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Whitish mark in the living hinge of flip top cap

Whitish mark in the living hinge of flip top cap

(OP)
Hi, I'm Noel, handling injection molding stuffs. I would to ask regarding living hinge problem in PP flip top caps. We observed a whitish mark in the living hinge of the flip top cap. This happened right after ejection in the mold
Is this normal or if not, what would be the probable causes and why?

Thank you.

RE: Whitish mark in the living hinge of flip top cap

Can you provide any pictures?

RE: Whitish mark in the living hinge of flip top cap

(OP)
The issue is whitish mark in the hinge part of the flip top cap.
My hunch is that a stress whitening occurred right after ejection of the caps in the mold. I suspect that they have in mold closing mechanism in their injection machine which will flex the hinge (before ejection) to provide orientation . Thus, may result to whitish marks. Is this normal?

RE: Whitish mark in the living hinge of flip top cap

Never seen that before.
Could be several things causing it: bad part design, bad mold design or wrong material selection.
Could also be wrong processing conditions.
Needs further investigation.

Paul Kuklych
http://www.improve-your-injection-molding.com

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