Thermal Dynamics SIGNATURE PAK 1250XRTM, Owner'S Manual

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5
The cutting torch also uses a secondary gas (Zone A,
Figure 1-D) which assists the high velocity plasma gas in
blowing the molten metal out of the cut and allowing a
fast, slag-free cut. The secondary gas also cools the torch.
Compressed air, supplied by either a cylinder or plant air
system, or CO2 is normally used as the secondary gas.
The plasma gas flows into the torch through the positive
lead, around the electrode, and out through the tip orifice.
The secondary gas flows into the torch through the nega-
tive lead, down around the outside of the torch liner, and
out between the tip and shield cup around the plasma 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.
1.5 THEORY OF OPERATION (continued)
GENERAL INFORMATION
Plasma Gas Flow
(continued)
Gas Distribution
Figure 1-D Theory of Operation
Because DC current alone is not sufficient to initiate and
maintain the pilot arc, high frequency is superimposed on
the direct current.
DC power is also used for the main cutting arc. The
negative output is connected to the torch electrode
through the torch lead. The positive output is connected
to the workpiece via the work cable and to the torch
through a contactor and resistor.
Two pressure switches (PS1 and PS2) act as an interlock
for the gas supply. If supply pressure falls below mini-
mum requirements the pressure switches will open,
shutting off the power to the contactors, and the GAS
indicator will go out. When adequate supply pressure is
available the pressure switches close, allowing power to be
resumed for cutting.
High Frequency
Main Cutting Arc
Interlocks
Pilot Arc
,,
,,
,,
,
,
,
, ,
A-00002
Workpiece
Power
Supply
+
_
C
B
A