Machinery's Handbook, 31st Edition
Gas Tungsten Arc Welding 1599 The electrode selected must suit the application and the current capacity of the power source. Table 19. Current Ranges for EWP and EWZr GTAW Electrodes
Ampere Range AC Balanced
Ampere Range AC Unbalanced
Electrode
in. 1 ∕ 16 3 ∕ 32
(mm) (1.6) (2.4) (3.2)
EWP
EWZr
EWP
EWZr
30–80
60–120 100–180 160–250 200–320
50–100 100–160 150–210 200–275
70–150 140–235 225–325 300–400
60–130
100–180 160–240
1 ∕ 8
(4)
5 ∕ 32
Table 20. Electrode and Current Recommendations for Carbon, Low-Alloy, and Stainless Steels
Electrode Diameter
Filler Rod Diameter
Material Thickness
Current Range (amps)
in. 1 ∕ 16
(mm) (1.6) (3.2) (4.8)
in. 1 ∕ 16 3 ∕ 32 3 ∕ 32
(mm) (1.6) (2.4) (2.4)
in. 1 ∕ 16 3 ∕ 32
(mm) (1.6) (2.4) (3.2)
DCEN EWTh
60–100 150–170 180–220
1 ∕ 8
3 ∕ 16
1 ∕ 8
1 ∕ 4 260–300 Note: The shielding gas is argon at 15 to 20 cu ft/h (CFH). For stainless steel, reduce the current by approximately 10 percent. (6.4) 1 ∕ 8 (3.2) 5 ∕ 32 (7.2)
Table 21. Recommendations for GTAW Welding of Aluminum with EWP Electrodes Using AC and High-Frequency Current
Filler Rod Diameter
Material Thickness
Electrode Diameter
AC Current Range
in. 1 ∕ 16
(mm) (1.6) (3.2) (4.8)
in. 1 ∕ 16 3 ∕ 32
(mm) (1.6) (2.4) (3.2)
in. 1 ∕ 16 3 ∕ 32
(mm) (1.6) (2.4) (3.2)
(amps) 40–70
70–125 110–170
1 ∕ 8
3 ∕ 16
1 ∕ 8
1 ∕ 8
1 ∕ 4 170–220 Thoriated Electrodes: In contrast with the pure EWP electrodes, thoriated electrodes have a higher melting temperature and up to about 50 percent more current-carrying capacity, with superior arc starting and arc stability. These electrodes are typically the first choice for critical DC welding applications, but do not have the potential to maintain a rounded ball shape at the tip. The best welding mode for these electrodes is with the tip ground to a tapered or fine point. (6.4) 5 ∕ 32 (4) 3 ∕ 16 (4.8) Zirconiated Electrodes: Tungsten electrodes with zirconium are practical for critical applications and have less sensitivity to contamination and superior current capacity than pure tungsten electrodes. Protecting and Prolonging Electrode Life: To improve tungsten electrode life, the tip should be tapered in accordance with the manufacturer’s recommendations. There must also be preflow, postflow shielding gas coverage to protect the electrode before and after the weld. When possible, high frequency should be used to avoid scratch starts, which contaminate the electrode. The shortest possible electrode extension should be employed, to avoid the possibility of the electrode touching the filler or weld metal. The grinding wheel used to sharpen the tungsten must not be contaminated from grinding other metals or with dirt.
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