The common methods used in cutting metal are
oxygas flame cutting, air carbon-arc cutting, and
plasma-arc cutting. The method used depends on the
type of metal to be cut and the availability of equipment.
As a Steelworker, oxygas or air carbon-arc equipment
is the most common type of equipment available for
your use. Oxygas equipment is explained in this chapter
and air carbon-arc cutting is covered in chapter 7.
The oxygas cutting torch has many uses in steel-
work. At most naval activities, the Steelworker finds the
cutting torch an excellent tool for cutting ferrous metals.
This versatile tool is used for operations, such as bevel-
ing plate, cutting and beveling pipe, piercing holes in
steel plate, and cutting wire rope.
When using the oxygas cutting process, you heat a
spot on the metal to the kindling or ignition temperature
(between 1400°F and 1600°F for steels). The term for
this oxygas flame is the PREHEATING FLAME. Next,
you direct a jet of pure oxygen at the heated metal by
pressing a lever on the cutting torch. The oxygen causes
a chemical reaction known as OXIDATION to take place
rapidly. When oxidation occurs rapidly, it is called
COMBUSTION or BURNING. When it occurs slowly,
it is known as RUSTING.
When you use the oxygas torch method to cut metal,
the oxidation of the metal is extremely rapid and part of
the metal actually burns. The heat, liberated by the
burning of the iron or steel, melts the iron oxide formed
by the chemical reaction and accelerates the preheating
of the object you are cutting. The molten material runs
off as slag, exposing more iron or steel to the oxygen jet.
In oxygas cutting, only that portion of the metal that
is in the direct path of the oxygen jet is oxidized. The
narrow slit, formed in the metal as the cutting pro-
gresses, is called the kerf. Most of the material removed
from the kerf is in the form of oxides (products of the
oxidation reaction). The remainder of the material is
molten metal that is blown or washed out of the kerf by
the force of the oxygen jet.
The walls of the kerf formed by oxygas cutting of
ferrous metals should be fairly smooth and parallel to
each other. After developing your skills in handling the
torch, you can keep the cut within close tolerances;
guide the cut along straight, curved, or irregular lines;
and cut bevels or other shapes that require holding the
torch at an angle.
Partial oxidation of the metal is a vital part of the
oxygas cutting process. Because of this, metals that do
not oxidize readily are not suitable for oxygas cutting.
Carbon steels are easily cut by the oxygas process, but
special techniques (described later in this chapter) are
required for the cutting of many other metals.
OXYGAS CUTTING EQUIPMENT
An oxygas cutting outfit usually consists of a cylin-
der of acetylene or MAPP gas, a cylinder of oxygen, two
regulators, two lengths of hose with fittings, and a
cutting torch with tips (fig. 4-1). An oxygas cutting
outfit also is referred to as a cutting rig.
In addition to the basic equipment mentioned above,
numerous types of auxiliary equipment are used in
oxygas cutting. An important item is the spark igniter
that is used to light the torch (fig. 4-2, view A). Another
item you use is an apparatus wrench. It is similar in
design to the one shown in figure 4-2, view B. The
apparatus wrench is sometimes called a gang wrench
because it fits all the connections on the cutting rig. Note
that the wrench shown has a raised opening in the handle
that serves as an acetylene tank key.
Other common accessories include tip cleaners, cyl-
inder trucks, clamps, and holding jigs. Personal safety
apparel, such as goggles, hand shields, gloves, leather
aprons, sleeves, and leggings, are essential and should
be worn as required for the job at hand. Information on
safety apparel is also contained in chapter 3 of this text.
Oxygas cutting equipment can be stationary or port-
able. A portable oxygas outfit, such as the one shown in
figure 4-3, is an advantage when it is necessary to move
the equipment from one job to another.
To conduct your cutting requirements, you must be
able to set up the cutting equipment and make the
required adjustments needed to perform the cutting op-
eration. For this reason it is important you understand
the purpose and function of the basic pieces of equip-
ment that make up the cutting outfit. But, before discuss-
ing the equipment, lets look at the gases most often used
in cutting: acetylene, MAPP gas, and oxygen.