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Repairing plastic hinges

Plastic hinges are fatigued - how can I fix them?

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Michael Gilligan05/04/2023 19:12:03
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Posted by Peter Greene 🇨🇦 on 05/04/2023 18:16:06:


You're the one staring at the actual article of course, Rob, but it might not be as bad as you think. I have a daily pill reminder with 7 compartments that I've used continually since 1986. I expect many here have too. I remember wondering at the time how long the 'living hinges' (what the artsy designers called them at the time) could last. But none of the seven has failed in all that time though they've "showed signs of fatigue" for years.

.

I worked at KODAK in the early-mid 1970s, and we were using such hinges on the backs of the little 110 cameras: It was soon convincingly demonstrated that it matters A LOT how soon after ejection from the moulding machine the hinge is first flexed … Get it right and they last for ages, but let it cool too much before that first flex and the hinge is doomed to fail.

Trouble is … the end user doesn’t know whether they have a good ‘un or a bad ‘un.

MichaelG.

Peter Greene05/04/2023 21:49:27
865 forum posts
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Interesting, Michael, and makes sense to exercise the hinge while the material is still partly plastic. For small volumes the hinge could probably be closed by the operator upon ejection from the core, but I wonder how they could automate it for large volumes such as pill containers.

Grindstone Cowboy10/04/2023 17:54:00
1160 forum posts
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Hi chaps

Sorry for the delay in replying, been away on holiday.

It's a genuine Mitutoyo, but unsure of the age as I bought it at a car show many years ago. One of the three hinges is definitely parting company. Not sure if age or storage conditions have a bearing on it, but I can see that the box has bowed slightly so the axis of the hinge pins (for want of a better description) is not a straight line. I guess that puts extra stress on it.

Rob

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