filler metal has considerable strength when hot, and it
pipe periphery for a length of 2D (nominal) or 2
has the narrowest freezing range (solidifies quickest) of
inches (whichever is less) plus the socket depth.
Reassemble piping and fittings by using the same
additional advantage, since a quick-freezing filler metal
method you used for new installations. All silver-brazed
has much better weldability than one that remains
piping sections that have been removed for repairs, and
mushy over a wide temperature range.
newly fabricated sections, must be hydrostatically
tested before they are installed. Procedures for
Most of the commercial braze welding filler metals
conducting hydrostatic tests will be discussed in
are modifications of this 60/40 copper-zinc-zinc alloy,
with small additions of tin, iron, nickel, manganese,
silicon, and other elements.
Strong braze-welded joints depend on proper
preparation, the use of the correct technique, the
Braze welding is used to make a groove, fillet, plug,
strength of the filler metal, and coalescence of the filler
or slot weld using a copper-base alloy filer metal with
metal and the base metal. The strength of a
a melting point above 800°F but below that of the base
braze-welded joint does not depend upon a thin film of
metal. The filler metal is not distributed in the joint by
filler metal between close fitting surfaces as is true in a
capillary attraction. In the past, this process has been
silver-brazed joint. Heavy deposits of silver-base filler
called brazing. Earlier in this chapter, we said that all
metals have low strength values. However, heavy
brazing is done by capillary attraction. Braze welds are
deposits of copper-base braze welding filler metals
made without melting the base metal, although some
frequently attain strength comparable to welded joints.
fusion may occur between the filler metal and the base
Adequate preparation, which includes thorough
metal. This method is very useful for repairing cast iron
cleaning, is essential in braze welding. Remove all
foreign matter such as oil, grease, and oxides. The metal
The fact that braze welds are made without melting
on the underside and on the top of the joint must be
the base metal simplifies the welding procedure. Since
bright and clean. If the parts to be joined or repaired are
braze welding requires less heat, the speed of welding
less than one-fourth inch thick, it is not necessary to vee
or larger must be beveled to about a 90-degree vee.
The lower temperatures required for braze welding
mean that preheating is also easier. As a rule, braze
Coarse-grained soft castings are harder to tin than
welding operations can be done with only local
close-grained castings. A cast-iron part that has been in
preheating; that is, preheating only that portion of the
contact with fire will sometimes be difficult to tin. The
part to be braze welded. This makes it possible to repair
same is true of castings that have been exposed too long
broken castings and other parts in place, thus saving the
to steam and oil at high temperatures. Also, it may be
time and expense of disassembling and reassembling.
difficult to tin castings that have been in salt water or
chemicals for some time. One way to make such pieces
Braze welding is widely used to repair gray iron
easier to tin is to alternately heat and cool the casting.
castings. It is used not only to repair broken castings,
When tinning is difficult, it may be necessary to remove
but also to rebuild worn parts, such as gear teeth or valve
the affected surfaces of the metal so that it will take the
disks and seats. You can also repair and rebuild pistons,
rotary valves, guides, and other sliding surfaces on
pumps, engines, and machinery.
When you have cleaned the parts, the next step is to
align them. Obviously, the parts must be kept in proper
Braze welding should not be used to repair or
alignment and kept that way during the brazing process.
rebuild castings where the difference in color between
You can do this best by using clamps and by tack
the filler metal and cast iron would be objectionable.
Nor should it be used to join parts that will be subjected
to temperatures above 650°F, or to repair working parts
In braze welding, a casting must be heated along the
or containers used in chemical processes.
line of the weld. This sets up strains caused by
The best filler metal for braze welding is a naval
expansion and contraction, unless the casting is
brass that has a copper-zinc ratio of about 60 percent
properly preheated. In a small casting, up to about a
copper and 40 percent zinc. This ratio produces the best
hundred pounds, the heat from the torch is enough to
combination of high tensile strength and ductility. This
preheat the entire casting. Larger castings should be