Table 7-4.Table of Recommended Electrode Sizes, Current Settings, and Cutting Speeds for Carbon-Arc Cutting Different Thicknesses
of Steel Plate
More information on wearfacing applications may
The carbon-arc method of cutting is successful on
be obtained from the NCF Welding Materials Hand-
book, NAVFAC P-433.
Metals can be cut cleanly with a carbon electrode
arc because no foreign metals are introduced at the arc.
The cutting current should be 25 to 50 amps above the
welding current for the same thickness of metal.
The carbon electrode point should be ground so that
it is very sharp. During the actual cutting, move the
carbon electrode in a vertical elliptical movement to
undercut the metal; this aids in the removal of the molten
metal. As in oxygen cutting, a crescent motion is pre-
ferred. Figure 7-52 shows the relative positions of the
electrode and the work in the cutting of cast iron.
cast iron because the arc temperature is high enough to
melt the oxides formed. It is especially important to
undercut the cast-iron kerf to produce an even cut.
Position the electrode so the molten metal flows away
from the gouge or cutting areas. Table 7-4 is a list of
cutting speeds, plate thicknesses, and current settings
for carbon-arc cutting.
Because of the high currents required, the graphite
form of carbon electrode is better. To reduce the heating
effect on the electrode, you should not let it extend more
than 6 inches beyond the holder when cutting. If the
carbon burns away too fast, shorten the length that it
extends out of the electrode holder to as little as 3 inches.
Operating a carbon electrode at extremely high tempera-
tures causes its surface to oxidize and burn away, result-
ing in a rapid reduction in the electrode diameter.
Carbon-arc cutting does not require special gener-
ators. Standard arc-welding generators and other items
of arc-welding station equipment are suitable for use.
Straight polarity direct current (DCSP) is always used.
Because of the high temperature and the intensity
of the arc, choose a shade of helmet lens that is darker
than the normal shade you would use for welding on the
same thickness of metal. A number 12 or 14 lens shade
is recommended for carbon-arc welding or cutting.
AIR CARBON-ARC CUTTING
Air carbon-arc cutting (ACC) is a process of cutting,
piercing, or gouging metal by heating it to a molten state
Figure 7-52.Carbon-arc cutting on cast iron.
and then using compressed air to blow away the molten