I copied this explanation from another forum I belong to on old engines,it’s pretty detailed but it makes it a lot easier to explain. Mark
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 (sodium carbonate), and electricity. There is nothing magical about the process; anybody old enough to remember chrome car bumpers is familiar with 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 de-rusted, unlike media blasting, needle-scaling or acid-dipping. The only thing that will be removed is RUST (Iron oxide, or Fe2O3). The best part, unlike abrasive blasting, ALL rust will be removed from the microporosity of the metal being de-rusted. 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. In the case of severe pitting, the pits will remain, but they will be completely rust-free and ready to accept paint and/or filler.
When done PROPERLY, with Sodium Carbonate or Sodium Bicarbonate, electrolytic de-rusting will NOT harm steel, Babbitt, lead, copper, brass, or aluminum. That means with a properly-sized tank, you can submerge and de-rust a complete engine. Using other electrolytes can and WILL harm some metals, such as Babbitt or aluminum.
SPEED: Let’s face it, the object you want to de-rust didn’t get rusty overnight, and electrolysis will probably NOT de-rust it overnight, either. The speed of the process is determined by equality of surface area between the object being de-rusted, 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 electrolysis, as a general rule, ions are being replaced versus 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 de-rusted 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 de-rusted 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 added.
If the tap water in your area has a high mineral content, using demineralized water may yield better results.
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 de-rusted 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 (e.g., due to breakage), 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 volts 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 electricity.
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 de-rusted. 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, which will eventually develop porosity 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 lose time cleaning the anodes, or lose 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 scum (usually brown) 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 de-rusted 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 de-rusted 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 may hurt your sleeping arrangements).
CONTAMINATION: In order to avoid contamination of the electrolyte solution, objects being de-rusted should have all grease, oil and dirt removed beforehand. Objects that have rusted in a salt-water environment (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 de-rust while the adjacent piece remains rusted.
CONNECTIONS: It is necessary to make a good electrical connection to the object being de-rusted 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 de-rusted 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 (remember the Hindenburg?). 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 its two basic components - Hydrogen and Oxygen - and when they are recombined by ignition of the mixture, the fire burns at about 4280° Fahrenheit. 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.
Well, that should take care of most of your questions. Beyond that, you might have to ask a pointy-headed scientist!
