FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 4. Metal Structure, Welding, and Brazing | 5. Welding and Brazing | 4-88. Brazing
9/27/01
AC 43.13-1B CHG 1
replace the bar-shaped electrodes. The metal
to be welded is moved between them, and
electric pulses create spots of molten metal
that overlap to form the continuous seam.
4-88. BRAZING. Brazing refers to a group
of metal-joining processes in which the bond
ing material is a nonferrous metal or alloy with
a melting point higher than 425 C (800 F), but
lower than that of the metals being joined.
Brazing includes silver brazing (erroneously
called silver soldering or hard soldering), cop
per brazing, and aluminum brazing.
NOTE: Never weld over a previously
brazed joint.
a. Brazing requires less heat than welding
and can be used to join metals that are dam
aged by high heat. However, because the
strength of brazed joints is not as great as
welded joints, brazing is not used for structural
repairs on aircraft. In deciding whether braz
ing of a joint is justified, it should be remem
bered that a metal, which will be subjected to a
sustained high temperature in use, should not
be brazed.
b. A brazing flux is necessary to obtain a
good union between the clean base metal and
the filler metal. There are a number of readily
available manufactured fluxes conforming to
AWS and AMT specifications.
and its alloys, a neutral flame is preferred, but
if difficulties are encountered, a slightly re
duced flame is preferred to an oxidizing flame.
e. The filler rod can now be brought near
the tip of the torch, causing the molten bronze
to flow over a small area of the seam. The
base metal must be at the flowing temperature
of the filler metal before it will flow into the
joint. The brazing metal melts when applied to
the steel and runs into the joint by capillary at
traction. In braze welding, the rod should
continue to be added, as the brazing pro
gresses, with a rhythmic dipping action; so that
the bead will be built to a uniform width and
height. The job should be completed rapidly
and with as few passes of the rod and torch as
possible.
f. When the job is finished, the metal
should be allowed to cool slowly. After cool
ing, remove the flux from the parts by im
mersing them for 30 minutes in a lye solution.
(1) Copper brazing of steel is normally done
in a special furnace having a controlled atmos
phere, and at a temperature so high that field
repairs are seldom feasible. If copper brazing
is attempted without a controlled atmosphere,
the copper will probably not completely wet
and fill the joint. Therefore, copper brazing in
any conditions other than appropriately con
trolled conditions is not recommended.
c. The base metal should be preheated
slowly with a mild flame. When it reaches a
dull-red heat (in the case of steel), the rod
should be heated to a dark (or purple) color
and dipped into the flux. Since enough flux
adheres to the rod, it is not necessary to spread
it over the surface of the metal.
d. A neutral flame is used in most brazing
applications. However, a slightly oxidizing
flame should be used when copper-zinc, cop-
per-zinc-silicon, or copper-zinc-nickel-silicon
filler alloys are used. When brazing aluminum
(a) The allowable shear strength for copper
brazing of steel alloys should be 15 thousand
pounds per square inch (kpsi), for all condi
tions of heat treatment.
(b) The effect of the brazing process on the
strength of the parent or base metal of steel
alloys should be considered in the structural
design. Where copper furnace brazing is em
ployed, the calculated allowable strength of
Par 4-87
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