Rust scale removal

A phosphoric acid dip works great for items you'll be painting. It leaves a black (iron phosphate?) stain on the surface. This is the main active ingredient in many rust preparations and rusty metal primers. I buy it as "Lime Away" at my local Fleet Farm.
Many here swear by a solution of vinegar and table salt. Slow, but just leave it in the bucket. be sure the part is completely immersed, it will leave a mark at the liquid surface.
If you'd like to strip that rust off FAST, use Muratic acid. Follow quickly with a water rinse and a dip or spritz of a base solution. I use my purple degreaser spray bottle. if you don't cancel out that acid quickly, you get an almost immediate thin film of rust.
There's also an electrolytic method. I don't remember the details.
Karl

The American way is to throw it away and buy new import stuff. (but, the right menagerie of wire brushes is the best!)

Electrolysis. No question about it (and very widely and regularly described - just search).
Electrolysis is effective, but it does take days. OTOH, you can just leave it running unattended, so that's not a big problem. Very low labour overall.
Phosphoric acid doesn't remove anything, it converts existing stable rust into a reasonably good paint primer. Useful, but it's not a removal process.

works well, takes overnight or so. Apparently now available at AutoZonws instead of just mailorder.
-- Regards, Carl Ijames carl.ijames at verizon.net

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I use muriatic acid quite a bit - it is the fastest rust remover (on the order of minutes, depending on the severity of rust). The base rinse isn't necessary if you do a good water rinse. The hotter the better. The part will rust even if all the acid is rinsed off because it is so clean - there is no oxide coating. I *immediately* dip in my wax solution (see Iggy's thread). You can *see* it rust if it isn't protected.
One time I had a badly pitted part that I de-rusted and neutralized with some sodium base (TSP maybe). I got rust back right away, so I de-rusted again and it rusted again! I de-rusted a 3rd time without the base neutralizer and it was OK. I concluded that the acid and base reaction was making sodium chloride (table salt!) which was "sticking" in the pits and promoting re-rust.
HTH, Bob
Wait, wait!! The above is a "line" that I have believed and repeated, but I just had some second thoughts. If it's the clean-ness of the derusted part that promotes rust, why don't just-machined surfaces rust as fast? What could be cleaner that freshly cut steel? So I take it all back about the "why" and just stick with what I do and that it works: 1. immerse in acid 2. hot water rinse (& scrub off the crud) 3. protect with wax (oil works too)
Bob
BTW - "rust removal" is probably in the top 3 FAQ's - there is a ton of info in the archives.

1. Sandblasting/Bead blasting
Requires a HUGE amount of air (think compressor on trailer) Free blasting makes a HUGE mess need eye, ear protection + airline respirator for free blasting Cabinet blasting takes up a lot of room Owning a real sandblaster + cabinet is spendy blasting will remove paint, rust, scale and leave bare metal blasting is extremely effective, no limit to size of parts (entire ships!)
2. Wire brushing
Buy heavy knotted cup brush and heavy knotted disk brush for heavy rust Running angle grinders real tough on wrists/hands (think carpal tunnel) brushes throw wires - eye protection a must wire brushing quickly knocks off most of rust but tough to get it all slow to remove some paint/scale some parts can have rust/scale/paint in areas difficult to brush relatively low tooling cost, can address many jobs quickly
3. Acid dips
Muriatic acid dangerous to handle, potentially illegal to store (Kalifornia) some say acid dips -> hydrogen embrittlement must be followed by neutralizing dip, hot water rinse disposal of chemicals tricky, can be major issue in urban environment real hard to do large parts (truck bed?)
4. Electrolytic derusting
Simple, cheap, effective for small parts (can fit in 5 gallon bucket) Uses garage sale auto battery charger, box of washing soda, some wiring ~ $20 Problem with reaction slowing as anode oxidizes if anode is steel can use stainless but problem with hexavalent chrome in solution - BAD can use graphite, high current density will erode anode over time, $$$ have heard of using lead sheet, don't know good/bad yet ??? Lots of incomplete information on Web about procedure Optimal setting calculation MUST include surface area of part For higher currents, using DC welder has been reported, should work fine can be hard to do large parts (truck bed?) can do spot EDR with carbon rod/cotton batting wetted in solution
5. Chemicals/Other
Naval jelly - never did much for me, extremely slow/weak "rust neutralizers" e.g. Jasco Metal Prep Knorrostol - works really great on small parts, I use it all the time, A+++ ... etc.
Big topic.
GWE

Ive been having marvelous luck with electrolysis.
Gunner, not talking about his leg hair.... "I think this is because of your belief in biological Marxism. As a genetic communist you feel that noticing behavioural patterns relating to race would cause a conflict with your belief in biological Marxism." Big Pete, famous Usenet Racist

Good Stuff. Thanks.
I have remembered one thick liquid I used was called Rust Rem. I am in UK and have not heard of some of the above. Lots of food for thought!
Regards George.