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J Harp
03-12-2011, 08:55 AM
I need to remove a broken brass screw from a carbon electrode. can a I use my derusting setup for this?

Lew Hartswick
03-12-2011, 09:11 AM
> can a I use my derusting setup for this?<
Not knowing what that is I couldn't say.
I think [note! think] that carbon, as in graphite, will not be atacked by
an acid, I would try , on a bit of the carbon, a drop of Nitric acid and if
no reaction would then proceed to disolve the brass with that.
...lew...

J Harp
03-12-2011, 11:51 AM
Thanks Lew; I tried the electrolisis, don't think it's going to work, it'l make a big green glob on the exposed brass but doesn't seem to reduce it's size.
I don't have a source for nitric acid, plus I've heard it's pretty nasty stuff, so I'll probably just have to replace it. The body of the screw is only about 3/32 and I doubt I could drill it without destroying the electrode.

K Barton
03-12-2011, 11:53 AM
I need to remove a broken brass screw from a carbon electrode. can a I use my derusting setup for this?

If I was going to try this I would use Sulferic Acid, as it will react with both the copper and the zinc in the Brass, to form either Copper Sulphate, or Zinc Sulphate in solution thereby removing the screw.

Ken

CountZero
03-12-2011, 12:09 PM
ferric chloride will dissolve the brass

Dr Stan
03-12-2011, 12:10 PM
If I was going to try this I would use Sulferic Acid, as it will react with both the copper and the zinc in the Brass, to form either Copper Sulphate, or Zinc Sulphate in solution thereby removing the screw.

Ken

and you can get sulfuric acid in the plumbing section of Home Depot etc as a drain opener.

drmico60
03-12-2011, 12:48 PM
Sulphuric acid will not dissolve the copper in the brass in the cold. Nitric acid will dissolve copper and zinc but beware of the gases that come off. The best bet would be one of the printed circuit board etchants such as ferric chloride or ammonium persulphate. It will be hard to decontaminate the carbon after using either of these.
Mike

Al Messer
03-12-2011, 05:06 PM
Household Ammonia will disolve Brass.

J Harp
03-12-2011, 05:53 PM
Gave it two hours in the battery acid, no luck.
I used a carbide burr in the Dremel to cut away enough of the graphite that I could get hold of the screw with pliers, still wouldn't budge. Found a brass screw with nut which would fit the wire terminal, chucked it, cut the head off and faced it. Drilled it 5/64 about 3/16 deep, and filed the stub of the old screw down till it would go in the hole.

I fluxed the pieces and soft soldered them together. Now I have a working vaporizer again. I just don't buy the throw away philosophy, if I can think of a way to fix it I will. Thanks for the ammonia tip Al, I'll try to remember that in case I have to do another one.

dhenry2001
03-13-2011, 08:20 AM
Contrary to some well intentioned advise, Home Depot doesn't sell "Sulfuric Acid" ie. "Battery Acid", as drain cleaner. Usually drain cleaner is a combination of sodium hydroxide (bleach), and sodium hypo-chlorate (lye) which I believe are both "basic chemicals", the opposite of acids. If either are mixed with sulfuric acid (you will be producing some pure chlorine gas) and we will be potentially losing several of our beloved Home Shop Machinist BBS members due to chlorine gas poisoning. People are poisoned or die every year from mixing drain cleaners and acids. Don't take my word for it, check with the American Association of Poison Control Centers.
I've seen some "Questionable" advice offered on this website (and many others) about different topics concerning such things as electrical wireing, welding tank storage, and other topics that if followed, have the the potential of getting someone injured.
There is a wealth of good advice available on this website, and I'm sure everyones intentions are good, but if there is any doubt about safety, check with an expert. Just my two cents. Good day.

Circlip
03-13-2011, 10:48 AM
Err,Sulfuric (Sulphuric in the mother country) does dissolve Copper.

H2SO4 + Cu = CuSO4 + H2, Copper Sulphate (Sulfate) and Hydrogen or it did when I was at school. The Zinc is reduced to Zinc Sulfate (Sulphate).

Regards Ian

rollin45
03-13-2011, 10:50 AM
ammonia will do the job

rollin'

joeloeffler
03-13-2011, 11:42 AM
The trumpet shop where I work uses a chemical bath that is largely sulfuric acid (granted, we add some mystery powder...) to strip nickel from trumpet valves that will be eventually resized by re-plating. If we break off a tap or steel screw on a brass part, we dump whatever it is in the strip tank for a few days till the offending steel is gone. The brass seems none the worse for the experience.

drmico60
03-13-2011, 12:09 PM
Err,Sulfuric (Sulphuric in the mother country) does dissolve Copper.

H2SO4 + Cu = CuSO4 + H2, Copper Sulphate (Sulfate) and Hydrogen or it did when I was at school. The Zinc is reduced to Zinc Sulfate (Sulphate).

Regards Ian

Sulphuric acid will not dissolve copper at room temperature. Copper is below hydrogen in the electrochemical series so it cannot displace hydrogen from the acid. Hot concentrated sulphuric acid will convert copper to copper sulphate according to the equation:
2 H2SO4 +Cu = CuSO4 + 2 H20 + SO2
This reaction is basically an oxidation reaction rather than a displacement reaction.
Mike

lazarus
03-13-2011, 04:00 PM
Hello HSM members, 1st time here. I've read a lot of very helpful tips on this site. Thanks for being here and sharing.

Quote:J Harp Gave it two hours in the battery acid, no luck.

If the OP used battery acid from a battery, or refill box/bag, it would have had to be boiled off till a dense smoke forms. If used straight from the battery, it will be severely diluted.

I'm not saying it will eat brass, just that battery acid must be distilled to get any good strength sulfuric acid.

Ben

J Harp
03-13-2011, 04:08 PM
Thanks for all the responses. I solved the problem without removing the broken screw, just built onto it. A whiff of acid fumes does me no good, I have respiratory problems, so I try to avoid strong chemicals whenever I can. I do appreciate the tips on chemistry.

Bill736
03-14-2011, 10:01 PM
I think it's best to mention that one post above switched the chemical identifications of chlorine bleach and lye. The active ingredient in chlorine bleach is sodium hypochlorite. Lye is sodium hydroxide, or potassium hydroxide. And another thing...all that work to save a cheap steam vaporizer ? I use them, but they only last about 8-10 months or so, before I spend another $20 on a new one. They used to be made to take apart and clean the carbon electrodes, but I notice more recent ones are not made to be taken apart. In any case, they tend to overheat after they get older, and will start to melt the plastic top housing . Be careful about using one too long.

J Harp
03-14-2011, 11:22 PM
Mine must have been the made to take apart kind, just remove four screws and pull the electrodes out and clean the crud off. I've done that several times and its still going strong with no evidence of overheating. Guess I'm cheap, I'd rather fix something than spend the twenty to get a newer model that's bound to be of lesser quality.

I did notice the mixup between lye and bleach, but I'm not chemically savvy enough to get in much of a discussion on the subject, so I let others handle the correction.

Circlip
03-15-2011, 03:42 AM
Sulphuric acid will not dissolve copper at room temperature.

Ahh, right, so the green colouration in the pickling bath in the Metalwork section at school, wasn't Copper Sulphate generated by sticking in Silver Soldered lumps of Copper to dissolve the flux and the coating on steel placed into the same bath wasn't really Copper??

Wonder what we were doing wrong, and NO heat involved.

Regards Ian.

ptjw7uk
03-15-2011, 04:27 AM
Not sure what the greenish lumps where in the pickling bath but memory serves that in my youth I spent many hours at the chemical bench analysing the copper content of brass and I can tell you that we used 25% sulphuric acid and it only dissolved the brass when on the hotplate until it fumed!
Dont know what the fumes did to me but the lab coats never lasted that long!

Peter

drmico60
03-15-2011, 01:10 PM
Ahh, right, so the green colouration in the pickling bath in the Metalwork section at school, wasn't Copper Sulphate generated by sticking in Silver Soldered lumps of Copper to dissolve the flux and the coating on steel placed into the same bath wasn't really Copper??

Wonder what we were doing wrong, and NO heat involved.

Regards Ian.

When the copper was silver soldered the surface of the copper is oxidised to copper oxide (the black colour on the heated copper). When this is dunked in the pickling solution will dissolved the copper oxide to form copper sulphate but the copper itself is not attacked.
Mike

KyMike
03-15-2011, 08:48 PM
>>> I need to remove a broken brass screw from a carbon electrode. can a I use my derusting setup for this? <<<

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I see you are in Louisville. Next time you need nitric acid, check with Antec Inc., 721 Bergman St., 635-2352. They have all sorts of chemicals in small quantities.

Mike