Bodywork and Glass - Rust - Elecrolytic de-rusting
Thanks to Wolfsburg Willy for writing this up in the 80-90 Technical Questions & Answers
One of my tank straps fell in two a few days ago (1987 Syncro) so the dreaded 'tank-out' could be postponed no longer. Getting hold of a new tank strap was a different matter; it was either stainless steel from Germany (139 Euro Ouch!) or secondhand! However, Syncrospares came up with the goods and Jon supplied a S/H strap, although it was in his words "a bit rusty" but a least it was in one piece. I didn't fancy doing this job again in the foreseeable future so I did some research into derusting/rust prevention, coming up with an excellent article:
Here's what I did:
Buy washing soda from Morrisons (about £1.20)
Obtain big plastic bucket (the article does say to use your imagination regarding the container, depending on the shape and size of the piece to derust)
Piece of wood to use as a support across the bucket top
Piece of mild steel for anode, in this case the mesh from a disposable barbeque
About a tablespoon of soda to a gallon of water. If you have trouble locating the washing soda, others have reported success with baking soda. Also household lye will work just fine. It's a tad more nasty -- always wear eye protection and be sure to add the lye to the water (NOT water to lye!!!) The solution is weak, and is not harmful, though you might want to wear gloves. NOTE: It is the current that cleans, not the solution; nothing is gained by making a more concentrated solution -- DON'T!
Here's what the strap looked like when I received it:
Here's the actual setup: Cathode (-ve) > Rusted part: Anode (+ve) > Sacrificial steel object
Here's the strap after 24 Hrs. in the bucket:
Nice and clean!
Points to note
The mesh wasn't very good 'cos
(a) it has a low surface area and
(b) it's fairly thin and turned to mush after using it for three pieces. I eventually used an old panel saw after removing the handle, which proved ideal (high carbon steel).
Other articles on electrolytic rust removal waffle on about current density etc. I just attached the battery charger and left it on normal charge without a problem.
I dried the strap on the top of our woodburner. It got pretty hot, without getting red hot. It turned the surface iron, which was black when it came out of the bucket, to a deep brown, which looked like rust (see picture 3). This wouldn't however wire brush off, so I guess it's a form of iron which we're unfamiliar with.
It easily took several coats of cold zinc and looks the DB's.
There is gas given off from the process, obviously hydrogen and oxygen, but the amount is negligible. I accidentally shorted out the charger and nothing blew up! Just make sure that you do it in a well ventilated space.
If you only use mild steel (but not stainless) for the anode then you can tip the resulting crud down the drain - it's just a solution of washing soda with some iron in it. The picture of the strap after treatment perhaps doesn't show clearly that it was almost 100% free of rust. The only bits remaining were deep in the seams formed by welding the mild steel to the pump cradle and I think that I could have got rid of that if I'd been patient enough.
You can't overdo this process - if you immersed a perfectly clean piece of steel as the cathode then nothing will happen. So as a self-regulating process you can leave it and forget about it for 24 Hrs (though overnight is usually sufficient).
If you try this you need to take both the pieces (sacrificial anode and part that you're derusting) out of the solution once or twice and brush the crud off with a plastic scrubbing brush - it will speed up the process. (Obviously, a quick degrease and wire brush larger rust flakes first will also probably speed things up a lot - Ed)
NB. An 'intelligent' charger won't work properly as far as I can see (measured only 0.22V when on), so seems to need a 'dumb' charger, any cheap 4A charger should do - Ed.
PS. An old blunt wood saw is ideal as the sacrificial anode. Large surface area and long enough to dip down into a deep plastic kitchen wastebin (typ about 8 gallons to do a rear spring, < 1/2 kg of Soda)
If you use a stainless electrode, hypervalent chromates can be formed, which are:
a) Cancerous to the skin
b) Illegal to dispose of in the earth or down the drain
There are no obvious advantages in using stainless steel anyway, the method aims to convery any iron oxide (rust) back to plain iron
Use rubber gloves; work in a well ventilated space; don't work in areas where children can gain access un-accompanied.
Wash, dry and heat with sun or blow dryer etc, then treat with something like Dinitrol RC800 or RC900 The a good paint (Chassis Black is tough)
This original article was reproduced in www.Stovebolt with permission of Ted Kinsey, the original author.
Follow that stovebolt.com link above and it leads also to a downloadable pdf with even more information.