I deal a lot with hydraulic components that come from an underground mine, and before my current place of employment, I worked at a company that primarily dealt with hydraulic systems used in industrial phishing equipment. If I was to name one thing that is common to the hydraulic parts that come from these distant industries - it would have to be the rust! Tons of it! For everything that I get from the mine or the sea comes rusty as hell. I hate cleaning, and cleaning rusty stuff sits in a league of its own! Just look at the components I have to work on:
I believe that delivering a repaired component in the same rusty state that it came in is unprofessional (unless, of course, it's an emergency, and promptness of the repair is more important than the aesthetics). So, as you can imagine, getting rid of rust on bodies, casings, valves, fittings, manifolds, and whatnot is a part of my daily routine.
For a very long time, my primary weapons for dealing with rust have been - a high-pressure washer (for external cleaning), a slew of mechanical, wire-brush-based means, a phosphoric acid rust remover (for "special cases"), and substantial amounts of elbow grease.
Mechanical rust removal is a labor-intensive exercise, and the use of acid-based chemicals, aside from being "not very environment friendly", has other disadvantages, so I have always been on the lookout for an alternative rust removing technique that would make my work a little bit easier, and maybe a little bit less nasty.
And for a very long time, I have been hearing and reading about the so-called electrolytic rust removal. People say that it works wonders, but somehow I've always been reluctant to try this method out lest it could scrap a very expensive part. Removing rust from an old saw blade is one thing, but putting a thousand bucks worth of a precision lapped endplate in a dubious bubbling solution seemed like a risky business, so I thought about it, a lot, but never gave it a shot. That is - until now.
I have been repairing a lot of Rexroth A10VO140s lately, and since these pumps (and motors, and everything else) come from core drilling rigs that are constantly washed over with extremely corrosive mine waters, everything comes in rusty as hell. And so, I accumulated enough of old housings and end-plates from the units damaged beyond economically justifiable repair, to safely give the "electrolysis method" a try. "F### it!" - I said - "if it works it works. Anything to make cleaning easier!"
Behold the supplies: a random plastic container (I use these to store disassembled units), some scrap metal welded in a box shape to serve as the sacrificial electrode (anode, or positive), our trusty power supply, current and voltage regulated, which is very handy and very safe, and a bucket of PH+, bought at a local store, which is, essentially, pure sodium carbonate (Na2CO3):
At first, I decided to "go slow", and picked this small manifold for the first try:
I filled the container with about 5 galons of water and put this much sodium carbonate in it. Then I connected the positive lead to the metallic cage, the negative - to the manifold to be cleaned, submerged it into the solution, and "cooked for a couple of hours at two amps":
The part came out covered in a dark substance, and when I tried to brush the blackish goo away, I was very pleasantly surprised to see that it comes off very easy, a lot easier than the rust I am used to, (and I mean - a lot!), and most importantly, it reveals a very clean surface underneath!
Ok, I am sold! Let us try something "more important". How about this end-plate here. I washed it with a high-pressure washer to knock off the loose stuff, and then let it "simmer" at 4 amps for about 4 hours. Like I said before - I was not sure how this process would affect "sensitive places" - like the lapped surface or the bearing race cavity. I left the bearing race in place "just in case", by the way.
Once again, the part came out covered in a dark, almost black residue, which I first washed off with the high-pressure washer and then effortlessly brushed off with a wire brush. Seriously - the amount of effort I had to put into removing the black residue was a lot less than I am used to with the "normal" rust. The surfaces looked way cleaner as well. There was, however, some rust left in the "hard sports", and I am sure that if I put it back for another 4 hours it would probably go away, but even in this condition, the part looked way better than I was used to seeing. Especially after so little cleaning. I also saw zero effect on the surfaces I was so worried about. Very impressive!
It seems that the right way to do this is to wash the part first, then run it through the electrolyte bath for some time (apparently a long time), and then wash it again, brush off the goo, and then wash it with a petrol solvent so that it doesn't rust again. So, I used this technique on the other half of the body, and this time I let it sit for the whole 24 hours at 2.5 amps. And just have a look at the results!
This process seems to remove the rust from the smallest pores and cavities. I can promise you one thing - it took a whole lot more time, but a whole less elbow grease! I put the part into the bath, flipped the switch, and forgot about it for a day, and then when it came out - boom! Magic! A perfectly clean housing after but a couple of minutes of brushing.
Now how about an "impossible task" then. I had this manual DVC lying in scrap. These are pretty cheap, and it came from the mine so "disfigured", that I simply replaced it. I knew first hand how much brushing it would take to take it to a more or less "decent appearance", so I threw it in the bin and forgot about it. I wonder how my "magic bath" will fair?..
The pictures below show the valve in its "original" state. Then how it came out after a 24-hour "simmer" and a pass under a pressure washer. Note that the process seems to have knocked off some of the oxidation on the aluminum as well. And then it shows the body after I brushed it.
Who is scrap now?!! By the way, I had no difficulty in removing the levers, which seemed to be rusted solid. I did connect another wire to make sure that the current goes through these rods.
Important points that I took from these "experiments":
In all - I am very, very pleased with the results, and I will continue to use this method to aid in cleaning "non-urgent" rusty parts. Most likely I will be putting together a more professional "cleaning apparatus". When I have it done and used, I'll post my thoughts, so, stay tuned!