Tweco CE Ultima 150 - Manual (Page 17)

Manual 0-2530 11 SECTION 2: GENERAL INFORMATION
By forcing the plasma gas and electric arc through a small
orifice, Thermal Arc torches deliver a high concentration
of heat to a very small area. The stiff, constricted plasma
arc is shown in Zone C. Direct current straight polarity
(DCSP) is used for plasma welding, as shown in the illus-
tration.
The exclusive Dual-Flow design of Thermal Arc welding
torches uses a shield gas, shown by the small arrows. The
shield gas surrounds the plasma arc and channels it to
the workpiece, shielding the welding puddle.
Coolant from the coolant recirculator flows through the
liquid cooled power leads to the torch head and back.
The plasma arc is infinitely variable from soft to stiff. Most
applications can best be accomplished with a softer arc
(lower plasma gas flow). Full penetration or ‘keyhole’
welding requires a stiff arc (high plasma gas flow).
Individual welding torch instruction manuals contain
detailed information on these parameters.
2.08 Theory of Operation
A. Plasma and Shield Gases
Plasma and shield gases flow through the ULTIMA-
150 at rates set at the console flowmeter controls. The
flow rate of each gas is indicated on the front panel
flow meters. Solenoid valves inside the unit turn the
gases on and off. The gas pressure interlock shuts the
system down if plasma gas pressure falls below 25
psi (175 kPa).
The plasma gas flows through the positive (black)
torch lead, around the electrode and gas distributor,
and out through the tip orifice. The shield gas flows
through the negative (yellow) torch lead, around the
torch front end and out through the shield cup.
Two pressure switches act as an interlock for the gas
supply. If supply pressure falls below minimum re-
quirements the pressure switches will open, shutting
off the power to the contactors, and the GAS indicator,
will go out. When adequate gas supply pressure is
available the pressure switches close, allowing power
to be resumed for welding.
B. 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.
Direct current (DC) alone is not enough to start the
main welding arc. High frequency is used momen-
tarily. The high frequency jumps between the tip and
electrode with the DC following, then the high fre-
quency turns off. The Pilot Indicator will be lighted
when the pilot arc is enabled.
C. Current Control
The welding current is controlled by remote or at the
power supply. The weld arc ON/OFF is controlled
remotely by the user - by remote pendant, foot control,
or remote signal.
D. Coolant Flow
Coolant flows from the coolant recirculator, through
the negative torch lead to the torch head and returns
through the positive torch lead. The coolant pressure
interlock shuts the system down if the coolant pres-
sure falls below 35 psi (245 kPa).
E. Welding Current
The power supply provides the welding current. The
negative (green) output is connected to the torch elec-
trode through the liquid cooled lead. The positive
output is connected to the workpiece through the work
cable.