B-1
OPERATION
B-1
THERMAL PROTECTION
If the duty cycle is exceeded, a thermal protector will
shut off the output until the machine cools to a reason-
able operating temperature. The Power Switch will
Illuminate if this condition occurs, which is an auto-
matic function of the AC 120 and does not require
user intervention. Output will resume once the
machine cools.
MAKING A WELD
(See Figure B.1)
Insert the bare part of the electrode into the electrode
holder jaws and connect the work clamp to the weld-
ing piece. Make sure to have good electrical contact.
Turn the AC 120 on. Lower Helmet or while holding
shield in front of face strike the electrode work point
on the workpiece as if striking a match. Do not hit the
electrode on the workpiece, which will damage the
stick electrode and make striking an arc difficult.
Immediately after striking the arc try to maintain a dis-
tance from the workpiece that is equivalent to the
diameter of the electrode used. Maintain this distance
continually during the weld.
Refer to the "Learning to Weld" section in this manual
for more information on:
• How to correctly strike an arc.
• The correct welding position.
• Proper travel speed.
Once the electrode is burned down turn the machine
off and remove the stub by opening the jaws of the
electrode holder and insert a new electrode. The
welded work piece and electrode stub are hot after
welding, allow time to cool down before touching or
use pliers to move. Always make sure the AC 120 is
turned off before setting down the Electrode Holder.
ELECTRODE SELECTION
For best results use genuine Lincoln Electric
Fleetweld 37 electrodes in the 1/16" or 5/64" size.
This is suitable for welding up to 14ga steel.
LEARNING TO WELD
The serviceability of a product or structure utiliz-
ing this type of information is and must be the
sole responsibility of the builder/user. Many vari-
ables beyond the control of The Lincoln Electric
Company affect the results obtained in applying
this type of information. These variables include,
but are not limited to, welding procedure, plate
chemistry and temperature, weldment design, fab-
rication methods and service requirements.
No one can learn to weld simply by reading about it.
Skill comes only with practice. The following pages
will help the inexperienced welder to understand weld-
ing and develop his skill.
The Arc-Welding Circuit
The operator’s knowledge of arc welding must go
beyond the arc itself. He must know how to control the
arc, and this requires a knowledge of the welding cir-
cuit and the equipment that provides the electric cur-
rent used in the arc.
Figure B.1
is a diagram of the
welding circuit. The circuit begins where the electrode
cable is attached to the welding machine and ends
where the work cable is attached to the welding
machine. Current flows through the electrode cable to
the electrode holder, through the holder to the elec-
trode and across the arc. On the work side of the arc,
the current flows through base metal to the work cable
and back to the welding machine. The circuit must be
complete for the current to flow. To weld, the work
clamp must be tightly connected to clean base metal.
Remove paint, rust, etc. as necessary to get a good
connection. Connect the work clamp as close as pos-
sible to the area you wish to weld. Avoid allowing the
welding circuit to pass through hinges, bearings, elec-
tronic components or similar devices that can be dam-
aged.
CENTURY® AC 120
WORKPIECE
WORK CABLE
ELECTRODE CABLE
ELECTRODE
ELECTRODE HOLDER
ARC
WORK CLAMP
CENTURY
WORKPIECE
WORK CABLE
ELECTRODE CABLE
ELECTRODE
ELECTRODE HOLDER
ARC
WORK CLAMP
CENTURY
FIGURE B.1