Workshop Basics: Brazing
People seem to be afraid of brazing metal, and there really isn’t any need. Although a brazed joint isn’t as strong as a welded joint, it doesn’t mean that welding is superior. Brazing can even be preferable to welding in some situations, particularly where you are working with alloys or thin sheets of metal.
The non-permanent nature of a brazed joint can also be an advantage if you need some flexibility in a structure. It’s much easier to reheat and reposition a brazed joint than it is to break and re-tack a weld.
You can think of brazing as hot soldering. Unlike a welded joint (Where the two jointed surfaces become fused together), there is no blending of metals in a brazed joint. The two pieces of metal that you are joining together are held in place solely by the metal in the brazing rod.
The brazing rod is essentially a stick of low melting point metal, and there are several different types to choose from. Some rods are designed for specific types of metal (like aluminium, or copper), and other rods are meant for ferrous metals. Many brazing rods have a layer of flux around them, and this helps ensure that the metal in the rod will stick cleanly to the jointed surfaces.
Brazing is quite easy to do, provided that you have the right equipment:
- A propane torch is pretty much essential for brazing, and an extra butane torch can come in useful for providing a little extra directed heat to larger joints. Brazing is just like soldering: The aim of the process is to heat the joint sufficiently to melt the brazing rod, and not to head the rod directly.
- Flux is also essential in my opinion. Although most brazing rods have flux around them these days, there is never enough to ensure a good joint. Painting a little flux around the jointing surfaces makes for a much less painful process.
- A good selection of pliers, clamps, and other holding tools are extremely useful when brazing. Metal transfers heat well, so holding the work in your hand while brazing is a pathway to disaster. Gloves and goggles are necessary for obvious reasons. Hot metal can spit, crack, and even shatter unexpectedly, and if you value your sight you should wear goggles.
- Clean the pieces to be jointed with wire wool (or a grinding wheel, if you are that way inclined.
- Clamp the pieces in place with a vice or other holding device, and then add flux.
- Heat up the area of the joint with the propane torch, and bring the brazing rod into contact with the joint and the flame. The rod should melt easily, and the molten brazing rod should flow over the joint. Remember that certain metals need special brazing rods, check to make sure that you are using the correct rod for the job.
- Remove the heat, and allow the piece to cool before cleaning with wire wool or a brush.
It’s rather sad that this sort of thing isn’t being taught in many schools, for health and safety reasons. It’s a simple technique that can be very useful to anyone who has even the slightest technical or mechanical inclination.