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how to eliminate flakes caused by tunnel gate at part ejection?
2

how to eliminate flakes caused by tunnel gate at part ejection?

how to eliminate flakes caused by tunnel gate at part ejection?

(OP)
We are molding glass filled PBT and are getting small specks of material that come from the gate area when the part is separated from the tunnel gate during mold opening.  These small specks then stick to the mold face (where they are smashed flat)and have the potential of ending up on the parting line of the finished part on the next shot.  We have tried sharpening the gates, using different shapes of gates, gating into the movable or stationary sides of the mold and yet the problem persists.  Does anyone have any suggestions or is this to be expected?

RE: how to eliminate flakes caused by tunnel gate at part ejection?

2
One thing that I have seen happen often is that there will be a sharp edge on parting line above the tunnel gate or where the downspout transitions into the cold slug well. When the downspout is pushed out, the back of it will rub on this edge and break off a small piece of plastic that is then left in the tool. If this is the case, a large radius on the edge will eliminate it. Also, check for delamination in the runner. If the downspout is deep and the plastic is delaminated, the skin can crack when it is pushed out and leave flakes behind. Hope this helps.

RE: how to eliminate flakes caused by tunnel gate at part ejection?

(OP)
Yanish- thanks for the response.  We have seen the sharp edge problem in other cases and it has helped to radius them.  In this case however, there is no evidence of the downspout being scraped on the way out.

RE: how to eliminate flakes caused by tunnel gate at part ejection?

we have tried to eliminate that same problem and ended up using a blast of air to blow off the specks between cycles

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