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What is Brazing?
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.
Advantages of Brazing
- Strong: A properly designed, prepared and brazed joint will approach the strength of the materials being joined.
- Leak Tight: The brazing process fills the joint with metal via capillary attraction, resulting in hermetic leak-tight joints.
- Permanent: Two or more components brazed together become a single, structurally sound part.
- Cross-Section Independent: Brazing allows the joining of thin sheet metal components or parts together with greatly different thicknesses or thermal masses.
- Dissimilar Materials: Braze filler metals are available to achieve the joining of dissimilar materials, including different metals or even ceramics to metals.
- High Temperature: High temperature filler metals are well suited for high service temperature applications.
- Economical: Complex assemblies with numerous joints can be brazed together in one simple operation, eliminating the need for intricate, expensive machining and/or casting. Additionally, numerous parts can be batch processed resulting in significant savings over one-at-a-time welding of each joint on each part.
- Clean: The assemblies emerge from vacuum or hydrogen furnaces clean and oxide free, thereby eliminating expensive clean up.
- Dimensional Control: Brazing is done at much lower temperatures than welding and the heat is distributed much more uniformly, thereby greatly reducing or eliminating thermal stresses. Distortion and shrinkage can be controlled or eliminated during brazing to minimize or eliminate the need for post-braze machining.
- Quality: Quality braze joints are assured by using proven, automated furnace braze cycles.
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