Tweco 51 with SL100SV CutMaster - Manual (Page 23)

Manual 0-4640 2-7 INTRODUCTION
2
2.08 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.
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 cutting arc then transfers to the workpiece through the column of plasma gas in Zone C.
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A-00002
Workpiece
Power
Supply
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C
B
A
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. 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 start cartridge, around the electrode,
and out through the tip orifice.
The secondary gas flows down around the outside of the torch start 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.