Unimig RAZOR MULTI 175, Operating Manual

Page: 43 / 56

43
RAZOR MULTI 175/220
OPERATING MANUAL
16. MMA: Welding Guide
One of the most common types of arc welding is Manual Metal Arc welding, also known as MMA 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. They are covered with a flux that gives
off gaseous vapours that serve as a shielding gas and provide 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 a 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 a 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. The flux on the electrode performs many different
functions.
These include:
• Producing a protective gas around the weld area.
• Providing fluxing elements and de-oxidisers.
• 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 adding filler metal to the molten pool. These additional functions
are provided mainly by the covering on the electrode.
Core wire
Flux coating
Gas shield from flux melt
Arc with core wire melt
Flux residue forms slag cover
Weld metal