LESSON VII ©
COPYRIGHT 2000 THE ESAB GROUP, INC. FLUX
CORED ARC WELDING ELECTRODES FOR
CARBON AND LOW ALLOY STEELS 7.1 INTRODUCTION
Gas shielded
flux cored electrodes for welding carbon steels were developed in the early
1950’s and were made commercially
available in 1957. This process was developed to combine
the best features of submerged arc welding and CO2 welding.
The combination of the
fluxing ingredients in the core and the external CO2
gas shield produce high quality welds
and a stable arc with a low spatter level. Initially, these electrodes were
available only
in the larger diameters (5/64"-5/32") and were for use in the flat or horizontal
positions on heavy
weldments. In 1972, small diameter gas shielded flux cored electrodes for
weld- ing in all
positions were developed, and this greatly expanded the flux cored arc welding
field. 7.1.0.1
Self shielded flux cored electrodes
were made available shortly after the gas shielded
types were introduced and both have gained industry wide acceptance for specific
applications. The major differences
of the two types were covered in Lesson II and should be
reviewed at this time. 7.2 MANUFACTURING
FLUX CORED ELECTRODES Manufacturing
flux cored electrodes requires close controls. Since the weld metal is a
combination of the metal sheath and
the flux ingredients, both must be closely checked for size
and chemical composition before fabrication begins. 7.2.0.1
Since the space within the wire is
limited, particle size of the ingredients be- comes
very important, so that the particles will “nest” together. Flux
ingredients must be totally
mixed or blended and measures taken to prevent segregation of the elements before
fabrication. 7.2.0.2
Most flux cored electrodes are manufactured
from a flat metal strip that is passed through
a mill where forming rolls progressively shape it into a U-shaped section. A
me- tered amount
of granular flux is fed into the formed strip. It then passes through the
closing rolls,
forming the strip into a tube and tightly compressing the core material. See
Figure 1. 7.2.0.3
The tube is then pulled through a series
of drawing dies that reduce it to its final size,
and further compress the flux to lock it in place within the tube.
