tinedge 15th April 2007, 08:30 PM Hi there
I have a project where I am considering soldering a copper sheet to a metal sheet,( steel, tinplate, zincalume etc).
From memory depending on the choice of metal used some form of chemical reaction can form over a period of time & create problems.
Unfortunatley I have long since forgotten the name of this reaction so I can't even look it up on the web.
Any suggestions or is my memory making something out of nothing?
Regards & many thanks
Mike
ozwinner 15th April 2007, 08:42 PM Electrolysis?
Al :)
Wood Butcher 15th April 2007, 09:03 PM Galvanic reaction (which is caused by a form of electrolysis;))
Wikipedia is a good start if you want some further reading
http://en.wikipedia.org/wiki/Galvanic_corrosion
2shane 15th April 2007, 10:01 PM Hmm it's only relative......
Copper and other metals reacting.... It's ONLY an issue relative to the ENVIRONMENT (humidity / free water / oxygen / salts or ionic solutions) and the proportional surface areas....
i.e. Brass Valves and copper piping screwed into a locomotive boiler... corrosion is not an issue.
Iron rivets in huge copper plates, submerged in salt water.... Rivets are gone in a week.
Copper and other metals soldered together, in a low humidity environment, indoors, occasionally wiped with WD-40, thin oil or waxy polish..... Corrosion is not an issue.
Metal Head 16th April 2007, 01:57 PM I would have thought brazing was the way to go, but then what would I know I am ony a machinist:wink:.
MH
eddie the eagle 16th April 2007, 02:40 PM crevice corrosion and galvanic corrosion are the killer, Mike.
With regards to the comment on a brass valve in a boiler, the steel around the valve thread goes.
However, as shane(?) pointed out, if the thing is dry, then there's no problem. Humidity or water exposure is.
Cheers,
eddie
joe greiner 16th April 2007, 10:56 PM Google [galvanic series area]. The first hit I got seems to be quite comprehensive.
http://www.eaa1000.av.org/technicl/corrosion/galvanic.htm
In general, the farther apart two metals are in the series, the more likelihood of corrosion, with the lower-number metal sacrificial. Area effects can ameliorate or exacerbate this phenomenon. See corollaries near the bottom of the page. For example, stainless steel rivets in aluminium sheets (like airplanes), OK; other way around, very bad.
[BTW, this is why they weld zinc or magnesium sacrificial anodes to ship hulls. (Steel welding strap cast in the anode.)]
Joe
tinedge 20th April 2007, 07:25 PM Hi guys
Thanks for the numerous replys .....this helps heaps. It certainly managed to jog my memory ref. what I should have remembered from those metal work classes so long ago....if only I hadn't been wagging!!!
Many Thanxs
Mike
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