Lincoln Electric POWER-ARC 4000 SVM103-A Service Manual page 26

B-11
1. POWER SOURCE
2. ELECTRODE CABLE
3. ELECTRODE HOLDER
4. ELECTRODE
5. OUTPUT TERMINALS
6. WORK
7. WORK CLAMP
8. WORK CABLE
THE WELDING CIRCUIT
When everything is connected properly, the current
from the power source causes the electrode to melt
and bond the metal being welded. Figure B.3. shows
the components of the basic welding circuit. The cir-
cuit starts at the electrode cable connection and ends
at the work cable connection. Current flows from the
POWER-ARC 4000 through the electrode cable, the
electrode holder, the electrode, and across the arc.
On the work side of the arc, current flows through the
work to the work clamp, the work cable, and back to
the machine. The circuit must be complete for current
to flow. That means the work clamp must be tightly
connected to clean base metal. You should remove
any paint or rust as necessary to get a good connec-
tion. Also, you need to connect the work clamp as
close as possible to the area you want to weld. Avoid
letting the welding circuit pass through hinges, bear-
ings, electronic components or similar devices that
can be damaged by high current.
POWER-ARC 4000
OPERATION
FIGURE B.3 – WELDING CIRCUIT CONNECTIONS
5
2
4
3
1
8
6
7
THE ARC
The electric arc is made between the work and the tip
of the electrode. You make a gap for the arc in the
welding circuit by holding the electrode tip 1/16 to 1/8
inch (1.6 to 3.2 mm) away from the work. You must
establish the arc and hold it as you move the arc along
the joint you're welding. The arc melts both the elec-
trode and the base metal of the work as you move.
Figure B.4. shows what's happening in the welding
arc. The arc itself is the electric current flowing
between the tip of the electrode and the work. Its
temperature is about 6000°F (3316°C). The arc is very
bright and cannot be looked at with the naked eye
without risk of painful and perhaps permanent injury.
A very dark lens specifically designed for arc welding
must be used with the handshield or headshield when-
ever viewing the arc.
The arc melts the base metal and actually digs into it.
The molten metal forms a pool or crater and tends to
flow away from the arc. As it moves away, it cools and
solidifies. Slag forms on the top of the weld and pro-
tects it as it cools.