Civil Engineering Reference
In-Depth Information
a silicate binder. The heated coating converts into a shielding gas to ensure that there
is no oxidation or atmospheric contamination
∗
of the weld material in the arc stream
and pool. The coating residue forms as a slag on the weld surface (provided enough
time exists for the slag to float to the weld surface) and some is absorbed. The coating
also assists in stabilizing the electric arc during the welding process.
9.2.1.2
Submerged Arc Welding
The SAW process is an automatic welding process where the bare metal consumable
electrode is covered with a granular fusible flux material. This flux shields the arc
stream and pool. Economical and uniform welds with good mechanical properties,
ductility and corrosion resistance are produced by the modern SAW process.
9.2.1.3
Flux Cored Arc Welding
The FCAW process is often semiautomatic and uses a continuous wire as the con-
sumable electrode. The wire is annular with the core filled with the flux material.
†
In this manner the flux material at the core behaves similarly to the coating in the
SMAW or granular flux in the SAW process.
9.2.1.4
Stud Welding
Stud welding is essentially an SMAW process made automatic. The stud acts as the
electrode as it is driven into a molten pool of metal. A ceramic ferrule placed at the
base of the stud provides the molten pool of metal and also serves as the electrode
coating for protection of the weld.A complete penetration weld (with a small exterior
annular fillet weld) is achieved across the entire stud shank or body. This welding
process is used extensively in the fabrication of composite steel and concrete beams
and girders (Chapter 7).
9.2.1.5
Welding Electrodes
Electrodes commonly used for structural steel welding are designated as E60XX or
E70XX. These electrodes have a consumable metal tensile strength of 60 and 70 ksi,
respectively. The “XX” in the electrode designation refers to numbers that describe
other requirements related to use, such as welding position, power supply, coating
type, and arc type/characteristics. Low hydrogen electrodes are often specified to
provide superior weld properties and preclude possible embrittlement of the weld
from absorbed hydrogen.
9.2.2 W
ELD
T
YPES
Welds are groove, fillet, slot, or plug welds. Slot and plug welds exhibit poor fatigue
behavior and are not recommended for use on steel railway superstructures.
∗
Generally, in the form of nitrides and oxides, which promote brittle weld behavior.
†
Exterior coatings on the continuous wire would be removed while being fed through the electrode holder
to reach the arc.
