Date: Thu, 11 Oct 2001 21:04:26 -0700 From: "Crist J. Clark" <cristjc@earthlink.net> To: "Gary W. Swearingen" <swear@blarg.net> Cc: freebsd-chat@FreeBSD.ORG Subject: Re: Use of the UNIX Trademark Message-ID: <20011011210426.D293@blossom.cjclark.org> In-Reply-To: <6xzo6xssir.o6x@localhost.localdomain>; from swear@blarg.net on Thu, Oct 11, 2001 at 03:47:56PM -0700 References: <007701c15216$867d47c0$1401a8c0@tedm.placo.com> <a05101003b7eb12fedac9@[194.78.144.28]> <6xzo6xssir.o6x@localhost.localdomain>
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On Thu, Oct 11, 2001 at 03:47:56PM -0700, Gary W. Swearingen wrote:
> Brad Knowles <brad.knowles@skynet.be> writes:
>
> > I've used such cylinders in Oxyacetylene cutting torches, and
> > brazing, but I don't recall them ever being able to generate
> > enough heat to do proper welding.
>
> I think enough heat is not the problem, but things like controllability
> and impurities (eg, Oxygen, air) in the weld are the main reason for
> using other technologies for common welding tasks.
>
> Also, I'll bet a tank of compressed air is a lot cheaper than one of
> either Oxygen or Nitrogen.
I've never seen a commerial cylinder of air. I don't know if you can
buy one. I would think that for the vast majority of applications it
is cheaper to buy an air compressor than to buy cylinders of air.
> Anyone know if highly compressed air is
> a dangerous fire hazard along the lines of Oxygen (but less so, of
> course)?
Air is about 80% nitrogen, 20% oxygen. When you compress it, it is
about 80% nitrogen, 20% oxygen, the concentrations don't
change. Making some approximations, the reactivity of the gas is
driven by the partial pressure of oxygen. The partial pressure of
oxygen in air is about 1/5 of that in pure oxygen. Compressed air is
about "five times" less reactive than pure oxygen, whatever that
means.
> Also, does anyone know if different gases work better than others
> (ignoring dangerousness) because of their different compressibilites?
> (I'm not even sure what that means, but I know I can get more power
> out of squeezed rubber than squeezed steel.)
That probably is not going to drive the choice. If you want to go buy
a cylinder of gas for this use, nitrogen is ideal. It's cheap,
non-flammable, non-toxic, and other properties are good for
this. Oxygen is more expensive and explosive. Carbon dioxide is toxic
and has a big temperature drop when throttled, you can get
ice. Helium, argon or another noble gas is great but way more
expensive.
--
Crist J. Clark | cjclark@alum.mit.edu
| cjclark@jhu.edu
http://people.freebsd.org/~cjc/ | cjc@freebsd.org
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