Tweco 42 CutMaster Operating Manual - Manual (Page 14)

CUTMASTER 42
INTRODUCTION 2T-2 Manual 0-5141
2T.03 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 electrically
conductive. The plasma arc cutting and gouging 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 enters Zone B, where a
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.
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. Direct current (DC) straight polarity is used for
plasma cutting, as shown in the illustration.
Zone A channels a secondary gas that cools the torch. This
gas also assists the high velocity plasma gas in blowing the
molten metal out of the cut allowing for a fast, slag - free cut.
A-00002
Workpiece
Power
Supply
+
_
C
B
A
Typical Torch Head Detail
B. Gas Distribution
The single gas used is internally split into plasma and
secondary gases.
The plasma gas flows into the torch through the negative
lead, through the starter cartridge, around the electrode,
and out through the tip orifice.
The secondary gas flows down around the outside of the
torch starter cartridge, 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.
D. Main Cutting Arc
DC power is also used for the main cutting arc. The nega-
tive 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
pilot wire.
E. Parts - In - Place (PIP)
The torch includes a 'Parts - In - Place' (PIP) circuit. When
the shield cup is properly installed, it closes a switch. The
torch will not operate if this switch is open.
Torch Trigger
PIP Switch Shield Cup
To Control
Cable Wiring
Torch Switch
Art# A-09595_AB
Parts - In - Place Circuit Diagram for Hand Torch