Subject: Re: Carbon electrodes

From: C++ Freak <[email-masked]>
Date: 29 Jul 1996 13:46:17 GMT

Ordinary 4.5 Volts flat batteries for $2 each can be a good source.
They have 3 cells in it with a carbon rod (1/4" diameter, 3" length) each.
However, the rest is mainly MnO2 which could stain your clothes unwashably
and should be treated as hazardous waste. They work well for currents up to
150 A ,but are consumed rather quickly.

Graphite stirring rods available at jewelry supply shops do better.
They have less wear during usage and are environmentally friendly 
(no obsolete MnO2 waste).

I tried both with an electric AC 150 A welder and it really gets hot
(over 2000 C in the bath, 3000 C in the arc). Charcoal also works, but
is consumed VERY QUICKLY.
Using a graphite crucible as one electrode and a stick as the other seems
tempting, but the metal dissolves the crucible carbon easily.

There are a few BUTs:

- Arc is hard to control and sustain. It is easily be disrupted.
  Metal vapor may facilitate it (touch the metal when starting).
- Temperature hard to control.
- Amounts to be molten are minimal (max. 20 grams of iron @ 150 A)
- Virtually no refractory can withstand such temperatures (MgO is best)
  Even the 'high-temp grade' alumina melts and vaporizes easily.
- In carbon-dissolving metals (platinum group metals, including iron) the
  vaporized carbon dissolves which makes it brittle
- High vaporization losses of metal

But it melts cleaner than under an oxyfuel torch.
Check earlier postings on this (keyword "arc") it in this newsgroup.
If you have better experiences please email me.

NEVER LOOK DIRECTLY INTO THE ARC WITH(OUT) ANYTHING BUT AN ARC WELDING MASK !!!
or the night after you'll sit upright in your bed with painful eyes and keep
both yourself and your wife/girlfriend from sleeping.

Check Don Klipstein's arc page:

http://www.misty.com/~don/carbarc.html

Klaas