Gas (flame) brazing is a process, where the gas flame is the heat source, directly heating up the brazed joint to the required temperature. The flame is achieved as a result of combusting mixtures of different flammable gasses and vapours of liquid fuels with oxygen or air. Torches are the devices designed for the needs of the process just described.
The feasibility of using various gasses for gas brazing depends on many factors, which include the net calorific value of the fuel (i.e.: the amount of heat in joules or calories emitted as a result of combusting 1m3 of gas), flame temperature, contents of non-flammable parts, effects on the quality of the brazed joint, cost of fuel, safety of use, ease of transport and storage, etc. From that point of view, hydrocarbons (e.g. acetylene, methane, ethane, propane), hydrogen, illumination gas, natural gas, coal gas as well as petrol and kerosene vapours seem to be the best. Properties of the major fuels used for gas brazing are presented in the table below:
|Flame temperature combustion in oxygen |
|Gas content on % (volume) which presents an explosion risk in mixture|
|with air||with oxygen|
1)At 15oC and 0.1 MPa