©
COPYRIGHT 2000 THE ESAB GROUP, INC. LESSON
VIII 8.3 METHODS
OF HARDFACING Hardfacing
may be applied by a variety of methods and processes. The method chosen
depends on a number of factors:
a. Size and
configuration of the part. b.
End use of the hardfaced part. c.
Depth of overlay required. d.
Quality or smoothness of the overlay. e.
Properties of the deposited overlay. f.
Composition of the base metal. g.
Available forms of the filler metal. h.
Availability of the equipment necessary. i.
Operator skill. 8.3.1
Oxyacetylene
Surfacing -
The oxyacetylene process, an early method of apply-
ing surfacing alloys, is still in use
today. The equipment is low in cost and consists of a
torch, hoses, oxygen cylinder, acetylene
cylinder, and two pressure regulators. Unlike oxyacetylene
welding, a thin surface layer of the part in the immediate area being
hardfaced, is brought to melting temperature.
The hardfacing alloy is simultaneously melted
into the molten area where it flows and spreads, and is fused to the surface in
a thin smooth
layer, with little dilution from the base metal. This method is commonly
referred to as
“sweating”. 8.3.1.1
The oxyacetylene process lends itself
to servicing small parts, and fills grooves and
recesses well. Other advantages are low dilution and low temperature gradients
which minimize
stresses and subsequent cracking. The operator requires much skill, and
the deposition
rate is very low. The process does not lend itself to automation, although
some automatic
set-ups have been developed. 8.3.2
Shielded
Metal Arc
Surfacing -
SMAW, as described in Lesson II, is a versatile
method of depositing hardfacing materials.
The electrode has a flux coating to assure weld cleanliness.
The equipment is the same as for SMAW and consists of a power source,
