MoldMaking Technology

AUG 2018

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Page 44 of 83 43 insulators and high-temperature purging compounds when switching from a dark to a light color. Production Issues Preventing manifolds from fully expanding during start-up is number one on the leak list or is the root cause of total encap- sulation. Many manifolds and components are designed to be completely dependent on an appropriate soak time to fully seal the rear of the nozzle to the manifold, and the nozzle's front seal (which is radial) to the cavity gate. However, production requirements usually rule, so unfortunately, the "hurry-and- get-it-running" mandate is all too common, even as more emphasis is directed toward educating processors about how critical a proper start-up is. Molders need to either use the manufacturer's recommended procedures or create their own and be diligent in doing so. Other mistakes, such as shutting off the water and leaving on heaters over a weekend, will quickly degrade the plastic in the manifold as well as critical seals and o-rings. This also will cook applied lubricants in piston cups and other valve-gated components. Another bad practice is turning the water on after the mold has reached the processing temperature. This does not speed the start-up process. A better idea is to heat the manifold before the nozzles and bridge. This allows the manifold ports to slide more easily across the rear of the nozzles during expansion, minimizing the drag between these two components. Operators should perform the reverse when shutting down the manifold. This approach—because nozzles heat up quicker than manifolds— reduces the chance of burned material, as the operator waits for the manifold to reach processing temperature. Another big concern is the presence of contaminated res- ins in silos, conveying lines, gaylords, hoppers, hoses, dryers, grinders and any other resin paths. Proper cleaning before the plastic hits the mold is essential because these resins stick and clog manifold flow passages, nozzles and nozzle tips. Controllers, electrical connectors and cables also need a maintenance plan for periodic inspections and testing as well as a designated storage area. Maintenance Issues Repair technicians must clean and inspect moving parts for wear, damage and lubrication levels, especially when the tooling is close tolerance, and operating in unclean condi- tions that are high in heat and under pressure. Otherwise, small scuffs turn into minor leaks that result in major leaks. Improper removal, cleaning and reassembly of delicate tool- ing and critical seals will influence manifold performance and, in some cases, void the manufacturer's warranty. It is imperative for repair technicians to possess a working knowl- edge of the impact of heat expansion and residue levels on preload, seals, valve-pin function and stack height. Electrical knowledge is also key for proper heater and thermocouple inspection, testing, removal and installation. Valve-gated systems that are air-based, oil-based or mechani- cally actuated add another level of complexity for technicians even though they all contain the same basic parts (valve pins, valve-pin bushings, cannisters or piston housings, pistons and a variety of internal and external seals). A lack of proper lubrication, rough handling of components during a PM or incorrect assembly will cre- ate dings, scratches or burrs that cause wear. Technicians often overlook the cleaning of air lines through the mold base and small inlet holes that actuate the valve pis- tons, which affects operating pressures. Valve-pin actuation pressure reduces when these lines and holes get clogged from dirty air or off-gas weeping. This results in uneven and sluggish movement from one cavity to When a manifold runs too long in between cleanings (or in this case about 1,500,000 cycles) a high level of residue contamination clogs air passages in the plates and components. Technicians must clean all plates and tool- ing thoroughly before reassembly. Cleaning this 48-cavity mold by hand would be mediocre and time-consuming, so an ultrasonic tank is indispensable in this instance.

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