Brazing and Braze Welding are joining processes where a filler metal is placed at the joint and the
temperature is raised to melt the filler metal into the joint. The strength of the
joint depends upon the adhesion at the interface as well as the contact area
of the joint. Consequently, the surface should be clean and free from rust,
oil, and other contaminants. Filler metals melting above 840°F are used in
brazing, and those that melt below this temperature are used in soldering.
In braze welding, the filler metal is deposited in the joint and fills it by capillary action. The heat source is usually an oxy-acetylene torch. The filler metal is selected to avoid embrittlement of the joint as well as any galvanic corrosion. Fluxes are often used to prevent oxidation, remove oxides, and reduce fuming. Brazing flux is most often made of borax, boric acid, borates, fluorides, or chlorides. Wetting agents may also be added to improve molten metal capillary action.
Furnaces may be used to braze whole assemblies of complex parts (such as jet engine blades and shrouds) and for diffusion brazing where the filler metal diffuses into the workpiece. This has proven effective for stronger lap or butt joints, and difficult operations. Dip brazing using molten salt or metal baths is also utilized. Infrared heating employing high-intensity quartz lamps is also used to braze thin parts.
