Can someone please explain to me why/how welding with CO2 is beneficial? I understand the purpose of welding gas as it relates to protecting the weld pool from oxygen. It is my understanding though that a "non-reactive" gas such as Ar or He must be used. I don't think CO2 is considered non-reactive.
Also, is there any time when 75-25 or 100% CO2 is used and Ar cannot be used?
1.) CO2 is primarily used as a shielding gas in GMAW in the short circuiting transfer mode on mild steel. It provides greater penetration than the mixed gasses such as 75/25. However the Argon mixes produce less spatter. Also some argon/C02 and Ar/C02/O2 gas combinations are used to achieve spray transfer.
2.) You are correct. CO2 is considered reactive as is O2 when used as a GMAW shield gas.
3.) Straight argon is generally not used with GMAW in Short Circuiting or Spray transfer modes applied to mild steel.
CO2 is much cheaper than argon so if the job can be done with it cleanly it is often a good choice.
www.weldreality.com has vast amounts of text on this subject and is a good place to look for technical data.
Another great place is your very own U.S. Army online welding data bank at http://www.adtdl.army.mil/cgi-bin/atdl.dll/tc/9-237/toc.htm
Thanks Lawrence, I've seen bits and pieces of those military training welding manuals all over the net and have been asking around for quite some time as to their source with no luck. I'll be adding the link and some of the reference to my site soon. http://www.brainfarth.com/bone.html Thanks again.
-Brainfarth
Actually, the biggest use for welding with CO2 is with flux core arc welding. It provides better operating characteristics than solid wire with CO2. The main reason to have a reactive gas in the weld shielding gas, is that the arc is more stable. CO2 is also cheaper, and as compared to high argon mixes, is more comfortable for the welder (less heat).
Another consideration with CO2 is along with greater penetration, you get more smoke and more spatter. If clean-up and/or air quality are concerns, you may want to use a mixed gas.
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