Brazing

Brazing is a joining process in which a filler metal is melted and drawn into a capillary formed by the assembly of two or more work pieces. The filler metal reacts metallurgically with the workpiece(s) and solidifies in the capillary, forming a strong joint. Unlike welding, the work piece is not melted. It is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the adjoining metal. Brazing differs from welding in that it does not involve melting the work pieces and from soldering in using higher temperatures for a similar process, while also requiring much more closely fitted parts than when soldering. The filler metal flows into the gap between close-fitting parts by capillary action. The filler metal is brought slightly above its melting (liquidus) temperature while protected by a suitable atmosphere, usually a flux. It then flows over the base metal (known as wetting) and is then cooled to join the work pieces together. It is similar to soldering, except for the use of higher temperatures. A major advantage of brazing is the ability to join the same or different metals with considerable strength.

Brazing can join dissimilar metals such as aluminum, silver, copper, gold, and nickel. Flux is often used during brazing. It is a liquid that promotes wetting, which lets the filler flow over the metal parts to be joined. The filler obviously must have a melting temperature below that of the metal pieces. The brazing process can employ various heat sources such as torch, flame, acetylene, gas/air, induction, resistance, infrared, oven, and furnace. The process of brazing uses filler metals and alloys such as silver, copper, and zinc. Flux is necessary for brazing to remove and prevent reformulation of surface oxides on the base metals.