Match List I (Welding Defects) with List II (Causes) and select the correct answer :
List I
A. Spatter
B. Distortion
C. Slag inclusion
List II
1. Damp electrodes
2. Arc blow
3. Improper cleaning in multipass welding
4. Poor joint selection
Option (A)
Option (B)
Correct Option:
Question Solution:
Spatter: It is caused by arc blow.
Porosity is caused by the damp electrodes because they contain moisture and when the welding is taking place the evolution of the gases takes place, it leads to porosity.
Distortion is caused by the uneven distribution of the stresses and poor joint selection.
Porosity in the welding is caused by the presence of gases which get entrapped during the solidification friction process. The main gases that causes the porosity are hydrogen, oxygen and nitrogen. Though there are other gases such as the argon helium, carbon dioxide that are also present in the weld pool. In view of their insolubility would not cause porosity.
Hydrogen is the main cause of the porosity in the weld pool. Porosity if present in the large quantity would reduce the strength of the joint.
Distortion is caused mainly because of the shrinkages that takes place in the weldments.
Slag inclusion: Slag is formed by the reaction with the fluxes and is generally lighter, in view of its lower density, it will float on top of the weld pool and would be chipped off after solidification. However the stirring action of the high intensity arc would force the slag to go into the weld pool and if there is not enough time for it to float, may get solidified inside the fusion zone and ends up as the slag inclusion.
The factor causing the slag inclusion are:
(i) High viscosity of the weld metal.
(ii) Rapid solidification.
(iii) Insufficient welding heat.
(iv) Improper manipulation of the electrode.
(v) Under cut on the previous pass.
Slag inclusion like porosity, weakens the metal by providing discontinuities.