Good design is the beginning of a strong bond. In order to ensure the highest strength of the joint, the overlap length is usually 4 times the thickness of the thinnest substrate. For the knee joint, this is the easiest to do. But if this option is not appropriate, a flat-tipped joint will be the next good choice. The second major consideration in joint design is joint clearance, such as the distance between joint surfaces. Since the brazed workpiece works by capillary action, the joint gap determines the effect of capillary action. For most solders in the copper-phosphorus and silver-based alloy series, the ideal weld gap is 0.001-0.005 inches. When brazing metals of different materials, the thermal expansion rate of each metal at the brazing temperature must be considered when determining the joint gap.

 

Cleaning before welding

 

Optimal capillary action occurs on clean brazed workpieces. For oily surfaces, organic solvents or organic solvent vapors should be used for cleaning; any oxidized surfaces need to be sandblasted.

 

Flux

 

Once the workpiece has been cleaned, its surface must be protected from oxidation during the heating cycle. The unprotected workpiece surface is quickly oxidized by the gas flame, preventing effective capillary action. Proper flux (or protective atmosphere) prevents the workpiece and filler metal from being oxidized during heating. When copper is soldered to copper using copper-copper solder products, no additional flux is usually required because phosphorus can act as a deoxidizer in the alloy.

 

Assembly and clamping

 

Maintaining a consistent alignment (in the correct position) of the workpiece during the brazing process is extremely important to ensure effective capillary action. Usually can be achieved by the gravity of the workpiece itself, but also by some other auxiliary weights. When clamping the workpiece, the fixture should be designed as small as possible and the material's thermal conductivity is weak to reduce the heat loss of the brazed joint during heating.

 

Select filler alloy

 

There are several factors to consider when choosing a solder alloy. The first is the compatibility of the connected metals, joint gaps, welding temperature, heating method, operating temperature and environmental factors.

 

heating

 

There are many methods of brazing heating, but the most common is torch heating. The entire device is heated uniformly to the brazing temperature. Once the workpiece reaches brazing temperature (the surface usually shows a dark red glow), the brazing alloy begins to be brazed. Capillary action will cause the solder alloy to fill the workpiece and complete the joint connection.

 

Cleaning after welding

 

After welding, the metal is allowed to cool and solidify naturally. Because the flux is corrosive, any residue may eventually affect it and weaken the joints. You can use hot water to soak and scrub the flux residue. When the flux begins to corrode and may leave harmful residues, pickling must be performed in this case to remove the residues.

Brass Brazing Alloy