Lincoln Electric IM348 AC-225-GLM - Manual (Page 10)

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Figure 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 possible to the area you wish to
weld. Avoid allowing the welding circuit to pass through
hinges, bearings, electronic components or similar devices
that can be damaged.
This arc-welding circuit has a voltage output of up to 79
volts which can shock.
FIGURE 1—The welding circuit for shielded metal arc
welding.
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 and the holder is held by the welder. A gap is made
in the welding circuit (see Figure 1) by holding the tip of
the electrode 1/16-1/8” away from the work or base metal
being welded. The electric arc is established in this gap and
is held and moved along the joint to be welded, melting the
metal as it is moved.
Arc welding is a manual skill requiring a steady hand, good
physical condition, and good eyesight. The operator con-
trols the welding arc and, therefore, the quality of the weld
made .
What Happens in the Arc?
Figure 2 illustrates the action that takes place in the electric
arc. It closely resembles what is actually seen during weld-
ing.
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, 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. The very dark lens, specifi-
cally designed for arc welding, must be used with the 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 molten 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 cooling.
FIGURE 2—The welding arc.
The function of the covered electrode is much more than
simply to carry current to the arc. The electrode is com-
posed of a core of metal wire around which has been
extruded and baked a 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.
The principal differences between various types of elec-
trodes are in their coatings. By varying the coating, it is
possible to greatly alter the operating characteristics of
electrodes. By understanding the differences in the various
coatings, you will gain a better understanding of selecting
the best electrode for the job you have at hand. In selecting
an electrode you should consider:
1. The type of deposit you want, e.g. mild steel, stainless,
low alloy, hardfacing.
2. The thickness of the plate you want to weld.
3. The position it must be welded in (downhand, out of
position).
4. The surface condition of the metal to be welded.
5. Your ability to handle and obtain the desired electrode.
ELECTRIC SHOCK can kill.
Carefully review the ARC WELDING SAFETY
PRECAUTIONS at the beginning of this
manual.
WARNING