Electro Gas Welding:
Electro Gas Welding is an arc welding process that uses an arc between a continuous filler metal electrode and the weld pool, employing vertical position welding with backing to confine the molten weld metal. Electro gas welding is very much similar to electro slag welding except that an inert gas such as carbon di oxide is used to shield the weld from oxidation and there is a continuous arc as in the case of submerged arc welding, to provide the heat for heating the weld pool.
Again, the flux, instead of being supplied to the weld zone through a hopper, is incorporated into the electrode itself in the form of flux-cored electrodes, or sometimes the process may be carried out without using the flux in which case there is no flux covering on the top of the molten metal pool.
Electro gas welding process is used for welding low and medium carbon steels, alloy steels, and austenite stainless steels.
Plates from 12.5 to 75 mm in thickness can be welded. For thicker plates, it is preferable to use electro slag welding instead of electro gas welding because it may be difficult to obtain adequate shielding gas coverage with the latter process.
CO2 gas is used as an inert gas to protect the welding from atmospheric contamination.
History of Electro gas welding:
The first thick plate vertical welding method was electro slag welding. The demand arose immediately for equipment that would apply the process to thinner sections. Then, in 1961, laboratory studies with an electro slag welding machine adapted to feed auxiliary gas shielding around a flux-cored electrode revealed the vertical welding of 13mm thin plates. This technique is called electro gas welding.
Features of Electro gas welding:
1. High deposition single pass welding with code quality welds
2. Carriage and rail system to handle vertical seams up to 3 m
3. Linear oscillator to weld up to 40 mm of the plate in a single pass
4. Powered lateral travel frame to create an “indoor” atmosphere for high-quality site welding
5. Weld thickness ranges from 12 mm to 75 mm.
6. Metals welded are steel, titanium, and aluminium alloys.
Applications of Electro gas welding:
Building of Storage tanks, Vertical Vessels, Blast Furnaces, Chemical Furnaces, Ship Building, thick-walled and large diameter pipes, Bridges, etc
Advantages of Electro Gas Welding:
1. Weld is better visible to the operator
2. Restarting the weld is quicker.
3. Welded joints have better mechanical properties such as impact strength
5. Less angular distortion due to a small number of welding passes
6. The heat–affected zone can be softened and embrittle, caused by the welding heat input.
Disadvantages of Electro Gas Welding:
1. The welds produced are not as clean and crack-free as those produced by electro slag welding.
2. It has more porosity, particularly for thicker jobs.
3. Incomplete Fusion to One Sidewall is caused by asymmetric thermal conditions such as poor heat distribution and insufficient heat
4. Overlap is caused by weld metal flowing out of the joint without melting the base metal.
5. Hot cracking can be caused by the partial dissolution of the copper molding shoes. Here, the cracks are generally near the surface.
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