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AUTOPRO 155S
ARC-WELdING CIRCUIT
FIGURE B.3
(See Figure B.3)
Work Cable
Work Clamp
Work Piece
Current flows through the electrode cable and electrode holder to
the electrode and across the arc. On the work side of the arc, the
current flows through the 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.
An electric arc is made between the work and the end of a small
metal rod, the electrode, which is clamped in a holder and the
holder is held by the person doing the welding. A gap is made in
the welding circuit (see Figure B.3) 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.
Electrode Cable
Electrode Holder
Electrode
Arc
ELECTRIC ARC
(See Figure B.4)
FIGURE B.4
Action that takes place in the electric arc.
This figure closely resembles what is actually seen during
welding. The "arc stream'' is seen in the middle of the figure. 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 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
cooling.
The function of the covered electrode is much more than simply to
carry current to the arc. The electrode is composed of a core rod
of metal with an extruded chemical covering. The core rod 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.
B-3
OPERATION
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