Shielding Gas

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Shielding gas

From Wikipedia, the free encyclopedia

Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gastungsten arc welding. Their purpose is to protect the weld area from atmospheric gases, such as oxygen, nitrogen, carbon dioxide, and water vapour. Depending on the materials being welded, theseatmospheric 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.Improper choice of a welding gas can lead to a porous and weak weld, or to excessive spatter; the latter, while not affecting the weld itself, causes loss of productivity due to the manpower needed to removethe scattered drops.

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 inwelding. These inert gases are used in gas tungsten arc welding, and also in gas metal arc welding for the welding of non-ferrous materials. Pure argon and helium are used only for some nonferrousmetals. 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 insmall, controlled quantities, can improve weld characteristics.
Applications
The applications of shielding gases are limited primarily by the cost of the gas, the cost of the equipment, and by thelocation 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...
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