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Torch Angle (Continued)
workpiece surface conditions or plate compositions.
An angled torch cuts faster on thinner-gauge material.
For example, rusty or oily plates require more preheat,
The intersection of the kerf and the surface presents a
or slower travel speeds than clean plates. Most
knife edge which is easily ignited. Once the plate is
variations from the ideal condition of a clean, flat,
burning, the cut is readily carried through to the other
low-carbon steel plate tend to slow down cutting action.
side of the work. This avoids problems of non-drop
cuts, incomplete cutting on the opposite side of the
For a very rusty plate, set as big a preheat flame as
thicker plate, gouging cuts in the center of the kerf and
possible on the torch and run it back and forth over the
similar problems.
line to be cut. Extra preheat passes do two things.
First, they span off much of the scale that interferes
Travel Speed
with the cutting action, and they put extra preheat into
the plate to allow improved cut quality and speed.
Each job has a best cutting speed. A high quality cut
will be obtained on plate up to about 2 in. thick when
Cut a little bit slower when working with high-strength
there is a steady "purring" sound from the torch and
low-alloy plates (ASTM A-242 steel), or full alloy
the spark stream under the plate has a 15 degree lead
plates (ASTM A-5 14). Also, because these steels are
angle; the angle made by the sparks coming from the
more sensitive to notching than ordinary carbon steels,
bottom of the cut in the same direction the torch is
use low oxygen pressure.
traveling. If the sparks go straight down, or even
backwards, travel speed is too high.
Clad carbon alloy, carbon stainless, or low-carbon--
high-carbon plates require a lower oxygen pressure,
Nature of the Workpiece
and perhaps a lower travel speed than straight
low-carbon steel. Be sure the low-carbon steel side is
Variations in cut quality are the result of different
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