Gas tungsten arc welding
Tungsten electrodes as per AWS
- EWP. Pure tungsten . green colour
- EWce-2. 97.3% Tungsten.2% cerium oxide.orange colour
- EW-La1 98.3% Tungsten. 1%Lanthanum oxide. Black colour
- EW-Th1. 98.3 Tungsten. 1% Thorium oxide. Yellow colour
- EW-Th2. 98% Tungsten.2% Thorium oxide. Red colour
- EW Zr1. 99.1 %Tugsten . 0.25% Zirconium oxide . Brown colour
EWG. 94.5 %Tungsten. Remainder not specified. Gray colour
Shielded gases:
1.Argon 99.5% purity – Almost all materials
2.Argon + 5% hydrogen – stainless steel, nickel alloys
3.Argon +25% Helium – Aluminium alloys
4.Nitrogen – copper alloys
Parameter guidelines:
Stainless steels:
1.Thickness(mm) 0.8 2 4
2.Current(amps) 15-30 70-110 110-200
3.Electrode dia(mm) 1 1.5-2 2
4.Filler wire dia(mm) ——- 2 2-3
5.Welding speed(mm/min) 300-350 175-225 100-150
6.Argon flow rate(lit/min) 3 4 5
Argon is used more extensively than helium for shielding because argon offers the following advantages:
1. Smoother, quieter arc action;
2. Reduced penetration;
3. Cleaning action when welding materials such as
aluminum and magnesium;
4. Lower cost and greater availability;
5. Lower flow rates for good shielding;
6. Better cross-draft resistance; and
7.Easy arc starting
Argon 5% hydrogen can be used for deep penetration.
Stainless steels and nickel base alloys are welded for tube to tube sheet welds.