Which phenomenon pulls contamination up onto the hot tungsten?

• A. gas pressure
• B. surface tension
• C. gravity
• D. magnetic field

Answer: (B)

Surface tension in the molten weld pool causes capillary action that drags liquid up along the hot tungsten electrode. When the arc melts metal and oxides, the liquid metal wets the tungsten and climbs the electrode surface to minimize its surface area. This wetting pulls contaminants—like oxides—from the pool onto the tungsten, contaminating the tip and degrading arc stability and weld quality. Gas pressure and gravity don’t actively move molten metal upward toward the tungsten, and magnetic fields aren’t a controlling factor in this TIG setup, so the pulling mechanism is the surface-tension-driven wetting of the tungsten by the molten metal.