5
Specific Recommendations
LOW CARBON MILD STEEL
Short arc welding should be used for
welding thin materials in the flat position, bridging large gaps and all
welding out-of- position. Either CO2
or Ar-CO2 mixtures may be used. The conditions
in Table 8-1* were developed
using a C-25 (75% Ar - 25% CO2)
mixture. From the standpoint of arc stability, weld bead shape,
minimal spatter and resulting mechanical
properties of the weld, C-25 yields the best results for general
short arc welding.
For spray arc welding, Ar-O2
and Ar-CO2 mixtures may be used. For the same
reasons given above, the best
mixture for this type of welding is 95% Ar - 5% 02(0-5)
or C-8 since CO2 will not produce a spray
transfer. 95% Ar - 5% 02
was used to develop the conditions found in Table 8-2*. Spray arc welding should
be used in the flat position for single
or multi-pass welding of thicker material. When low currents are used,
vertical welds can be made using a
downhill arc travel. Either
the backhand or forehand welding technique may be interchangeably used for welding
in the flat position
with no adjustments to the conditions. Generally, the forehand technique provides
better visibility of the
weld joint and a flatter weld puddle. The backhand technique yields better penetration
and is sometimes found
to be easier by the inexperienced welder. In
addition, the vertical up and the vertical down technique can be used, but not
interchangeably. The travel speeds
associated with vertical down welding are much higher than that of vertical up.
Vertical down is usually
preferred for welding thinner material (up to 1/4 in. (6.4mm) thick) where speed
is important, and for root
passes in multi-pass welding. Vertical up welding is recommended for welding thicker
material where quality
and strength are required because of less tendency to ”cold lap.”
Figure
8-1 shows accurate burn-off characteristics for various size carbon
wires and Figure 8-2 shows
the deposition
rates for these wire-feed speeds. *Tables
8-1 and 8-2 are located at back of book
