From owner-freebsd-chat Thu Oct 11 21: 5:14 2001 Delivered-To: freebsd-chat@freebsd.org Received: from snipe.mail.pas.earthlink.net (snipe.mail.pas.earthlink.net [207.217.120.62]) by hub.freebsd.org (Postfix) with ESMTP id A302337B408 for ; Thu, 11 Oct 2001 21:05:08 -0700 (PDT) Received: from blossom.cjclark.org (dialup-209.245.129.110.Dial1.SanJose1.Level3.net [209.245.129.110]) by snipe.mail.pas.earthlink.net (8.11.5/8.9.3) with ESMTP id f9C44wd12438; Thu, 11 Oct 2001 21:04:58 -0700 (PDT) Received: (from cjc@localhost) by blossom.cjclark.org (8.11.6/8.11.3) id f9C44Y502451; Thu, 11 Oct 2001 21:04:34 -0700 (PDT) (envelope-from cjc) Date: Thu, 11 Oct 2001 21:04:26 -0700 From: "Crist J. Clark" To: "Gary W. Swearingen" Cc: freebsd-chat@FreeBSD.ORG Subject: Re: Use of the UNIX Trademark Message-ID: <20011011210426.D293@blossom.cjclark.org> Reply-To: cjclark@alum.mit.edu References: <007701c15216$867d47c0$1401a8c0@tedm.placo.com> <6xzo6xssir.o6x@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <6xzo6xssir.o6x@localhost.localdomain>; from swear@blarg.net on Thu, Oct 11, 2001 at 03:47:56PM -0700 Sender: owner-freebsd-chat@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org On Thu, Oct 11, 2001 at 03:47:56PM -0700, Gary W. Swearingen wrote: > Brad Knowles 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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message