Tweco 6000GST Cutting Systems - Manual (Page 17)

Manual 0-2690 2-3 INTRODUCTION
B. Torch Supply Leads
The following applies to the Torch Supply Leads only:
The Torch Supply Leads are made up of individual hoses
and cables. The Torch Supply Leads are part of the sys-
tem to interface the Master Power Supply to the Arc
Starter Box. The Torch Supply Leads are available to ex-
tend the Arc Starter Box from the Power Supply up to
125 ft (38.1 m).
2.04 Options And Accessories
These items can be used to customize a standard system
for a particular application or to further enhance perfor-
mance (refer to Section 6 for ordering information).
• Spare Parts Kits
Kits contain replacement front-end torch parts and
tools. Spare parts kits are available for air, oxygen
(O2), and multi-gas cutting.
2.05 Introduction to Plasma
A. Plasma Gas Flow
Plasma is a gas which has been heated to an extremely
high temperature and ionized so that it becomes elec-
trically conductive. The plasma arc cutting and goug-
ing processes use this plasma to transfer an electrical
arc to the workpiece. The metal to be cut or removed
is melted by the heat of the arc and then blown away.
While the goal of plasma arc cutting is separation of
the material, plasma arc gouging is used to remove
metals to a controlled depth and width.
In a Plasma Cutting Torch a cool gas such as air or
nitrogen (N2) enters Zone B (refer to Figure 2-2),
where a pilot arc between the electrode and the torch
tip heats and ionizes the gas. The main cutting arc
then transfers to the workpiece through the column
of plasma gas in Zone C.
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;
;
;
;
;
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A-00002
Workpiece
Power
Supply
+
_
C
B
A
Figure 2-2 Typical Torch Head Detail
By forcing the plasma gas and electric arc through a
small orifice, the torch delivers a high concentration
of heat to a small area. The stiff, constricted plasma
arc is shown in Zone C (Figure 2-2). Direct current
(DC) straight polarity is used for plasma cutting, as
shown in the illustration.
Zone A (Figure 2-2) is used as a secondary gas that
cools the torch. This gas assists the high velocity
plasma gas in blowing the molten metal out of the
cut allowing for a fast, slag-free cut. Compressed
air, supplied by either a cylinder, plant air system or
CO
2
is normally used as the secondary gas.
B. Gas Distribution
The plasma gas flows into the torch through the posi-
tive lead, through the gas distributor, around the elec-
trode, and out through the tip orifice.
The secondary gas flows into the torch through the
secondary gas hose, down around the outside of the
torch gas distributor, and out between the tip and
shield cup around the plasma arc.
C. Pilot Arc
When the torch is started a pilot arc is established
between the electrode and cutting tip. This pilot arc
creates a path for the main arc to transfer to the work.