Quality checks of stick electrode coating involves
Smoothness of coating: if extrusion pressure is less or more than the specified then coating will have rough surface, it is termed as under pressure and over pressure in quality language.
Drop test: from certain height electrode is dropped on the flat surface, if the coating is broken or peels of then it not accepted. To check the fragility of the coating this test is carried out
Visual after baking: after baking of electrode there may be possibility of cracking in coating, thus visual is carried out. And also sometimes there may be more shrinkage in coating as binder evaporates resulting in variation in surface finish and coating diameter.
Concentricity of electrode coating:
This is the most important quality check of electrode coating. This ensures uniform thickness of the coating around the core wire.
In SMAW process, the coating crater, or the cup-like formation of the coating, that extends beyond the melting core wire, performs the functions of concentrating and directing the arc.
Concentration and direction of the arc stream is attained by having coating crater, somewhat similar to the nozzle on a water hose, directing the flow of weld metal. When the coating is not concentric to the core wire, it can cause the condition as show in fig B.
The poor arc direction causes inconsistent weld beads, poor shielding, and lack of penetration. The electrode burns off unevenly, leaving a projection on the side where the coating is the heaviest.
Reference: ESAB arc welding technology manual
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