Tweco PCM-62 Machine Torch - Manual (Page 26)

OPERATION 4-6 Manual 0-2817
B. Travel Speed
Proper travel speed is indicated by the trail of the arc
which is seen below the plate ( Figure 4-7). The arc
can be one of the following:
1. Straight Arc
A straight arc is perpendicular to the workpiece
surface. This arc is generally recommended for
the best cut using air plasma on stainless or alu-
minum.
2. Leading Arc
The leading arc is directed in the same direction
as torch travel. A five degree leading arc is gener-
ally recommended for air plasma on mild steel.
3. Trailing Arc
The trailing arc is directed in the opposite direc-
tion as torch travel. Generally recommended for
Nitrogen Plasma.
Standoff Distance
Straight Arc
Trailing Arc
Leading Arc
Direction of Torch Travel
A-02590
Figure 4-7 Machine Torch Operation
For optimum smooth surface quality, the travel speed
should be adjusted so that only the leading edge of
the arc column produces the cut. If the travel speed
is too slow, a rough cut will be produced as the arc
moves from side to side in search of metal for trans-
fer.
Travel speed also affects the bevel angle of a cut.
When cutting in a circle or around a corner, slowing
down the travel speed will result in a squarer cut.
The power source output should be reduced also.
Refer to the approriate Power Supply Operating
Manual for any Corner Slowdown (CSD) adjustments
that may be required.
C. Piercing With Machine Torch
To pierce with a machine torch, the arc should be
started with the torch positioned as high as possible
above the plate while allowing the arc to transfer and
pierce. This standoff helps avoid having molten metal
blow back onto the front end of the torch.
When operating with a cutting machine, a pierce or
dwell time is required. Torch travel should not be
enabled until the arc penetrates the bottom of the
plate. As motion begins, torch standoff should be
reduced to the recommended 1/8 - 1/4 inch (3-6 mm)
distance for optimum speed and cut quality. Clean
spatter and scale from the shield cup and the tip as
soon as possible. Spraying or dipping the shield cup
in anti-spatter compound will minimize the amount
of scale which adheres to it.
4.09 Recommended Cutting Speeds
Cutting speed depends on material, thickness, and the
operator’s ability to accurately follow the desired cut line.
The following factors may have an impact on system per-
formance:
• Torch parts wear
• Air quality
• Line voltage fluctuations
• Torch standoff height
• Proper work cable connection
NOTES
This information represents realistic expectations
using recommended practices and well-maintained
systems. Actual speeds may vary up to 50% from
those shown.
Refer to Appendix Pages for cutting speed chart
information as related to the Power Supply used.