A heat source is generally applied to the joint to increase the temperature of the filler metal and that of the surfaces to be joined. This temperature must exceed the melting point of the brazing alloy. The surfaces to be joined are also heated in order to increase the wetting properties of the filler metal, thus facilitating the process itself.
Torch brazing is by far the most common method of brazing. Torch brazing is a procedure where the heat is applied using a gas flame placed on or near the joint being brazed (most used gasses are acetylene, hydrogen or propane). It is recommended for small production volumes or in specialized operations.
There are two main categories of torch brazing in use: manual, and automatic.
In induction brazing the parts to be joined and the filler material are heated through an electromagnetic field that is generated by the alternating current from an induction coil. The induction coil is designed based on the specific geometric form of the joint. This technique is mostly recommended for automated systems where heat is localized due to a more efficient energy transformation process made possible from induction.
These furnaces are often conveyor fed, allowing parts to be moved through the hot zone at a controlled speed. During the heating stage the brazing metal melts and it then re-solidifies in the cooling stage. This technique is mostly recommended for large production volumes where a very accurate temperature control is needed.
BATCH TYPE FURNACE
During this type of brazing, each batch of production is processed separately in a sealed furnace. The atmosphere inside the furnace can be either a reactive gas, or an inert gas such as argon or nitrogen. Hydrogen can be also used in order to control oxidation. The main advantage of this technique is the accurate temperature and atmosphere control during the brazing process.
This type of brazing is most often used to braze materials that react easily to gases such as nitrogen or oxygen, and when parts cannot endure the presence of fluxes and contaminants. A pump system is used to remove the gases inside the furnace.