Removing rust and scale

As you can see i have tried to clean some metal parts and old tools with the Phosphoric acid about 4-1 ratio,
I would say the results are mixed, first up it is real good on body steel or black steel,
But i would not use it on any cast, tool or spring steels, or any other steels or alloys
I had a failure with a piece of spring steel which shattered after being left in over night.
So some advise has been that the acid can make the spring steel metal more brittle, so I guess there is some truth in that.
Some good lessons i have learnt here,
Jim

Was just revisiting this old post, and you guys came up with same great solutions (no pun intended!) on batching up different concoctions to descale and de-rust parts.
Whilst doodling around with those wheelstuds, I turfed a brake drum and safety bead off a split rim into a plastic drum of molasses and water, having no great time frame to work to.
The safety bead was quite grungy with rust, brake drum so-so. I know it is regarded as a slow process, and does seem to work better on really hot days, but I took it out once a day, scrubbed the black filmy looking crud off it, gave it a touch up with the wire wheel on a 4" angle grinder and after about the third try, came out looking pretty good.
Does anyone know if there are any long term effects on metal (NOT alloys) by leaving them in this solution for a few days? Seems that whilst it has that slimy film on it, keeps light rust from reappearing. Reason asked is it may be some time before I reassemble everything and as the inner surface of the brake drum is in pretty good nick, don't want to undo whats been achieved. I even thought that by drying it out with compressed air and then just giving it a very light coat of some el-cheapo $2 shop spray paint to keep the rust at bay, can always wipe off the brake surface of the inner drum with thinners before putting back together. Outer drum paint will soon wear/burn off. Or is there some sort of spray on compound that you would use.
Dave.

Dave, I have some sheet metal cab parts in a molasses bath and they have been in there over a year. I checked them the other day and they look as good as new. There are some very feint scores, which were for marking out holes in the factory, and these are still visible, so there was nothing except rust being removed, even after a year.

G'day Dave, I've left metal parts in molasses for longer periods with no bad effects. If you want to take them out to make room for something else, then I paint the part with Penetrol or if still a bit of deep pitted rust then use phosphoric acid which converts the rust. The Penetrol tin says not to use it under two-pack paint, but I have done that after several months when it is completely dry/cured.

Geoff

Just having a look on Google and see some bloke getting good results from white commercial grade vinegar. He used about half a cup on a few rusty washers, but added a couple of capfuls of common old Hydrogen Peroxide. About six hours later, hosed them off and came up pretty damn good.
Dave