The Shop > Tools
De-Rusting - Experiments with Citric Acid.
Manxmodder:
--- Quote from: John Stevenson on February 25, 2014, 08:45:41 AM ---I use brick and patio cleaner which is a diluted form of hydrochloric acid.
i use this to descale steel plates before drilling as the black scale plays havoc with the drills and surface grinding just clogs the wheel.
It works in about 4 hours to descale 20 6" plates on both sides, be interesting to see how the citric acid will work on these ?
--- End quote ---
John, I also use brick acid and find it really effective on rusted items.
I've also used a stronger commercial hydrochloric solution known as Scalene pickle,used to remove scale from forgings and castings prior to machining.
A couple of days back I cleaned up a very old and heavily rusted Record spokeshave that someone donated to me.
Got it spray painted and reassembled today,it's an absolute cracker to use :clap:
superc:
Hmm, my first thought is the camera didn't lie. That rust in the first 'after' pictures really is there. Just because the human eye doesn't see it, does not mean the camera is making it up. Sure, changing the lighting, or adding a filter, or even changing film or aperture speeds may bring out an image more akin to what the human eye/brain sees, but that doesn't make what the camera saw vanish.
Acids corrode, that is what they do. I think you would get a better overall picture of the effectiveness of acid baths over time by digging the pieces out a draw 3 or 4 months later and see if the rust the camera saw progressed or not.
Have I used acid baths? Sure every week. Usually phosphoric acid in combination with manganese (commercially available as Jasco Metal preparation, Must for Rust and some other names). Treated my X2 table with that stuff too. The chemicals literally destroy the rust by converting iron oxide to iron phosphate.
Yes thick rust gets the wire brush (maybe a shot of oven cleaner and a rinse to remove oils). But there is a another method that works very well. Electrolysis.
If you aren't familiar try tubalcain's video
You can use a charger like he does, or even a deep cycle 12 volt marine battery. The process is self-limiting anyway. When it is done, it is done. I have a dozen 60 year old pieces of field equipment (and stored in a field too) that now and then needs repair. Often the bolts are very rusty. Snow and rain will do that. When I encounter them I electrolysis them, then when it is done and dry I Jasco prep them, and either oil them or paint them as appropriate. I haven't hit something that needed those treatments twice yet.
John Stevenson:
--- Quote from: superc on February 25, 2014, 04:23:00 PM ---Hmm, my first thought is the camera didn't lie. That rust in the first 'after' pictures really is there. Just because the human eye doesn't see it, does not mean the camera is making it up.
--- End quote ---
Not sure I agree with that statement.
Couple of months ago I took some photos inside the workshop of a T&C grinder I was going to put on Ebay.
When i came to list it and uploaded the pictures it looked to be covered in rust.
Went back outside and no - perfectly clean and dry, not a mark anywhere.
I finally had to drag it over to a door to get some pics that actually looked the same as the machine.
Took a photo of a Burgundy leather cloth room divider at the weekend, bloody thing came out purple ??
It's Burgundy leather cloth and photographed during daylight hours.
Manxmodder:
--- Quote from: Pete W. on February 25, 2014, 07:35:53 AM ---Hi there, Andrew,
There was a story some years ago about a bloke who was walking his dog in the country and came across a lathe half buried (end-up) in the ground. Maybe it had been used to anchor a tether for a grazing horse or some such. Anyway, the walker negotiated a change of ownership with the land owner and took the lathe home and started work. According to the story (workshop myth?) the lathe was eventually restored to an adequate working condition.
So, maybe there's still some hope for the Myford capstan lathe that I have here. It's been languishing years and looks a right wreck.
Some years ago, I learned of a process for repairing plated finishes, including hard anodising. It was an electrolytic process and used an absorbent pad to hold the electrolyte so it could be used on mechanisms or parts that would be too much trouble and expense to dismantle and immerse in a tank. I wonder if an absorbent pad could be used to hold citric acid solution in contact with rusted items?
--- End quote ---
The answer to the pad question is most definitely yes that technique works but the pad needs to be kept wet with solution and to that end it is best to cover the pad with polythene to minimise loss due to evaporation.
Another point worth mentioning is make sure all traces of acid are removed from metal pieces after treatment or corrosion soon sets in again.
Whenever I de-rust components in acid I follow up by soaking them in hot water a couple of times to ensure all traces of acid is leached out of the metal.
Deionised water from the dehumidifier tank is better again for this purpose....OZ.
Pete W.:
Hi there, all,
Thank you for your various contributions.
Well, it's been a lot longer than I intended but I finally took the calipers out of the citric acid. They'd been in there for twelve days! I rinsed them with clean tap-water and then with methylated spirits and dried them on the radiator before taking some 'After' photos. Here's the first one:
And the other side:
And here are a couple of close-ups of some detail, first the maker's name:
And the screw thread and adjuster:
These photos were taken in natural (sunny) daylight on the bathroom window-sill. As before, I used MicroSoft Photo Editor to tweak the brightness and contrast slightly.
I think the citric acid has done a thorough job of removing the rust. Of course, this process cannot put metal back so the surface is frosted and covered in fine pits. The worst casualty of the rust is the adjusting thread, it would be interesting to examine the female thread inside the half-nuts. If it weren't for that visible thread damage, it would only need a new pivot piece and spring-bow to make these calipers usable again. However, that was not my objective - I merely used these calipers because they were to hand and very rusty (see my opening post).
When I employ this process for real, I shall degrease the object first, using either washing-up liquid or a solvent. And, of course, the object would require re-oiling after the de-rusting treatment.
For now, I regard these experiments as complete - I just need to decide whether to throw the used citric acid solution down the drain ...
or to keep it 'in case I need it'!! :lol: :lol: :lol:
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