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OPERATION
B-5 B-5
LF-72/74 SINGLE/DUAL
1. REMOTE VOLTAGE CONTROL KIT
The optional remote voltage control kit adjusts the
arc voltage from the minimum to the maximum volt-
age of the welding power source. Rotate the knob
counterclockwise to reduce the arc voltage and rotate
the knob clockwise to raise the arc voltage.
2. BURNBACK AND POSTFLOW TIMER KIT
The optional Burnback and Postflow Timer Kit gives
control over the shielding gas at the end of the weld
and prepares the end of the wire for the next arc start.
Additional shielding gas protection is often required
when welding aluminum, stainless steel or exotic
alloys.
When stitch welding, set the postflow time to maxi-
mum for best results.
Burnback Timer
The burnback timer range is OFF to 0.25 seconds.
The burnback timer controls the additional amount of
time the power source output remains ON after the
wire drive has stopped feeding wire. Burnback
adjustment prevents the wire from sticking to the weld
at the end of a weld and helps to condition the wire for
the next weld.
To set the burnback time, adjust the knob to approxi-
mately 0.03 seconds and then decrease or increase
the time as desired.
Postflow Timer
The postflow timer range is OFF to 10 seconds.
Postflow is the time from when the power source out-
put turns OFF until the postflow timer expires. Use
postflow to protect the weld while the weld cools.
3. THERMAL LED, MOTOR OVERLOAD
The thermal light illuminates when the wire drive
motor draws too much current. If the thermal light illu-
minates, the wire drive will automatically shutdown for
up to 30 seconds to allow the motor to cool. To start
welding again, release the gun trigger, inspect the gun
cable, liner (and conduit). Clean and make repairs as
necessary. Start welding again when the problem has
been safely resolved.
For best results, keep the gun cable and conduit as
straight as possible. Perform regular maintenance
and cleaning on the gun liner, conduit and gun.
Always use quality electrode, such as L-50 or L-56
from Lincoln Electric.
4. COLD FEED/GAS PURGE SWITCH
Cold Feed and Gas Purge are combined into a single
spring centered toggle switch.
To activate Cold Feeding, hold the switch
in the UP position. The wire drive will
feed electrode but neither the power
source nor the gas solenoid will be ener-
gized. Adjust the speed of cold feeding
by rotating the WFS knob. Cold feeding,
or "cold inching" the electrode is useful
for threading the electrode through the gun.
Hold with toggle switch in the DOWN position to acti-
vate Gas Purge and let the shielding gas flow. The
gas solenoid valve will energize but neither the power
source output nor the drive motor will be turned on.
The Gas Purge switch is useful for setting the proper
flow rate of shielding gas. Flow meters should always
be adjusted while the shielding gas is flowing.
5.
2 STEP - TRIGGER INTERLOCK SWITCH
The 2 Step - Trigger Interlock switch
changes the function of the gun trigger. 2
Step trigger operation turns welding on
and off in direct response to the trigger.
Trigger Interlock operation allows welding
to continue when the trigger is released
for comfort on long welds.
Place the toggle switch in the DOWN position for 2
Step operation or in the UP position for Trigger
Interlock operation.
2 Step Trigger
2 Step trigger operation is the most common. When
the gun trigger is pulled, the welding power source
energizes the electrode output and the wire feeder
feeds wire for welding. The power source and wire
feeder continue welding until the trigger is released.