©
COPYRIGHT 2000 THE ESAB GROUP, INC. LESSON
VIII of the processes,
which makes it necessary to deposit three or more layers to attain the full
properties of the surfacing material.
8.3.6
Gas
Metal Arc
Surfacing -
Gas metal arc surfacing is not widely used for hardfacing
since most of the iron based alloys can be deposited more economically by
other methods. It is used somewhat
for out-of-position surfacing where the low penetration of
the short circuiting transfer mode produces low dilution. It is also used
for depositing non-ferrous
alloys, such as aluminum-bronze, which cannot be applied by other methods.
8.4 SURFACING
WITH POWDERS The
processes previously discussed utilized hardfacing alloys in the form of solid
or tubular rods
and wires. Hardfacing alloys are also available in powdered form, and their
method of application
is quite different from the standard welding methods. Hardsurfacing powders
are used for restoring worn surfaces
and are widely used by original equipment manufac- turers
on new parts which require small hardened surfaces. The four major methods
for applying powder
metal hardfacing alloys are: flame spray, manual torch, plasma spray, and
plasma arc welding.
8.4.1
Flame
Spray Process
- The flame spray process is accomplished with a special
gun-like apparatus which utilizes an
oxyacetylene or oxyhydrogen flame. An air orifice aspirates
the powder into the flame and deposits it on the surface. As the molten
particles strike
the surface, they flatten out and cool instantaneously. The bond is mechanical
since there is
no fusion with the base metal. If desired, fusion can be accomplished in
a subse- quent
fusing operation with an oxyacetylene burner. 8.4.1.1
The process is very effective for shafts
or small cylindrical parts which are rotated on
a lathe while being surfaced. The surface must be cleaned and grit-blasted
before applying
the powder for a good initial bond. Deposition thickness can range from
1/32 to 3/ 32
inches. 8.4.2
Manual
Torch Process
- The manual torch process utilizes a special oxyacety-
lene torch which has a small hopper
from which the surfacing powder is aspirated into the fuel
gas stream. Application of the surfacing powder and fusion to the base metal
take place in
one operation. Single pass deposit thickness can range from 0.030 to 0.050
inches. 8.4.3
Plasma
Arc Spray
and Plasma
Arc Welding
- These are two processes used
to deposit powdered metal surfacing
alloys utilizing a plasma arc torch. The plasma arc
