Acid eats rust.
Acid also eats metal parts.
Any acid will quickly remove rust, so will sand blasting or an angle grinder.
Fast brutal and usually very damaging.
Try putting a piece of iron or steel into ANY acid, and leave it there for a month, there will be nothing left to remove.
Now try something very different.
Make up a VERY strong alkali solution of lye (caustic soda) (NaOH) in water.
Toss in some Zinc chips, and boil it up in a steel container.
It will convert Iron oxide (rust) back to pure iron. The hotter and stronger the solution, the faster it works.
It not only stops rust, it actually reverses the rusting process.
Very strong alkali has no effect whatsoever on iron or steel, you can leave a part in there for a year and it will not have any effect at all. That is the secret.
It will however rapidly dissolve any non ferrous metal parts, so make absolutely sure there are no brass or aluminium parts in what you are de rusting.
Not only will it reverse the rusting process, the part will stay rust resistant for a very long time without painting or any other treatment.
The trick is not to remove rust, but to reverse the rusting process.
The strong alkali solution also quickly strips and dissolves paint and grease, which is an added bonus.
Putting iron or steel parts into any strong acid to remove rust, is like using a shotgun to clean a wound.
Last edited by Silver Shadow; 10-08-2012 at 01:37 AM.