Shop Floor Talk  

Go Back   Shop Floor Talk > Welding and Metalworking Forums > General Technical Information

SFT Search:   
Thread Tools Display Modes
Old 12-21-2004, 12:30 PM
Franz Franz is offline
Join Date: Jun 2004
Posts: 5,731
Default Electrolytic Rust Removal

Electrolytic rust removal is a simple non-labor intensive method of removing rust from an object,
using nothing more than water, washing soda, and electricity. There is nothing magic about the
process; anybody old enough to remember chrome bumpers remembers the electroplating process.
In the case of electrolytic rust removal, the system is plating rust from an object you want to
restore onto a junk electrode.

The same process is also very effective for removing corrosion from brass and copper, using the
same electrolyte.

The process is NON destructive, to the steel or iron object being derusted, unlike media blasting
needle scaling or acid dipping. The only thing that will be removed is RUST. The best part, unlike
abrasive blasting, ALL rust will be removed from the microporosity of the metal being derusted.
When all rust has been removed the process will STOP by itself, and good steel will not be eroded.

The process does NOT restore the metal to original condition, it merely removes RUST.

When done PROPERLY, with Sodium Carbonate or Sodium Bicarbonate, electrolytic derusting will
NOT harm steel, Babbitt, lead, copper, brass, or aluminum. That means with a properly sized tank,
you can submerge and derust a complete Hit & Miss engine. Using other electrolytes can and WILL
harm some metals, such as Babbitt or Aluminum.

SPEED: Lets face it, the object you want to derust didn't get rusty overnight, and electrolysis will
probably NOT derust it overnight either. The speed of the process is determined by equality of
surface area between the object being derusted, and the accumulating electrodes, as well as by
the voltage/amperage applied, and the electrolyte used.

Here's a brief explanation of what is happening in the tank:

During the electrolysis as a general rule, ions are being replaced vs elements. So the Ferric Oxide
is probably being converted to Ferric Carbonate. Also any pollutants that are in the original water
and any contaminants on the part being derusted will lend their ions to the mix. There may be
Calcium Carbonate, Sodium Chloride and who knows what else in there. Basically there will be
Hydroxyls, Carbonates, Oxygen, Hydrogen, Sodium, Iron, and maybe some Calcium or Chlorine in
the soup. The only compounds that will be lost will probably be Hydrogen and Oxygen; anything
else will remain in the soup as soluble salts (some Sodium Carbonate and maybe Ferric Carbonate)
or as solids which will either precipitate and fall to the bottom, remain suspended in the soup,
attach to the anode or remain on the surface of the derusted part.

I'm just a dummy who knows the process works.

Solution: 1 tablespoon of Arm & Hammer Super WASHING soda per gallon of water. This is the
BEST working solution for the electrolyte. On the off chance you can't obtain Washing Soda
(sodium carbonate) in the supermarket laundry aisle, Baking Soda (sodium bicarbonate) will work,
although it will offer slightly less productivity in the tank.
Over time, the solution level will drop due to evaporation and the breakdown of water into Hydrogen
and Oxygen. Only water needs to be added to replenish the solution, no additional soda needs to be

If the tap water in your area has a high mineral content, using demineralized water may yield better

The solution will freeze, at about 30° Fahrenheit. Generally this isn't a problem, at least for me,
because I don't enjoy working in a cold area. If the solution does freeze, it will easily thaw by applying
voltage to the object being derusted and the accumulating electrode. Freezing will NOT harm the
electrolyte solution. Frozen solution may harm some objects that are suspended in the solution when
it freezes, so use common sense.

VOLTAGE: The process works best with either 12 or 24 volts DC, easily obtainable from a battery
charger. Voltages above 24 volt don't really offer any greater efficiency, and generally seem to get
wasted off as heat in the solution. Heat doesn't add anything to the process, other than wasting

AMPERAGE: Basically any DC voltage source will work, from a trickle charger to a plating power supply.
Too much amperage, just as excessive voltage, wastes off as heat. The best way to regulate the
amperage operating in the tank is by controlling the amount of submerged surface area of the
accumulating electrodes.

POLARITY: Positive (+) DC is attached to the accumulating electrode, and Negative (-) DC is attached
to the object being derusted. All you really need to remember is Positive Accumulates. If the polarity
of the DC source is not known, attach the wires and energize the system. Small bubbles will rise from
the NEGATIVE object. Correct a reversed connection immediately; allowing your prized object to
accumulate material from the sacrificial anode can rapidly cause pitting. The bubbling is also a good
way to verify that the process is working.

BATTERY CHARGERS - If you use a charger as a power supply, some of the newer "automatic chargers
will not start generating current into the tank, unless you use a battery along with the charger.

ELECTRODES & OBJECTS BEING DERUSTED - Both need to be suspended so they cannot come into
contact with the bottom of the tank or the sludge that accumulates there to prevent shorting the
power supply, or wasting current by passing it through the sludge.

TANK - Plastic tanks work about the best, and that includes digging a pit and lining it with plastic
sheeting. Unfortunately, my neighbor has taken an attitude, so I haven't been able to experiment
using his pool as a tank, but he might go on vacation. The process can be done in a steel barrel, BUT
extreme care needs to be used to preclude the barrel from becoming an energized surface, witch will
eventually develope poroscity in the barrel.

The best anode material I have found is carbon or graphite. It works 24/7 and leaves the rust in the
bottom of the tank, so you don't loose time cleaning the anodes, or loose operational speed due to
coated electrodes. If you can't locate graphite electrodes, used lawnmower blades or old car leaf
springs will work but they will require cleaning about every 4 hours.

Whatever you do, DO NOT use stainless electrodes; they make some very nasty hazmat called Hexavent
Chromium that is POISONOUS and will give you nasty diseases, and it is absorbed through your skin.

The process works best "line of sight" so to speak, so multiple electrodes are often beneficial. Arranging
several accumulators around the perimeter of the tank generally works well, and minimizes the possibility
of short circuiting.

SCUM: As the process runs, a layer of brown (usually) scum will form on top of the solution. This doesn't
happen 100% of the time, but a scum layer is not anything to worry about. Before withdrawing the object
being derusted from the tank, it's a good idea to shut off the electricity, and skim off the scum before
pulling the object.

CLEANING: When objects are removed from the tank, they will often have a black coating that looks
like the object has been smoked. This is normal. The best way to remove this coating is to wash it
using a stiff brush in a solution of dish soap and water before the coating dries. If the coating is
allowed to dry on the object, it will be nearly impossible to remove.

DRYING: After washing derusted objects, the best procedure is to either sun dry or dry in a 200° oven.
If you use your wife's oven be prepared to sleep on the couch, not that drying will hurt the oven but it
will hurt your sleeping arrangements.

CONTAMINATION: In order to avoid contamination of the electrolyte solution, objects being derusted
should have all grease, oil and dirt removed beforehand. Objects that have rusted in a salt water environ-
ment such as ocean water need to have as much salt leached out as possible, before electrolysis. Failing
to remove salt first will radically shorten the useful life of the electrolyte solution.

CRACKS, etc.: Objects such as multi-piece assemblies that have mated surfaces are difficult to derust
without disassembly. A great amount of time will be required to electrolytically remove rust between the
sliding surfaces such as a vise. Pieces that have cracks will perform similarly in an electrolysis tank, and
it will take time to remove the rust from the crack.

MULTIPLE PIECES: Assemblies of multiple pieces (such as machinery) usually require an electrical
connection to each piece. Rust does not conduct electricity, so unless the pieces are connected cleanly
together, generally the connected piece will derust while the adjacent piece remains rusted.

CONNECTIONS: It is necessary to make a good electrical connection to the object being derusted and
the power supply. As previously stated rust is not electrically conductive, so it may be necessary to scrape
or grind a connection point on the object before the process can begin. Alligator clips are generally
acceptable connectors BUT solid copper clips should be used. The cheaper plated steel clips will usually
self erode when submerged in the tank.

Accumulating electrode surface area relative to area being derusted governs both achievable speed and
amperage, but you need to be careful because you can get the solution damn HOT.

Also remember, this process generates Hydrogen gas, so take appropriate precautions. The area
immediately above the tank is a PERFECT atmosphere for a very rapidly burning fire, often called an
EXPLOSION by uninformed people who are in the process of explaining to the fireman filling out the
report next to the big red truck. Electrolysis breaks water down into it's 2 basic components - Hydrogen
and Oxygen - and when they are recombined by ignition of the mixture, the fire burns at about 4280°F.
Keep ALL potential sources of ignition away from the top of the tank and surrounding area.

For you speed freaks, don't even think of hooking up the DC welder to get faster results. It is possible
to boil the solution, and that really sucks in a plastic tank. NO, I didn't do it and had I been the speed
freak who did, I certainly wouldn't have posted that brilliant move.

Much information has been posted on the web suggesting using lye, caustic soda or drain cleaner for
an electrolyte to speed up the process. This is BAD information, and the use of lye is dangerous. There
is also no appreciable increase of process speed achieved using lye, so I don't see where taking the risks
associated, and dealing with the HazMat created or safe disposal of caustic solution is worth it.

Last edited by Shade Tree Welder; 07-07-2013 at 03:42 PM. Reason: Cleaned it up some.
Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Web Search:

All times are GMT -5. The time now is 12:21 PM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.