Welding specialist Sean Young of Air Products outlines the role and benefits of different shielding gas compositions and how Air Products strives to best meet customer needs.
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True to its promise of outstanding customer service and secure and reliable supply, Young says that Air Products always places emphasis on each customer’s needs. “First, we ensure that we can always supply the gases our customers need. Second, we try to ensure that the best possible gas is used for each of their welding applications, since this is critical for improving weld quality and efficiency and to reduce unnecessary costs,” he says.
The role and benefits of shielding gases
Sean Young starts by noting the importance of protecting a molten weld pool from atmospheric contamination and oxidation, using either fluxes or shield gases. “Flux is used in shielded metal arc (SMA) electrodes and submerged arc processes, while shielding gases, are used in gas metal arc welding (GMAW), gas tungsten arc welding (GTAW) and most of the flux-cored welding processes,” he says.
“Reviewing the specific criteria related to a customer’s processes and providing guidance is essential. An assessment of the procedure, material and its thickness, and the preferred metal transfer should be conducted. Furthermore, to optimise the choice and ultimate quality of the weld, the porosity, spatter, penetration, bead profile and fusion are also considered,” he suggests.
The most frequently used mixtures and shielding gases with respective applications are:
- Argon: used for most GTAW applications and GMAW of non-ferrous materials.
- CO₂: used mostly for GMAW of steels in dip transfer mode.
- Ar/CO₂, Ar/O₂ and Ar/CO₂/O₂ gas mixtures: used for GMAW of carbon steel, stainless steel and other steel grades.
- Ar/He and Ar/H₂ mixtures: used for advanced GTAW applications.
- Ar/He/CO₂ and Ar/H₂/CO₂ mixtures: used for GMAW.
Argon and carbon dioxide both play a core shielding role in GMAW applications as they protect the weld metal from atmospheric oxygen and other contaminating elements.
Explaining the difference between the use of pure CO₂ and argon for GMAW welding, Young says that pure CO₂, which is the original shielding gas for GMAW, is widely used for general purpose welding of steel and is an effective shielding gas that prevents porosity. “Due to its inclination towards large droplet formation, however, it is restricted to the dip-transfer mode of metal transfer. Using pure CO₂ as the shielding gas can cause large volumes of spatter, which reduces the metal transfer efficiency, while increasing the welder’s arc time and the post-weld cleaning requirements,” Young explains.
Argon, on the other hand, is generally the dominant gas in any mixed shielding gas composition. In its pure form, argon is an inert gas, used to keep other gases away from the welding zone to prevent chemical reactions with the newly deposited, molten weld metal. Argon gas shielding is used in almost all GTA welding as well as for GMAW of aluminium alloys; copper and its alloys and other oxygen-sensitive materials.
Describing the role of mixing argon with small quantities of more active gases such CO₂ and O₂, he says these additives tend to make metal transfer softer and more stable, which reduces spatter. “Improved transfer stability makes the welding process less sensitive to welding parameters and more tolerant to voltage and current variations. This ultimately results in a reduction in machine set-up time and a noticeable improvement in overall productivity,” he says, adding that, for example, an argon/O₂ shielding gas mixture with 2% O₂ is ideal for most stainless steel welding applications.
“To improve the penetration of carbon steel joints, CO₂ can be added to the argon in a two-part mix. CO₂ increases the heat of the welding arc, which increases penetration and welding speed. He cautions that there is an approximate 20% CO₂ limit in the argon CO₂ mix, above which spatter and instability outweigh the penetration and speed advantages. “About 15% CO₂ is optimal, and in the case of thinner materials where deep penetration is not needed, 5% CO₂ is sufficient,” Young advises.
Describing the proven benefits of three-part mixtures, he says that each gas additive plays a different role in optimising the metal transfer and weld-metal properties for particular applications. He cites the three-part mixtures consisting of argon with a maximum of 15% CO₂ and 3% O₂, which deliver improved arc stability, penetration and bead profiles, while spatter is minimised and metal transfer characteristics are optimised.
“Three-part mixtures are extremely easy to use and the welding stability allows for more variations in setting parameters. Their use for steel-based welding will increase quality, productivity and efficiency, which ultimately leads to measurable increases in profitability.
“At Air Products, we strive to be a trusted partner to each our customers by providing them with the best solutions for their businesses, based on our knowledge and technical expertise. Our approach is simple: We determine the most suitable gases for a customer’s welding processes. Thereafter the customer can focus on the efficiency of the processes while we focus on a secure supply of the gases that best meet their specific requirements,” Young concludes.
