Lincoln Electric IM10067 CENTURY AC120 - Manual (Page 12)

B-2 OPERATION B-2
ELECTRIC SHOCK can kill.
Carefully review the ARC WELDING
SAFETY PRECAUTIONS at the begin-
ning of this manual.
------------------------------------------------------------------------
The electric arc is made between the work and the tip
end of a small metal wire, the electrode, which is
clamped in a holder. A gap is made in the welding cir-
cuit (see Figure B.1) by holding the tip of the elec-
trode.
Arc welding is a manual skill requiring a steady hand,
good physical condition, and good eyesight. The oper-
ator controls the welding arc and, therefore, the quali-
ty of the weld made.
What Happens in the Arc?
Figure B.2 illustrates the action that takes place in the
electric arc. It closely resembles what is actually seen
during welding.
The “arc stream’’ is seen in the middle of the picture.
This is the electric arc created by the electric current
flowing through the space between the end of the
electrode and the work. The temperature of this arc is
about 6000°F. (3315°C), which is more than enough
to melt metal. The arc is very bright, as well as hot,
and cannot be looked at with the naked eye without
risking painful injury. A very dark lens, specifically
designed for arc welding, must be used with a hand or
face shield whenever viewing the arc.
The arc melts the base metal and actually digs into it,
much as the water through a nozzle on a garden hose
digs into the earth. The molten metal forms a pool or
crater and tends to flow away from the arc. As it
moves away from the arc, it cools and solidifies. A
slag forms on top of the weld to protect it during cool-
ing.
The function of the covered electrode is much more
than simply to carry current to the arc. The electrode
is composed of a core of metal wire with an extruded
chemical covering.
The core wire melts in the arc and tiny droplets of
molten metal shoot across the arc into the molten
pool. The electrode provides additional filler metal for
the joint to fill the groove or gap between the two
pieces of the base metal. The covering also melts or
burns in the arc. It has several functions. It makes the
arc steadier, provides a shield of smoke-like gas
around the arc to keep oxygen and nitrogen in the air
away from the molten metal, and provides a flux for
the molten pool. The flux picks up impurities and
forms the protective slag.
Four simple manipulations are of prime impor-
tance. Without complete mastery of these four,
further welding is more or less futile. With com-
plete mastery of the four, welding will be easy.
1. The Correct Welding Position
Beginners will find it easier to learn how to control
the welding arc using the two-handed technique
shown below. This requires the use of a head-
shield.
a. Hold the electrode holder in your right hand.
b. Touch your left hand to the underside of your
right.
c. Put the left elbow against your left side.
(For welding left-handed it is the opposite.)
If you are using a hand shield, hold the electrode
holder in your right hand and the hand shield in your
left. (For welding left-handed it is the opposite.)
Whenever possible, weld from left to right (if right-
handed). This enables you to see clearly what you
are doing. Hold the electrode at a slight angle as
shown in Figure B.3.
2. The Correct Way to Strike an Arc
Be sure the work clamp makes good electrical con-
tact to the work.
CENTURY® AC 120
WARNING
FIGURE B.2
FIGURE B.3
SOLIDIFIED SLAG BASE METAL SHIELDING GASES ELECTRODE COVERING WELD METAL ARC
SOLIDIFIED SLAG
BASE METAL
SHIELDING GASES
ELECTRODE
COVERING
WELD METAL
ARC