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 Starting a Cut (Continued)
Machine piercing starts are essentially the same as
hand piercing starts. Some machines are equipped
When hand piercing for a start, the flames should
with torch lifters so that torches can be moved up as
impinge on the plate surface while the torch is moved
the pierce is started. Other machines have "Hi-Lo"
with small circular motions over the area to be
pierced. When a hot spot is formed, the cutting
devices with a heavy preheat flame for making a hot
oxygen is turned on slowly while the torch is raised
spot without getting the tip too close to the plate
surface. Some machines also have an oxygen ease-on
simultaneously, and travel is started along the line of
valve so that cutting oxygen will build up to full
cut .
volume slowly. Cutting oxygen and travel should
always be started simultaneously. Always protect the
A hole can be pierced in very thin plate without
cutting tip from blown slag.
moving the torch, however, it is very important to raise
the torch on thicker plate as travel begins. If this is not
SPECIAL CUTTING JOBS
done, slag will blow out and hit the torch tip, either
getting it dirty or burning it. Travel should never be
directly away from the operator because slag and
Gouging
sparks will emerge in a direction opposite the line of
cut and may cause bums.
Gouging applications include removing tack welds,
defective welds, blowholes or sand inclusions in
castings, welds in temporary brackets or supports,
Another hand piercing method is to make a hot spot,
then rotate the torch so the tip is angled away from the
flanges from piping and heads, and old tubes from
direction of travel. Start the cutting oxygen, rotate the
boilers. Gouging is also used in demolition work and
to prepare plate edges for welding.
torch until the tip is perpendicular to the plate, then lift
the torch and keep it moving along the line of cut.
4-21
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