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5.2 The Self-Shielded (Gasless)
FCAW Welding Arc (DC-)
Figure 1 illustrates the action taking place in the self
shielded gasless FCAW welding arc. It closely resembles
what is actually seen while welding.
Figure 1
Cored Wire
Protective Slag
Weld Metal
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 wire electrode
and the base metal. The temperature of this arc is about
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 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 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.
The function of the cored wire electrode is much more than
simply to carry current to the arc. The wire core is
composed of fluxes and/or alloying ingredients around
which a steel sheath has been formed. It is simply a stick
electrode turned inside out in a continuous wire form.
The cored wire melts in the arc and tiny droplets of molten
metal shoot across the arc into the molten pool. The wire
sheath provides additional filler metal for the joint to fill the
groove or gap between the two pieces of base metal.
The core materials also melt or burn in the arc and perform
several functions. They make the arc steadier, provide a
shield of smoke-like gas around the arc to keep oxygen
and nitrogen in the air away from the molten metal, and
provide a flux for the molten pool. The flux picks up
impurities and forms the protective slag on top of the weld
during cooling.
After running a weld bead, the slag may be removed with a
chipping hammer and wire brush. This improves
appearance and allows for inspection of the finished weld.
Machine size and output characteristics limit the size and
type of wire electrode which can be used.
5.3 The GMAW (MIG) Welding Arc (DC+)
Figure 2 illustrates the GMAW (MIG) welding arc. Solid
wire does not contain fluxes or ingredients to form its own
shielding and no slag forms to protect the molten weld
metal. For this reason, a continuous even flow of shielding
gas is needed to protect the molten weld metal from
atmospheric contaminants such as oxygen and nitrogen.
Shielding gas is supplied through the gun and cable
assembly, through the gas nozzle and into the welding
zone.
Figure 2
Solid wire
electrode
Page 14
Burning of core materials
inside
wire
electrode
results in shield of gas.
Arc Stream
Gas nozzle
Shielding gas
REDI-MIG 325
When comparing the GMAW and FCAW processes, you
can see that the principal difference between the two lies in
the type of shielding used. GMAW uses gas for shielding,
thus we have Gas Metal Arc Welding. FCAW uses the
melting or burning of the core ingredients for shielding, and
is thus termed Self-Shielded Flux Cored Arc Welding.
Gas Metal Arc Welding (MIG) is capable of welding a wide
range of mild steels in all positions, however, more skill is
required for out-of-position welding with the GMAW
process.
5.4 Process Selection
By gaining knowledge of the differences between the two
processes, you will be able to select the best process for
the job you have at hand. In selecting a process, you
should consider:
For GMAW (MIG) Process
1. Can I afford the extra expense, space, and lack of
portability required for gas cylinders and gas supply?
2. Do I require clean, finished-looking welds?
If you have answered yes to all the above questions
GMAW may be the process for you. If you have answered
no to any of the above questions, then you should consider
using the FCAW process.
For FCAW (Innershield) Process
1. Do I want simplicity and portability?
2. Will welding be performed outdoors or under windy
conditions?
3. Do I require good all position welding capability?
5.5 Common Metals
Most metals found around the farm, small shop or home
are low carbon steel, sometimes referred to as mild steel.
Typical items made with this type of steel include most
sheet metal, plate, pipe and rolled shapes such as
channels and angle irons. This type of steel can usually be
easily welded without special precautions. Some steels,
however, contain higher carbon levels or other alloys and
are more difficult to weld. Basically, if a magnet sticks to the
metal and you can easily cut the metal with a file, chances
are good that the metal is mild steel and that you will be
able to weld the material. In addition, aluminum and
stainless steel can be welded using the an aluminum
welding kit. For further information on identifying various
types of steels and other metals, and for proper procedures
for welding them, we suggest you purchase a copy of "New
Lessons in Arc Welding".
Regardless of the type of metal being welded, in order to
get a quality weld, it is important that the metal is free of oil,
paint, rust or other contaminants.
5.6 Machine Set up for the Self-Shielded
(Gasless) FCAW Process
1.
Ensure the machine has the correct drive roll and parts (all
required parts for cored wire welding are supplied in the
Innershield (Gasless) Welding Kit KA1440-3).
2.
See the Welding Procedure Guide on the inside of wire
feed section door for information on setting the controls.
3.
Set the "Voltage" and "Wire Speed" controls to the settings
suggested on the Welding Procedure Guide for the welding
wire and base metal thickness being used.
4.
Check that the polarity is correct for the welding wire being
used. See Section 1.5 for instructions on changing polarity.
5.
Connect work clamp to metal to be welded. Work clamp
must make good electrical contact to the work piece. The
work piece must also be grounded as stated in the "Arc
Welding Safety Precautions" at the beginning of this
manual.
IMA 599B
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