Now we discuss the pros and cons of sending a flashed manifold out for repair versus performing this task in-house. This article will begin to deal with the disassembly, troubleshooting, cleaning and reassembling of a typical, and flashed 16-cavity valve gate manifold.

Obviously there are many different makes of hot runner manifolds currently being used in the making of plastic parts today. Relevant (and most critical) design differences that will affect a manifold’s potential to leak concerns how the nozzles, sprue and any cross-overs (or bridges) are connected to the manifolds. These components are either bolted to, threaded into or rely on a compression stack, and sometimes a combination of all three. Each type has its trade-offs concerning required maintenance of the system and the overall ease of installing replacement parts, such as thermocouples, nozzles, nozzle tips and heaters.

  Regardless of flowery forecasts made by manifold sales folks, the ease at which a manifold system can be maintained will not be apparent until the system has some hours on it (a million cycles would be nice), giving internal components, pockets and tooling clearances time to collect vent residue (greasy film or powders) and weepage (gooey, degraded plastic).
Also impacting manifold condition are molds stressed through weekend shut-downs and hurried Monday morning start-ups along with touchy gate/valve pin tip configurations that promote out-of-spec gate vestiges—forcing processors to fiddle with the parameters.

  Some systems require a complete teardown just to replace a nozzle heater or thermocouple. On others, if specific components are disturbed or removed they too must be completely disassembled and cleaned before reassembly to ensure proper component stack dimensions.
The level of disassembly/reassembly (labor hours and skill level) required over time to replace basic components along with the usage (cost) of the components will determine the true ease of maintenance with the system.

  But obviously, any manifold that encapsulates easily (easily meaning that if a strict start-up procedure is not followed to the letter, the system has the capability to blow at multiple locations) will not be a popular choice among those of us who have to fix or run them.
For the sake of fairness and consistency, we will examine areas of concern regardless of the manifold make and model. 

 In manifold maintenance, the same five basic principles that apply to a mold also apply to an encapsulated manifold. The only difference is that troubleshooting the source of the leak could be ongoing throughout the repair process as plastic is removed and more tooling is exposed—allowing better visual inspection of seal areas and components, right up through assembly of the cleaned components.
Here is an overview of the five basic steps that will occur on an encapsulated system:

1. Disassemble
Remove the valve pins and clamp plate, and disassemble mold to gain visual access to the back of manifold.

Pay attention to tooling clues that can point to the leak source (bent, broken or galled valve pins and the amount and type of residue around the pin).

Remove enough plastic as to facilitate separating the manifold and electrical box from the plate, so that you can clean these components separately.

2. Clean
Clean clamp plate, manifold plate channels, counter-bores and valve pins (ultrasonic).

Clean nozzles, heater and thermocouple wires and manifold (by hand).

3. Troubleshoot
Inspect seal areas of components for obvious cracks and plates for hobbing and bolts for looseness.

4. Assemble
Reassemble to stage one.

Electrical check.

Final reassembly to stage two.

5. Final Check
Electrical check ramping heaters up to processing temp with water flowing through appropriate channels.

 Let’s begin with the mold in the press. The first noticeable sign of a flashed manifold is usually when smoke is seen rising from the top of the stationary side, or plastic oozing from places it shouldn’t … then the panic and finger pointing ensues.

 But there are other, more subtle clues that might point to a manifold leak, such as molds that produce periodic incomplete shots, shorted out heaters and thermocouples in a particular quadrant.

Paying attention to these signs can alert a processor to a possible manifold malfunction and allow them to shut a mold down before the manifold is totally encapsulated.   

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