Which Gas Do I Use for Each Welding Application?
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Employee Spotlight Congratulations to Gary Farrell our Fill Plant Manager on 40 years of service to General Air! Gary is our first 40 year employee, and we celebrated this special occasion at the beginning of February. Thank you Gary for 40 years of service! Tech Talk So, Which Gas Do I Use for Each Welding Application? Last month Steve Duren looked at a specific welding application and resultant potential savings using SliverShield 7 for Gas Metal Arc and Flux Cored Arc welding. This month I would like to do a broad stroke educational and reference guide of gases used for Gas Tungsten Arc, Gas Metal Arc, and Flux Cored Arc welding applications. All arc welding processes utilize some method of protecting the molten weld pool from the atmosphere. Without proper gas shielding, deleterious effects such as porosity and reduced weld strength occur when the molten metal reacts with oxygen and nitrogen from the atmosphere. Selecting the proper shielding gas depends upon the metal being welded, the weld quality or metal properties desired, process performance and cost of the gas. with Art Waskey Gas Tungsten Arc Welding (GTAW) Gas Tungsten Arc Welding (GTAW) is performed primarily with two inert gases: argon, and helium. The chief factor influencing the effectiveness of a shielding gas is the gas density. Argon, with an atomic weight of 40, is about one and a half times heavier than air and ten times heavier than helium. Argon after leaving the torch nozzle tends to form a blanket over the weld, whereas helium tends to rise rapidly from the arc area. Argon When choosing a shielding gas, a fact that must be considered is the ionization potential of the gas. Ionization potential is measured in volts and is the point where the welding arc will be established between the electrode and the workpiece through the shielding gas. The ionization potential for argon is 15.7 volts, whereas helium is 24.5 volts. Therefore, argon will maintain a stable arc at a much lower welding level than helium (150 amps and lower). Argon also has a low thermal conductivity which means it is not a good conductor of heat. This results in a more compact, “pinpointed” arc area. Helium Due to a higher thermal conductivity, helium produces an expanded arc column, but with the heat at the center of the arc more intense, it creates a deeper penetration than argon. Therefore, helium or argonhelium mixtures are desirable on thick material and where high travel speeds are desired. www.generalair.com Gas Products|Welding Equipment|Cryogenics Continued... 2 877.782.8434 Hydrogen Just as helium is mixed with argon to take advantage of the best features of both gases, hydrogen is mixed with argon to further constrict the arc and produce a cleaner weld with a greater depth to width ratio (penetration). This mix is used primarily for welding austenitic stainless steel and some nickel alloys and increases travel speeds. Nitrogen Nitrogen when mixed with argon provides the capability of producing more energy to the work than argon alone. This can be particularly beneficial when welding materials of high conductivity such as copper. General Air GTAW recommendations: Description Composition SilverShield #1 75% argon/25% helium SilverShield #2 50% argon/50% helium ½-¾“ copper SilverShield #3 25% argon/75% helium SilverShield #11 97.5% argon/2.5% hydrogen SilverShield #12 95% argon/5% hydrogen Applications all ferrous and non-ferrous materials ¾- 1¼” aluminum, magnesium, titanium, 1¼”-up aluminum, magnesium, titanium, ¾“-up copper manual stainless steel automatic stainless steel Gas Metal Arc Welding (GMAW) Many different mixtures of shielding gases have been developed over the years depending on the type of transfer. Short Circuit Transfer- Steel CO2 shielding gas has long been a popular selection for short circuit transfer. It produces a deeper penetration than other pure gases, with slightly narrower bead width, With a hotter arc, it yields slightly faster travel speeds. Spatter is often a problem when using CO2 and because of the deep penetration, it is not recommended for steel thicknesses less than 1/8”. Argon-CO2 mixtures are preferred if reduced spatter, good weld appearance, and better mechanical properties are required. Opinions differ, but generally 8 to 10% CO2 is the minimum allowable mixture to ensure circuit transfer. A mixture of 92% argon- 8% CO2 is sometimes used as a “dual purpose” gas for it can be used on thin gauge steel (while short circuiting) or used with a spray transfer in the flat and horizontal positions on steel. Short Circuit Transfer- Stainless Steel 90% helium 7½ argon- 2 ½ CO2 is the most widely used gas for short circuiting on stainless steel. The helium helps to spread the arc, argon is a stabilizer, while the small amount of CO2 gives a good central penetration weld bead. The CO2 content must be kept fairly low to avoid carbon pick up. Short Circuit Transfer- Aluminum Argon spray transfer welding can generally be done in all positions. However, a short circuiting transfer or pulse-type transfer can be helpful when welding on thin aluminum. Spray & Pulse Transfer- Steel Although CO2 gas yields a globular transfer on steel at high current densities, we will include it here with spray transfer. Please note that the American Welding Society classifies spray transfer on mild steel as requiring at least an 80% argon mix. It produces a deep penetration, high deposition weld with significant spatter. Argon-O2 mixtures of up to 5% oxygen produce a hot arc with good wetting action into the weld joint. Continued... Did you know? General Air can save you money by implementing fabrication solutions that increase output and reduce labor costs. Contact our Productivity Enhancement Team at 303.892.7003 for more information. 3 www.generalair.com Gas Products|Welding Equipment|Cryogenics 877.782.8434 Argon-CO2 mixtures of up to 8% CO2 produce a tighter, more stable spray transfer on steel than argonoxygen and are more acceptable to smaller thicknesses. Spray & Pulse Transfer- Stainless Steel Argon-oxygen mixtures up to 2% oxygen produce a hot arc with good wetting action. Spray & Pulse Transfer- Aluminum Argon is widely used for welding in the spray transfer and can be generally done in all positions due to the fast freezing properties of aluminum. Argon-helium is used as the thickness increases. This will provide more heat and wetting action as the mass of aluminum increases. Helium is used for very thick sections of aluminum and provides added wetting ability with some sacrifice in penetration. Flux Cored Arc Welding (FCAW) Flux Cored Arc Welding (FCAW) is quite similar to Gas Metal Arc Welding as far as operation and equipment are concerned. However, the electrode is not solid but consists of a metal sheath surrounding a flux core. The electrode begins life as a flat metal strip, which is formed first into a ‘U’ shape. Flux and alloying materials are deposited into the ‘U’, which is then closed into a tube by a series of forming rolls. As in Gas Metal Arc Welding, the flux cored process depends on a gas shield to protect the weld zone from atmospheric contamination. The gas is either applied separately, in which case the electrode is referred to as a gas shielded, flux cored electrode, or it is generated from the decomposition of gas forming ingredients contained in the flux core (referred to as self shielding). In addition to the gas shield, some flux cored electrode produces a slag covering for further protection of the weld metal as it cools. Other metal cored products rely exclusively on the gas for shielding. These products are available in steel and stainless steel wires. CO2 is used widely with steel, flux cored products. Manufacturers formulate some wires that run better on CO2. Because CO2 is a less expensive gas, savings can be found with the proper formulated product. Argon-CO2 mixtures of up to 25% CO2 produce a tighter, stable spray transfer with very little spatter on steel and stainless steel. For thinner materials a lower CO2 concentration is recommended. General Air GMAW & FCAW recommendations: Description Composition Applications SilverShield #2 50% argon/50% helium spray, pulsed spray- ¾- 1¼” aluminum, magnesium, titanium, ½-¾” copper SilverShield #3 25% argon/75% Helium spray, pulsed spray- 1¼”-up aluminum, magnesium, titanium, ¾“-up copper SilverShield #4 98% argon/2% oxygen spray, pulsed spray- Steel and Stainless Steel SilverShield #5 95% argon/5% oxygen spray, pulsed spray- Steel SilverShield #6 90% argon/10% CO2 short circuit, spray, pulsed, FCAW- Steel SilverShield #7 85% argon/15% CO2 short circuit, spray, pulse,FCAW- Steel SilverShield #8 75% argon/25% CO2 short circuit, FCAW- Steel SilverShield #9 90% He/7.5% Ar/2.5%CO2 short circuit- Stainless Steel SilverShield #10 96.3% Ar/2.8% CO2/1%H2 short circuit, spray, pulsed- Stainless Steel SilverShield #20 81% Ar/18% He/1%CO2 short circuit, spray, pulsed- Steel SilverShield #23 91% Ar/5% CO2/4%O2 short circuit, FCAW- Steel SilverShield #24 90% Ar/8% CO2/2%O2 short circuit, FCAW- Steel SilverShield LF 75% Ar/15% CO2/10%He short circuit, spray, pulse, FCAW- Steel www.generalair.com Gas Products|Welding Equipment|Cryogenics 4 877.782.8434
