Re-plasticising of plastic – old watch.

[gerry maddenParticipant @gerrymadden53711]

I have a 47 year old Seiko watch. Unfortunately the manufacturers in their wisdom at the time chose to incorporate a couple of plastic components. These have now succumbed from the from aging and embrittlement. Fortunately one of these plastics, a little gear, is now available in steel, for repairs.

The other part is a slightly complex moulded ring, roughly around 29mm diameter 2x2mm in section. This holds the face in place when the back is tightened. Over the years, at cleaning time, this ring has been found cracked and has been repaired by epoxy. However, the ring now appears to be crumbling at contact points and releasing particles in the movement.

I have toyed with the idea of making a new one from something like delrin of ptfe but this wont be an easy task because of the various cut-outs and other features.

In the meantime I have managed to find “new” ring, well, “unused” one (they are rare) and Im wondering about using it in the watch to save me some hard work. However I suspect this ‘new’ part was probably manufactured around the time of the original. It may therefore already be embrittled to a greater or lesser extent, depending on storage temperature.

A few times the subject of ‘plasticiser migration/out-gassing’ has been described on this forum. What I’m wondering is whether there is anyway to re-infuse plasticiser into this material and hopefully give the part a longer lease of life?  … I’m thinking of some kind of vacuum process, such as used to infuse preservative into wooden fence posts. Anyone have any knowledge of this?

Gerry

[Dave SParticipant @daves59043]

No idea about reinvigorating it, but if you have your hands on a complete unmolested part I would at least take measurements and make a drawing (or better a CAD model) for future use.

If you can model it then a 3D print would be viable.

There may be features which are artifacts of the original manufacture method which could be simplified.

Dave

[David JuppParticipant @davidjupp51506]

Only certain plastics have plasticisers incorporated (most commonly PVC).  I’m very sceptical about any success with trying to re-incorporate plasticisers – they are usually incorporated when the plastic is molten.

Many plastics don’t need plasticisers.

Deterioration of plastics is most commonly due to exposure to UV light.  Temperature can have an effect, and some chemicals/oils might cause stress cracking of certain plastics.

Depending upon the material, an unused part might be almost as good as when it was made.

[gerry maddenParticipant @gerrymadden53711]

@ Dave S – yes you are absolutely right.  I have already planned to do this. I did try to reverse-engineer the old one but it was a hopeless case. Being so badly out of shape after so many repairs that it was impossible to get sensible diameters off it. The new one is nice and round, and I can use my toolmakers microscope to measure it reliably.

As for redundant features, right again, there may be some which I can ignore. I have the watch so can do some ‘trial fits’ and see what collides and what doesn’t.

 

@ David Jupp Thanks for your information. This ring sits under the face, not above it so if out of any UV. Of course there could have been oil vapours from the lubes used in the watch which might have attacked the plastic.  I am hoping the new one is in better condition than the old but other than by fitting it, I can think of a way I can be at all sure. Its not so much the cracking that concerns me as the arcs of the ring tend to stay in place until the back is removed. It’s more the crumbling at presure points which sends hard particles/dust around the movement. I don’t really want to have to service this watch again in my lifetime 🙂

Gerry

 

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