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 What's the difference between brazing, soldering and welding

Brazing has been defined as a group of joining processes specially arranged in a manner to produce coalescence of materials. The process involves heating of these materials at a brazing temperature by using a filler metal which has a liquidus above 840°F (450°C), and below the solidus of the base metals. Also, the filler metal is distributed in the joint by capillary action. 

  • The brazing process consists of the broad heating of the base metals to the point where the filler metal, applied to the joint area, will be melted and drawn by capillary action through the entire joint. After cooling, the brazed joint constitutes a strong metallurgical bond between the filler metal and the two base metals.
  • Two outstanding characteristics of a brazed joint are its high strength, and the low heat at which it is made. A properly made brazed joint will generally be stronger than the metals being joined. And the temperature at which the joint is made is much lower than the melting temperature of the metals being joined. 
  • A brazed joint "makes itself," in the sense that capillary action, rather than operator manipulation, is responsible for flowing the filler metal completely through the joint. But even a properly designed joint can turn out imperfectly unless you follow correct brazing procedures.

In the case of soldering, the only fact which distinguishes it from brazing is the filler metal used, since, here the liquidus is below 840°F (450°C).

Welding involves the process of fusion which takes place along with the melting of base metal and a filler metal.


Why should I braze? 

  • Sturdy joints
  • Cheap temp/lower cost
  • Base metals integrity is maintained
  • Dissimilar joints are efficiently joined
  • Well defined joint appearance
  • Easy acquirement of skills
  • Components can be batch processed
  • Process thermal cycles are predictable
  • Component distortion is minimized or eliminated
  • Thin-to-thin or thin-to-thick members can be joined
  • Small and wide gap sizes can be filled
  • Specialized labor is not required


What is capillary action?

 The American Welding Society states that capillary action is the force by which liquid in contact with a solid is distributed between closely fitted faying surfaces of the joint to be brazed or soldered.

Many factors affect capillary action. The major influences are those that affect the capillary spacing or gap and those that affect the surface energy of both the liquid alloy and the surface to which the braze alloy is to be in contact.

The key to successfully achieving a good brazed connection is surface preparation.  The presence of contaminants or oxides prevents the filler metal from coming into contact with one of the surfaces to be brazed.  In the case of minor oxidation, the pours of the surfaces to be brazed will be sealed by the oxide.  This prevents the capillary action and, ultimately, the brazing from occurring.  Hence, the initial cleanliness of the surfaces to be brazed is extremely important, but it is equally important that the cleanliness of these surfaces be maintained during the brazing process.


 Is P&I ISO 9001 & AS9100 certified?

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