From: Wayde Allen (wallen@boulder.nist.gov)
Date: 05/05/00-03:16:42 PM Z
On Fri, 5 May 2000, Rod Fleming wrote:
> The "copper" rods are used in gas welding, not arc- it's just an anti-rust
> plating.
I think I agree with what you've said, but I don't think we are talking
about the same thing as far as "copper coated rods" go.
Yes, copper or rather copper clad brass rods are used with the acetylene
welders for brazing. The few carbon arc rods are a different animal, and
the ones I've seen seemed to have a very thin copper coating. I'd guess
to provide a low resistance path to help striking the arc.
> Not that difficult. They used clockwork mechanisms for WW2 searchlights,
> which were carbon arc.
I had assumed as much. So I guess the main concern is to get a slow
continuous feed?
> Personal experience with the carbon-arc brazing
> attachments for hobby welders suggests that you'll get 5-10 minutes out of a
> fixed position arc before the rods shorten so much that the arc dies. But
> you are getting an awful lot of light in that time. A problem might be that
> the intensity of the light from the arc may vary depending on the gap- I
> have not tested for this.
Agreed!
> You don't need to. Any hobby welding shop will sell a little low amp welder
> of about 120 to 150 amps, with a "brazing attachment" (they are useless for
> brazing BTW :-)for under £100.
My experience as well. I've seen several carbon arc brazing attachments,
but have never actually seen anyone use one for its intended purpose.
> flash, which was where this began. You would need to design out the heat
> issue and also the issue of deposition, because there will be some, even
> though no flux is present, but these problems should not be insurmountable,
> and you would have the huge advantage of not having to deal with potentially
> lethal power caps.
Yes, we mostly agree. I don't particularly agree about the supposed "huge
advantage" of not dealing with power capacitors. The carbon arc does get
by with a much lower voltage, but is a high current circuit. A flash uses
high voltage and relatively low current. High voltage isn't so much the
problem, although it does increase the chance of the discharge jumping out
to get you. For example, the spark you get from shuffling your feet
across the carpet is on the order of 100,000 volts, and I don't know of
anyone dying from that kind of discharge. What makes power circuits
dangerous is the much larger currents involved. Both the welder (carbon
arc) circuit and the power capacitor circuit should be treated with
respect.
- Wayde
(wallen@boulder.nist.gov)
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