Simple question...

[ZINOM]

I was thinking the other day, and wondered why when you weld electrically you need a protective "atmosphere" (gasses or flux coating)....but when using a torch, no protection from oxides and nitrides is necessary.

It seems like a simple question but I'm sure the answer is complex....and interesting.

Thanks for any input.

John

[macona]

When you burn fuel in a torch you get H2O and CO2. Both of these are relatively inert when it comes to most metals. Exception being Stainless where you cant weld or cut with a torch.

CO2 is used as a cover shield for mig. Basically anything to keep the N2 and O2 away from the metal when its molten.

[PTSideshow]

As has been said, inert atmosphere around the molten metal, to prevent embrittlement, and oxides forming in the metal pool which is the bane of all liquid metal working techniques. Along with a host of other problems. You what to displace all the oxygen for it.
:D

[camdigger]

"no protection"?!?? I was always under the impression that the torch flame itself provided sheilding. In fact, IIRC there is a reference book on torch welding that recommended a slightly carburizing flame specifically to avoid any free, unconsumed oxygen in contact with the weld puddle.:confused:

[ZINOM]

I KNEW you guys would shed some light on this for me....as usual :)

Thanks for the time.

John

[oldtiffie]

When you burn fuel in a torch you get H2O and CO2. Both of these are relatively inert when it comes to most metals. Exception being Stainless where you cant weld or cut with a torch.

CO2 is used as a cover shield for mig. Basically anything to keep the N2 and O2 away from the metal when its molten.

Argon is also used as an inert gas in MIG - TIG too? There are a whole range of specialist shielding gas "mixes".

You can cut but not weld pretty well anything that is electrically conductive - SS included - with a plasma-arc cutter.

You can cut and weld pretty well anything metallic - SS included - with a "Cobra" torch.

http://bbs.homeshopmachinist.net/showthread.php?t=25480

http://www.google.com.au/search?hl=en&q=cobra+torch&btnG=Search&meta=

Check the links and videos here:
http://amweld.com.au/index.htm

http://www.cobratorches.com/1.html?sm=15933

[macona]

100% Argon can only be used for Mig aluminum and Tig only. Its a mess if you try to mig steel with it.

Plasma is a whole different process than torch cutting. Torch cutting relies on an exothermic reaction of oxygen and the iron in the steel. Once the cut is started you cam maintain cutting with oxygen alone. Fuel is no longer needed.

Plasma is a two fold cutting process, there is the extreme hear of the arc plus a chemical reaction of the plasma gas and the metal being cut. This applies to steel and stainless. There are actually special gas mixes for higher end plasmas with o2 being used as plasma gas for steel.

When you cut things copper and aluminum you are relying solely on the plasma arc as the plasma gas really does not react with the metal. Thats one of the reasons you get less cut capacity when cutting aluminum.

You can cut non-metallic thing with plasma as well. Put a sheet of steel over what you want to cut and the plasma will cut through that as well, Supposedly you can cut glass this way. Never tried it.

I remember seeing one of the henrob aka cobra torches when I was a kid. They were a toy then and a toy now.

[PTSideshow]

I remember seeing one of the henrob aka cobra torches when I was a kid. They were a toy then and a toy now.

Spoken from somebody that has probably never used one.

I have had one for years and it does everything they claim. As with anything in life, practice does make it better.
:D

[oldtiffie]

I support PTSideshow.

The "Henrob"/"Cobra" is not, never was, and won't be a replacement for a commercial MIG/TIG in a commercial environment - it was never meant to be - and so - isn't.

But what it is is a very good tool for the smaller user or HSM-er who has an oxy-acet set, but doesn't have the power supply - or the funds or floor-space for an industrial MIG especially, nor does he need the expense and inconvenience of buying and filling multiple bottles of different gas-mixes for different material that he may only use occasionally or rarely. No MIG torch "consumables" either.

I have one - and it is great. It takes up no bench-top or floor space and is as easily moved as my oxy-acet set.

I haven't checked, but I've been told that they are very reasonable on eBay and CraigsList.