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At Engweld we stock a wide range of equipment to supply the welding, fabrication and engineering industries. Our equipment includes a broad range of brazing equipment, including brazing rods, brazing consumables and other brazing supplies.
During the brazing process, two metals are permanently joined together using just a torch, and a fille metal, otherwise known as a brazing rod. Once completed, a brazed joint possesses immense strength, especially when compared to soldered joints.
Take a look at one of our most popular brazing kits here: Mapp Pro+ Brazing Kit - Engweld
What is brazing used for?
The brazing process is used to join two pieces of metal together, in a similar way to soldering and welding, but we’ll get into the differences between these three methods in the section below.
It involves the application of heat to the assembly or the joint, followed by the addition of filler metal, otherwise known as a brazing rod or brazing consumable. The filler metal must have a lower melting point than the assembly, or the metals which require joining, to ensure that the base metals do not melt. Once heated, the brazing rod is placed into the heated joint, where it melts, filling the joint, and once cooled, the joint has a strong and solid bond.
Brazing, soldering and welding all involve joining two or more pieces of metal together, with the key difference being the temperature that is used to do so. Although brazing and soldering both require a filler metal to be used, whereas not all welding methods require a filler metal.
Brazing and soldering are essentially the same processes, apart from the temperatures used to solder being much lower than those used in brazing. During soldering, the filler metal is melted at temperatures below 450°C, while during brazing the filler metal is melted at temperatures above 450°C.
Six steps to successful brazing
While brazing itself is a fairly simple process, the real skill required comes in the form of the overall design and engineering of the joint. However, even the best-designed brazing joint can have faults if the six basic steps of preparing the joint. These procedures are as follows:
Ensure a good fit
In order to distribute the molten filler metal around the base metals, brazing uses capillary action. This means that in order to ensure a sufficiently strong joint, the filler metal must be carefully placed to allow the capillary action to take place, and to work effectively. In most cases, this will typically mean that a close clearance is needed, ranging from 0.001 inches to 0.005 inches, although the optimal joint gap, or clearance, for most filler metals is around 0.0015 inches.
Properly clean the metals
Again, in order for the capillary action to take place effectively, all the metal surfaces must be properly cleaned. This is because oil, dust, grease, dirt, rust and scale can all hinder the capillary action, and they will actually form a barrier between the brazing materials and the base metals.
Flux all parts
What is flux? Flux is a critical chemical compound used in the atmospheric brazing process, which shields the joint area from the air, which in turn prevents oxide contamination, which, if allowed to form, will inhibit the filler metal from bonding to the base metal surfaces.
Flux can be applied in virtually any manner, so long as it completely coats the joint surfaces. Typically coming in a paste format, the most convenient method is often to brush it on, although it can also be applied via an applicator gun when high volume is needed. Flux should be applied just before brazing, as this prevents it from drying out and flaking off before brazing begins.
Although you should bear in mind that different fluxes are formulated for different metals, conditions and temperatures. So choose a flux that is formulated for your brazing application.
Once you have cleaned and fluxed all your components, then you are ready to put the assembly together. It is critical that all components are held in place for the brazing process, and that they remain in the correct alignment during both heating and cooling cycles.
Often the best methods are the most simple, so, if the weight and the shape of the components permit, simply hold them together with gravity!
The key thing to remember during the actual brazing process is to not heat the base metal past its melting point, for obvious reasons! Instead, the brazing rods must be heated to the point of melting, allowing capillary action to spread the molten filler metal around the joint. Once the assembly has been heated to brazing temperature, then it is time to deposit the filler metal.
You just apply heat evenly and broadly across the base metals, but be sure to prevent uneven heating, which you can check by monitoring the flux. If the flux changes colour uniformly, then you are evenly heating the base metals, if it changes colour nonuniformly, then the heat is not being distributed evenly.
Once you have successfully heated the assembly evenly, it is time to add the filler metal. Simply hold the brazing rod or wire, otherwise known as the brazing consumables, against the heated joint area; a portion of the brazing rod will then melt off before capillary action draws the molten metal around the whole joint area.
Finally, once the assembly has been brazed, the last step is to clean it. This is an essential step, as virtually all fluxes used for brazing are corrosive, and cleaning is typically a two-step process.
Removing the flux is generally a fairly simple process and most fluxes are water-soluble, this means that once the filler metal has completely solidified, immersing the entire assembly in hot water will result in the residual flux cracking and flaking off. In some instances, stubborn flux can be helped off with a light brushing from a wire brush.
Once the flux has been removed, use a light pickling solution to ensure that any areas which were not protected by the flux during brazing do not have any oxides left on the surface.
If you would like any further information on our brazing rods, brazing consumables, or brazing in general, please do not hesitate to contact us.
See also blow torches for related products in this category