Shrinkage-induced sag
Shrinkage-induced sagging occurs when the molten weld pool evaporates too quickly due to excessive heat input and gravity. This leads to waste of material and can cause uneven weld spacing and stresses.
Physicochemical Mechanism of Action
The molten weld pool evaporates under the influence of temperature and gravity. If evaporation is too fast, sagging occurs. This happens because the gas (oxygen) is repelled faster than the liquid weld material.
Metallurgical Relevance & Welding Risks
Shrinkage-induced sagging can lead to unequal weld joint gaps and stresses. This increases the risk of cracks and component failure. Additionally, material is wasted, which is economically unfavorable.
Workshop Practice & Instructions
To avoid shrinkage-related sagging, heat input should be controlled and not too high. An optimal evaporation rate can be achieved by carefully regulating temperature and gas flow. A typical target is an evaporation rate of about 1-2 % per minute, depending on the material used.