Slag is a nonmetallic component that exists in the weld, on the surface or between layers.
Slag inclusion is a type of welding defect
that is easily visible in the weld.
The slag is usually spherical or needle-shaped, with dimensions ranging from a few micrometers to several millimeters and can penetrate the entire thickness of the weld.
The presence of slag causes concentrated stress which reduces the durability and productivity of the weld metal. The amount of slag allowed is specified in the manufacturing requirements of the solder joint.
Slag inclusion causes:
Slag inclusion - causes
The phenomenon of the slag inclusion is as a results of following reasons:
- Welding current density is too small ,which is difficult to provide enough heat for molten metal and it leads to the fact that slag might be impossible to float on the weld surface
- The welding speed is too fast.
-The weld edge is not completely cleaned or workers do not remove layers of slag before welding.
- Welding angle and travel rate of welding rod are not suitable.
- Welding pool is cooled down too fast to float slags
How to prevent the slag inclusion
Slag inclusion remedies
- Increase current density and increase the arc stop period.
- Adjust the welding speed, don't let occur the situation of mixture between slag and the weld pool or slag flows forward in the melting zone
- Clean up the edge and get rid of all slags of the previous welding layers before welding
- Make an approriate adjustment for the electrode angle and electrode travel rate
- Reducing rapid cooling of the weld pool