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October 2017 9 history, complexity level and required main- tenance skills. More importantly, proper manifold maintenance depends upon an understanding of its critical functioning areas (flow paths, seal areas, cooling channels) and its dimensional relationship with the cavities (gates and nozzle tips). The first step when working on any man- ifold is identifying the goal of the work, which determines and verifies the specific maintenance plan. For example, is it routine preventive maintenance, or a new or repetitive problem with a mold or part? When it comes to manifolds, the more specific question may be, is preventive maintenance done at an appropriate cycle count? Or, does the PM cycle frequency need adjustment? Once the shop sets a goal and strategizes a mainte- nance plan, there are general preparation, disassembly and re-assembly steps to follow for proper hot runner mainte- nance. These steps are general guidelines when working on most systems. Always check with your hot runner supplier for their recommendations on the proper techniques and sequences. Preparation Guidelines 4 Go to the crib and verify that the necessary tooling is in-house to support the maintenance plan. Necessary tooling includes heaters, thermo- couples, nozzles, nozzle tips, valve pins and valve pin bushings. 4 Confirm the estimated downtime with the production/molding department. 4 Review past maintenance history to deter- mine the most efficient method for mold and manifold disassembly. Most manifolds are removed from the manifold retaining plate in the horizontal position for safety and efficiency, but some are removed more easily in the standing or the vertical position. 4 Determine a proper removal procedure for the electrical control box (for example, with nozzle heater and thermocouple wires con- nected or individually disconnected) and the best disconnection method for the manifold heater wires (for example, disconnected from the manifold or from the control box). 4 Identify critical areas and special tools that may be necessary for disassembly. Examples include wooden spacer blocks to carry the manifold weight and to avoid damage to protruding nozzles, rubber caps to protect nozzle tips during manifold removal, eye- bolts versus jack screws, a hand lift versus an overhead hoist and a technician's hands versus a slap hammer for valve pin removal. 4 Check all heaters and thermocouples for resistance and shorts using an ohmmeter before disassembly, then record the readings. To do this faster, use a portable hot runner mold testing system, such as the Mold Check- er from Fast Heat, which tests hot runner manifolds to ensure that resistances of all thermocouples and heaters are within range. FIGURE 2: When using a fixed gate system (where there are no valve pins), remove the "A" cavity plate before removing the rear clamp plate to expose the nozzle tips, and measure and record the distance from the nozzle tip to the nozzle plate.

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