Brazing

Joining metals by flowing a thin layer, capillary thickness, of nonferrous filler metal into the space between them. Brazing temperatures are in excess of 427C.

Bonding results from the intimate contact produced by the dissolution of a small amount of base metal in the molten filler metal, without fusion of the base metal. Sometimes, the filler metal is put in place as a thin solid sheet or as cladding and the composite is heated as in furnace brazing. The term brazing is used where the temperature exceeds some arbitrary value, such as 430C.

The term soldering is used for temperatures lower than the arbitrary value.

Aluminium Brazing

Some aluminum sheet products are made up of a strong core alloy that is clad with a thin layer of a high-silicon alloy which has a much lower melting point than the core (see also "Clad Products"). This allows a complex shape, such as a car radiator, to be fabricated then heated to a temperature that is sufficient to melt the cladding while leaving the core intact. The thin skin of oxide film that covers the surface of aluminum needs to be removed for effective brazing.

Arc Brazing

A brazing process wherein the heat is obtained from an electric arc formed between the base metal and an electrode, or between two electrodes.

Block Brazing

A brazing process in which bonding is produced by the heat obtained from heated blocks applied to the parts to be joined and by a nonferrous filler metal having a melting point above 427C (800F), but below that of the base metal. The filler metal is distributed in the joint by capillary attraction.

Braze Welding

A method of welding by using a filler metal that liquefies above 450C (842F) and below the solid state of the base metals. Unlike brazing, in braze welding, the filler metal is not distributed in the joint by capillary action.

Controlled Atmosphere Brazing

This process uses a non-corrosive powdered flux and an inert gas atmosphere. Sometimes also described by the trade name "Nocolok".

Dip Brazing

A brazing process in which bonding is produced by heating in a molten chemical or metal bath and by using a nonferrous filler metal having a melting point above 427C (800F), but below that of the base metals. The filler metal is distributed in the joint by capillary attraction. When a metal bath is used, the bath provides the filler metal.

Film Brazing

A process in which bonding is produced by heating with a molten nonferrous filler metal poured over the joint until the brazing temperature is attained. The filler metal is distributed in the joint by capillary attraction.

Flux-Dip Brazing

The component is immersed in a molten salt which acts as a flux as well as a heat source for melting the clad layer. The fluxes are corrosive and all traces must be removed after brazing.

Furnace Brazing

A process in which bonding is produced by the furnace heat and a nonferrous filler metal having a melting point above 427C (800F), but below that of the base metals. The filler metal is distributed in the joint by capillary attraction.

Hydrogen Brazing

A method of furnace brazing in a hydrogen atmosphere.

Induction Brazing

A process in which bonding is produced by the heat obtained from the resistance of the work to the flow of induced electric current and by using a nonferrous filler metal having a melting point above 427 C (800 F), but below that of the base metals. The filler metal is distributed in the joint by capillary attraction.

Resistance Brazing

A brazing process in which bonding is produced by the heat obtained from resistance to the flow of electric current in a circuit of which the workpiece is a part, and by using a nonferrous filler metal having a melting point above 427C (800F), but below that of the base metals. The filler metal is distributed in the joint by capillary attraction.

Torch Brazing

A brazing process in which bonding is produced by heating with a gas flame and by using a nonferrous filler metal having a melting point above 427C (800F), but below that of the base metal. The filler metal is distributed in the joint of capillary attraction.

Vacuum Brazing

Components are heated in a high vacuum, completely free of oxygen. The clad alloy must contain magnesium as an alloying addition. At the brazing temperature, the heat and vacuum causes the magnesium to "boil" out of the molten metal thereby breaking up the brittle oxide skin into small, harmless shards.

See also: American Welding Society, Soldering, Welding.

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Subjects: Mechanical Engineering