Importance of CO2 in Welding
While looking to improve welding performance, the choice of shielding gas by steel fabrication companies is significant. The primary purpose of shielding gas is to prevent exposure of the molten weld pool to oxygen, nitrogen and hydrogen contained in the atmosphere since reaction of these elements with the weld pool can create a variety of problems, including porosity and excessive spatter. Different shielding gases play important roles in determining weld penetration profiles, arc stability, mechanical properties of the finished weld and the transfer process. This is where carbon dioxide (CO2) plays a crucial role as a shielding gas in gas metal arc welding of carbon steels. This topic will be explored further in this blog.
Features of CO2 for Welding
Many MIG welding applications lend themselves to a variety of shielding gas choices, which depend on certain considerations. The cost of the gas, finished weld properties, preparation and post-weld clean up, the base material, weld transfer process and your productivity goals all need to be considered when selecting a shielding gas. Argon, Helium, Carbon Dioxide and Oxygen are the four most common shielding gases used in MIG welding, with each providing unique benefits and drawbacks in any given application. Carbon Dioxide (CO2) is the most common of the reactive gases used in MIG welding and the only one that can be used in its pure form without the addition of inert gas.
CO2 is also the least expensive of the common shielding gases, making an attractive choice when material costs are the main priority. Pure CO2 provides very deep weld penetration, which is useful for welding thick material; however, it also produces a less stable arc and more spatters than when it is mixed with other gases. It is also limited to only the short circuit process. For many fabrication companies which use advanced technologies in welding, including those that place emphasis on weld quality, appearance and reducing post-weld cleanup, a mixture of between 75 – 95 percent Argon and 5 – 25 percent CO2 will provide a more desirable combination of arc stability, puddle control and reduced spatter than pure CO2.
Benefits of CO2 in Welding
- Improved Penetration – Carbon dioxide shielding provides better joint penetration as it promotes high arc voltage during custom welding and assembling. In this way, you can achieve good results for sidewall and root penetration.
- Cost-Benefit – The advantage of low cost enhances its worth among other shielding gases. Using carbon dioxide shielding instead of oxygen, will not allow oxidation in the weld metal, as oxygen does. Being heavier, it provides better shielding characteristics. Though it is cheaper than Argon and Helium but comparatively fewer quality welds are obtained.
- Add-on Oxidizing – Due to the high-temperature arc, carbon dioxide dissociates into carbon monoxide and oxygen that encourages oxidation. In this case, a little bit oxidizing may prove an accompaniment to GMA welding of carbon steels, by reducing the polar spots during the process as the polar spot’s formation may cause unstable arc and spatter during welding. During spray transfer mode electrodes are connected to positive terminals (anode) of the power source and workpiece with negative (cathode), this type of settings constitutes to reverse polarity.
- Removal of Rust – This gas assists in the removal of rust present on the joint. It eliminates rusting by reacting with rust oxides, and in this way, other impurities are also removed. Apart from atmospheric protection, it also helps to prevent weld defects like porosity, lack of fusion, lack of penetration in the weld metal.
The Last Word
With the rise of MIG and TIG welding over the last century, gas is now accepted as a common commodity in workshops. There are many reasons as to why CO2 is often preferred as the shielding gas for GMA welding of carbon steels. It is enormously versatile and, in addition to the above, it helps to improve toughness and reduce surface tension of welds. Thus, the air we breathe out on an ongoing basis during our lives is a greenhouse gas – but is essential to gas welding projects!