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Author: Subject: The old aspirin trick
sodium_stearate
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cool.gif posted on 13-9-2022 at 17:40
The old aspirin trick


Many years ago I learned a neat trick for very easily and quickly
stripping off the enamel from an enameled magnet wire.

Take an aspirin tablet, place it on a suitable surface such as a scrap of wood.
Lay the enameled wire on the aspirin. Heat both from the top, pressing
gently down, using a hot soldering iron. The aspirin turns brown and starts
bubbling as the enamel burns off of the wire. The result is a very clean
bright bare copper wire, and a somewhat melted brown remaining portion
of the aspirin tab.

Great useful technique when one needs cleanly stripped enameled wire
ends. Now for the chemistry question: What is going on there?
Why does this work so well to eliminate the enamel that was on the wire?




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[*] posted on 13-9-2022 at 18:54


What kind of enameled wire? Urethane or polyimide?



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sodium_stearate
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[*] posted on 14-9-2022 at 14:52
The old aspirin trick


The kind of enameled wire that is coated with an insulating layer.
That's what kind it is.

As for the chemical makeup of this enamel layer, your guess is as good as mine.:D

[Edited on 14-9-2022 by sodium_stearate]




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[*] posted on 14-9-2022 at 16:02


Either way, the aspirin might be doing a couple things. One is melting and forming a protective layer around the copper so it can be heated without oxygen. It might also be reacting with oxygen or formed copper oxide, itself being oxidized in the process. If that cant prevent oxide formation, it might also be acidic enough to remove the oxide that forms on the copper and leave a shiny surface.



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[*] posted on 14-9-2022 at 20:58


It is probably forming phenol which is known to be exceptional at removing urethane coatings. See: https://www.sciencedirect.com/science/article/am/pii/S030094...
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[*] posted on 15-9-2022 at 11:28


Quote: Originally posted by sodium_stearate  

As for the chemical makeup of this enamel layer, your guess is as good as mine.:D

[Edited on 14-9-2022 by sodium_stearate]


Urethane coatings melt at soldering temperatures, polyimides don't. Pretty easy to tell them apart.




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[*] posted on 15-9-2022 at 23:50


Quote: Originally posted by sodium_stearate  

As for the chemical makeup of this enamel layer, your guess is as good as mine.


Nylon 6/6
Polyurethane

Attachment: Nysol Safety Data Sheet.pdf (146kB)
This file has been downloaded 205 times





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[*] posted on 16-9-2022 at 11:44


As I understand it the PU coatings are the cheapest and usually "good enough". It's also pretty much "self fluxing", at least on the smaller wire diameters.



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[*] posted on 18-9-2022 at 02:07


Oh yay, I can finally teach instead of only learn in this forum!

Aspirin will pyrolyse largely into phenol, among other things. I once did that, for the purpose of getting phenol, to use as a nylon solvent, to smooth out nylon 3d prints. It worked! Nylon isn't easily dissolved by most solvents, but phenol does it well! Whether it does anything to polyurethane I don't know, but it remains a powerful solvent so it makes sense it would work on most laquers.

So, you heat it up, it pyrolyses to phenol, which happily dissolves the laquer which is now also hot and therefore all melty and reactive. The mix of phenol and laquer can probably be absorbed by the bulk material of the aspirin pill like a sponge, and therefore is removed from the wire. Any phenol left on the wire will evaporate at soldering temperatures so it won't affect the soldering.

Edit: Also, thanks for the tip. I've never known in the 10+ years I've been an electronics designer lol

Quote: Originally posted by Fulmen  
As I understand it the PU coatings are the cheapest and usually "good enough". It's also pretty much "self fluxing", at least on the smaller wire diameters.


Yeah that's more "theoretically" solderable than it is practically. I've never come across enamel wire that was easy to solder. Sure, the ones that aren't sold as solderable are basically impossible to solder without mechanically removing the enamel, but the solderable kind is still way more annoying to solder than a bare copper wire. It almost always has to be a two step process of first tinning the wire thoroughly, and you need to ensure it burns through the enamel, and then you can solder it.

[Edited on 18-9-2022 by Junk_Enginerd]
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cool.gif posted on 20-9-2022 at 15:26
The old aspirin trick


Thanks guys. Phenol is a great explanation.
Learned this trick from a guy who was using fine enameled wire as
jumper wires on a miniature circuit using many ICs.

Can also use 30 ga. kynar insulated wirewrap wire for these jumpers,
but this guy claims that the enameled coil wire is less bulky.

But please do try the aspirin trick some time. You will be amazed.




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[*] posted on 21-9-2022 at 11:53


What does it do to the soldering iron tip? The tips for my iron are 30 bucks a piece, so I'd hate to wreck one just to strip enamel wire. Most tips are iron plated copper, when the iron plating is damaged the tips dissolve pretty fast.



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[*] posted on 24-9-2022 at 11:19


Good thought. Last time I tried the aspirin trick I was using an old
soldering iron with tips I did not really care about. Since then, I've
moved on to using a nice temperature controlled outfit that has
good durable tips, so having hot boiling phenol on it probably is not
a good idea. Probably best to use an old iron with a junk tip for this.:D




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[*] posted on 2-10-2022 at 07:54


Quote: Originally posted by Twospoons  
What does it do to the soldering iron tip? The tips for my iron are 30 bucks a piece, so I'd hate to wreck one just to strip enamel wire. Most tips are iron plated copper, when the iron plating is damaged the tips dissolve pretty fast.


I can't promise anything of course, but I can't imagine anything in an aspirin would damage it. Phenol is just an organic solvent, so it won't attack any metal afaik. Maybe the -acid part can damage it though? If I recall correctly, salicylic acid breaks down to phenol and acetic acid. Acetic acid isn't too aggressive on iron, but it's a slight risk I suppose.
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