Brazing is a process that joins two pieces of base metal when a melted metallic filler — the braze — flows across the joint and cools to form a solid bond. Similar to soldering, brazing creates an extremely strong joint, usually stronger than the base metal pieces themselves, without melting or deforming the components. Two different metals, or base metals such as silver and bronze, are perfect for brazing. This method can be used to make a bond that is invisible, is resilient in a wide range of temperatures and can withstand jolting and twisting motions.
The process of brazing is the same as soldering, although the metals and temperatures differ. Pipes, rods, flat metals or any other shape of metals can be brazed, as long as the pieces fit neatly against each other without large gaps. Brazing can handle more unusual configurations with linear joints, whereas most welding is done for spot welds on simpler shapes.
Preparing the Metals
Before brazing can begin, the entire area to be joined must be cleaned, or the melted braze mixture will clump instead of flow, making an inconsistent joint. The surface is then washed, and melted flux is applied. Flux removes oxides, prevents more oxidation during brazing and smooths the surface so that braze flows evenly across the joint.
The torch for this process uses fuels such as acetylene and hydrogen to create an extremely high temperature, often between 800° and 2,000° Fahrenheit (between 430° and 1,100° Celsius). The temperature must be low enough that the base metals don't melt but high enough to melt the braze. Torches have sensitively controls to reach the proper temperature, depending on the associated melting points.
Applying the Braze
To complete the joint, the braze is applied. Braze, like solder, comes in a stick, disc or wire, depending on the user's preference or the shape of the joint. After the base metals near the joint have been heated with the torch, the braze is applied to the hot pieces so that the braze melts and flows around the joint. This means that it penetrates the joint, working into every crevice. If the process was performed correctly, the bond is very strong after it cools and solidifies.
This process offers many advantages over spot welding or soldering. For instance, a brazed joint is smooth and complete, creating an airtight and watertight bond for piping that can be easily plated so the seam disappears. It also conducts electricity like the base alloys. Only brazing can join dissimilar metals that have different melting points, such as bronze, steel, aluminum, wrought iron and copper.