Cleaning aluminium off polyurethane

Try Mek (pvc pipe joint cleaner) or Acetone.

Foam Eater or gunfoam cleaner from screwfix (pg 113 in the catalogue)

Robi

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In article , Ed writes

I'm glad I saw Robin's reply before posting mine, as I had thought set polyurethane was not soluble in any organic solvent. However, one of the ingredients (2-aminoethanol, or ethanolamine) is pretty alkaline (and is probably acting as a reagent not a solvent) and might etch the aluminium. I would suggest you test it on some offcuts first.

If not, you may have to resort to other means. Whereas epoxy resin can be softened by heating, this is definitely not recommended for polyurethane, as its decomposition products are very toxic.

For such jobs as this, assuming you have a couple of items and not a thousand, I find fingernails are as good as anything - remove the bulk with a stick and finish off with your nails when doing something like watching the box.

This might be fiddly for a threaded part, so alternatively it may be worth trying a tight-fitting plastic nut (a self-locker might do it)* or making a plastic thread chaser. Anything which is softer than aluminium but capable of providing a firm surface (renewable if necessary).

Never tried this precise job, just offer these thoughts FWIW.

David

Sodium hydroxide solution will effectively remove aluminium from polyurethane foam, and if used in judicious concentration, perhaps molar, will leave the foam untouched.

A copper sulphate and common salt solution will have the same effect, but be a bit slower and more controllable. It may stain the foam though.

:)

To clean foam from aluminium however, heating in air at a responsible temperature, perhaps 450 C, will do the job. You will probably get cyanide, carbon monoxide, etc formed. Carbon and nitrogen will diffuse through and mingle with the outer layer of aluminium despite any oxide layer - but it ain't iron, and afaik it won't case-harden it.

There used to be a product called LS-13 which worked reasonably well (if you can get ahold of some, wet with product, wait a minute, and rinse off in water). There are still similar-ish products available to the semiconductor industry, especially those used to clean solder resist and/or varnish from boards, which will clean off many polyurethanes - but a polyurethane designed not to be removed may well not be removable, except by burning off.

Most builder's type PU foams should yield to simpler chemistry however. Try Foam Eater. Note, it's highly toxic. Very nasty stuff.

The usual solvents almost certainly won't work.

Good catch!

I didn't know that Foam Eater contained ethanolamine, thought it was just diethylene glycol ether.

Looking at the MSDS, it contains 10-30% ethanolamine. It almost certainly will etch Al. Probably too fast to be useable too, although perhaps worth a test.

The circuit board cleaning compounds I mentioned are mostly meant for cleaning copper - I don't know offhand which are suitable for use with Al, you'd have to look it up. It's quite likely there will be at least one that's suitable though, for instance I'm pretty sure Electrolube (and probably most other suppliers) do one that's specifically Al compatible.