©
COPYRIGHT 1998 THE ESAB GROUP, INC. LESSON
II 2.5.7.1
Flux cored welding generates fumes,
that for environmental reasons, must be removed
from the welding area. This is usually done with an external exhaust system,
but welding guns
with internal fume extractors have been developed. They are heavier than
the regular gun
and must be properly maintained so that the extracting mechanism does not
disturb the shielding gas.
2.5.8
SHIELDING
GASES -
Carbon dioxide is the most widely used gas for auxiliary
shielding of the flux cored electrode.
The other commonly used gas is a mixture of 75% Argon
and 25% CO2.
2.5.8.1 A
carbon dioxide shield produces deep penetration and the transfer is globular.
As previously
discussed, CO2 will
dissociate in the heat of the arc. To counteract this
characteristic, deoxidizing elements
are added to the core ingredients of the electrode. The
deoxidizers react to form solid oxide
compounds that float to the surface as part of the slag covering.
2.5.8.2 The
addition of Argon to CO2
will increase the wetting action, produce a smooth arc
arc, and reduce spatter. The
transfer is spray-like, and the penetration is somewhat less than
with the straight carbon dioxide.
2.5.8.3 While
some flux cored electrodes are designed to operate well on both the 100%
CO2
or the 75/25 mixture, others are formulated specifically for the CO2
shield or the Argon/ CO2
mixture. If the recommended gas is not used with these electrodes,
the weld chemistry may
be affected. The reason for this is that inert gas, such as Argon, does
not react with the other
elements; therefore, allowing them to be transferred across the arc into the weld
metal. An electrode
designed for CO2 shielding
contains deoxidizing elements, such as silicon and manganese.
If a high percentage of Argon is used in the shielding medium, a large portion
of these elements
may pass into the weld metal causing the weld metallurgy to be less ductile
than intended.
2.5.8.3 The
opposite happens with electrodes formulated for a 75/25 mixture. These
electrodes are usually designed for
high yield and tensile strength. If a high percentage of CO2
is used with them, the CO2
may react with the elements needed to attain these strength levels,
thereby preventing them from passing
into the weld metal. 2.6
SUBMERGED ARC WELDING
Submerged Arc Welding (SAW)
is different from the previously explained arc welding
processes in that the arc is not visible.
The arc is submerged beneath loose granular flux. A
continuous electrode is fed by automatic
drive rolls through an electrode holder where current
