3.3.3
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 vapours 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 lectrode 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 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 rovided mainly by the covering on the
electrode.
The Metal Wire Core works as conductor of the current that
maintains the arc. The core wire melts and is deposited into
the welding pool. The covering on a shielded metal arc welding
electrode is called Flux.
3.3.4
MMA
Welding
Fundamentals
Electrode Selection
As a general rule, the selection of an electrode is straight forward,in that it is only a matter of selecting
an electrode of similar composition to the parent metal. However, for some metals there is a choice of s
everal electrodes, each of which has particular properties to suit specific classes of work. It is
recommend to consult your welding supplier for the correct selection of electrode.
3.3.5
MMA
Welding
trouble
shooting
The following chart addresses some of the common problems of MMA welding. In all cases of
equipment malfunction, the manufacturer’s recommendations should be strictly adhered to and
followed.
