Another Gas Question

By Niekie3 (***)

Date 07-02-2002 19:28

I see nobody has replied to your question. I believe it is because it would require such a long and involved answer. I will however get the string going by giving a couple of general points: (I assume you are referring to GMAW and not FCAW)

1) With more than about 20% CO2, you can not get spray transfer. The 75/25 mix is more typical of a FCAW gas mixture than GMAW gas mixture.
2) The Ar + 3%O2 gas is more typical of the gas used for welding stainless steels rather than C/Steels, although then it is more typical to use up to 2% O2.
3) Ar + 4 - 8% O2 is typically used for welding C/Steel in spray transfer mode.
4) Both CO2 and O2 helps to make a fluid weld pool, although O2 is stronger in this regard.
5) Both CO2 and O2 can lead to element loss from the weld pool.
6) O2 can lead to oxides within the weld pool.
7) CO2 can lead to C pick-up within the weld pool.

My suggestion is to use either Ar + 10-20% CO2 or one of the Ar + CO2 + O2 mixes for the general welding of C/Steel.

Regards
Niekie Jooste

By Brian F. (*)

Date 07-03-2002 12:27

Thank you for your help.

By miguel P (*)

Date 07-03-2002 23:28

I just want to say a couple of thing about the myths in MIG welding.
1.- You say with more than 20% CO2 YOU CAN NOT GET SPRAY TRANSFER. THAT`S NO TRUE. YOU CAN PRODUCE SPATTER FREE SPRAY TRANSFER WITH ARGON + 20 CO2 WITH ALL COMMON DIAMETERS OF MIG WIRE. SET THE FOLLOWING PARAMETERS: WIRE DIAMETER 0.035. 420 IPM AND START WITH A MINIMUM OF 27 TO 28 VOLTS. ONCE SPARY TRANFER IS STABLISHED INCREASE THE VOLTAGE BY 2 OR 3 VOLTS SO A DISTINCT GAP OF 3 mm EXIST BETWEEN THE WIRE TIP AND THE WELD.
WITH ARGON + 25% CO2 YOU CAN GET SPRAY TRANSFER WITH WIRE DIAMETERS 0.045 AND LARGER. SET TEH WIERE FEDEER TO 420 IPM, 35 VOLT. HOWEVER THE WELDER PREFER TO WORK WITH LOWER PARAMETERS.
2. TO WELD STAINLESS STEELS WITH ARGON + 3%O2 IT`S NOT A GOOD PRACTICE. THE OXIGEN IS VERY OXIDIZING AND THE STAINLESS STEEL IS VERY AFFINITY TO OXIGEN. THE RESULT: A SOOT BLACK OXIDE ON THE METAL DIFFICULT TO CLEAN. I RECOMMEND TO USE A ARGON + 3% CO2 FOR STAINLESS STEEL APPLICATIONS. THIS PERCENT OF CO2 DOES NOT AFFECT THE CARBON CONTENT OF THE STEEL.
3. ARGON + 4 TO 8 % O2 ARE CONSIDER A LOW ENERGY MIX. THE STEEL WELDING DOES NOT BENEFIT OF THIS. THE RIGTH MIX FOR CARBON STEEL WELDING APPLICATIONS ARE ARGON + 15 - 20 CO2 (THICKNESS 2.5 AND LARGER). THIS MIX IMPROVE THE ELECTRON FLOW, INCREASE THE PENETRATION, BETTER WELD FLUID, LESS POROSITY POTENTIAL, PROVIDE A MORE DENSE, WIDER, AND HIGHER ENERGY PLASMA, LESS SENSITIVITY TO MILL SCALE.
4. THE O2 IS NOT STRONGER THAN CO2 IN TO MAKE A FLUID WELD POOL. SEE POINT 3.
5. I AGREE.
6. I AGREE.
REGARDS
MIGUEL.

By Wildturkey (**)

Date 07-03-2002 13:26

Brian,
Such a short question that has a long answer. Check out this link to Lincoln Electric. It is a MIG/MAG welding guide. I think it will answer most of your questions. If you have any more, then post them and we will try to answer them.
http://content.lincolnelectric.com/pdfs/products/literature/c4200.pdf

By Brian F. (*)

Date 07-03-2002 14:56

Great link! Thanks.