Brazing joins two pieces of base metal as a molten metal filler flows through the joint and cools to form a strong bond. Similar to welding, brazing creates an extremely strong joint, often stronger than the base metal piece itself, without melting or deforming the component. Two dissimilar metals or base metals such as silver and bronze are well suited for brazing. Using this method creates an invisible bond, is resilient over a wide temperature range, and can withstand shock and twisting movements.
Although the metals and temperatures are different, the brazing process is the same as soldering. You can braze pipe, rod, flat metal, or any other shape as long as the parts fit neatly into each other without large gaps. Brazing handles more unusual configurations with linear joints, while most welding is spot welded on simpler shapes.
First, the entire area to be joined must be cleaned, otherwise, the molten brazing mixture will clump instead of flow, creating an inconsistent joint. Clean the surface, then apply molten flux. Flux removes oxides, prevents more oxidation during brazing, and smoothes the surface so that the brazing material "flows" evenly through the joint.
Next, collect the torch and braze the alloy. Torches use fuels such as acetylene and hydrogen to generate extremely high temperatures, typically between 800° F and 2000° F (430 – 1100° C). The temperature must be low enough to ensure that the base metal does not melt, but high enough to melt the solder. The torch has sensitive controls to achieve the proper temperature based on the relevant melting point.
Finally, the joint is completed by brazing. Brazing, like solder, comes in rods, disks, or wires, depending on your preference or the shape of the joint. After heating the base metal near the joint with the torch, bring the wire over the hot piece, causing the solder to melt and flow around the joint. What brazers mean by "flow" is that it penetrates the seam, into every cavity. If the brazing is done correctly, when the bond cools and sets it is virtually unbreakable.
Brazing has many advantages over spot welding or soldering. For example, brazed joints are smooth and complete, creating an air- and water-tight bond for the pipe, and can be easily plated so that the seam disappears. It also conducts electricity like the base alloy. Only brazing can join dissimilar metals with different melting points, such as bronze, steel, aluminum, wrought iron and copper.
