Chapter 29 Shielded Metal Arc Welding 793
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content and for high-deposition, out-of-position welds on thick plate. Many
types of low-hydrogen electrodes, such as EXX16, EXX18, and EXX28, are
available for use in SMAW. Low-hydrogen electrodes are the most widely
used SMAW welding rods for power generation, general fabrication,
shipbuilding, and pipeline welding.
An E7018 electrode is useful for welding in all positions, with the
exception of vertical-down. An E7018 electrode has a 25% to 40% iron powder
content that facilitates a smooth, quiet arc, generating low spatter. The
E7018 produces medium penetration and high-fill deposition. This electrode fi
produces a moderately heavy slag that is easy to remove.
Arc Length
Arc length is the distance from the electrode to the
base metal. An arc with correct length and amperage
produces a sharp, crackling sound like that of frying
bacon. Correct arc length is related to electrode
diameter. Maintaining the proper arc length is essential
for developing and maintaining the oxygen-free shield
around the molten weld pool. If the arc is too long,
the protective envelope collapses, Figure 29-24. A long
arc causes turbulence in the weld pool, resulting in
splashing and dispersion of spatter, or metal droplets, r
around the area of the bead. See Figure 29-25.
Examine the weld bead to determine if the arc
length is correct. Arc length for 1/16″ and 3/32″ ″
diameter electrodes should be about 1/16″. Arc length
for 1/8″ and 5/32″ ″ electrodes should be about 1/8″. ″
Electrode Angle
Under most conditions, the electrode is held nearly
perpendicular to the work, although tilting it ahead
10° to 15° in the direction of travel (referred to as a drag
angle) increases visibility of the weld pool. For welding
in the fl at, horizontal, and overhead positions, use a fl
drag welding technique. When uphill welding, tilt the
top of the electrode 10° to 15° down, away from the
direction of travel. This is referred to as a push angle.
See Figure 29-26.
The energy of the arc, combined with the
directional cup formed by the flux at the electrode fl
tip, creates arc force. Arc force is the force generated
by the heat from the electric arc and the burning of
the flux. When properly directed, the arc force aids in penetration of the fl
base metal. If the electrode angle is allowed to drop too much, the arc force
is directed over the molten weld pool at an angle that distorts the shape
and disturbs the calmness of the molten pool. The result is a long arc and
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Figure 29-24. Excessive arc length results in
spatter and collapse of the O2-free envelope.
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Figure 29-25. Spatter is the result of holding an arc
length that is too long.