Tweco Max 300 w-TD-750 - Manual (Page 29)

Manual 0-2557 23 OPERATION
The arc characteristics vary with gases used, cutting
speed, material, and thickness. Air plasma normally
produces a straight arc (on stainless or aluminum),
while nitrogen plasma generally creates a 5° trailing
arc.
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 transfer.
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 Control Module 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 - 3/8 inch (3 - 9 mm) dis-
tance for optimum speed and cut quality.
A standard shield cup is recommended for most ma-
chine cutting applications. The touch cup (short shield
cup) is designed for light gage cutting where arc volt-
age measurement is needed for a standoff control. Do
not allow an exposed torch tip to contact the work-
piece.
A method called “running start” is recommended
when piercing with a machine mounted torch. The
torch should be positioned far enough off the cutting
line to allow the pierce to be complete before the cut-
ting line is reached. This allowance depends on the
thickness of the material and the torch travel speed.
Piercing the plate is not recommended on plates hav-
ing a thickness greater than 3/4 in (19 mm). Blowback
from the piercing operation can shorten the life of torch
parts. All piercing should therefore be done as quickly
as possible and at maximum amperage (140 amps)
and maximum standoff.
Pierce off the cutting line and then continue the cut as
needed. 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 mini-
mize the amount of scale which adheres to it. This
can siggnificantly increase shield cup life.
4.08 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
• Operator experience
• Torch standoff height
• Proper work cable connection
• Alloy content of material
NOTE
This information represents realistic expectations
using recommended practices and well-maintained
systems. Actual speeds may vary from those shown
in the charts dependiWã on the alloy content of the
selected material.
For completecutting speed chart data refer to Appendix
II.
4.09 Gouging
WARNINGS
Be sure the operator is equipped with proper gloves,
clothing, eye and ear protection and that all safety
precautions at the front of this manual have been
followed. Make sure no part of the operator’s body
comes in contact with the workpiece when the torch
is activated.
Disconnect primary power to the system before dis-
assembling the torch, leads, or power supply.
CAUTIONS
Sparks from plasma gouging can cause damage to
coated, painted or other surfaces such as glass, plas-
tic, and metal.
Check torch parts. The torch parts must correspond
with the type of operation. Refer to Section 4.04,
Torch Parts Selection.