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These include:
- Producing a protective gas around the weld area
- Providing uxing 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 ller metal tothe molten pool. These
additional functions are provided mainly by the covering on the electrode.
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
several electrodes, each of which has particular properties to suit speci c classes of work. It is
recommend to consult your welding supplier for the correct selection of electrode.
The size of the electrode generally depends on the thickness of the section being welded, and the
thicker the section the larger the electrode required. The table gives the maximum size of electrodes
that maybe used for various thicknesses of section base on using a general purpose type 6013
electrode.
Correct current selection for a particular job is an important factor in arc welding.With the current set
too low, di culty is experienced in striking and maintaining astable arc. The electrode tends to stick to
the work, penetration is poor and beads with a distinct rounded pro le will be deposited.Too high
current is accompanied by overheating of the electrode resulting undercut and burning through of
the base metal and producing excessive spatter. Normal current for a particular job may be
considered as the maximum, which can be used without burning through the work, over-heating the
electrode or producing a rough spattered surface.The table shows current ranges generally
recommended for a general purpose type 6013 electrode.
- Arc Length
To strike the arc, the electrode should be gently scraped on the work until the arc is established. There
is a simple rule for the proper arc length; it should be the shortest arc that gives a good surface to the
weld. An arc too long reduces penetration, produces spatter and gives a rough surface nish to the
Average thickness
of material
electrode diameter
1.0-2.0 mm
2.0-5.0 mm
5.0-8.0 mm
>8.0 mm
15
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Maximum
recommended
2.5 mm
3.2 mm
4.0 mm
5.0 mm
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