CUTMASTER A80, A120
Manual 0-5119 2T-3 INTRODUCTION
2T.05 Introduction to Plasma
A. Plasma Gas Flow
Plasma is a gas which has been heated to an ex-
tremely 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 re-
move metals to a controlled depth and width.
In a Plasma Cutting Torch a cool gas enters Zone
B, where a pilot arc between the electrode and the
torch tip heats and ionizes the gas. The main cut-
ting arc then transfers to the workpiece through
the column of plasma gas in Zone C.
Typical Torch Head Detail
By forcing the plasma gas and electric arc through
a small orifice, the torch delivers a high concentra-
tion 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.
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 negative output is connected to the torch elec-
trode through the torch lead. The positive output
is connected to the workpiece via the work cable
and to the torch through a pilot wire.
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