Cutting Quality; Cut Angle - ESAB B Series Installation, Operation And Maintenance Manual

SECTION 5

5.1 CUT ANGLE

Cut squareness is always a concern when using nitrogen
gas. The cut angle is referred to as either being positive
or negative (Figure 5-1). With a positive cut angle, the top
dimension of the part is slightly less than the bottom
dimension. With a negative cut angle, the top dimension
is slightly greater than the bottom dimension. The cut
angle is controlled by standoff (arc voltage), cutting
speed, and cutting amperage. If the cutting speed and
amperage are correct and the part has an excessive
positive angle, the standoff is too high. Begin lowering the
arc voltage in increments of 5 volts, observing cut
squareness. There will always be slight top edge round-
ing of the part when using nitrogen.
The optimum torch height is just before the part begins to
develop a negative cut angle. To expand upon the other
two variables, if the torch standoff is correct, too fast of a
cutting speed will result in a positive cut angle; too slow of
a travel speed will result in a negative cut angle. Too high
or too low of current also produces a positive cut angle.
Oxygen plasma will also produce the same positive or
negative cut angle as nitrogen. The cut angle is controlled
by the torch standoff (arc voltage) cutting speed, and
cutting amperage. The major difference is the sharp top
edge of the part. The positive angle changes but the sharp
top edge remains. If speeds and currents are correct,
lower the arc voltage in increments of 5 volts until the cut
angle begins to go negative or the cut face is under cut.
At this point, increase voltage until positive angle reap-
pears. This is the optimum cut squareness for these
conditions.
B
POSITIVE (+) CUT ANGLE
Bottom dimension "A" is
greater than dimension "B"
A
B
NEGATIVE (-) CUT ANGLE
Bottom dimension "A" is
less than dimension "B"
A
Figure 5-1. Cut Angle
71

CUTTING QUALITY