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Old 17th May 2017, 11:59 am   #1
PJL
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Default Alternative to Alum to dissolve rusty steel

I am trying to remove the remains of a very rusted in threaded steel rod from a blind hole in a brass end cap. I am using Alum and it is both slow and does not attack the rust, only clean steel exposed when I drilled out as much as I dare.

Has anyone had success with other chemical methods?
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Old 17th May 2017, 12:47 pm   #2
M0FYA Andy
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Default Re: Alternative to Alum to dissolve rusty steel

Is there any sort of electrolytic method you could use?
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Old 17th May 2017, 3:33 pm   #3
M0FYA Andy
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Default Re: Alternative to Alum to dissolve rusty steel

Will that not dissolve the brass as well?
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Old 17th May 2017, 3:46 pm   #4
G4YVM David
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Default Re: Alternative to Alum to dissolve rusty steel

Ive used Fertan rust treatment. Might be worth a try

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Old 17th May 2017, 8:33 pm   #5
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Default Re: Alternative to Alum to dissolve rusty steel

Phosphoric acid is used to attack rust. Dilute acid is called Coca Cola. Jenolite is more concentrated but doesn't taste so good.
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Old 17th May 2017, 9:06 pm   #6
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Default Re: Alternative to Alum to dissolve rusty steel

What diameter is the rod and the hole?

Professionals would use a spark-erosion machine

https://en.wikipedia.org/wiki/Electr...tion_machining

rather than trying to dissolve it (brass is tricky chemistry, being an alloy). I've had this technique used in the past to remove sheared-off steel studs from an aluminium alloy Jaguar engine-casting. Not cheap, but it works amazingly well.

The other option is an "anticlockwise drill bit" - for example http://www.phantomdrills.co.uk/shop/...and_drill_bits to drill down into the steel screw. The combination of heat from the drilling, and the unscrewing-torque as the drill-bit bites into the steel, coupled with the fact that once there's a hole through the steel it will 'relax' slightly from its grip in the thread - often the broken-off screw/stud will unscrew itself when you've only drilled a short way into it!
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Old 17th May 2017, 9:08 pm   #7
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Default Re: Alternative to Alum to dissolve rusty steel

Evapo-Rust worked pretty well on really rusty tools that suffered in a flood. I purchased mine from here:

http://www.frost.co.uk/evapo-rust-su...-us-quart.html

It might be worth a try on your task, but even if it isn't quite doing what you want, it is still worthwhile having some of this stuff in the workshop.
No connection, just a satisfied customer.
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Old 17th May 2017, 9:17 pm   #8
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Default Re: Alternative to Alum to dissolve rusty steel

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Originally Posted by TrevorG3VLF View Post
Phosphoric acid is used to attack rust. Dilute acid is called Coca Cola.
I follow what you are trying to say, but not quite correct - Coca-Cola contains dilute phosphoric acid (along with other stuff such as sugar and a bunch of secret ingredients). Incidentally, the old-style de-scaler used to contain phosphoric acid, too, but the modern stuff has replaced this with citric acid on the grounds of toxicity, I would think.

As it happens, there are several liquids called "phosphoric acid". They are chemically related, but any more on this would be both off-topic and boring to everyone else.
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Old 17th May 2017, 10:31 pm   #9
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Default Re: Alternative to Alum to dissolve rusty steel

Oxalic acid was used to remove cast iron brake dust from trains. I believe it is quite toxic and had to be used with care.
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Old 17th May 2017, 10:45 pm   #10
emeritus
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Default Re: Alternative to Alum to dissolve rusty steel

Have you tried heating it? Brass has a coefficient of linear expansion about 1.5 times greater than steel, so the steel should become looser the hotter it gets. I haven't had to try it with Brass/steel, but Brass has a coefficient of expansion only slightly less than Aluminium, and when I had to replace an aluminium piston in my car engine, it had to be heated to about 200 deg C in an oil bath to allow the steel gudgeon pin to be removed. At that temperature it just fell out, whereas at room temperature it was absolutely immovable.
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Old 18th May 2017, 1:17 am   #11
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Default Re: Alternative to Alum to dissolve rusty steel

I would have guessed that any chemical that would attack the steel would very likley take the zinc out of the brass, if not the copper too.

Phosphoric acid reacts to form an inhibiting layer of phosphate on steel, so that will not work well.

I tend to go with Tanuki on this; spark erosion or mechanical methods.

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Old 18th May 2017, 7:22 pm   #12
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Default Re: Alternative to Alum to dissolve rusty steel

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Oxalic acid was used to remove cast iron brake dust from trains. I believe it is quite toxic and had to be used with care.
Oxalic acid is most certainly toxic. It is present in small quantities in rhubarb (much more in the leaves, which is why you shouldn't eat them!). It also dissolves aluminium - if you cook rhubarb in an aluminium saucepan, the pan comes out shiny.
I wouldn't recommend anyone who isn't knowledgeable to use oxalic acid because of the toxicity factor, but it is good at removing rust stains from baths, sinks, etc.. (I am a trained research chemist).
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Old 18th May 2017, 7:30 pm   #13
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Default Re: Alternative to Alum to dissolve rusty steel

Oxalic acid is the active ingredient in Bar Keepers Friend cleaning powder.
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Old 18th May 2017, 8:13 pm   #14
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Default Re: Alternative to Alum to dissolve rusty steel

Alum is used by clock restorers so is pretty safe with brass. It's even used with aluminium. The threaded shaft is about 7mm diameter and it had completely rusted through at the entry point to the brass end cap!

I have ordered some oxalic acid primarily to try to remove some stains from a piece of dilapidated antique furniture but I will try it on this. Meanwhile I have persisted with the Alum and am about 80% done but it leaves the rust residue in the thread which is difficult to scrape off. It's not helped by being a blind hole as the gases hold the liquid back. Alum has had no affect on brass but I am not sure how bakelite knobs would cope as it has been at boiling point for a few hours so far.

Last edited by PJL; 18th May 2017 at 8:19 pm.
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Old 18th May 2017, 9:00 pm   #15
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Default Re: Alternative to Alum to dissolve rusty steel

I use Viakal which is a domestic acid limescale remover on heavily corroded brass. It strips the oxides and verdigris very well and does not discolour the brass unless left for a long time. Whenever you clean brass this way, you have to follow up with conventional cleaning as it reveals the corrosion damage on the surface layer of the brass.
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Old 18th May 2017, 10:14 pm   #16
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Default Re: Alternative to Alum to dissolve rusty steel

Quote:
Originally Posted by PJL View Post
it leaves the rust residue in the thread which is difficult to scrape off.
Can you run a tap into the hole to clear the thread?
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Old 18th May 2017, 11:36 pm   #17
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Default Re: Alternative to Alum to dissolve rusty steel

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Originally Posted by catswhisker8 View Post
Try Hydrochloric Acid (carefully!) I drip it on with a cotton bud or old small paintbrush-always works as reacts with ferric oxide but NOT for the Health and Safety people! Concentration is usually only about 25% and it's available on-line and good DIY outlets (plumber's depots also). GREAT FOR LOOSENING GRUB SCREWS.
A good place to ask ( if memory serves) is local monumental mason ( AKA gave stone maker), as I seem to remember that they use Hydrochloric Acid to clean old statues.
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