Tweco PCM-120 Machine Torch - Manual (Page 29)

Manual 0-2698 4-9 OPERATION
B. Gouging Parameters
Gouging performance depends on parameters such
as torch travel speed, current level, lead angle (the
angle between the torch and workpiece), and the dis-
tance between the torch tip and workpiece (stand-
off).
Characteristics of Recommended
Gases for Plasma Arc Gouging
Type of Gas Type of Material
Plasma Secondary
Carbon
Steel
Stainless
Steel
Aluminum
Air Air Excellent Good Fair
Nitrogen Air Good Good Fair
Nitrogen CO2 Good Good Good
Ar/H2 Nitrogen Good
Excellent
(Over 3/4 in)
Excellent
Ar/H2 Argon Good Excellent Excellent
Figure 4-11 Gas Characteristics
C. Torch Travel Speed
Optimum torch travel speed for gouging is between
20 and 120 inches per minute (0.5 and 3.0 meters per
minute). Travel speed is dependent on current set-
ting, lead angle, and mode of operation (hand or
machine torch).
D. Current Setting
Current settings depend on torch travel speed, mode
of operation (hand or machine torch), and the amount
of material to be removed.
E. Lead Angle
The angle between the torch and workpiece depends
on the output current setting and torch travel speed.
At 35 amps, the recommended lead angle is 35°. At a
lead angle greater than 45° the molten metal will not
be blown out of the gouge and may be blown back
onto the torch. If the lead angle is too small (less than
35°), less material may be removed, requiring more
passes. In some applications, such as removing welds
or working with light metal, this may be desirable.
A-00280
35˚
Workpiece
Torch Head
Standoff Height
1/4 - 3/8"
Figure 4-12 Gouging Angle and Standoff Distance
F. Standoff Distance
The tip to work distance affects gouge quality and
depth. A standoff of 1/4 - 3/8 inch (6.3 - 9.5 mm)
allows smooth, consistent metal removal. A smaller
standoff may result in a severance cut rather than a
gouge. A standoff greater than 3/8 inch (9.5 mm) may
result in minimal metal removal or loss of transferred
main arc.
G. Slag Build-up
Slag generated by gouging on materials such as car-
bon and stainless steels, nickels, and alloyed steels,
can be removed easily in most cases. Slag does not
obstruct the gouging process if it accumulates to the
side of the gouge path. However, slag build-up can
cause inconsistencies and irregular metal removal if
large amounts of material build up in front of the arc.
The build-up is most often a result of improper travel
speed, lead angle, or standoff height.