take care that the flow of slag or oxide is clean and unimpeded through the metal.
The torch should be moved forward just fast enough to allow oxidation to take,
place clear through the material, as the cut progresses.
g. Procedure (general}.
(1) Attach the proper cutting tip, for the thickness of the metal to be
cut, to the torch and adjust the oxyacetylene pressure in accordance with the
torch-cutting instructions (fig 16).
(2) Adjust the preheating flame to neutral.
(3) Hold the torch firmly with one hand in such a manner as to permit the
operation of the cutting-oxygen lever or trigger with the same hand. Use the other
hand to steady the torch head and maintain its position in relation to the work.
Hold the torch perpendicular to the work with the inner cones of the preheating
flames about 1/16 inch above the end of the line to be cut. Hold the torch
stationary in this position until the spot has been raised to a bright red heat.
Then, open the cutting-oxygen valve slowly but steadily over the line to be cut.
(4) If the cut has been started properly a shower of sparks will fall from
the opposite side of the work. The movement of the torch, along the line of the
cut, should be just fast enough for the cut to continue to penetrate the work
completely. When done properly, the cut will be clean and narrow, similar to one
made by a saw.
(5) When cutting billets, round bars, or heavy sections, time and gas are
saved if a bur is raised with a chisel at the point where the cut is to start.
This small portion. will heat quickly and cutting will start immediately. A
welding rod can also be used to start a cut on heavy sections, and when so used it
is called a "starting rod".
h. Cutting steel and cast iron.
(1) General. Plain carbon steels, with a carbon content not exceeding 0.25
percent, can be cut without special precautions other than those required to obtain
cuts of good quality. On the other hand, certain steel alloys develop high
resistance to the action of the cutting oxygen making it difficult, and sometimes
impossible, to propagate the cut without the use of special techniques.
(2) High-carbon steels. The action of the cutting torch on these metals is
similar to a flame-hardening procedure, inasmuch as the metal adjacent to the
cutting area is hardened by being heated above its critical temperature and
quenched by the adjacent mass of cold metal. This condition can be minimized or
overcome by preheating the part: at 500F to 600F before the cut is started.
(3) Waster plate on alloy steel. The cutting action on an alloy steel is
difficult to cut by the usual procedure, and can be improved by clamping a mild
steel "waster plate" tightly to the upper surface and cutting through both
thicknesses. This waster plate method will cause a noticeable improvement in the
cutting action because the molten steel dilutes or reduces the alloying content of
the base metal.
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