Author Topic: De-Rusting - Experiments with Citric Acid.  (Read 15088 times)

Offline Pete W.

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De-Rusting - Experiments with Citric Acid.
« 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. 
Best regards,

Pete W.

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #1 on: February 24, 2014, 04:09:48 PM »
Pete,

I've been known to add a squeeze  of washing up liquid to the citric acid bath to lower the surface tension where bits are a bit grubby - look at my thread on rebuilding the Edwards box pan folder where I de-rust the folding teeth
Andrew Mawson
East Sussex

Offline krv3000

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #2 on: February 24, 2014, 04:33:32 PM »
hi dam good post i my self use old car battery acid i wunder haw long thows test peces took to mack and did he cheet we will never no i don't think they do out like that thes days when the yung ones are serving ther time

Offline Pete W.

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #3 on: February 25, 2014, 03:27:50 AM »
Hi there, all,

Andrew and Bob, thank you for your comments.

As promised (threatened?), I took a couple more photos of the test pieces, in daylight this time.  They've come out a more realistic colour than the previous shots that were taken by artificial light.



and



I also acted on Andrew's suggestion and added a few squirts of washing-up liquid yesterday evening to the bath containing the calipers.  I didn't stir the bath then but, by this morning, the washing-up liquid had mixed in.  It had formed a sort of flaky deposit floating on the surface of the liquid.  I removed as much of that as I could to show the contents of the bath below.  The first picture seemed to show the beginnings of a steely grey colour.



To try to make it clearer, I used MicroSoft Photo Editor to tweak the gamma, with this result:



Later today, I'll remove the calipers from the bath, rinse and dry and take another photo or two.  I'll be particularly interested in the screw thread and the parts that have to run in contact with each other. 
Best regards,

Pete W.

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #4 on: February 25, 2014, 05:26:57 AM »
To encourage you regarding screw threads:

Some years ago I acquired a Roundhead Colchester Student that was in bits - previous owner had dismantled it for transport and never put it together with the result that the lead screw, which was left in a damp garage was very rusty and, I thought, a right off. I rebuilt the lathe having the ways re-ground and started hunting for a replacement lead screw. While this was going on I popped the old one in a vertical length of underground drain pipe with a stopper at the lower end, full of citric acid. Pulled it out a few days later not expecting much, and it shone ! Careful examination showed that it was barely touched and perfectly usable, and indeed I used it for best part of ten years ! I suspect that different steels come out better than others. I expect that leadscrew was EN8 or similar

I understand the the volume of rust is something like 14 times that of the previous steel that made it, so quite horrible looking things probably haven't lost much original material.
Andrew Mawson
East Sussex

Offline MetalMagus

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #5 on: February 25, 2014, 07:29:43 AM »
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


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.

Offline Pete W.

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #6 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? 
Best regards,

Pete W.

If you can keep your head when all about you are losing theirs, you haven't seen the latest design change-note!

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #7 on: February 25, 2014, 07:57:14 AM »
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:
Andrew Mawson
East Sussex

Offline John Stevenson

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #8 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 ?
John Stevenson

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #9 on: February 25, 2014, 09:14:37 AM »
It will work John, but I can't give figures re: relative speed
Andrew Mawson
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Offline Manxmodder

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #10 on: February 25, 2014, 03:23:48 PM »
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 ?
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:
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Offline superc

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #11 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.  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.
« Last Edit: February 25, 2014, 06:09:00 PM by dsquire »

Offline John Stevenson

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #12 on: February 25, 2014, 04:58:36 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. 

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.

John Stevenson

Offline Manxmodder

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #13 on: February 25, 2014, 05:28:05 PM »
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?

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.
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Offline Pete W.

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #14 on: March 05, 2014, 04:24:52 AM »
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: 
Best regards,

Pete W.

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #15 on: March 05, 2014, 07:47:43 AM »
Should have used it on your pancakes yesterday on Shrove Tuesday
Andrew Mawson
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Offline tom osselton

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #16 on: March 05, 2014, 01:42:31 PM »
Did you add more citric over the 12 days or used the same strenght?

Offline Pete W.

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #17 on: March 05, 2014, 02:40:39 PM »
Hi there, Andrew and Tom,

Andrew, we had a surprise visit from family last evening bringing us an Indian take-away so pancakes were postponed. (It was a thank-you for a little paper-work help we'd rendered while #1 step-son was away working in foreign parts.)

Tom, no, I just left the solution as it was before I added the washing-up liquid (see an earlier post).  I did stir it at intervals though. 
Best regards,

Pete W.

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Offline Pete W.

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #18 on: May 02, 2014, 08:38:48 AM »
Hi there, all,

I recently bought a Myford accessory, the one with a 2 Morse taper shank and a replica of the Mandrel nose.  It was a bit rusty so I decided to give it the citric acid treatment.

I didn't think to take a 'before' photo so I had to rustle the picture from the eBay listing - here's a cropped version of it:



I gave the item a good massage with water and washing-up liquid to get rid of any oil or grease, rinsed it off and then immersed it in citric acid solution, about four slightly heaped dessert spoons full in a 1 lb jam-jar of water.

After 24 hours immersion, it didn't look very different!  It hadn't fizzed or bubbled like my earlier experimental objects did.  I assume that the surface deposit wasn't the usual sort of rust.  However, when I removed the item from the 'vat' (aka 'jam jar'), I was able to rub off most of the deposit with my fingers.  A good rinse, a shake and a rinse in methylated spirits got us to this stage:



and the other side:



and a couple of views of the flange:



and:



As you can see, the surface is pitted and frosted between the pits.  The photos make it look rustier than it does to the naked eye.  Maybe I should have left it in the solution for longer, I still might do that.  Otherwise, I might spin it in the lathe and apply some steel wool and/or some fine wet-and-dry paper.  Watch this space! 
Best regards,

Pete W.

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Offline efrench

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #19 on: May 04, 2014, 01:46:13 AM »
I use PhotoShop, but Microsoft Photo Editor also can change the color balance to make your pictures look more natural.
If you include a bit of white, black, or grey in the picture it will make the process easier.

Offline Arbalist

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #20 on: May 04, 2014, 05:56:59 AM »
I'm with superc, I use a battery charger and washing soda. I've de rusted quite a few parts using this technique now.

Offline NeoTech

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #21 on: May 10, 2014, 05:45:29 AM »
I've had success with citric acid + vinegar mixes. But after powerwashing and drying i have been blasting em with soda (more or less baking soda). to get that final grit out of there without disturbing the metal. So if you have a small blasting cabinet and dont need to run sand in it i can really recommend that method. Takes a bit more effort with the acid step but you kill off less metal which is good in my case (car restorations). =)
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Offline Pete W.

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #22 on: May 10, 2014, 08:56:06 AM »
Hi there, all,

Once again, thank you all for your contributions.   :mmr: 

I'm with superc, I use a battery charger and washing soda. I've de rusted quite a few parts using this technique now.

No way would I dispute the effectiveness of the electrolysis methods but I currently don't have anywhere I could set up the gear for it.  I understand that with some choices of electrolyte the process emits a corrosive mist - I wouldn't risk that in my main workshop.

I wanted to experiment with the citric acid method to see how effective it can be and I started this thread specifically to record and share my results.

The phosphoric acid (aka 'Jenolite') process is OK for non-contact surfaces but it does leave a dimensional change that I wouldn't want on, for example, machine slides or running contact surfaces.  I intend to use it on some rusty patches on the tin shed roof (see my thread, Pete W's Tin Shed Project') but I'm going to have to be careful where the rusty steel meets the still-galvanised surface. 
« Last Edit: May 11, 2014, 04:40:42 AM by Pete W. »
Best regards,

Pete W.

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Offline Arbalist

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Re: De-Rusting - Experiments with Citric Acid.
« Reply #23 on: May 10, 2014, 10:33:13 AM »
The problem with any type of acid is that it will eat away the parent material as well as the rust. With Electrolysis it does, I'm told, only attack the rust. I've not been aware of any fumes but I tend to do this type of thing in the garden anyway, well away from tools and machinery.


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Re: De-Rusting - Experiments with Citric Acid.
« Reply #24 on: May 10, 2014, 11:07:23 AM »
Electrolysis will give off oxygen and hydrogen in an exactly explosive mix  :bugeye:

It is very effective where the rusted parts can be in 'line of sight' of the other electrode. However for 'hidden rust' in things like a nut and bolt still screwed together it is not effective. In this situation citric acid is very effective, as the rust converts to soluble salts which go into solution allowing more to penetrate further into the small gaps between components. Very few of the acids used for rust treatment form soluble salts. Citric acid is very mild and in several years of using it I've not had problems of base metal disolution leaving parts in for extended periods
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