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 Oxygen Supply (Continued)
Starting a Cut
Cuts can be started at an edge or any other point on the
results from undersized piping coming into a plant, or
surface of a plate.
regulators that do not have sufficient capacity for
making heavy cuts. Deficient cutting oxygen supplies
There are several ways to start an edge cut, but the
often result from very long hoses, hoses too narrow in
most common procedure is to position the tip (either
diameter, or hoses that have been chopped up and
by hand or by machine) so that the preheat flames heat
patched together with couplings.
the top comer of the plate while the cutting oxygen
hole is centered over the comer. When the plate
When depressing the oxygen lever results in a large
becomes bright cherry-red, turn on the cutting oxygen
pressure drop, something is wrong. This pressure drop
and start torch travel.
is most readily seen in two-hose torches because
insufficient oxygen causes the preheat flame to
Another edge-starting technique is preheating the
become very carburizing when the cutting oxygen
plate. Move the torch slowly back and forth along the
valve is opened. Check the regulator and the oxygen
line of cut several times for a distance equal to the
piping system immediately.
plate thickness. Pull the torch slightly away from the
edge, turn on the cutting oxygen and begin torch
Cutting oxygen is usually at least 99.7 percent pure.
travel. A cut started with this technique allows normal
When lower purity oxygen gets into the lines, it is just
cutting speeds the moment the torch reaches the plate
about impossible to make a decent cut at respectable
edge.
speeds. Impure oxygen is often the last thing one
suspects, and is often not discovered until a cylinder
Piercing is used to start cuts at some point away from
change - and suddenly everything starts working the
way it should.
an edge when the shape or location precludes an edge
start.
4-20
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