Maybe this has been posted before, but I was unaware of this.
I have been assembling my quadcopter and as advised have used red loctite # 271 to lock the metal nuts and the prop mounts.
I have used it all up and bought some blue loctite #243 and have used it on some of the nylon nuts last night and have just noticed today that it has eaten away the part of the nylon bolt inside the nut and the nylon nuts are soft and easily split in two with my thumb nail.
I must hold my hands up and admit that I didn't realise that threadlock could do this to plastic, but thought I would bring it to everybodys attention.
Martinp
Comments
Update for all
On re-examination of the bolts I must confess that the loctite has only actually eaten the polycarbonate bolts and nuts, it doesn't seem to have had the same effect on the nylon ones. I'm still going to keep it well clear of any plastics in the future though. : )
I think that before we say that a particular chemical degrades another one, we have to be sure that the chemicals/materials we are testing are actually what they claim to be.
You would be very surprised at what gets passed off as 'plastic' when you buy parts online, and you would be horrified to learn than some of it may actually be recycled medical waste, such are the horrors to be found in the market that is fasteners, ESP. when they are sourced in Asia.
A quick check of the Loctite site and the relevant data-sheets make it vey clear exactly what a given product is compatible with and when it should be used. The moral is RTFM, or in this case RTFDS.
Thanks all for your individual experiences, I don't feel as much of an idiot now for using it on the nylon bolts, I'm wondering now if I should strip my quad back down and replace all the nylon connectors in the frame or just leave them now as the damage is done. They don't seem to have deteriorated any, but there again it could be quite spectacular if the frame came apart in mid flight!!
It seems to me that besides the plastic eating theory several people have mentioned, Locktite expands as it dries, with disastrous results for plastic frames, etc.
Again, a good product for metal on metal, but the moral seems to be, keep away from plastics.
An expensive lesson in my case.
Turned an R/C Graupner Bell helicopter into a display model.
yep.....
They are mainly self locking because when under a minor torque they stretch , thereby pulling the nut threads into the bolt threads more strongly, the key is that you do not over tighten them so that the "stretch" is made permanent and they fatigue and then fail. A lubricant only really works if the surfaces can move over one another freely, even if you loosen off a nylon nut & bolt they will still self lock to a certain extent if the threads are molded correctly.
I spent a significant amount of time looking at Nylon, PC &PE when we produced a cheap mechanical plug-in timer that had to run reliably 24/7/365/5
That is because despite what you may hear , nylon is usually self lubricating:- that means a form of lubricant is expelled from inside the material as part of a continual chemical process.
It should not be able to attack nylon 9 or nylon 66, it sounds like there is something else mixed in with the nylon (maybe PC, ABS), if the nuts are from a China supplier then that would explain it, the nightmare of my life was bloody Chinese plastic suppliers and their fiddles.
Get a nut and drop it in some nail varnish thinner.
check out this guide
http://catalog.gpi.net/Asset/Chemical-Compatibility-Ver-6.pdf
Thanks all, as I said I was unaware that it could attack plastic in that way.
@Chris, the various grades of locktite come in different colours, red, blue and green I believe, you're supposed to select the correct grade according to components that you are locking and what their duty is.
@Ellison, I was simply taking on board the general advice of the forum that vibration is a problem and nuts can undo themselves.
@Jesse, you're correct I had to use the cooker to release two of the spinners (after I had removed the spinners from the motor shafts)
@Sgt Ric, I'll follow your advice in the future and only use it in metal to metal from, and I'll use blue or green and avoid red I think.
Major fail.
Now I only use it for metal to metal!
The locktite does not dissolve the plastic, but will cause it to become extremely brittle and crack easily. This does not happen with all plastics however, I have a feeling polyethylene would be ok with it. In RC Helicopters the rule is that locktite is used for metal to metal, and CA (superglue) is used for metal to plastic connections. I always use one or the other when assembling any model, and clean the threads first with alcohol to remove any oil before assembly.
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