Brazing Tips - silvaloy.com

Seven Steps to Successful Brazing

1) Design and Fit Up
A strong brazed joint begins with its design. To assure maximum strength, the joint should be designed with an overlap of three to four times the thickness of the thinner member. This is the most readily accomplished by a lap joint, but where that is impractical, a scarf joint is the next best choice. The second major consideration in joint design is joint clearance, i.e., the distance between the faying surfaces. Because brazing works through capillary action and joint clearance defines the capillary, this is a critical consideration. For most brazing alloys in the B-CuP and B-Ag families, a joint clearance of between .001" and .005" is optimal. When joining dissimilar metals, always consider their differential rates of thermal expansion when determining joint clearance at brazing temperatures.

2) Pre-Braze Cleaning
Optimal capillary action will occur only when the metals being joined are clean. Oil and grease should be removed with a chemical solvent or by vapor degreasing. Any surface oxides should be removed by abrasive cleaning.

3) Fluxing
Once the metals to be joined are cleaned, it is essential to protect them from oxidation during the heating cycle. Oxygen from the gas flame will quickly result in oxide formation on the surface of unprotected metals and prevent effective capillary action. Proper fluxing (or a protective atmosphere) protects both the base and filler metals from oxide formation during heating. Wolverine's line of brazing fluxes, including Ultra Flux and Black Flux, are engineered to provide optimal protection. When joining copper to copper using one of the Silvaloy B-CuP alloys, an external flux is usually not necessary as the phosphorous in the alloy acts as a deoxidizing agent.

4) Assembly and Fixturing
Maintaining alignment of the base metals throughout the brazing process is important to assure effective capillary action. This can often be accomplished by gravity alone, or gravity with some additional weight. When parts require fixturing, fixtures should be designed with the smallest possible mass and of materials with poor heat conducting properties to minimize heat loss away from the braze joint during heating.

5) Filler Metal Selection
A number of factors should be taken into consideration when selecting a brazing alloy for a particular application. Chief among them are compatibility with the metals being joined, joint clearance, brazing temperature and heating method, service temperature and environment and appearance. Please refer to our Technical Documents section of our website for technical details on our most popular alloys or Call 1.800.225.2130 to contact a Wolverine Sales Representative to assist you in selecting the best Silvaloy brazing alloy for your application.

6) Heating
There are a number of heating methods available for brazing, the most common of which is torch brazing. Bring the entire assembly up to brazing temperature evenly. Once the parts are at brazing temperature (usually indicated by a dull red glow), apply the brazing alloy to the joint. Capillary action will draw the brazing alloy into the joint.

7) Post-Braze Cleaning
After brazing, allow the metal to solidify by air-cooling. Because flux is corrosive, any residue left on the assembly may eventually attack and weaken the joint. Remove any flux residue by immersing in hot water and brushing off. When the flux has been saturated a more pernicious residue may result; in this case an acid bath may be necessary to remove the residue.