©
COPYRIGHT 1998 THE ESAB GROUP, INC. LESSON
II 2.5.3
Current
Density - Flux cored
arc welding utilizes the same principles of current
density, as explained in section 2.4.1,
but there is one significant difference between the flux
cored electrode and the solid electrode.
With the flux cored electrode, the granular core ingredients
are poor electrical conductors and therefore, the current is carried primarily
through the outer metal sheathing.
When an equal diam- eter
cross section of the two are compared (See Figure 19),
it is seen that the flux cored electrode has a
smaller current carrying area than the solid electrode.
This greater concentration of current
in a smaller area increases the burnoff
rate. 2.5.3.1
When all other factors are equal,
the deposition rate of the flux cored
electrode is somewhat higher than the
solid electrode.
2.5.4
EQUIPMENT
- The equipment used for flux cored arc welding is the same as
shown previously in Section 2.3.2.2,
Figure 12, with the exception that the self shielded method
does not need the external gas apparatus. 2.5.4.1
Flux cored arc welding is done with
direct current. All of the gas shielded electrodes
are designed for DCEP operation. The
self shielded electrodes are either designed specifically
for DCEN or DCEP. 2.5.5
Power
Source - The recommended
power source is the direct current constant voltage
type. The constant current type can be used but with less satisfactory results.
2.5.6
Wire
Feeder - The function
of the wire feeder in FCAW is the same as discussed in
the section on GMAW. Since the
flux cored electrode is tubular in construction, precautions
must be taken not to flatten the electrode.
To facilitate feeding by means other than pressure
alone, specially designed feed rolls
with knurled or grooved surfaces are used. Some feeders
use four feed rolls rather than two
to minimize unit pressure on the electrode. 2.5.7
The
Welding Gun
- As compared to GMAW, the main difference in FCAW welding
guns is in those used with the self
shielding process. The gun is somewhat more compact due
to the absence of an external gas shielding
nozzle. Since the self shielding process normally requires
a longer electrode extension, the self shielding gun may have an insulated guide
tube (Refer back
to Figure 18) to give stability to the electrode. Water cooled guns are
available for high
duty semi-automatic welding and for automatic welding. FIGURE
19 CURRENT PATH
1/16" FLUX-CORED
ELECTRODE 1/16"
SOLID ELECTRODE
