Gardner Business Media

Hot Runner Technology OCT 2017

Gardner Research

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F E AT U R E 10 Hot Runner Technology 4 Map the position of each thermocouple and heater to verify their connection to the cor- rect pin on the electrical connectors. Record the results (see Figure 1, page 8). Disassembly Guidelines 4 Remove the "A" cavity plate in a fixed gate system (no valve pins) to expose the nozzle tips before removing the rear clamp plate. Then measure and record the distance from the nozzle tip to the nozzle plate (see Figure 2, page 9). This dimension is critical to the relationship between the gate area and the land area and can be the root cause of parts that suffer long gate issues (like a spike of plastic sticking out from the gate location). This dimension also serves as a reference point to ensure that the nozzles are positioned correctly after the mold is reassembled. 4 Ground the electrical controller directly to the mold, if using a controller to check the heater and thermocouples and if using wooden spacer blocks. The blocks will prevent the mold from being grounded through the steel bench, creating a shocking situation. 4 Warm up nozzles to 250°–350°F (depending on the resin) when removing the pins from a valve-gate system. This eases the extraction of the valve pins from the manifold system which prevents the resistance of cold plastic that can damage the valve pins. 4 Move the valve pins back or to the open position while they are warm. This prevents damage to the tips on delicate valve pins and protects them if the cavity plate gets jammed on the leader pins and does not come off evenly during its removal. 4 Number every tip to a home position for accurate reassembly, so the valve pins take a seat (or running fit) in their related valve pin bushing during production. 4 Handle valve pins carefully when remov- ing them, placing them on a bench or in a cleaning basket when cleaning and drying them and when returning to the bench and reinstalling them into the mold. Care- less handling will create dings or bend the fragile tips. 4 Take additional reference measurements from the manifold plate to the manifold or to any expansion spacers located at the top of the manifold before removing any bolts that are securing the manifold. These measurements help verify that everything was put back together correctly. Measure closest to the corners of the manifold to determine the flatness of the manifold in relation to the manifold plate. If one or more corners varies by 0.010 inch or more, it is likely that the manifold does not sit flat on the nozzles, which points to a potential tooling stack problem. 4 Clean and stone an area before taking any measurements. This helps ensure more ac- curate readings. 4 Measure from the top of the bridge to the manifold plate and down to the manifold when a manifold bridge is part of the system. This measurement is useful during reassembly. 4 Note wiring routes through the plates and use wire labels to identify the correct heat- er and thermocouple positions. 4 Remove the manifold bolts and carefully lift out the manifold once all the measure- ments are taken and all the wire clips are removed. If the nozzles are bolted to the manifold plate, removing the manifold might require extra force to break the plas- tic connection between the nozzles and the manifold feed channels. 4 Document this procedure with images, as damage can occur if prybars are jammed in the wrong area. If the nozzles are not Manifolds fail because of the way we put them together, not because of the way we take them apart.

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