How to Braze Metal
Brazing metal, or braze welding, uses a relatively low heat to weld metal together. The bronze-based rod used in brazing allows the base metal to be heated to 900 degrees Celsius rather than a standard fusion welder's 1,500 degrees Celsius. The metal undergoes less stress, which is ideal for metals like cast iron that become brittle at high temperatures. Propane torches can be used to braze metal, but an oxyacetylene torch gives you more control of the flame and heat, and is easier to hold while working.
- Clean the base metal with sandpaper, fine-toothed file or a grinder. The metal's surface should be shiny and free of oil and dirt.
- Coat the joint with flux. If you are using a rod with flux in it already, be especially careful during the physical cleaning in step 1.
- Use magnetic clamps to hold the work in place, or any other clamping system you have available. Do not touch the surface of the metal with your bare hands because this will leave oils and residue that may impede the brazing process.
- Heat the torch you are using to complete the brazing. If you are using a propane torch, focus the flame on the end so that it is as blue and stable as possible.
- Begin heating the metal with a gentle painting motion. This will heat the work and also evaporate the water in the flux.
- Heat the metal until it becomes pink hot, consistently using a sweeping motion so you do not overheat the metal in one place.
- Introduce the brazing rod into the joint once the metal is heated sufficiently. The key here is to allow the heat of the metal itself to melt the rod, not the torch. If the joint is V-shape or especially deep, make a few passes with the brazing rod to fill the space in with the brazing metal.
- Allow the welded part to cool in sand or water.
- Clean and polish the work after it has cooled and inspect your work for gaps. Repeat brazing if needed.
Things You Will Need
- Metal to be welded
- Magnetic clamps
- Oxyacetylene torch or propane torch
- Borax flux
- Sandpaper, grinder, or fine-toothed file
- Brazing rod appropriate for the job
- Be aware of the differences in the brazing rods you choose. Some are more suited to specific tasks than others.
- Always wear face, body and hand protection when brazing.
- Weld metal cannot easily be matched in color with the base metal. Carefully select an appropriately colored brazing rod that matches your base metal.