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 Preheat Flame Adjustment (Continued)
Cutting-oxygen pressure and travel speed affect the
A simple test will quickly show the best oxygen
tendency of slag to stick to the bottom of a cut. This
pressure to use for any given tip.
tendency increases as the amount of metallic iron in
the slag increases.
Put a low volume, soft flame on the tip, then turn the
cutting oxygen on and vary the pressure to find the
Two things can cause high iron content in slag. Too
best looking stinger (visible oxygen cutting strewn).
much cutting-oxygen pressure - Oxygen forced
Low pressure gives a very short stinger, maybe two to
through the kerf so fast that it blows out molten iron
three inches long, that breaks up at the end. Increase
before it can be oxidized. Cutting speed too fast - Not
pressure to define and lengthen the stinger. This is the
enough time to thoroughly oxidize the molten iron,
correct cutting oxygen pressure for a given tip. The
with the same result as high oxygen pressure.
long stinger will remain over a fairly wide pressure
range, but as oxygen pressure is increased, the stinger
Coupling Distance
returns to the short, broken form it had under low
pressure. If too much oxygen pressure is used,
The distance between the end of the flame cones and
concavity may show on the cut surface.
the workpiece is the coupling distance. Some consider
the distance between tip and workpiece to be the
Too much oxygen pressure notches the cut surface
coupling distance, however, since flame lengths vary
because the high velocity oxygen is blowing the metal
with different fuels and flame adjustments, the distance
and slag out of the kerf so fast that the cut is
between the end of the preheat cones and the
continuously being started. If the pressure is too low,
workpiece is the preferred measure (Figure 4-3).
the operation will slow down too much. Excessive
drag and slag dormation result, and a wide kerf maybe
found at the bottom of the cut.
4-15
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