Tweco 1000 Cutting Systems - Manual (Page 31)

Manual 0-2710 4-7 OPERATION
C. Piercing With Torch
To pierce with the 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 1/16 - 1/4 inch (1.6 -
6.4 mm) distance for optimum speed and cut quality.
Piercing the plate is not recommended on plates hav-
ing a thickness greater than 1/2 inch (12.7 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 amper-
age 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 dip-
ping the shield cup in anti-spatter compound will
minimize the amount of scale which adheres to it.
This can significantly 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 depending on the alloy content of the
selected material.
For complete cutting speed chart data refer to Appendix
2.
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.
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 corre-
spond with the type of operation. Refer to Section
4.04, Torch Parts Selection.
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