Design

A good design is the beginning of a strong joint. To ensure the joint has the highest strength, a lap length that is four times the thickness of the thinnest base material is often chosen. For lap joints, this is the easiest to achieve; however, when this option is not suitable, a plug joint will be a good alternative. The second major consideration in joint design is the gap of the joint, such as the distance between the mating surfaces. Because capillary action occurs in brazed workpieces, the joint gap determines the effectiveness of capillary action. For most brazing alloys in the copper-phosphorus and silver-based alloy families, a joint gap of 0.001-0.005 inches is ideal. When brazing different types of metals, it is essential to consider the thermal expansion rates of each metal at brazing temperatures when determining the joint gap.

Pre-weld Cleaning

The best capillary action occurs on clean brazed workpieces. For workpieces with oil stains on the surface, they should be cleaned with organic solvents or organic solvent vapors; any oxidized surfaces need to be sandblasted.

Flux

Once the workpiece is cleaned, it is necessary to prevent its surface from oxidizing during the heating cycle. Unprotected workpiece surfaces will quickly oxidize due to gas flames, hindering effective capillary action. The correct flux (or protective atmosphere) can prevent oxidation of both the workpiece and filler metal during heating. The Wolverine flux product series, including ULTRA flux and black flux, provides ideal and effective protection. When using SILVALOY copper-phosphorus filler metal products for welding copper to copper, additional flux is usually not required because phosphorus in the alloy can act as a deoxidizer.

Assembly and Clamping

Maintaining consistent alignment of workpieces (in proper position) during brazing is crucial for ensuring effective capillary action. This can usually be achieved by relying on the weight of the workpieces themselves or with some additional weights. When clamping is necessary, fixtures should be designed to be as small as possible and made from materials with low thermal conductivity to reduce heat loss at the brazed joint during heating.

Choosing Filler Alloy

When selecting a brazing alloy, several factors need to be considered. First is the compatibility of the metals being joined, followed by joint gap, brazing temperature, heating method, working temperature, and environmental factors also require attention. If you need specific technical specifications for our alloys, please refer to the technical documentation section on our website or call 1.800.225.2130 to contact our sales service representatives; we will assist you in finding the most suitable filler alloy for your needs.

Heating

There are now many methods for brazing heating; however, the most common is furnace torch heating. The entire assembly should be evenly heated to brazing temperature. Once the workpiece reaches brazing temperature (the surface typically appears dark red), filler alloy should be applied for brazing. Capillary action will guide the filler alloy into the workpiece to complete the joint connection.

Post-weld Cleaning

Allow metals to cool naturally after welding. Because fluxes are corrosive, any residues may ultimately affect and weaken joint integrity. Hot water can be used to soak and wash away flux residues. When flux has begun to corrode and may leave harmful residues, acid cleaning must be performed to remove debris.