©
COPYRIGHT 2000 THE ESAB GROUP, INC. LESSON
VIII weld cables,
and an electrode holder. Surfacing may be performed in all positions and
although the deposition rate is low,
this process is especially useful where many short welds
are to be made. This method is used extensively for field repair and rebuilding
of equipment.
The arc power may be either direct or alternating current. Dilution
level is higher
than in the oxyacetylene method, but can be kept to a minimum by using the proper
welding current, using a weaving bead
instead of a stringer bead and keeping the electrode in
the puddle rather than on the base metal. 8.3.3
Gas
Tungsten Arc
Surfacing -
This process utilizes the same equipment and procedures
as GTAW as discussed in Lesson II. Deposition rate is low, but deposits
are of high quality
as long as efforts are made to keep dilution to a minimum. Normal dilution
is somewhat greater
than in oxyacetylene surfacing. Although argon, helium or mixtures of
these gases may be used, dilution is
the lowest when using pure argon. Gas Tungsten Arc
Surfacing is used for many of the same
type of applications as the oxyacetylene process. These
are usually small wear surfaces which require a smooth high quality deposit.
8.3.4
Flux
Cored Arc
Surfacing -
Two types of continuous tubular electrodes are available
for hardsurfacing; self-shielded and those which require a gas shield.
8.3.4.1 The
self shielded type are by far the more popular, and in the hardfacing field,
are known as “open arc wires”,
indicating that they do not require externally applied granu-
lar flux or shielding gas. Deposits
are comparable to those made with coated electrodes, but
there is no stub loss. Since no shielding gas or flux handling equipment
are necessary and
the deposition rate is high, it is the most economical process for depositing
hardfacing materials.
Portability of the equipment allows this process to be used for hardfacing
heavy equipment
in the field, as well as in the shop. Dilution is higher than that of coated
elec- trodes,
but lower than that of submerged arc welding. 8.3.4.2
The gas shielded cored wires are used
to a lesser extent. The shielding gases are
used to reduce oxidation and minimize alloy loss. The use of CO2
as a shielding gas has
a tendency to increase penetration and thereby, increase dilution. Shielding
gas and gas handling
equipment also add to the deposition cost. 8.3.5
Submerged
Arc Surfacing
- Submerged arc welding utilizes both solid and
tubular wires, and a granular flux.
It lends itself to automatic operation and is used for
production surfacing of large numbers
of parts in shops. The deposition rate and travel speeds
are high, and the penetration is deep. Weld beads are smooth and of good
quality. Heat
input is high and for this reason, this process is not recommended for use on
austen- itic manganese
steels. The deep penetration causes the highest dilution (up to 50%) of
all
