Page 209 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

194 Chapter Three

the workpiece and a bare wire electrode, the tip of which is sub-
merged in the flux. Since the arc is completely covered by the flux, it
is not visible and the weld is made without the flash, spatter, and
sparks that characterize the open-arc processes. The nature of the
flux is such that very little smoke or visible fumes are developed.
The process is typically fully mechanized, although semiautomatic
operation is often utilized. The electrode is fed mechanically to the
welding gun, head, or heads. In semiautomatic welding, the welder
moves the gun, usually equipped with a flux-feeding device, along the
joint. High currents can be used in submerged arc welding and
extremely high-heat input levels can be developed. Because the cur-
rent is applied to the electrode a short distance above its arc, relatively
high amperages can be used on small-diameter electrodes, resulting
in extremely high current densities. This allows for high deposition
rates and deep penetration.
Welds made under the protective layer of flux (Fig. 3.10) are excel-
lent in appearance and spatter-free. The high quality of submerged
arc welds, the high deposition rates, the deep penetration characteris-
tics, and the easy adaptability of the process to full mechanization
make it popular for the manufacture of plate girders and fabricated
columns.
One of the greatest benefits of the SAW process is freedom from the
open arc. This allows multiple arcs to be operated in a tight, confined
area without the need for extensive shields to guard the operators
from arc flash. Yet this advantage also proves to be one of the chief
drawbacks of the process; it does not allow the operator to observe the
weld puddle. When SAW is applied semiautomatically, the operator
must learn to propel the gun carefully in a fashion to ensure uniform
bead contour. The experienced operator relies on the uniform forma-
tion of a slag blanket to indicate the nature of the deposit. For single-
pass welds, this is mastered fairly readily; however, for multiple-pass
welding, the skills required are significant. Therefore, most sub-
merged arc applications are mechanized. The nature of the joint must
then lend itself to automation if the process is to prove viable. Long,
uninterrupted straight seams are ideal applications for submerged
arc. Short, intermittent welds are better made with one of the open-
arc processes.
Two electrodes may be fed through a single electrical contact tip,
resulting in higher deposition rates. Generally known as parallel elec-
trode welding, the equipment is essentially the same as that used for
single-electrode welding, and parallel electrode welding procedures
may be prequalified under AWS D1.1-98.
Multiple-electrode SAW refers to a variation of submerged arc
which utilizes at least two separate power supplies, two separate wire

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