On Wed, 24 Nov 2004 22:47:02 -0600, "Tim Williams"
wrote:

Propane and air, at atmospheric pressure, will certainly get you there but
you need to confine the heat.

No, that's not it.

Steel isn't cut by "propane and oxygen", or even "acetylene and
oxygen". The fuel gas is just there to heat the steel to ignition
temperature, the actual cut is done by a reaction between pure oxygen
and steel. If you do try and cut with just heat rather than oxidation,
you'll find the kerf fills with molten iron slag anyway. In a big
cut and a thermic lance, you can even take the heating torch away and
run with a pure oxygen feed to a pure steel flame.

Air is only 21% oxygen, which isn't enough to cut steel by burning it.
If you tried you'd also have an excess of notrogen in there which
would be "robbing" the oxygen and contributing little heat. You can't
even fix this by using high-pressure compressed air.

--
Smert' spamionam