Brazing, which utilises a wide variety of heat sources, is often classified by the heating method used. To achieve brazing temperature, some methods heat locally (only the joint area), others heat the entire assembly (diffuse heating).
Some of the more widely used methods are highlighted below:
Localised Heating Techniques
In this method, the heat required to melt and flow filler metal is supplied by a fuel gas flame. The fuel gas can be acetylene, hydrogen, or propane and is combined with oxygen or air to form a flame. This process is readily automated and requires low capital investment. Torch brazing requires the use of a flux, so a post-braze clean is often required.
High frequency induction heating for brazing is clean and rapid, giving close control of temperature and location of heat. Heat is created by a rapidly alternating current which is induced into the workpiece by an adjacent coil.
This is a process in which heat is generated from resistance to an electrical current (as for induction brazing) flowing in a circuit which includes the workpieces. The process is most applicable to relatively simple joints in metals which have high electrical conductivity.
Diffuse Heating Techniques
Furnace brazing offers two prime advantages: protective atmosphere brazing (where high purity gases or vacuum negate the need for flux) and the ability to control accurately every stage of the heating and cooling cycles. Heating is either through elements, or by gas firing.
This involves immersion of the entire assembly into bath of molten braze alloy or molten flux. In both cases the bath temperature is below the solidification point of the parent metal, but above the melting point of the filler metal.
Brazing - a guide to best practice