I have a bunch of used c-pap face masks with magnetic clasps that I would like to recover the magnets from. Unfortunately the clasps consist of a magnet embedded in very hard tough thermosetting plastic. Sawing or cutting the clasps is too likely to break the magnet inside (broke two already), and the plastic can’t be burned off because that would probably exceed the Curie limit of the magnets. Online research advises me that thermosetting plastics are extremely resistant to solvents; at least neither the kerosene or acetone I tried did a thing. If I could even soften the plastic some that would make chipping it off less laborious.
I’d start with a blow dryer to see if I could loosen up the plastic enough that a razor blade could cut through it. Hot/boiling water might work as well.
I know you said sawing won’t work, but maybe a dremel since that’s a bit more controllable. Even if it’s just to get a score line around it so you can use something to pry it apart.
Another option, depending on how badly you want these magnets, would be to use sandpaper and elbow grease.
Do you happen to know what kind of plastic it is?
thermoplastics, by definition, soften when exposed to heat and can be repeatedly reshaped by heating and cooling. Thermosets are usually at least partially cross-linked and therefore do not generally soften when exposed to heat (although they will degrade and essentially break down if the heat is high enough, which will destroy the material for any future use). Try using a heat gun to see if the material softens and becomes pliable. If so, you are good to go.
Nope, at least not until you set the plastic on fire, which as I said would probably damage the magnets. Definitely thermosetting.
Paint stripper?
In particular one based on methylene chloride. That stuff will eat or soften a lot of recalcitrant polymers.
You can buy all shape and size of neodynium and ceramic magnets online for fractions of a dollar per unit at Amazon.com and other retailers. Is it really worth your time to try to cut/melt/burn a thermosetting plastic housing to extract these magnets?
Stranger
Who knows? It’s not like I “need” them– I end up donating them for crafts projects. I got started doing this because I use a c-pap and decided salvaging the magnets was worth it because the price was right (free). After some trial and error I worked out a method to efficiently do this with my c-pap’s magnetic clasps; but the clasps in this other model (I asked around for donations) is far more intractable. Just stubbornness I guess but I hate being defeated by inanimate objects.
You need something really unpleasant, like hot N-Methyl-2-pyrrolidone.
Generally, when I want to do this, I cut the plastic as close to the magnet as possible, and then nibble away the rest with big wire cutters.
That’s what I ended up doing and it’s really slow and laborious; I was hoping to streamline the process.
P.S. You do?
I always try to save rare-earth magnets.
I have a huge collection from hard drives.
I think they banned those strippers a few yrs ago, because I was trying to find some, and couldn’t (at least in non-commercial use). Maybe some industrial aircraft/automotive products have them, but not in general hardware stores. But if you know of a brand, please let me know!
There are soldering iron tips that are like an Xacto knife blade. When up to temperature this should allow you to slice along the magnet surface quickly to remove almost all the plastic, with little heat transfer to the magnet. I use them for various plastic cutting and removal. But be careful. They are sharp when new. Check a hobby or electronics store for a cheap iron that will accept such a tip. A soldering iron is not expensive and comes in handy now and then.
Methylene Chloride; Regulation Under the Toxic Substances Control Act (TSCA)
A Rule by the Environmental Protection Agency on 05/08/2024
Just curious, are the magnets “glued” or stuck to the plastic, or once you get through the plastic does the magnet come out cleanly?
If it’s glued there some chance of dissolving the glue with some kind of solvent.
Another vote for “what kind of plastic is it?”. For instance, if it’s anything containing acrylic or acetate, such as the popular ABS, then acetone (commonly sold as nail-polish remover) will do the trick.
I certainly recognize the sentiment.
But a LOT of stuff is made to be undisassemblable (is too a word, neener).
I’ve decided some engineers are simply more determined to put it together than I am determined to take it apart.
The latter, but since the surrounding plastic form-fits to the magnets you have to chip them half or more free before you can get them out.
So, the magnets are cast into the plastic.
This seems like the canonical example of “more trouble than it’s worth”.
As noted above, more recently, but not exactly a surprise. I think anything with methylene chloride vanished here in Oz sometime before. Last time I looked, available paint strippers were much tamer. Methylene chloride is horrid stuff. I remember using strippers based on it ages ago, and it behaved like something born of the underworld. Just a drop on the skin stung for ages. But it ripped into just about any paint you tried it on.