Welding
Non-Ferrous
Metals
Treating
Welding
Cast Iron
Welding
Ferrous
Metals
1
BRAZE WELDING
Up to this point, we have been talking
about the fusion welding of
carbon steel, and in the chapters immediately following
this, we shall talk about the fusion welding of cast iron, of stainless steel,
and of non-ferrous metals. In fusion
welding, the filler rod always has a melting point approximately the same as the
melting point of the metal to be
joined, and both the filler metal and the base metal are actually melted and fused
together. Braze welding is a
process of almost equal importance
to the user of an oxy- acetylene welding outfit. It closely resembles fusion
welding in several important respects.
It is used to produce joints of excellent strength in steel, in cast iron, and
in copper and
some copper alloys. However, in braze welding, the filler metal always has a melting
point well below the
melting point of the base metal, and the base metal is never melted.
Years ago, the process we now term
”braze welding” was commonly known as ”bronze-welding”. Ever
since the process
was renamed ”braze welding”, there has existed a degree of confusion
between the terms ”brazing” and ”braze
welding”. The American Welding Society definitions for ”brazing”
and ”braze welding” both stipulate that the filler
metal must have a melting point above 4250C
(8000F). However, the definitions state that
in brazing the filler
metal is drawn into a tight-fitting
joint by capillary attraction;
in braze welding the filler
metal is deposited in the joint
by other than capillary attraction.
We shall talk about the use of the flame in brazing operations in another
chapter. The
basis for the braze welding process is that both brass and bronze* will flow onto
properly prepared surfaces of higher-melting-point
metals or alloys to form a bond or molecular union which has excellent strength.
The base metal
is never melted. It is merely raised to the temperature at which the filler metal
will tin –
form a smooth film – on
the surface of the joint. Although the temperatures involved are much lower than
those required for the fusion welding
of steel, braze welding is primarily an oxy-acetylene process. The intense heat
of the oxy-acetylene flame quickly
raises the base metal to the proper temperature for tinning.
The welder can control every variable factor involved:
the temperature of the base metal, the melting of the filler rod, and the condition
(neutral or slightly oxidizing)
of the flame. *Traditionally,
”bronze” was considered an alloy of copper and tin, ”brass”
an alloy of copper and zinc. Today, while all alloys designated as
”brass” contain a lot of
zinc, several alloys commercially labeled ”bronze” also contain zinc,
and some contain no tin.
