oxidizing flame is a bit more difficult to make than the
regulators and the torch from the system, double check
adjustment for other flames. To adjust for the
the cylinder valves to make sure they are closed
oxidizing flame, first adjust to a neutral flame and then
securely, and reinstall the cylinder valve protection
open the oxygen valve until the inner cone is about
cap.
one-tenth of its original length. An oxidizing flame
makes a hissing sound, and the inner cone is somewhat
pointed and purplish in color at the tip. The oxidizing
OXYACETYLENE CUTTING
flame has a limited use and is harmful to many metals.
When it is applied to steel, the oxidizing flame causes
Oxyacetylene cutting is the most commonly used
the molten metal to foam and give off sparks. This
method of cutting ferrous metals by the application of
means that the extra amount of oxygen is combining
heat. The principle of oxyacetylene cutting is simple.
with the steel, causing the metal to burn. However, the
The metal is heated to its ignition temperature by
oxidizing flame does have its uses. A slightly oxidizing
oxyacetylene flames. Then a jet of pure oxygen is
flame is used to braze weld steel and cast iron, and a
directed at the hot metal, and a chemical reaction
stronger oxidizing flame is used for fusion welding of
known as OXIDATION takes place. Oxidation is a
brass and bronze. You will have to determine the
familiar chemical reaction. When it occurs rapidly, it
amount of excess oxygen to use in this type of flame
adjustment by watching the molten metal.
is called COMBUSTION or BURNING; when it
occurs slowly, it is called RUSTING. When metal is
being cut by the oxyacetylene torch method, the
EXTINGUISHING THE FLAME
oxidation of the metal is extremely rapid-in short, the
To extinguish the oxyacetylene flame and to
metal actually burns. The heat liberated by the burning
secure equipment after completing a job, or when work
of the iron or steel melts the iron oxide formed by the
is to be interrupted temporarily, the following steps
chemical reaction, and it also heats the pure iron or
should be taken:
steel. The molten material runs off as slag, exposing
more iron or steel to the oxygen jet.
1. Close the acetylene needle valve first; this
extinguishes the flame and prevents a flashback.
In oxyacetylene cutting, only that portion of the
(Flashback is discussed later in this chapter.) Then close
metal that is in the direct path of the oxygen jet is
the oxygen needle valve.
oxidized. Thus, a narrow slit (called a kerf) is formed
in the metal as the cutting progresses. Most of the
2. Close both oxygen and acetylene cylinder
valves. Leave the oxygen and acetylene regulators open
material removed from the kerf is in the form of oxides
temporarily.
(products of the oxidation reaction). The remainder of
the material removed from the kerf is pure metal,
3. Open the acetylene needle valve on the torch and
which is blown or washed out of the kerf by the force
allow gas in the hose to escape for 5 to 15 seconds. Do
of the oxygen jet.
not allow gas to escape into a small or closed
compartment. Close the acetylene needle valve.
Since oxidation of the metal is a vital part of the
oxyacetylene cutting process, this process is not
4. Open the oxygen needle valve on the torch.
suitable for metals that do not oxidize readily, such as
Allow gas in the hose to escape for 5 to 15 seconds.
copper, brass, stainless steel, and so on. Low-carbon
Close the valve.
steels are easily cut by the oxyacetylene cutting
5. Close both oxygen and acetylene cylinder
process, but special techniques (described later in this
regulators by backing out the adjusting screws until they
chapter) are required for the oxyacetylene cutting of
are loose.
many other metals.
The foregoing procedure should be followed
The walls of the kerf formed by oxyacetylene
whenever work is interrupted for an indefinite period.
cutting should be fairly smooth and parallel. When you
If work is to stop for only a few minutes, securing
develop skill in handling the torch, you will be able to
cylinder valves and draining the hose is not necessary.
hold the cut to within reasonably close tolerances.
However, for any indefinite work stoppage, the entire
extinguishing and securing procedure should be
Also, you will be able to guide the cut along straight,
followed. For overnight work stoppage in areas other
curved, or irregular lines, and to cut bevels or other
than the shop, you should always remove the pressure
shapes that require holding the torch at an angle.
8-9
