Quote Originally Posted by JeffS View Post
Here are a few tips I've learned from many years of electrolytic de-rusting... but first the WARNING...

WARNING: Never use stainless steel or any other alloy containing chromium as the sacrificial anode in your de-rusting setup. If you do, you will create a highly toxic solution of hexavalent chromium. There is no legal way of getting rid of this hazardous waste, and no environmentally safe place to dump it. This is the only serious risk posed by electrolytic de-rusting, and one that is easily avoided by a proper choice of anode material.


One excellent choice for the anode is carbon. Scrap pieces of rods, sheets, and cylinders are available on ebay at low cost. The great thing about carbon is that it does not oxidize and only very slowly erodes away in the de-rusting bucket, keeping the solution much cleaner than if you use iron for the anode. I have pieces of carbon that have survived hundreds of hours in the bucket pretty much unscathed. A lot of these pieces are scraps and left-overs from EDM machine shops.

As Rasmus says, rebar from the local home improvement center is an excellent, completely safe, and inexpensive anode material. The only drawback is that it gets consumed rather quickly and adds a lot of rust to the bucket. If you see rust forming in your bucket it is not coming from the cathode (the part you are cleaning) because that rust is being chemically converted back to pure iron by reacting with the hydrogen at that electrode. The rust is comming from the anode, which (unfortunately for it) is bathed in pure corrosive oxygen.

Even if you do use rebar anodes, the water can get pretty digusting without effecting anything, so there's no need to change the water. I only change the water when I have a particularly tricky set-up and I want to see were the bubbles are forming on the part.

Baking soda, washing soda, and borax work well as electrolytes. I add about 1-2 tablespoons per gallon but it is really not critical. If you do not have a variable voltage power supply you can use the concentration of washing soda to regulate the amount of current so that you don't overheat your power supply. You only need enough current to form bubbles at the cathode... a few amps is plenty. Cranking up the current does not make the de-rusting go any faster.

As Frank and Rasmus have noted, de-rusting only occurs where there is line-of-sight coverage between the cathode and anode, so it might take a few different sessions to completely de-rust a complex shape. To de-rust deep threaded holes for example, you need to place an anode rod down into the hole for effective coverage. For my WRX spindles I used a 1 inch diameter carbon rod down through the middle to clean out the bearing area after de-rusting the outside surfaces with a different set-up.

When you remove a part from the de-rusting tank you will be amazed at how quickly a flash coating of new rust will form... it can happen in seconds right before your eyes as the part dries. Any other piece of metal hanging around your shop will have a protective surface layer... either purposely applied or a naturally forming oxide layer that protects the metal from further oxidation. But your freshly de-rusted part is virgin metal with no protective oxide layer and so it rusts the instant you remove it from the bucket. This flash layer is so thin that it does not affect anything, and you can paint right over it. But you can remove this rust and form a protective passivating layer by spraying on a "metal prep" solution containing phosphoric acid and zinc phosphate. Eastwood's product is called "After-Blast Metal Prep" and there are similar products from Jasco and others. This greatly improves the appearance of the part... it will literally look new and shiny after the prep treatment, and it does afford some amount of rust protection until the part gets painted.

Good luck... Jeff
Jeff,
Lots of good information here. Thanks for that. How did you secure a 1" rod through the spindle to ensure it doesn't touch the bearing contact surface?


Thank you!!
Frank