Brazing is the oldest technique for joining metals. The term brazing refers to a process of joining materials accomplished by melting only of the filler material. Base materials are heated to a temperature below their melting point but sufficient to result in a metallurgical bond.
The heat used for melting the braze material can come from several sources: torch, furnace, induction, and electrical resistance. Depending on the temperature it is defined as:
- soft brazing if T<450°
- strong brazing if T>450°.
Once molten, the filler material flows by capillary action into the joint, which is why surface cleaning plays a key role. Subsequent cooling causes the brazing agent to solidify and thus bring the two parts together.
- More design freedom due to the ability to join widely varying thicknesses, as the high heat required by welding can deform the thin thickness;
- Possibility of making irregular, uneven joints, as the brazing filler material can easily flow through irregular paths;
- Possibility of joining different materials with significantly different melting temperatures;
- In the case of furnace brazing, possibility of making several joints simultaneously within a single furnace.
- Strong brazing is used in the aerospace industry for the brazing of engine components, or in the energy industry for joining injector and burner parts.
- Soft brazing is used in the canning industry (mainly cans and jars), the automotive industry (radiator manufacturing), and the electronics industry (connector joining, often incorrectly referred to as soft welding of tin-lead alloys).
Apparently, already Phoenicians and Etruscans manifested the need to assemble metal pieces avoiding, however, the fusion of the two parts to be joined. Even the Leiden Papyrus, a very ancient document dating back to the 3rd century B.C., mentions a suitable method for doing so.
Through the centuries, that method remains extremely useful when it comes to joining metals without melting them down, and it is one of the most asked procedures in both the craft and industrial worlds.