Key Factors to Consider Before Beginning the Dip Brazing Process

Brazing

A popular metal forming process, brazing is one of the most versatile metalworking techniques available. During this process, melted filler metal is applied to the joint between individual components. The filler metal flows into space between the parts, under capillary action. The filler metal is then set to a temperature above its melting point, while any oxidation is removed with the use of a cleaning agent, such as a flux. (Typically, the filler metal has a lower melting point than that of the base metals of which the components being joined are made.) Once the filler metal flows over the base components and eventually cools, it connects the adjoining parts together to create a strong bond.  

The Process

Dip brazing, a specialized brazing process that primarily uses aluminum as the filler material, can be utilized for many different applications.

The filler used in aluminum dip brazing is generally comprised of almost 90% aluminum and a little more than 10% silicon. During the aluminum dip brazing process, metal components are assembled together, with the filler placed as close as possible to the joint while remaining outside of it. Heat is then applied to the entire metal assembly in an air furnace. The process gets its name from the next step, in which the complete assembly is dipped into a bath of molten salt. This dip serves as a medium for transferring heat, as well as a flux for the joint. In this high-temperature bath, the molten flux interacts with the surface of the assembly and joint, and the filler material then enters the joint and eventually solidifies. With the use of the flux, the filler material can adhere to the cleanest surface possible, allowing for an extremely tight seal between the parts.

The Design

Before initiating this process, however, some key factors should be considered to ensure a high-quality end product. The design of the assembly is significant, and working with the right metal alloy is critical, as it must be capable of withstanding the extremely high temperatures applied during the brazing process. It’s generally recommended that users avoid adding fixtures to the assembly, as these can impair the efficacy of the dip brazing process. Also, the joint itself should accommodate the positioning of the filler material and get as close as possible to the joint before brazing occurs. Even the type and length of the joint used can make a difference; typically, lap joints produce the best results. Keep in mind that lap joints should have enough clearance to account for the brazing’s capillary action.

Temperature and Material Considerations

The type of filler material used and the temperature selected can also have a significant impact on how well the brazing process works for a given assembly. Temperature has a direct effect on the outcome, as the filler’s alloying and wetting action increases as the brazing alloy’s temperature rises. While the brazing temperature should be higher than the filler’s melting point, it must not be too high either, as extreme heat can adversely affect the metal assembly. For example, if the temperature is too high, it may alter the filler’s ability to adhere to the base metal. Too-high temperatures can also cause heat-induced damage and even harm added fixtures on the assembly. Material choice, too, can influence the efficacy of the brazing process. The ideal material will depend on the specific application at hand. Making use of the proper brazing sheets helps ensure a uniform temperature throughout the material during the brazing process while imbuing the final product with additional strength. Aluminum is particularly well-suited to brazing processes, allowing for optimal performance and reliability.

Selecting the Right Brazing Technique

To ensure high product quality, it’s critical to carefully consider all of the above-mentioned factors before beginning a dip brazing project. Be sure your brazing service provider can assist you throughout the material selection process and work with you to determine the ideal method for your unique application.  

 

Resources

  1. http://lynchmetals.com/flux-brazing-alloys
  2. https://app.aws.org/wj/supplement/WJ_1974_10_s440.pdf
  3. http://www.machinedesign.com/basics-design/brazing-processes
  4. https://www3.epa.gov/region9/water/pretreatment/files/aluminum_dip_brazing_2007-3-11_inspection.pdf

 

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