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16th September 2012, 12:11 PM #1
Rust removal with Citric Acid - pictorial step by step
It seems there are two ways of efficiently removing rust from tools, and both methods have their afficianados:
1. Electrolysis
2. Citric Acid
Without making any comment on Electrolysis, I prefer the Citric Acid method. It's pretty quick, not very messy, and very effective.
You can read more about Citric Acid techniques here, and what follows is my method.
A couple of warnings:
This is a food grade acid (it's in many soft drinks), and in the 10% concentration used I have never had any burning sensation on my skin, but maybe you should wear gloves. The fumes that come off can be unpleasant, and you may wish to do this outside, or at least have plenty of ventilation. Be aware that depending on the time in the solution you may lose any laser etchings.
Acquiring the Citric Acid:
It should be available in most food supermarkets in the cake making section, at a cost of a couple of dollars for 75 grams This is a reasonably expensive way to buy it (but worthwhile if that's all you can get). I got mine in bulk from another forum member (it may not be food grade).
Making the solution:
A 10% solution is required. So for example, weigh out 100 grams of acid and add it to 900 mls of hot water. The hotter the water, the quicker the process. I usually use water at about 70-80 degrees celsius.
The process:
This is the saw before treatment.
I made up the solution, and predetermined the volume (height in the cylinder) to cover the saw plate but not contact the ferrule. I don't believe that CA will damage the timber (although it may discolour it), but any water based solution will cause the timber to expand in the ferrule, which will make the ferrule become loose (particularly as it is thirsty end-grain that would be exposed). In this case I need something less than 800mls, so I poured 750mls into the cylinder, before inserting the saw, and then added the balance to get the level spot on. You can see that the volume of the submerged saw plate has brought the level up to 850mls.
The time required in the solution will depend on how bad the rust is. You may want to remove loose rust with steel wool before insertion into the solution. This also preserves the usable life of the acid. In this case I had already used the solution the night before, and chose not to reheat it (have previously done this in a microwave, but wiped out the oven afterwards). So the temp of this water was about 15 degrees, and the time in the solution was about 90 minutes.
You must check the tools regularly, so as not to go too far, and cause pitting.
After a while (30-45 minutes), take the tool out and wipe off the gunk that has already been loosened. This gives the acid access to the deeper rust, and speeds things up considerably, and reduces the time in the acid (and therefore potential pitting).
When you are satisfied that all the rust is gone, remove the tool from the bath and wipe off the gunk again. Immediately give a good flush with water, and scrub it with a nylon brush under running water You could give it a dip in a Bicarb Soda bath to neutralise the acid, but I don't do this given the non-aggressive nature of the acid. Flushing has always been sufficient. You will find that the tool has a grey silky coating (we haven't really been able to establish what this is, but the best guess is Pearlite).
Note how the acid has pulled off the zinc molecules from the surface of the brass leaving pure copper. This is not a concern - it'll polish up just fine.
How you finish off the tool from this point depends on you and the tool. You may wish to leave this coating on the tool, depending on what tool it is, because it is less rust prone than bare steel. For example, I leave it on files. There are of course a number of different paths from here, and in this case I polished the saw plate with 800, 1600, 2500 Jost SG2 abrasive (similar to Wet & Dry but about 20 times more durable). The brass parts were given 2500 only and then Brasso.
You can see that the laser etched logo has completely gone (partly from the CA, and the rest due to polishing).
Last year we had a long debate about the virtues (or not) of sharpening files with an acid bath (not necessarily CA). The conclusion reached was not fully conclusive (were they sharper, or just really well cleaned?). What I can say is that you will find that files feel "grabbier" to the skin after a CA bath.
Something I discovered the night before whilst cleaning up some router bits: Citric Acid brings Tungsten Carbide up like new - shiny and sparkling. It dissolves and/or soften all the baked on dust, and a quick scrub with a nail brush produces what is apparently a brand new bit! We can deduce that the CA has nil effect on the Carbide because it is shiny straight out of the acid - therefore it will not dull the edges of the bit.
Here are a couple of other examples of CA treatment, and then polishing with a rotary brass brush:
And some files with the coating left in place:
USUAL DISCLAIMER: If you're even slightly silly then don't try this at home. If you don't know if you're silly or not then ask someone.
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16th September 2012, 12:28 PM #2
You can buy larger/cheaper quantities of citric acid from Bunnies et al - in the paint area, usually near the driveway paints - sold as White Knight concrete etcher.
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16th September 2012, 12:31 PM #3
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16th September 2012, 02:29 PM #4GOLD MEMBER
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Thanks for posting this, Brett, your results are excellent, what a beautiful looking saw. Where did you get the 800, 1600, 2500 Jost SG2 abrasive? I have never heard of this before
I also found Citric Acid on eBay in various bulk sizes, but I like the Bunnies option - thanks MSregards,
Dengy
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16th September 2012, 03:43 PM #5
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16th September 2012, 06:29 PM #6
I thought citric acid was also known as lemon juice !!
Fair Winds
Graeme
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16th September 2012, 06:56 PM #7GOLD MEMBER
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The two Japanese saw blades came up well after two goes in the CA bath. The black stuff was a real pain, so I recommend using gloves for this stage of the process - I had to use Oomph ( a citric acid liquid sold by Bunnies) to get the black off. Finally coated with some wax to keep from rusting
I tried a badly rusted try square (not mine) to clean, and after two goes of bathing in CA, then washing and scrubbing with steel wool, it was still rough to the touch, so I put it on the brass wire brush on the grinder. Was not pitted, and came up well, but looked terrible with all the black marks, presumably where the rust had been converted. Again, finished off with some wax - not worth doing all the polishing.
You are right about the smell; reminded me of sulphuric / hydrochloric acid from my student chemistry days. I actually left them all in the CA bath overnight for the 2nd immersion, no adverse affects that I could see.
Thanks for putting us on to this method, Brettregards,
Dengy
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16th September 2012, 08:55 PM #8
My pleasure Jill. Just watch out for the overnight thing - it may well cause pitting in steel (but not so much in cast iron).
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16th September 2012, 09:15 PM #9
Don't think I'll ever drink orange juice again
To be old and wise you must first be young and stupid!
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17th September 2012, 07:49 AM #10SENIOR MEMBER
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Citric acid is a much used product. My son who is a plasterer puts it in his mix to keep it from setting quickly and a friend who is a stingless beekeeper uses it to put into his sugar and water nectar substitute to convert the cane sugar sucrose to fructose and glucose.
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17th September 2012, 09:51 PM #11
Thanks for the post! Very clear and helpful. I have been using Electrolysis and look forward to trying this and compare the results.
Cheers,
Steck
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18th September 2012, 07:41 AM #12Senior Member
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If you live around Sydney join The Traditional Tools Group. We have citric acid in bulk for resale to members at a very good price (The Traditional Tools Group (Inc.)). On the website you'll also find a very good tutorial on using the stuff.
Cheerio,
Virg.
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18th September 2012, 07:54 AM #13
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15th October 2012, 01:33 AM #14
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11th December 2012, 11:49 AM #15Senior Member
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Hi guys,
Jill mentioned the black marks left after removing rust with acid looking terrible. I have also had this experience when using acetic acid rather than citric acid.
Do the black marks have any effect on the function/condition of the tool, or is it just an aesthetic thing? If it's just aesthetic I can live with it
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