Learning To Weld - Lincoln Electric AC-235 Manual

LEARNING TO WELD

The serviceability of a product or structure utilizing this type of information is and must
be the sole responsibility of the builder/user. Many variables 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, fabrication 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 welding and
develop his skill. For more detailed information order
a copy of "New Lessons in Arc Welding" listed on page
25.
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 circuit and the equip-
ment that provides the electric current used in the arc.
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.
WARNING
ELECTRIC SHOCK can kill.
Carefully review the ARC WELDING SAFETY
PRECAUTIONS at the beginning of this
manual.
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.
(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. The very
dark lens, specifically 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.
–11 –