Before:


Oxalic Acid + water = Crazy easy rust  removal! No scrubbing @ all,
just mix and let soak!

Dan  Gorsline.

Use with caution, Oxalic acid is very toxic. Andrew  Campbell.



I'm in the process of cleaning/restoring a Logan 825  lathe, Enco
6x26 knee mill, and many assorted tooling pieces that had been
sitting in the previous owners garage. Somehow they "appeared" in my
shop  back in January!

So far I'm using white vinegar and salt followed by  water/baking
soda rinse followed by HOT water rinse. Non-toxic and safely  dump on
my gravel driveway. Does a great job! In between the first two steps
some light fast brass wire brushing, or even wiping with a towel,
knocks off any rust that the vinegar hasn't taken off. I usually
start a  batch of parts one weekend. While they don't need a full
week, life  happens and I usually can't get back to them until the
next weekend. No  parts have suffered as far as I can tell from the
extended soak.

I  do have some metal prep and etch from Home Depot which is
essentially phosphoric acid. I have not had to resort to that yet,
but again it is safe and easy. It too would be followed by
water/baking soda rinse followed by HOT water rinse.

I have also purchased two carbon rods  from McMaster to set up a
reverse electrolytic rust cleaning tank. Uses  simple washing soda.
Again, safe and easy to use and dispose of. Just  beware it will
generate hydrogen so open area away from ignition source is
required. If hydrogen embrittlement of a part is a concern then a 30
minute bake in kitchen oven at 400°F will resolve the concern.

In  all cases once rust has been removed by the one of the cleaners
above, the  "cleaner neutralized" in the baking soda rinse, and the
part hot water  rinsed/heat soaked/dried I follow up by coating
parts/surfaces to be bare  metal with automatic transmission fluid. I
have wax available for applying  to bare metal tooling surfaces as
well. As weather warms and I can get  outside I'll be
priming/painting the surfaces that will not remain bare,  none of
which I have started to clean/strip yet.

In all cases I wear  rubber gloves, long sleeves, long pants, and
side shield safety glasses.  I'll use splash proof goggles when
getting to the phosphoric acid or  electrolytic rust removal.

I'm doing this cleaning/stripping/rust  removal all in basement, one
small half gallon or gallon tub of parts at a  time. So far no
complaints from my SO about odors so that is a plus as  well.

I do have a 20 gallon parts washer with mineral spirits in the
garage that I can use to preclean any really dirty/gunked up parts,
along with the garden hose and common detergents for dust/dirt
removal, and a vacuum cleaner for dust/debris clean up (along with
mouse nests and droppings in drawers!).

Bradly Chubb


Perhaps this is unfounded, but OA is an acid and acids do bad things
to aluminum.

The auto boys leave their aluminum wheel hubs out of the OA when
getting rust off of other wheel stuff.

Rich Goldman

The OA didn't appear to damage the aluminum housings at all. It has a
slightly tarnished irregular look, but looks like that'll clean up
w/some polish. The had some impossible to remove crust before the
dip/soak, 100% gone now.

How much citric acid per gallon?

Dan Gorsline


How much Citric Acid?

Depends on a lot of parameters ... How big a hurry you are in/amount of rust/type of corrosion/temperature/etc.

Most any acid will eat up rust. The secret is to damage the base metal as little as possible without poisoning too many endangered species.

I've tested on objects with aluminum components and observed no etching.

My recollection of chemical reactions is now 50+ years old, but I seem to remember that acids convert rust into various salts like chlorides, sulfates, nitrates, and phosphates and often take the base metal along with the rust in the process.

However, oxalates and citrates form complexes with iron and don't simply dissolve the crud like  strong acids do.

My wild-guess recipe for citric-acid rust remover is to start with enough water to submerge all the candidates for cleaning in a bucket of water.  Stir in citric acid powder, estimating the quantity of citric acid to at least equal  the weight of the rust that you hope to remove.  Set it in a nice warm place to work for a day or two. The process can be speeded up by stirring or by brushing the surface occasionally with a stiff brush or scouring pad.  Does not work well if the surface is contaminated with grease or paint.

Rinse well with hot water and coat lightly with oil or prime/paint immediately.

RBerglund


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