Page 206 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 191

raised too high, electrical-resistance heating within the unused
length of electrode will become so great that the coating ingredients
may overheat and “break down,” resulting in potential weld quality
degradation. SMAW also is used in the field for erection, mainte-
nance, and repairs. SMAW has earned a reputation for depositing
high-quality welds dependably. It is, however, slower and more costly
than other methods of welding, and is more dependent on operator
skill. Consequently, SMAW seldom is used for primary fabrication of
structures.

3.3.2 FCAW
Flux-cored arc welding (FCAW) uses an arc between a continuous
filler metal electrode and the weld pool. The electrode is always tubu-
lar. Inside the metal sheath is a combination of materials that may
include metallic powder and flux. FCAW may be applied automatically
or semiautomatically.
The flux-cored arc-welding process has become the most popular
semiautomatic process for structural steel fabrication and erection.
Production welds that are short, change direction, difficult to access,
must be done out-of-position (that is, vertical or overhead), or part of
a short production run generally will be made with semiautomatic
FCAW.
The flux-cored arc-welding process offers two distinct advantages
over shielded metal arc welding. First, the electrode is continuous.
This eliminates the built-in starts and stops that are inevitable with
shielded metal arc welding. Not only does this have an economic
advantage because the operating factor is raised, but the number of
arc starts and stops, a potential source of weld discontinuities, is
reduced.
Another major advantage is that increased amperages can be used
with flux-cored arc welding, with a corresponding increase in deposi-
tion rate and productivity. With the continuous flux-cored electrodes,
the tubular electrode is passed through a contact tip, where electrical
energy is transferred to the electrode. The short distance from the
contact tip to the end of the electrode, known as electrode extension or
electrical stickout, limits the buildup of heat due to electrical resis-
3
tance. This electrode extension distance is typically ⁄ 4 to 1 in for flux-
cored electrodes.
Within the category of flux-cored arc welding, there are two specific
subsets: self-shielded flux core (FCAW-ss) (Fig. 3.8) and gas-shielded
flux core (FCAW-g) (Fig. 3.9). Self-shielded flux-cored electrodes require
no external shielding gas. The entire shielding system results from the
flux ingredients contained within the core of the tubular electrode. The
gas-shielded versions of flux-cored electrodes utilize an externally

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