I can't believe the words 'urethane' and 'foam' don't occur anywhere in this thread. Let's rectify that.
Ok, so urethane foam decays over time, becoming a sticky, highly corrosive mess. It has to be removed from anywhere it's found in old test gear. Typical uses were:
* Air filters. (How badly this works out, depends on whether the fragments fell into or out of the equipment.)
* Sound damping inside cases. (Greatly dampening the enthusiasm of restorers, when they see the resulting mess.)
* Padding, to hold down PCBs or whatever. (Turning to gunk, dropping corrosive fragments all through the gear.)
* Molded shock-absorbing structures in carry cases. (Where it destroys whatever precious, high-cost item it was supposed to protect.)
If you're lucky, the mess can be relatively easily scraped off, and loose bits extracted with compressed air or a vacuum hose.
Then dealing with corrosion it caused is the same as for any corrosion.
But there are two worst cases:
* Where it's turned to tacky molasses, stuck to complex parts. Solvents and abrasion are the only way.
* Large blocks of sound-absorbing urethane foam are usually stuck on with a kind of very robust double-sided sticky tape. This stuff is even worse than the foam, because it's really, really hard to remove. You can scrape the foam off easily, but that leaves the tape. The tape glue is stronger than the tape, so it can't be peeled off (at room temp.) The tape seems to be resistant to typical solvents, so they can't be used to soften the glue underneath the tape. But otoh the tape is mechanically weak, so trying to peel it just gives you tiny pieces.
I really hate this stuff.
When it's adhered to metals, it can _sometimes_ be removed fairly easily by using a hot air gun to heat up the metal. This softens the glue, and if you're lucky the whole tape can be peeled off in one piece (or many.)
If that doesn't work, try heating the metal to just below 'too hot to touch', and rubbing the tape off with finger tips. I didn't find any substance/structure yet that works as well as fingertips for forcefully rubbing the tape off, so that limits the upper temperature for this method.
But right now, I have a plastic case off a paper tape punch, that had a lot of urethane foam (decayed to crap.) Hence lots of this tape left after scraping off the foam. The plastic is probably ABS, and so hot air gun heating is out of the question.
It sort of peels, but breaks frequently. Ultimately I'll get it all off that way, but it's a pain.
Has anyone a better method?