What is Silver Brazing?
Silver brazing is a joining process whereby a non-ferrous filler metal, the alloy is heated to melting temperature (above 800°F) and distributed between two or more close-fitting parts by capillary attraction. Silver brazing uses filler metals and alloys such as silver, copper, zinc, cadmium, etc.
At its liquidus temperature, the molten filler metal interacts with a thin layer of the base metal, cooling to form an exceptionally strong, sealed joint due to grain structure interaction. The silver brazed joint becomes a sandwich of different layers, each metallurgically linked to the other.
Silver brazing can employ various heat sources such as torch, flame, acetylene, gas/air, induction, resistance, infrared, oven, and furnace.
Flux is necessary for brazing to remove and prevent the reformulation of surface oxides on the base metals.
Silver brazing produces strong, sealed, leak-proof joints. Silver brazing uses filler metals in solid form, like rings and wire, slugs, washers, powder, and paste. Proper brazements begin with a good joint design.
Silver brazing produces joints that meet specifications that meet mechanical performance, electrical conductivity, pressure tightness, corrosion resistance, and service temperature. High production, metal joining operations often employ silver brazing.
Cadmium-free silver brazing alloys are available in paste form. Silver brazing is a popular method for joining or bonding ferrous and non-ferrous base metals like steel, stainless steel, copper, and brass. Silver brazing can be done on automatic machines for cost-efficient metal joining at high production rates.
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Process of Silver Brazing
Silver brazing uses the same basic methods as other brazing methods including fit for proper capillary action, cleaning of base metals, the use of flux, heat, and post braze cleaning.
When heating the assembly, heat uniformly, with greater heat on the thicker metal section If one metal has better heat conductivity than the other, apply more heat to the better heat conductor.
Note that filler metals flow to the higher heat source.
Cadmium oxide fumes formed by heating and melting of silver brazing alloys are highly toxic. To prevent injury to personnel, personal protective equipment must be worn and adequate ventilation provided.
It is essential that the joints be free of oxides, scale, grease, dirt, or other foreign matter. Surfaces other than cadmium plating can be easily cleaned mechanically by wire brushing or an abrasive cloth; chemically by acid pickling or other means.
Extreme care must be used to grind all cadmium surfaces to the base metals since cadmium oxide fumes formed by heating and melting of silver brazing alloys are highly toxic.
Silver Brazing Rod
Silver brazing, frequently called “hard soldering” or “silver soldering,” is a low-temperature brazing process with rods having melting points ranging from 1145 to 1650ºF (618 to 899ºC). This is considerably lower than that of the copper alloy brazing filler metals.
Uses Of Silver Brazing
Silver Brazing is a very versatile process and a good one for any welder to know. It can be used to join several different dissimilar metal combinations… stainless steel to copper to bronze to brass to carbon steel
Silver brazing is often used to join carbide tooling inserts for machining operations because, with silver brazing, the metal does not typically reach a critical transition temperature that could cause brittleness.
I once used silver braze to make a brass belt buckle that had stainless steel hardware on the back size. It is super useful and sometimes a better option than welding.