Hard-
Surfacing,
Building
Fusion
Welding
Carbon
Welding Non-Ferrous Metals
Heating
& Heat
Treating
Braze
Welding
Welding Cast Iron Welding Ferrous Metals
Brazing
&
Soldering
Equipment
Set-Up
Operation
Equipment
For
OXY-Acet
Structure
of
Steel
Mechanical
Properties
of Metals
Oxygen
&
Acetylene
OXY-Acet
Flame
Physical
Properties
of Metals
How Steels
Are
Classified
Expansion
&
Contraction
Prep
For
Welding
OXY-Acet
Welding
& Cutting
Safety
Practices
Manual
Cutting
Oxygen
Cutting By
Machine
Appendices
Testing
&
Inspecting
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.