CEMP-E
TI 809-26
1 March 2000
4. SUBMERGED ARC WELDING (SAW).
a. Process Principles. Submerged Arc Welding (SAW) uses a blanket of fusible granular material
called flux to shield the arc and molten metal. The arc is struck between the workpiece and a bare wire or
composite electrode, the tip of which is submerged in the flux. Since the arc is completely covered by
flux, it is not visible and the weld is made without the flash, spatter, sparks and smoke common for the
open-arc processes.
(1) The process is typically operated automatic, or fully mechanized, although semiautomatic
operation is often used. The electrode is continuously fed from a coil or spool to the welding gun, which
travels at a preset speed along the joint, preceded by a flux deposition system. In semiautomatic
welding, the welder moves the gun, usually equipped with a flux-feeding device, along the joint by hand.
(2) Flux feed may be by gravity flow through a nozzle from a small hopper atop the welding gun, or
it may be through a nozzle tube connected to an air-pressurized flux tank. Flux may also be applied in
advance of the welding operation, ahead of the arc, from a hopper run along the joint. Many fully
mechanized systems are equipped with vacuum devices to pick up the flux unfused after welding for
reuse.
(3) During welding, the heat of the arc melts some of the flux along with the steel and the tip of the
electrode. The tip of the electrode and the welding zone are always shielded by molten flux, surrounded
by a layer of unfused flux. As the electrode progresses along the joint, the lighter molten flux rises above
the molten metal in the form of a slag. The molten slag is a good conductor and provides an additional
path for the current, thus generating additional heat. The weld metal, having a higher melting (freezing)
point, solidifies while the slag above it is still molten. The slag then freezes over the newly solidified weld
metal, continuing to protect the metal from contamination while it is very hot and reactive with
atmospheric oxygen and nitrogen. Upon cooling and removal of any unmelted flux for reuse, the slag is
removed from the weld.
(4) Several electrodes may be used in series or parallel, and multiple beads can be placed when
using separate power supplies for each bead. Parallel electrode SAW uses two electrodes connected
electrically in parallel to the same power supply. Both electrodes are fed by means of a single electrode
feeder. For heat input calculation purposes, the total for the two electrodes is used. Multiple electrode
SAW uses at least two separate power supplies and two separate wire drives to feed two electrodes
independently. To minimize the potential interaction of magnetic fields between the two electrodes,
typical SAW setups have the lead electrode operating on DC current while the trail electrode is operating
AC.
(5) DC and AC welding machines of both conventional drooping voltage type or constant potential
type can be used for SAW. With drooping voltage, a voltage sensitive relay adjusts the wire feed speed
to maintain the desired arc voltage. With constant potential voltage, the arc length is self-adjusting,
similar to the action in FCAW. Welding currents typically range from 500 to 1000 amperes.
(6) Flux must be stored so that it remains dry. Fluxes in open or damaged bags, or in flux hoppers,
may become contaminated with moisture from the atmosphere, so exposure should be limited. The
guidelines of the flux manufacturer, as well as AWS D1.1 Section 5.3.3 regarding storage and usage of
the flux must be followed. When not in use, flux hoppers should be covered or otherwise protected from
the atmosphere.
(7) Because unmelted flux does not undergo chemical changes, it may be recovered for future
use. Flux recovery systems range from vacuum recovery systems to sweeping with brooms and pans.
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