Answer Happy

1.5 In GTAW the welding cable is connected to the tungsten electrode through a water-cooled copper contact tube, as shown in Figure 1.11. Why is the tube positioned near the lower end of the electrode instead of the top? 1.6 Measurements of the axial temperature distribution along the GTAW electrode have shown that the temperature drops sharply from the electrode tip toward the contact tube. Why? For instance, with a 2.4-mm-diameter W-ThO2 electrode at 150 A, the temperature drops from about 3600 K at the tip to about 2000 K at 5 mm above the tip. Under the same condition but with a W-CeO2 electrode, the tempera- ture drops from about 2700 K at the tip to about 1800 K at 5 mm above the tip (26). Which electrode can carry more current before melting and why?