Root concavity
Root concavity is a depression of the weld root below the base material surface, usually due to insufficient weld metal deposition at the back side.
Physical-Chemical Mechanism of Action
During the welding process, a weld forms between the materials to be joined. If the weld metal is not sufficiently deposited on the back side, an area remains unchanged and sinks below the surface of the base material.
Metallurgical Relevance & Risks in Welding
Root sag can lead to various problems: it increases stress in the weld, which can cause cracks or deformation. Furthermore, it can impair the mechanical properties of the weld and shorten its service life.
Workshop Practice & Instructions
To avoid root sag, it is crucial to ensure sufficient weld metal deposit on the back side. This can be achieved by careful selection of the welding process and parameters. For TIG welding, the polarity should be set so that the arc is distributed over the entire weld metal area. For MIG welding, sufficient gas shielding and correct gas flow are crucial.