Shielding Gas: Mixes & Applications

Considerations of shielding gases are limited by the cost of the gas and equipment, as well as the location of the welding. Argon is more costly, so this limits its practicality for many applications. Equipment used for delivery and storage of the gas is an additional cost. Shielded metal arc welding requires less expensive equipment so it is preferred for some applications.

Most welding processes that require shielding gases are done indoors. Atmospheric movements can disperse the shielding gas around the weld; the environment is more stable indoors and atmospheric gasses can be kept out of the weld zone.

Rate of Flow

The rate of gas flow depends upon weld geometry, speed, current, gas type, and metal transfer mode. A flat welding surface requires a higher flow because gas will disperse more quickly than a grooved surface. A faster weld speed means more gas for adequate coverage. A higher current means more gas. When working with helium, as opposed to argon, you’ll need more gas.

Variations of GMAW require different flow rates. Small weld pools of short circuiting and pulsed spray do well with about 10 L/min (20 ft3/hr). Globular transfer should be at 15 L/min (30 ft3/hr). The spray transfer variation normally requires more because of higher heat input and a larger weld pool; try for 20-25 L/min (40-50 ft3/hr).

Common Mixes

Argon and carbon dioxide mixes may be used for short arc welding of pipes, some flux cored arc welding, small-scale hobbyist welding, short circuit and spray transfer of carbon steel, low alloy steels, and general production. Specific application will depend on percentage of each gas in the combination. A 50/50 mix is good for the short arc welding of pipes, increase argon as you go through the previous list.

Argon oxygen mixes may contain one to five percent oxygen. O-5, or 95% argon/5% oxygen, is the most common gas for general carbon steel welding. The oxygen allows higher speed welding. More than 5% will oxidize the electrode, increasing porosity in the deposit (if deoxidizers are not used). Addition of 2% oxygen to argon is used for spray arc on stainless steel, carbon steel, and low alloy steel.  Oxygen encourages spray transfer, essential for spray arc and pulsed spray arc GMAW. A 1% oxygen addition to argon is used for stainless steel.

Argon helium, at 75/25 respectively, is used for nonferrous base with higher heat input for a good weld appearance. 50/50 is used for nonferrous metals thinner than 3/4 inch and high-speed mechanized welding. 25/75 is used for thick aluminum.

Argon hydrogen mix is primarily used for joining austenitic stainless steel with GTAW. Hydrogen increases heat input while reducing atmosphere and improving weld cleanliness. Hydrogen also improves travel speed when compared to pure argon.

There are many other gas mixes and applications. For more information consult your gas and welding supplier and your equipment’s manual. Baker’s Gas carries these industrial gases.