features for feeding powders and a group of powdered
of these jobs for surfacing, be sure that the edges of
metal alloys developed especially for this process.
grooves, comers, or recesses are well rounded to
These powders are packaged in moistureproof bellows
prevent overheating of the base metal.
Hard surfacing may be applied to all low-carbon
ahoy and stainless steels as well as to Monel and cast
iron. It is not intended for aluminum, copper, brass, or
ADVANTAGES OF THE POWDERED
bronze. Tool steels can also be surfaced, but they offer
METAL FLAME SPRAY PROCESS
difficulties caused by shrinkage and strain cracks. If tool
steels are surfaced, they should be in an annealed, not a
This process offers many advantages over the
hardened, condition. If necessary, heat treating and
conventional oxyacetylene and metal arc welding
hardening can be done after the surfacing operation.
processes. Absolute control of the thickness, width, and
Surfacing with special alloys is not done as often as
deposition of the deposit can be attained by regulating
brazing or braze welding. But when the technique is
the amount of ahoy released, the rate of travel, and the
used, it must be done perfectly, especially when
path of the torch. Deposits can be placed with pinpoint
chromium-cobalt ahoy is applied to carbon or chrome-
precision because only the torch tip is used rather than
moly valve parts for high-pressure, high-temperature
a tip and filler rod, or electrode holder and electrode.
piping systems. On the whole, the silver brazing, braze
This is especially true when it is used in confined and
welding, and surfacing processes are important among
hard-to-get-at spaces.
the welding procedures you will use in the welding
Powdered metal deposits are surface alloyed to the
shop.
base metal. They do not dig into the base metal and set
up fracture zones. There is also little or no problem with
underbead cracking. Deposit dilution, caused by base
metal pickup, is held to a minimum because of surface
POWDERED METAL FLAME
alloying.
PROCESS
The powdered metal flame spray process also has
Another welding process being used throughout the
advantages over the metal spray process. Although
Navy is the eutalloy process, which is most commonly
fusion sometimes occurs when the metal spray process
called the powdered metal flame spray process. This
is used, the deposits have, essentially, a mechanical
process was developed by the Eutectic Corporation,
bond. On the other hand, powdered metal deposits
formerly the Eutectic Welding Alloys Corporation.
actually surface ahoy to the base metal and, as a result,
The powdered metal flame spray process can, and
give a higher strength bond. Since the fuel gases propel
should, be used alone for certain applications, but it is
the alloy to the base metal surface, there is no
not necessarily a separate, isolated technique. It
compressed air equipment that might offer additional
combines with, and works to supplement, conventional
complications. Deposits made by the powdered metal
oxyacetylene and electric arc welding, if overlays and
flame spray process also have greater density than those
joining metals cannot be done by either of the two other
made by the metal spray process. When you prepare the
processes. It is very useful where the control of the
base metal, you need to ensure only that the surface is
shape and thickness of the deposit helps reduce
free of all dirt and grease. No time-consuming knurling
machining time. This process is used for the repair of
and roughing of the surface is necessary, as is required
both small and large parts. It is also used for surfacing
with the metal spray.
parts that are subject to abrasion, friction, and corrosion.
The powdered metal flame spray process uses the
low heat input principle. Control of the surface
TORCHES
temperature enables the powder to surface bond in the
shortest time. This eliminates unnecessary saturation of
The torches used in the powdered metal flame spray
the base metal with needless heat. Such overheating
process are precision instruments, manufactured to very
does nothing to promote bonding, and usually results in
close tolerances. They have very few moving parts and
distortion and stresses in the base metal.
require only routine cleaning and maintenance. These
The main elements of the powdered metal flame
torches are designed specifically for this process. They
spray process are a unique gas torch with special
should not be used for other gas welding applications.
9-17