4.2.3 Types of Electrodes
Electrodes for shielded metal arc welding generally comprise a coated, solid electrode wire (core) of
limited length (300 to 400 mm or 12 to 16 in long). Occasionally, the solid electrode can be replaced by
a metallic sheath containing metal powders with the objective of adding specific alloying elements to
the weld metal.
The covering on the electrodes can be applied either by an extrusion process or by dipping, though
extrusion is far more common. The covering itself contains several ingredients depending on the type
of electrode. The function of these ingredients is generally one of the following:
- provide a gas shield to prevent contamination of the weld metal by atmospheric gases
- provide a slag cover to protect the hot weld metal from atmospheric contamination and
control the bead shape
- scavenge some of the impurities in the weld metal
- stabilize the arc by promoting electrical conduction across the arc; this is especially important
for AC welding where the arc effectively goes out and needs to be re-established after each
current reversal
- provide a means to add alloying elements to enhance mechanical/corrosion properties, and iron
powder to increase deposition rate