Figure 8-22.—Cutting buttonhead rivets with a low-velocity cutting tip.
Special Cutting Techniques in the carburizing flame ignites when it combines with
the cutting oxygen deep in the kerf, thus increasing
Carbon steels containing up to 1.0 percent carbon
both the intensity and the distribution of the preheat.
are easily cut with the oxyacetylene cutting torch.
For cutting cast iron, the length of the feather on the
Nonferrous metals, however, and ferrous metals such
preheating flame should be approximately equal to the
as cast iron, carbon steels containing more than 1.0
thickness of the cast iron. A slightly less carburizing
percent carbon, and many alloy steels can be
flame is used for cutting stainless steel.
successfully flame cut only if special techniques are
used. These special techniques include using more
INTRODUCTION OF IRON OR LOW-
intense and more widely distributed preheat; using
CARBON STEEL.—Introducing iron or low-carbon
different flame adjustments; introducing iron or
steel into the cutting area greatly simplifies the cutting
low-carbon steel into the cutting area; varying the
of some metals. When the oxides of a metal have a
torch movements; and using fluxes.
higher melting point than the metal itself, the oxides
PREHEAT.—Preheating the metal before cutting
protect the base metal from the cutting action of the
reduces the amount of oxygen and fuel gas required to
oxygen. In such a metal, introducing iron or low-carb-
make the cut. It also tends to prevent or minimize
on steel into the cutting area solves the problem be-
distortion and to prevent surface hardness of the piece
cause the rapid oxidation of the iron or steel liberates
after the cut has been made. While preheating is
enough heat to melt the oxides that would otherwise
helpful in any cutting operation, it is essential for some
interfere with the cutting. When alloying elements are
of the metals and alloys that are not easily cut. The
responsible for the difficulty of cutting the metal, the
preheating temperatures generally used for
introduction of iron or low-carbon steel reduces the
oxyacetylene cutting range from 200° to about 600°F,
percentage of these alloying elements and so makes
although considerably higher temperatures are
the metal easier to cut.
occasionally used.
Several techniques are used to introduce iron or
Preheating is usually accomplished by using the
low-carbon steel into the cutting area. An easily cut
preheating orifices in the cutting tip. Special tips
steel waster plate may be clamped firmly to the surface
having larger and more numerous preheating orifices
of the metal to be cut; a steel welding rod may be fed
are available for cutting cast iron and other materials
into the kerf as the cutting proceeds; a bead of
that require intense and widely distributed preheat.
low-carbon steel may be deposited along the line of cut
Preheating furnaces are sometimes used to bring heavy
before the cut is made; or finely divided iron powder
sections to a uniform preheat temperature.
may be blown into the stream of cutting oxygen
FLAME ADJUSTMENT.—A neutral preheat-
through special orifices in the cutting tip.
ing flame is used for most oxyacetylene cutting. For Cast iron, chromium irons, stainless steels, and
some metals, however, other flame adjustments give various alloys having small ferrous content can be
better results. For example, a highly carburizing flame successfully cut with the oxyacetylene torch when iron
is used for preheating cast iron. The excess acetylene or low-carbon steel is introduced into the cutting area.
8-19
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