Tungsten Electrodes

Tungsten is a very hard, steel gray metal that does not melt or vaporize in the heat of the arc. Tungsten retains it's hardness even at red heat. It has the highest melting point of all metals. However, in cases where the wrong electrode type, incorrect electrode size, improper current setting or poor technique is employed, alone or in any combination, tungsten particles may be transferred across the arc.

There are several considerations in selecting tungsten for GTAW. One of the main considerations is the welding current. Several factors are used to determine the weld current including base metal and thickness, shielding gas and type of torch employed.

Too high a current setting will usually cause the tungsten to disintegrate, a term called tungsten spitting, embedding tungsten into the weld producing voids or hard spots in machining or grinding.  

Charts are readily available that recommend tungsten sizes for current carrying capacities.

Pure tungsten electrodes are preferred for welding aluminum and magnesium because they form a ball on the end and a wider arc cone. This is preferred due to the oxides associated with these metals. Pure tungsten will not have the current carrying capacities that other tungstens have. Pure tungsten can be identified by a green band.

Thoriated Tungsten *

Thoriated tungsten is formulated with a small amount of thorium oxide which adds desirable characteristics to the electrode. Thorium increases the current carrying capacity of the electrode. Thoriated tungsten will not ball like pure tungsten, instead small projections form on the end of the tungsten which causes the arc to wander when using an AC current.

Thoriated tungsten is generally used with a DC current with the end of the tungsten sharpened to a point and used mainly to weld stainless and other steel alloys. Due to the sharpened point and other characteristics the arc cone is narrow.

Jim Lawless
Service Manager
Superior Welding Supply Co
jlawless@supweld.com