Cutting with the acetylene turned off

[stuckmotor]

Every so often, I read that, after starting a cut, it's possible to turn off the acetylene and continue cutting using only oxygen. This is usually stated a part of an explanation that a torch burns metal instead of melting it. Has anyone here done this? Was the cut as good as if the acetylene had been on. Did the oxygen alone produce as much heat and distortion as both gasses would have? I'm tying to find out whether, the claim is true, and whether this is a practical method of cutting.

 

[Depmandog]

It is possible, but probably not practical for the average hobbyist. If you run the cut to fast you will lose the preheat and cutting will stop. If too slow, slag will build up / losing the preheat and the cut. More often then not, it's done in training classes to show proper preheat.

More success will be had in thicker material versus thinner.

Review the oxygen lance, a similar process. http://en.m.wikipedia.org/wiki/Thermal_lance
Which is oxygen cutting using a consumable iron tube. The iron tubing is consumed and provides oxidation that melts the material being cut. Some seriously thick material (like 6'!) can be pierced and cut using a lance.

 

[stuckmotor]

Thank you, Dean. I kind of figured, if it was practical there would be a button on a cutting torch to make turning off the acetylene easier. The link was interesting too.

 

[FarmDad]

 

[muddstopper]

I guess the video proves it can be done, but on that piece of metal, I could have had it cut before they got thru with the preheat. Doesnt seem practical for what I do.

 

[timster2]

Back when I knew everything I lost a bet to an old timer over this one. He used a welding torch not a cutting torch to cut some steel, preheated then cut off the fuel and used just the oxygen to make a cut. Cost me a few beers to learn that trick :drink:

 

[FarmDad]

IMO it is not practical for any real world application . It does demonstrate just how oxy/fuel cuts metal which can be real helpful to understand how to use it , and why you get the results that you get when getting started cutting and dont do things just quite " right " .

Oh and apparently if you practice it a bit you can get a few free beers LOL

 

[Arc weld]

Actually when cutting you are essentially rusting the steel away. The technical term for oxy/fuel cutting is rapid oxidation. Only if the steel is hot enough can cutting continue with only oxygen. On heavier steel it's common to preheat before and during cutting so you get the best cut and don't lose the cut. For cutting bevels they make special attachments that have 1 or 2 additional preheat torches to go along with the standard cutting tip. When cutting pipe with a beveler, it's common to run the torch around the pipe first to preheat it, then turn the cutting oxygen to cut it.

 

[N7943h]

I once was the proud owner of an old school bus that needed a new exhaust system from the manifold back and I went to an exhaust shop in Santa Maria to get a new system installed. The tech went to work removing the old system using only a oxy/acet welding torch which had the control knob on the front of the handle. He would preheat the metal and then turn off the fuel and cut with only the oxygen. He welded up the new system with the same torch. He only used that one tool. Very fast and impressive.

 

[stuckmotor]

All of these replies are very interesting. Thanks to everyone.