Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gas tungsten arc welding. Their purpose is to protect the weld area from atmospheric gases, such as oxygen, nitrogen, carbon dioxide, and water vapor. Depending on the materials being welded, these gases can reduce the quality of the weld or make the welding process more difficult to use. Other arc welding processes use other methods of protecting the weld from the atmosphere as well – shielded metal arc welding, for example, uses an electrode covered in a flux that produces carbon dioxide when consumed, a semi-inert gas that is an acceptable shielding gas for welding steel. An inert gas is any gas that, in a given circumstance, is not reactive. ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ... Gas metal arc welding (GMAW), commonly called metal inert gas (MIG) welding, is a semi-automatic or automatic arc welding process which utilizes a welding gun through which a continuous and consumable wire electrode and an inert or semi-inert shielding gas is fed. ... A high output GTAW and SMAW welding power supply Gas tungsten arc welding (GTAW) is commonly known as tungsten inert gas welding (TIG), however since some process variations utilize active (other than inert) shielding gases, the correct technical term is GTAW. In this process a non-consumable tungsten electrode is... General Name, Symbol, Number Oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16 (VIA), 2, p Density, Hardness 1. ... General Name, Symbol, Number Nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15 (VA), 2, p Density 1. ... Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. ... General properties of water vapor Evaporation/sublimation Whenever a water molecule leaves a surface, it is said to have evaporated. ... Shielded metal arc welding Shielded metal arc welding (SMAW) is also known as stick welding or manual metal arc welding (MMA) and is one of the most common forms of welding. ... An electrode is a conductor used to make contact with a nonmetallic part of a circuit (e. ... The flux visualized. ...

Common shielding gases

Shielding gases fall into two categories—inert or semi-inert. Only two of the noble gases, helium and argon, are cost effective enough to be used in welding. These inert gases are used in gas tungsten arc welding, and also in gas metal arc welding for the welding of non-ferrous materials. Semi-inert shielding gases, or active shield gases, include carbon dioxide, oxygen, nitrogen, and hydrogen. Most of these gases, in large quantities, would damage the weld, but when used in small, controlled quantities, they can improve weld characteristics. The noble gases are a chemical series. ... General Name, Symbol, Number Helium, He, 2 Atomic mass 4. ... General Name, Symbol, Number argon, Ar, 18 Chemical series noble gases Group, Period, Block 18 (VIIIA), 3, p Density, Hardness 1. ...

Applications

The applications of shielding gases are limited primarily by the cost of the gas, the cost of the equipment, and by the location of the welding. Some shielding gases, like argon, are expensive, limiting its use. The equipment used for the delivery of the gas is also an added cost, and as a result, processes like shielded metal arc welding, which require less expensive equipment, might be preferred in certain situations. Finally, because atmospheric movements can cause the dispersion of the shielding gas around the weld, welding processes that require shielding gases are only done indoors, where the environment is stable and atmospheric gases can be effectively prevented from entering the weld area.

References

• Cary, Howard B. and Scott C. Helzer (2005). Modern Welding Technology. Upper Saddle River, New Jersey: Pearson Education. ISBN 0131130295.