How to remove rust or paint from lots of pieces of small hardware
This is not an energy-saving idea, but it could save money, effort, and/or time.
I had a bunch of screwdriver bits that were rusty. This would also work on other small tools (allen wrenches, for example) or other small hardware -- nails/screws/nuts/bolts/etc.
Anyway, here's what you need:
- Cup-style mounted wire brush
- Heavy-duty plastic cup, a little bit wider than the wire brush
It should be pretty obvious to you by now, but if it's not...put the rusty stuff in the cup, mount the wire brush in the drill, stick the mounted wire brush in the cup, and pull the trigger. Do it just like mixing a milkshake. As it's running, reciprocate it in and out so the rusty items migrate above and below the wire brush.
After a couple minutes, they're mosly perfect. All that's left is rust that was in small spots, like the points of Torx and Philips bits. That will have to be removed by holding the bits individually in a Vise-Grip to use with the wire brush (or, if so equipped, a wire brush on a bench grinder).
Another option I thought of is a rock tumbler, but I don't have one. It may be pretty easy to make one from random junk around the house...but it would probably take a lot longer.
I've used some stuff from the Walmart automotive paint section called Klean-Strip Rust Remover "Jellied Rust Remover." It worked surprisingly well, and it says to keep away from paint so it probably strips paint away pretty well too. I'd try to electrolytic method Erik suggested first, then I'd try the Klean-Strip Rust Remover to get anything that is stuck on after that.
For chemical rust removal - You can get phosphoric acid from Home Depot for ~$15 per gallon. Commercial rust removers contain mostly phosphoric acid and come out to $30-$100 per gallon if you do the math. Phosphoric acid is nice in that it dissolves rust much faster then good metal, so you can soak your parts in it overnight, and not worry about loosing good metal. If you want quick and cheap rust removal and don't care if you remove some good metal get Muriatic Acid ~$7 a gallon - used for cleaning concrete. Make sure to wear organic-vapor charcoal-canister-type respirator, goggles and chemical rubber gloves - that stuff is nasty even if you work outside.
I've used electrolysis, but it will not work well on small parts as you would need to attach an electrode to each bolt and nut. Also, electrolysis is pretty much a line-of sight process, so you would have to rotate each part to get all sides clean.
wendywindy - I tried several brands of phosphoric acid based commercial rust removers, and don't recommend them. If you have more then just very light spot rust - phosphoric solution will take several hours to dissolve it, and usually just dries up before it does the job (and it's tough to remove once it's dry), so, unless you can submerge your parts in to phosphoric acid bath, I suggest you try other means.
For sheet metal, you most likely will have to cut-out all of the affected metal and weld-in a replacement patch, as rust mostly starts from behind the panel and you don't see it till you start getting holes in the metal. If you have rust because of external paint damage, then just wire-brush and paint over.
For structural steel - wire-brush on a drill or an angle grinder, though sand blasting is preferable if you have the equipment.