Welding TIG
In GTAW the arc is struck between the work-piece and a non-consumable tungsten electrode
The tungsten electrode should be alloyed with thorium when welding stainless steel. The argon gas is supplied through the electrode holder. This shielding gas, which should be 99.9% argon, shields the weld zone from the atmosphere, thus ensuring an oxide-free weld. The filler wire is fed into the arc from the side. This may be done either manually or automatically.
The welding of light-gauge stainless sheet in thicknesses of 0.5-1.5 mm, as well as the running of root welds, is sometimes carried out without using a filler and takes place by direct coalescence of the abutting faces. However, in the case of restrained fabrications, especially involving stabilised materials, there is a risk of crack formation if the bead is too light.
When welding heavy-gauge plate, a GTAW filler wire of the same type as the parent metal or with a higher alloy is required. The core wire of a covered electrode or a piece of the plate must never be used for GTAW.
The use of inner gas shield is generally necessary for the welding of pipe. Argon is usually used but cheaper gases such as nitrogen or formier gas can also be employed. This latter gas consists of a mixture of 92% nitrogen and 8% hydrogen. The additional gas shield is necessary for achieving a clean, oxide-free root surface.
While manual GTAW is more expensive than metal-arc welding, especially for sheets of over 2 mm in thickness, the automatic processes are more economical than metal-arc welding due to their speed and reliability. These are employed predominantly in batch production.
