Brazing is a very important metal-joining technique that continues to grow in usage each year in many industries around the world. Most people are familiar with welding and soldering, but many are not familiar with where brazing might fit into the overall metals-joining landscape.
Shown here are some images of common items we use around our home or shop that were created by joining pieces together using a brazing process. Figure 1 shows common vice-grip pliers, the gripping surfaces of which are specially hardened steel inserts that are brazed onto standard forged-steel tooling.
Figure 2 shows a sterling-silver knife in which the sterling-silver handle is brazed to a stainless steel blade. Figure 3 shows a bicycle frame in which the tubular structure of the frame is brazed together. Figure 4 shows a pair of aviator sunglasses in which all the tiny wire connectors are brazed together. Figure 5 shows a diamond-grit cutting blade in which all the diamond bits are brazed securely to the round blade around its periphery. Figure 6 shows one of our U.S. astronauts floating in space. His backpack life-support system contains a brazed heat exchanger to handle the liquids and air supply necessary for his survival in outer space.
As you can see, brazing is a widely used and vital joining process in our daily life. We will explore some of these applications in more detail in future columns, and we will also look more in-depth at some of the many brazing principles that enable such processes to be performed.
Let’s start by taking a closer look at how brazing, as a joining process, differs from soldering and welding. Take a look at the “thermometer” shown in figure 7. There is a line across the lower portion of that image separating brazing (above the line) from soldering (below the line). That’s right – temperature is pretty much the primary thing that differentiates soldering from brazing. That line across the image shown at 450°C (840°F) is merely an artificial line “pulled out of the air,” so to speak, to help separate the two methods of metals joining.
You will notice that there is a significant space between the melting temperature of zinc (787°F/420°C) and aluminum (1220°F/660°C). So, many years ago, professional engineering organizations agreed to use 800°F as a temperature that would separate brazing (above 800°F) from soldering (below 800°F). Note that only Fahrenheit is being talked about here, since most engineering at that time was focused in the U.S. and many countries of the expansive British realm around the world.