©
COPYRIGHT 1998 THE ESAB GROUP, INC. LESSON
II greater
than the current density of
the 1/4" wire at equal welding currents.
The resultant melt-off rate
of the solid wire is very high. If
we were to increase the current through
the 1/4" coated electrode
to increase the current density,
the resistance heating through
the 14" electrode length would be excessive,
and the rod would become so hot
that the coating would crack, rendering it
useless. The 1/16" wire carries the high current
a distance of less than 3/4", the approximate
distance from the end of the contact tip to the arc. 2.4.2
Metal
Transfer Modes
2.4.2.1 Spray
transfer is
a high current density process that rapidly deposits weld metal in
droplets smaller than the electrode
diameter. They are propelled in a straight line from the
center of the electrode. A shielding
gas mixture of Argon with 1% to 2% Oxygen is used for welding
mild and low alloy steel, and pure Argon or Argon-Helium mixtures are used for
weld- ing aluminum,
magnesium, copper, and nickel alloys. Welding current at which spray transfer
FIGURE 10 AREA
= .049 SQ. IN. AREA
= .0031 SQ. IN. CORE
WIRE FLUX
COATING COATED
ELECTRODE RELATIVE
SIZE OF ELECTRODES FOR WELDING AT 400 AMPS SOLID
WIRE 1/4"
1/16" .049
÷ .0031 = 16 A
A × 16 FIGURE
11 SPRAY
TRANSFER GLOBULAR
TRANSFER PULSE
TRANSFER MODES
OF METAL TRANSFER 1
2 3
SHORT CIRCUITING ARC METAL TRANSFER
takes place is relatively high and
will vary with the metal being welded, electrode diameter, and
the shielding gas being used. Deposition
rates are high and welding is usually limited to the flat
or horizontal fillet position. See Figure 11.
