Lincoln Electric IM10074 BULLDOG 5500 - Manual (Page 23)

B-9 OPERATION B-9
BULLDOG™ 5500
No one can learn to weld simply by reading about it.
Skill comes only with practice. The following pages
will help the inexperienced welder understand welding
and develop his skill. For more detailed information,
order a copy of the book “New Lessons in Arc
Welding.” (See Book Division section at rear of manual).
The operatorʼs 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 3 is a diagram of the weld-
ing circuit. The circuit begins where the electrode
cable is attached to the welding machine and ends
where the work cable cable is attached to the
machine. Current flows through the electrode cable to
the electrode holder, through the electrode holder to
the electrode 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 cir-
cuit 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 are welding. Avoid
allowing the welding circuit to pass through hinges,
bearings, electronic components or similar devices
that can be damaged.
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 that is held by the welder. A gap
is made in the welding circuit (see Figure 3) by hold-
ing the tip of the electrode 1/16 - 1/8” (1.6-3.2mm)
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 oper-
ator controls the welding arc and, therefore, the quali-
ty of the weld made.
What Happens in the Arc?
Figure 4 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 (3300°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 and possibly permanent injury. A very dark
lens, specifically designed for arc welding must be
used with the handshield or headshield whenever
viewing the arc.
The arc melts the base metal and actually digs into it,
much like water through a garden hose nozzle 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. Slag forms on top
of the weld to protect it during cooling.
Covering
Electrode
Shielding Gases
Arc
Solidified Slag
Weld Metal
Base Metal
FIGURE 4 - The welding arc.
ARC
WORK CABLE
WORK
ELECTRODE CABLE
ELECTRODE HOLDER
ELECTRODE
WELDING MACHINE
AC OR DC POWER
SOURCE AND
CONTROLS
FIGURE 3 - The welding circuit for (Stick) shielded metal arc welding. FIGURE 3 - The welding circuit for (Stick) shielded metal arc welding.