Table of Contents
What is Brazing?
Brazing is a metal joining process in which filler metal is melted and filled into the joint. Hence, joins the joint. Brazing does not melt base metal which needs to be joined. It is performed at a temperature above 450 degrees Celsius.
Use of flux in Brazing
Unless brazing operations are contained in inert environment a flux material (such as Borax) is used to prevent oxidation of molten filler material. Flux also serves purpose of cleaning contamination left on brazing surface. Flux also helps in capillary action by pulling the molten alloy into the joint.
Characteristics of good flux
- It should protect brazing joint until the metal gets solidified
- It facilitates wetting
- It has low viscosity
- It has low melting temperature
Some common filler materials used in brazing are
- Silver
- Gold – Silver
- Nickel alloy
- Bronze
- Brass
- Copper – Silver
- Copper
- Aluminum – Silicon
Following are some common techniques used for brazing
- Torch brazing
- Furnace brazing
- Silver brazing
- Braze welding
- Cast iron ‘welding’
- Vacuum brazing
- Dip brazing
Heating methods used for brazing
- Braze welding
- Blanket brazing
- Electron beam and laser brazing
- Infrared brazing
- Dip brazing
- Resistance brazing
- Furnace brazing
- Induction brazing
- Torch brazing
Advantages of Brazing over welding
- It produces a clean joint which does not need further finishing
- It provides tighter control over tolerances
- It produces less thermal distortion
- It requires less temperature
- It can also join dis-similar metals
- It is relatively easy to automate
- It may be either permanent or temporary joint
- It has high speed hence adaptable to mass production
- It has less chance of damaging base material
- Parts of varying thickness can be joined
- Slow rate of heating and cooling
Disadvantages of Brazing over welding
- Joint strength is less
- It can be damaged at high service temperatures
- It requires high degree of cleanliness of base material
- Joint colour is generally different than base metal which gives aesthetic disadvantage
Applications of brazing
It is used in HVAC, aerospace, construction, electronics etc. Examples ranging from air conditioning systems to jet turbine blades to fine jewelry.
Difference between brazing and soldering
The only difference between soldering and brazing is the temperature at which each process takes place. Soldering is done below 450 degrees Celsius and brazing is done above 450 degrees Celsius.
Difference between brazing and welding
- Brazing does not melt base metal but welding does
- Brazing requires less temperature but welding requires higher temperature
- Brazing does not fuse base metal but welding does
- In brazing filler material has low melting point compared to joining metal but in welding filler metal has high melting point compared to joining metal
- Brazing uses capillary action while welding uses fusion
Image source: By Naval Surface Warriors – 190807-N-WI365-1104, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=81142812