Tricks of the Trade | What Is Brazing?
Brazing joins two pieces of base metal when a melted metallic filler 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. Use this method to make a bond that is invisible, resilient in a wide range of temperatures, and can withstand jolting and twisting motion.
The process of brazing is the same as soldering, although metals and temperatures differ. You can braze pipes, rods, flat metals, or any other shape as long as the pieces fit neatly against each other without large gaps. Brazing handles more unusual configurations with linear joints, whereas most welding makes spot welds on simpler shapes.
First, you must clean the entire area to be joined or else the melted braze mixture will clump instead of flow, making an inconsistent joint. Wash the surface and then apply melted flux. Flux removes oxides, prevents more oxidation during brazing, and smoothes the surface so that braze “flows” evenly across the joint.
Next, you gather your torch and braze alloy. The torch uses fuels like acetylene and hydrogen to create an extremely high temperature, often between 800° F and 2000° F (430 – 1100° C). The temperature must be low enough that the base metals don’t melt, yet high enough to melt the braze. Torches have sensitively controls to reach the proper temperature depending on the associated melting points.
Finally, you complete the joint by applying the braze. Braze, like solder, comes in a stick, disc, or wire, depending on your preference or the shape of the joint. After the base metals near the joint have been heated with the torch, bring the wire to the hot pieces so the braze melts, flowing around the joint. By “flow,” brazers mean it penetrates the joint, working into every cavern. If the brazing was performed correctly, when the bond cools and solidifies, it is nearly unbreakable.
Brazing 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, such as bronze, steel, aluminum, wrought iron, and copper, with different melting points.