angelhair
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Welding Nichrome wire
I wish to join some o.8mm nichrome end to end using an oxy torch. before anyone says it's too small, you can't do it, let me say that I have done it
very well with thinner copper wire.
What I wan't to now is, is a neutral flame the right one to use?
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kilowatt
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Nichrome has quite a tenacious oxide coating, and so is much more difficult to join than copper. It may be possible with a neutral or reducing flame,
or it may require a TIG torch with it's inert shielding gas. I have accidentally welded nichrome wire by electrolysis in a molten salt bath before,
so this may be a good simple way to join it intentionally as well. All that is needed is the nichrome joint to be the cathode, and another piece of
nichrome wire to be the anode.
http://chrisf.4hv.org/projects/chem/HPIM1495.JPG
The mind cannot decide the truth; it can only find the truth.
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garage chemist
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I make my own type K thermocouples from the wires (one is nichrome, the other mostly nickel) with, incidentally, also 0,8mm diameter.
I do this by twisting the wires together on a length of about 3cm, briefly holding the twisted section into the flame to heat it, and then dipping it
in borax powder so that it sticks to the wire.
I then carefully heat the wire with the borax so that the borax loses its crystal water (foaming, steaming) and flows onto and between both wires and
covers them.
Then I melt the tip of the wires (0,5cm) together into a small sphere, using a small sharp flame (it's either neutral or oxidising, don't know for
sure). The molten borax dissolves the oxides- without borax or another flux, nichrome couldn't be welded because of its tough oxide layer.
The connection is very reliable and strong.
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Magpie
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Although my experience may not be relevant to your situation, I will relate it just in case it is.
It was just the other day when I needed to weld two ends of a nichrome wire for a heater element. So, I searched on the internet and some said that
the secret was using an acid flux (zinc chloride, HCl). So I tried it. Didn't work. Then I called the one man in my community that I thought might
have the answer: an AOOF owner of an antiquated electrical repair store - a dying breed - very rare. His crusty response was "you can't weld it."
I replied that I'd heard (on the internet, of course) that it could be silver soldered. He says "what good will that do if the melting point of
silver is below the operating temperature of the wire?" Duh. He said you have to use a SS crimp. So that's what I did. Works great.
[Edited on 27-10-2009 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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kilowatt
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You should send him some welded nichrome wires. I wonder what he'd think. 
The mind cannot decide the truth; it can only find the truth.
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densest
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I've welded nichrome wire two ways: oxy/gas and pulsed electrical spot welding.
For gas welding, carbon embrittles nichrome, so use a lot of flux (fluoride based flux is what I use) and prefer hydrogen before methane (natural gas)
before propane before acetylene. Use a somewhat oxidizing flame. It should hiss a little. There's a very nice little torch sold under the name "little
torch" which is very useful for that sort of work.
For spot welding, I use a homebrew capacitor/IGBT setup which delivers about 500A peak and tungsten electrodes. For that, you need to have a lot of
pressure and make sure the wires being joined have been cleaned until shiny. One zap and it's done.
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merrlin
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Quote: Originally posted by densest  |
For spot welding, I use a homebrew capacitor/IGBT setup which delivers about 500A peak and tungsten electrodes. For that, you need to have a lot of
pressure and make sure the wires being joined have been cleaned until shiny. One zap and it's done.
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A similar but somewhat cruder method for a butt weld is to connect each of two wires to a charged capacitor and shove them into opposite ends of a
short piece of glass tubing (e.g., capillary tubing) of slightly larger diameter. The arc melts the ends of the wires just before impact.
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Eclectic
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Yep, Oxy-gas with fluoride flux seems to work just fine.
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donalderrand
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Welding the dissimilar metals has too many complications. A common approach would be that you twist the nichrome to a double or triple ply for few
inches & then screw the clamp to your copper wire. This will reduce the resistance of nichrome near termination & therefore the heat that
generated near the termination. This will also lower heat loss down the copper.
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Chemetix
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Tig welding works fine for Nichrome and Kanthal, I've used nichrome as filler before but spot pulsing the two wires generates a blob of fused metal.
0.8mm should work well on the lowest amp setting.
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