Welding Processes Handbook
This explanatory guide to the commercially significant and commonly-used welding processes covers the design of welded joints, quality assurance and costing, and can be applied to all instruction levels.
TABLE OF CONTENTS Welding Processes Handbook
1.5: Shielding Gases
1.5 Shielding Gases
The most important reason to use a shielding gas is to prevent the molten metal from the harmful effect of the air. Even small amounts of oxygen in the air will oxidise the alloying elements and create slag inclusions. Nitrogen is solved in the hot melted material but when it solidifies the solubility decreases and the evaporating gas will form pores. Nitrogen can also be a cause of brittleness. The shielding gas also influences the welding properties and has great importance for the penetration and weld bead geometry.
Argon (Ar)
Argon is one of the most popular shielding gases thanks to its suitable properties. As an inert gas it has no chemical interaction with other materials. Therefore it is suitable for sensible materials such as aluminium and stainless steel. At MIG welding of mild steel an addition of CO 2 or a small amount of oxygen will increase the welding properties, especially for short arc welding. Contents of up to 20 % CO 2 improves the penetration (limits the risk of lack of fusion) while 5 8 % will give reduced spatter.
Helium (He)
Helium like argon is an inert gas. It gives more heat input to the joint. Mixed with argon it increases welding speed and is advantageous for the penetration in thick-walled aluminium or copper where it compensates for the high heat conduction.
Drawbacks with helium is a high cost and the low density. At TIG welding, high contents of helium will reduce the...
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