The Shop > Tools
De-Rusting - Experiments with Citric Acid.
MetalMagus:
Pete W,
Wow they bring back memories. I have a pair of those test pieces somewhere. Made them nearly 30 years ago. They where part of a phase test during my apprenticeship. It only passed if the gap all round the perimeter of the internal piece was less than a thou.
All done with hand tools, no machining allowed. I could file for England after making them. With callouses on my callouses.
Cheers
Sean
--- Quote from: Pete W. on February 24, 2014, 03:26:08 PM ---Hi there, all,
Several Modders have recommended the use of Citric Acid for de-rusting. I thought I'd try it out so I bought a 1 kgm bag on eBay.
Another eBay purchase of mine had been a job lot of workshop odds and ends, some of which were very rusty so I picked out three items as guinea pigs.
The first one is a derelict caliper, here are its pictures, before:
It was particularly rusty on the adjusting screw:
The other two items were someone's workshop test pieces (not mine, I hasten to add):
and
If they could speak, these last two could probably tell a tale or two, I bet the person who made them kept them in his toolbox for the whole of his career. I bet they weren't allowed to rust while he was fit and active.
I selected a food container left over from a Chinese take away and almost filled it with hot water from a recently boiled kettle. Then I immersed the test objects and added three level dessert spoons of the anhydrous citric acid.
The two test pieces started to fizz immediately and there was no visible rust remaining after about 45 minutes. So I removed them from the bath, rinsed and dried them and took 'after' photos:
and
They still look rusty in those pictures but I think that's a camera problem - to the Mk 1 eyeball in daylight, they look silvery and rust free. Maybe I'll try another couple of photos in daylight.
The calipers didn't seem to be very active so I added another dessert spoon of citric acid and parked the bath in a safe place. That was 48 hours ago and I think I can see some reduction in the rust on the caliper arms. The encrustation on the adjustment screw has collapsed but not all dissolved. I didn't de-grease the calipers before putting them in the bath so maybe they were oily and that's isolated them from the citric acid. I'll see how they look in daylight and maybe try some IPA on one leg and some washing-up liquid on the other and put them back in the citric acid.
So, that's all for now, more photos to follow.
--- End quote ---
Pete W.:
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?
awemawson:
I'm sure a pad would work fine if kept saturated, but I reckon you'd get cramp in your wrist before it was finished :clap:
John Stevenson:
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 ?
awemawson:
It will work John, but I can't give figures re: relative speed
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