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If the part is greasy/oily, degrease it. A
soak in the parts washer
followed by some drying time will work.
Find a PLASTIC container large enough to hold
the rusty part. For a
hood hinge, a 5-gallon pail might work. Or an office type waste
can, or a tall kitchen trash can.
Go to the supermarket and look for "Washing
Soda" in the laundry
detergent aisle. Its usually next to the "20-Mule Team Borax".
chemical is sodium carbonate. Its also used in swimming pools
as a pH increaser, available from any pool supply store. Check
ingredients label to verify 100% sodium carbonate. This is also
same chemical that is used as the neutralizer in the Prestone
Radiator Flush (the yellow cardboard can). You can substitute
soda (sodium hydrogen carbonate), but it will not work as well.
Fill the container with a solution of sodium
carbonate. Use about one
tablespoon of sodium carbonate in the container for each gallon
water, but the amount is not critical.
Submerge your part and attach the NEGATIVE clip
of your battery charger
to the part. Make sure you have contact with the metal (scrape
paint if necessary).
Insert a piece of scrap steel into the container,
making sure that it
does not touch the rusty part. Old concrete reinforcing bar,
pipe with any coating removed, hot rolled structural steel, cold
steel, old axle shafts...anything steel will work. Make sure
steel is long enough to protrude above the surface of the water.
can rig up something to suspend the steel if it is too short.
is your "sacrificial anode". See below for why you should
steel for the anode.
Connect the POSITIVE clip of the battery charger
to the sacrificial
anode. IMPORTANT: Make sure that the clip remains completely
the water at all times, or it will *literally* disappear!
Turn on the battery charger. For a new sacrificial
anode, the 6-volt
setting might be enough. If the ammeter goes off scale, raise
sacrificial anode so less is submerged and/or move it further
the rusty part and/or reduce the voltage. The amount of current
critical. A low current will require more time to de-rust the
high current will unnecessarily heat the water and make a lot
Given a choice, be patient and use the lower current.
Bubbling will occur. Hydrogen will be liberated
at the rusty part
(where the red rust is converted into black rust), and oxygen
sacrificial anode (where new red rust is formed). As the rust
removed from the part, microscopic rust particles will rise with
oxygen and form a brown scum on the surface. Keep the positive
of the foam! The sacrificial anode will form a rust layer. You
interrupt the process to wire-brush the rust off the anode from
time, so it keeps working efficiently.
The process works best line-of-sight, so the
rusty part may need to be
turned occasionally to expose all sides to the anode.
You can let it run indefinitely without any
damage to the de-rusted
part. Any heavy rust layer will be loose, or will fall off on
The time to completely de-rust the part will vary from minutes
days, depending on the volume of rust and the current.
When the part has been de-rusted, rinse it with
hot water and dry it
quickly. A hair dryer or heat gun works well for this.
The dry part will have a thin layer of loosely
adhered black rust. If
the geometry of the part is simple, it can be brushed off using
bristle wire brush or wire wheel on an electric drill. The part
then be submerged in dilute phosphoric acid for a while, agitating
occasionally. Wear nitrile gloves and splash goggles when working
acid. When the black rust disappears, treat the part with a conversion
coating (follow manufacturer's instructions. Dry it quickly,
35% phosphoric acid is available at Home Depot
as "Behr Concrete Cleaner
and Rust Remover". Dilute it with 4-5 parts water. The
*must* remain completely submerged in the acid, or an etched line
form at the air/liquid interface. This is due to atmospheric
dissolving into the liquid, making it extremely corrosive at the
The de-rusted part is now ready for painting
with the primer of your
You can do a Google search for electrolytic
rust removal if you want
more info. There are some very recent scientific papers on the
how the chemical process works. Museums use this process to de-rust
artifacts. Only the rust is removed; the base metal is unaffected.
You can scale the size of the bath up or down
to suit the size of the
part. Some plywood attached to stakes in the ground can be used
a large shallow pool; with a heavy plastic liner it can be used
de-rust an entire car frame. A large plastic storage tub can
be used to
de-rust an engine block. If the part is too big for the bath,
de-rust it in stages. The pH of the bath is >7, so it is not
even at the air/liquid interface. I use a tall kitchen trash
de-rust drive shafts. When one half is finished, I just turn
and finish the other end. 32-gallon Rubbermaid trash cans work
many large items.
Rusty parts that are "frozen" will
be loosened by this process. Wait
until after de-rusting before trying to break them loose! In
particular, do not apply any penetrating oil before de-rusting.
Paint will be loosened by the de-rusting process
because the hydrogen
bubble formation acts as a wedge to pry it from the surface.
want to use a chemical paint remover, its best to do so before
The de-rusting solution never goes bad. Just
replenish the water as
The de-rusting solution is only mildly alkaline,
and can be used to
water your garden. The rust accumulated at the bottom can be
feed plants that want a lot of iron in the soil e.g. raspberries
blueberries. Or just dump the liquid down the drain and put the
Remember: KEEP THE POSITIVE CLIP DRY AT ALL
TIMES, and do not allow the
rusty part to touch the anode!
SAFETY WARNING: Always unplug the battery charger
when reaching into
the de-rusting bath. If you don't, you will become part of the
be electrocuted! Long-gauntlet nitrile gloves are also recommended.
WHY TO NOT USE STAINLESS STEEL ANODES
Many people using the electrolysis method for
rust reduction swear by
stainless steel, stating (incorrectly) that it's not consumed,
clean and seems safe.
Stainless steel is indeed consumed when used in the electrolysis
process, although slowly. The main problem with using it is the
hazardous waste it produces. Stainless steel contains chromium.
electrodes, and thus the chromium is consumed, and you end up
poisonous chromates in your electrolyte. Dumping these on the
down the drain is illegal. The compounds can cause severe skin
and ultimately, cancer. Hexavalent chromate is poisonous. These
compounds are not excused from hazardous waste regulations where
household wastes are. These compounds are bad enough that government
regulations mandate "elimination of hexavalent chromate by
Does your electrolyte turn yellow? That's a sign of chromates.
have been using stainless steel for the anodes (positive electrodes),
wear rubber gloves when working with or near the liquids. If you
dispose of it, allow it to evaporate into powders and dispose
powders in sealed containers during your local "hazardous
Best bet - don't use stainless steel no matter
how tempting it is.
Bill in Boulder, "Engineering
as an Art Form!"
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