3.2.3
MMA
Welding
One of the most common types of arc welding is manual metal arc welding (MMA) or stick welding.
An electric current is used to strike an arc between the base material and a consumable electrode rod
or ‘stick’. The electrode rod is made of a material that is compatible with the base material being
welded and is covered with a flux that gives off gaseous vapors that serve as a shielding gas and
providing a layer of slag, both of which protect the weld area from atmospheric contamination. The
electrode core itself acts as filler material the residue from the flux that forms slag covering over the
weld metal must be chipped away after welding.
●The arc is initiated by momentarily touching the electrode to the base metal.
●The heat of the arc melts the surface of the base metal to form a molten pool at the end of the
electrode.
● The melted electrode metal is transferred across the arc into the molten pool and becomes the
deposited weld metal.
● The deposit is covered and protected by a slag which comes from the electrode coating.
● The arc and the immediate area are enveloped by an
atmosphere of protective gas.
Manual metal arc ( stick) electrodes have a solid metal wire core and a flux coating. These
electrodes are identified by the wire diameter and by a series of letters and numbers. The letters and
numbers identify the metal alloy and the intended use of the electrode.
The Metal Wire Core works as conductor of the current that maintains the arc. The core wire melts
and is deposited into thewelding pool.
The covering on a shielded metal arc welding electrode is called Flux.
The flux on the electrode performs many diferent functions.
These include:
● producing a protective gas around the weld area
● providing fluxing elements and deoxidizer
● creating a protective slag coating over the weld as it cools
● establishing arc characteristics
● adding alloying elements.
Covered electrodes serve many purposes in addition to filler metal tothe molten pool. These
additional functions are provided mainly by the covering on the electrode.
