De-Rusting - Experiments with Citric Acid.

[Pete W.]

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. 

[awemawson]

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

[krv3000]

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

[Pete W.]

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. 

[awemawson]

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.

[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

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.

[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 

[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

[Manxmodder]

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

[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]

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.

[Manxmodder]

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.

[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'!!          

[awemawson]

Should have used it on your pancakes yesterday on Shrove Tuesday

[tom osselton]

Did you add more citric over the 12 days or used the same strenght?

[Pete W.]

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. 

[Pete W.]

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! 

[efrench]

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.

[Arbalist]

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

[NeoTech]

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). =)

[Pete W.]

Hi there, all,

Once again, thank you all for your contributions.    

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. 

[Arbalist]

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.

[awemawson]

Electrolysis will give off oxygen and hydrogen in an exactly explosive mix 

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

[Pete W.]

Hi there, all,

As the photos at the start of this thread show, I found citric acid fairly effective in removing rust from steel parts.

I recently found some DTI stand parts among a job-lot I'd acquired some time ago.  They were rusty so I decided to give them the citric acid treatment.

They were also rather greasy so I swilled them in some isopropyl alcohol first and then carefully dried them.

I put them in a plastic pot with a couple of dessert spoons of citric acid crystals and topped-up with warm water.  So far, there is no apparent action!!!

It's the same batch of citric acid as I used back in February 2014 and it's been in a sealed container all that time.  Even if there had been some ingress of atmosphere or moisture, I can't think of any chemical reaction that could have reduced its effectiveness.  So, I'm          

[awemawson]

I reckon that the parts have some lacquer or whatever on the surface. I've stored crystals of citric acid for years and not had any degradation of it's effectiveness.

[Bluechip]

I've used the electrolytic caper many times and have been baffled why that didn't work occasionally.

I have been told anything that has a phosphate, Sherardized or gun-blue finish may well fail to clean up too well. The original finish may not be apparent.

This was long after I stopped so I cannot verify it ... 

Get another bit of rusty steel and try that, I see no reason why citric acid should 'go off' as it were ..

Dave

[hermetic]

I have some apple trees at my workshop,  that is why it is called "Appletree works" and every year I try to make cider, and some is superb, and some goes wrong! I use the wrong stuff for derusting, and it works very well indeed, have also used it with electrolysis, and that works too. Anything with a bit of acidity will dissolve the rust, I was well impressed with some thread guages that, to look at, were really too far gone, but they cleaned to the point where the engraving is chrystal clear, and most of them are perfect bright metal again, and all done in bad cider, with no electrickery! Citric acid I suppose!
Phil

[howsitwork?]

probably acetic acid from the alcohol breaking down rather than citric.

Interesting thread. I have tried electrolysis on drills , someone mentioned that this causes  "hydrogen embrittlement " of the tools? They still cut OK so don't know how true , or critical for use this is.

Ian

[Arbalist]

I tried some citric acid derusting on some nuts and bolts as it would have been a fag setting up the battery charger. It worked well enough but the surface finish was terrible compared to washing soda and a battery charger. Never again unless I want to blacken the surface afterwards.

[Pete W.]

Hi there, all,

Well, I decided to leave the parts in the citric acid solution and they did eventually start to bubble but only slowly.

This morning, I decided to check what progress had been achieved.  Here's a photo of the parts straight out of the 'bath':



I then rinsed the parts in fresh water and then in methylated spirit and allowed to air dry.  That got me to here:



The parts were covered with a fine dark-coloured sediment.  I went over them with a brass bristled suede brush and they came out quite well:



I finished off by coating the parts with 3-in-1 oil.  I think that these parts are now in a good enough condition to be returned to service.

It seems that my stock of citric acid crystals hadn't 'gone off', rather that there was some coating on the parts under the rust that slowed up the reaction or made progress less apparent. 

[Eugene]

I have tried electrolysis on drills , someone mentioned that this causes  "hydrogen embrittlement " of the tools? They still cut OK so don't know how true , or critical for use this is.

There's certainly the possibility it could happen, especially given the extended times the parts are subjected to.

Hydrogen embrittlement is a potential problem with hardened and spring steels, electro-plating and it's associated cleaning processes being a prime cause; even common or garden rusting can cause it on susceptible steels. Mild steel is unaffected. The process of embrittlement can be reversed by heat treatment so within industry it's SOP to remove the hydrogen immediately after plating. The usual temp is around 200 C for two hours, so the home brew de-rusting of taps, dies and suchlike can be usefully followed by a stay in the domestic oven; it certainly won't do any harm and if it avoids a broken tap (such fun ) then why not do it?

There was a time in my life when I designed a test rig for plated parts that were safety critical and used it to check what felt like several million spring washers to establish some sort of statistical regime. It was the second most boring job I ever did. Weeks and weeks of sitting on your duff waiting for something to go "ping" .... ooh the excitement.  H & S rules forbid the publishing of my most boring job; simply reading about it can permanently shut down a complete cerebral hemisphere.

The effect of cider on rust is probably due to the tannins as much as anything else. Some commercial de-rusters are made from manipulating the lees left over from the fermentation of grapes in wine making and utilising the tannins; we imported hundreds of barrels of the stuff from Italy and sold the resulting product as "FerTan". Or was it FerroPro? Or both? I think it was under licence anyway.

Eug