Silver Brazing

A joining process, silver brazing allows alloy, a non-ferrous filler metal, to be heated at a melting temperature above 800°F later distributed between two or more close-fitting parts by capillary attraction. The filler metal interacts with a thin layer of the base metal at liquidus temperature, the molten filler metal interacts with a thin layer of the base metal. The grain structure interaction leads to the formation of a strong, leak-proof, sealed joint. The silver brazed joint becomes a sandwich of different layers, each metallurgically linked to each other.

Forms of Heat Sources
Making use of filler metals & alloys as silver, copper, zinc, cadmium to name a few in solid forms like rings, wires, slugs, washers, powder & paste, silver brazing applies varied forms of heat sources such as :

• Torch
• Flame
• Acetylene
• Gas/air
• Induction
• Resistance
• Infrared
• Oven
• Furnace

The joints produced due to silver brazing beautifully meet the specifications touching upon varied aspects as mechanical performance, electrical conductivity, pressure tightness, corrosion resistance, and service temperature. Employment of silver brazing by high production, metal joining operations is the common practice. Used for joining or bonding ferrous and non-ferrous base metals like steel, stainless steel, copper, and brass, silver brazing process are generally done on automatic machines for cost-efficient metal joining at high production rates.

Silver Brazing Alloys
Silver brazing alloys are available in varied forms & their chemical composition is another point to be taken into consideration, since, the silver content in them differ in terms of the silver content, melting temperature and in flow temperature.

Chemical Composition
The most widely used silver alloys consists of 40 to 50% silver while 25 to 15% zinc is commonly used. The typical chemical composition for an alloy with a 607°C melting point & 618°C flow point consists of :

• 45% Ag
• 15% Cu.
• 16% Zn
• 24% Cd

Availability of Silver Brazing Alloys
Silver brazing alloys are available as:

• Rods
• Rings
• Foils
• Washers

Requirement of Flux in Silver Brazing Alloys
Flux forms an important part of silver brazing finer alloys. Available in a powder or paste form, flux is mainly applied either by dipping or spraying or brushing the filler rod end into it. The requirement for flux is for three main reasons which are :

• It lessens the surface oxides part
• It makes sure that the filler metal flows
• It wets the base metals satisfactorily

The flux residues should be removed after they are brazed from the assemblies, since, it prevents corrosion. The residues are removed by applying either of the these options.

• Throughly dry the residues after rinsing it in hot water
• Or follow the length procedure of scrubbing, applying a steam jet, wire brushing, abrasive blasting etc.

Silver Brazing Methods
Silver brazing methods make use of almost varied methods specially the torch brazing and furnace brazing method. Furnace brazing method though have additional advantages, since, that achieves high production rates in order to provide a high degree of reproducibility of results etc.

While oxyacetylene torch method used in silver brazing procedure are mentioned in details.

• Use a fine file, steel wool or emery cloth to mechanically clean the joints until bright metal is exposed.
• Support the joint by accurately fitting the joint closely.
• Properly apply the required flux.
• After heating it at an apt temperature, do the silver brazing of both the pieces at a uniform level.
• Apply the silver brazing rod.
• Later cool the brazed joint.
• Throughly remove the flux residue from the brazed joint.

Advantages
Though being quite costly, silver brazing filler alloys as well have some real vital plus points which are mentioned below :

• Silver filler alloy can be easily penetrated into narrow openings simply because of extremely fluid nature.
• The silver brazed joints are leak proof.
• Silver brazing economically execute the varied difficult tasks otherwise found difficult by welding.

Application
Used to be known as silver soldering earlier, silver brazing allows silver alloy fiber rod to be used for brazing purposes. Applied mainly for arts and in jewelry manufacturing, not many industries have silver brazing applications.

The varied applications of silver brazing method are as follows :

• It is preferred in place of other brazing alloys which might be causing excessive grain growth or damage to base metals. Silver brazing are rather used at such places where strong ductile joints are required.
  
  
• It is used for joining ferrous and nonferrous metals except AI, Mg, Pb and Zn alloys.
  
  
• Be it stainless steel, a non ferrous metal or alloy as copper, brass, silver filler alloys are used for brazing purpose.

The varied other usages of silver brazing are :

• Used popularly for joining carbide tips to the steel tool shanks
• Fixing up air conditioners' condensers and evaporators
• Making fuel tanks for tractor
• Making brass and steel bellows housing assembly