Tweco 1000 Cutting Systems - Manual (Page 17)

Manual 0-2710 2-3 INTRODUCTION
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).
• Remote Arc Starter
Optional Remote Arc Starter Assembly use to place
the torch arc starting circuits closer to the torch
head. Requires the Optional Torch Supply Leads.
• Torch Supply Leads (Optional)
NOTE
Lead lengths are from the Optional Remote Arc
Starter to the Torch Head Assembly .
The Torch Supply Leads are made up of individual
hoses and cables. The Torch Supply Leads inter-
face the Power Supply to the Optional Remote Arc
Starter. The Torch Supply Leads are available in
various lengths from 25 ft (7.6 m) to 100 ft (30.5
m). The Torch Supply Leads can extend the Re-
mote Arc Starter from the Power Supply up to 100
ft (30.5 m).
• Spare Parts Kits
Kits contain consumable front-end torch parts and
multi-purpose wrench.
2.05 Introduction to Plasma
A. Plasma Gas Flow
Plasma is defined as a gas which has been heated to
an extremely high temperature and ionized so that it
becomes electrically conductive. The plasma arc cut-
ting and gouging process 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.
;;
;;
;;
;
;
;
;
;
;;
;;
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.