Tweco 35A CutSkill Power Supply - Manual (Page 16)

CUTSKILL 35A
INTRODUCTION 2T-2 June 30, 2009
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. Main Cutting Arc
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 con-
nected to the workpiece via the work cable.