the center orifice for cutting. The compressed air in the
air jacket keeps water away from the cutting tip.
Oxygen Arc Cutting (OAC) Underwater
Oxygen arc cutting (OAC) uses an electrode and
electrode holder. The electrode holder is equipped
with an oxygen passage. The cutting oxygen flow is
controlled by a lever, Figure 29-18. The oxygen flows
through the hollow electrode to the kerf (cut).
Preheating is done by striking an arc between the
hollow electrode and the metal to be cut. Once the arc
is struck, the cutting oxygen lever is depressed and the
cutting begins. The arc and oxygen flow must be main-
tained as the torch is moved along the cutting line.
Oxygen arc cutting may be done above or below
water. Oxygen arc and plasma arc are two of the most
effective ways of cutting underwater.
Air Carbon Arc Cutting and Gouging
Air carbon arc cutting (CAC-A) uses an arc between
a carbon electrode and a base metal to heat and melt the
base metal. The electrode holder has holes just behind
the electrode through which high pressure air is blown.
This high pressure air blows the molten metal out of the
cutting area. While cutting goes through the entire thick-
ness of the base metal, gouging only carves out a
U-shaped groove in the base metal, Figure 29-19.
Exothermic Cutting
Exothermic cutting is a cutting process that once
started will continue to cut without any fuel gas or
electricity for an arc. Electrodes are filled with small
fuel rods that function as the heat source. Once the
electrode and rods start to burn, they will continue to
burn. Oxygen is used to accelerate the burning
process at a temperature of about 7600°F (4200°C).
The flow of high pressure oxygen also blows molten
metal away from the cutting area. Exothermic cutting
can cut any metal and also nonmetals like concrete.
This process can be used for underwater cutting.
Fuel rods in the electrode are called exothermic
cutting rods, Figure 29-20. These are usually 3/16″,
1/4″ or 3/8″ (4.8 mm, 6.4 mm, or 9.5 mm) in diameter.
Larger tubes, called burning bars, have a diameter of
.540″ up to 1.05″ (13.7 mm up to 26.7 mm), Figure 29-21.
Laser Beam Cutting (LBC)
Lasers (particularly the CO2 laser) can cut mild
steel, stainless steel, and even titanium cheaply and
quickly. Laser beam cutting (LBC) produces clean-cut
edges. Numerically controlled pulsed laser beams can
also be used to drill or pierce clean holes of extremely
small diameter in production parts. An oxygen jet is
sometimes used with laser beam equipment to drill or
pierce. Holes larger than .014″ (.36 mm) are generally
made with conventional drill bits.
Welding Technology Fundamentals
360
Figure 29-18. An underwater oxygen arc cutting (OAC)
torch. The arc furnishes the heat for cutting while oxygen oxi-
dizes the metal and blows it away. A hollow electrode carries
the cutting oxygen to the spot that is being cut. (Arcair, a
Thermadyne Company)
Figure 29-19. The air carbon arc cutting process is being used to gouge a groove into a base metal. High pressure air blows the
molten metal from the gouging area. (Arcair, a division of Thermadyne Industries, Inc.)