Brazing is a well established joining process that uses a braze filler metal to join almost any metallic or ceramic material. The closely fitted components being joined, along with the filler metal, are heated to a temperature above which the filler metal is completely melted. The liquid filler metal is pulled, by capillary attraction, into the volume between the components and completely covers the mating surfaces. The filler metal "alloys" with the components being joined and, when cooled, forms a permanent metallurgical leak tight bond.


Brazing and soldering are similar processes, but the term "brazing" is used when the joining process is performed above 840°F, while "soldering" is used below that temperature. The higher temperatures of brazing, coupled with the braze filler metals, results in a strong metallurgical bond. The lower temperature of soldering results in only a mechanical joint being formed.

Brazing differs from welding in that during brazing only the filler metal is melted. In welding, both filler metals and base metals are melted during the process.

To achieve a good braze joint the parts must be properly cleaned and protected from oxidation during the process. Oxidation protection is accomplished by fluxing or use of a controlled atmosphere. In addition, the components must be designed so that when they are at braze temperature they are properly aligned and a capillary is formed in which the liquid filler metal can flow. With proper joint clearance the joint strength will approach that of the base material. Also, a heating process must be selected that will produce the proper brazing temperature and heat distribution. For detailed information you can buy the American Welding Society Brazing Handbook www.aws.org or contact the brazing experts at Thermal-Vac Technology.