Basic Brazing Procedures

In the formation of a good brazed joints, capillary action plays a vital role than the operator skills. The engineering design of the joint assures the efficiency and long-lasting of joints. There is a number of procedures to follow which we have collected to just five basic steps. All these steps are simple and each of them is equally important for brazing operation. The first step includes cleaning of the metal surface and prepare it for brazing. After that fluxing of the joining parts is done. Then the metals are assembled, then the area to be joined is heated uniformly and filler is applied. Finally the brazed joints are cleaned to provide a better appearance.

Step By Step Procedures

Step 1: Surface Cleaning for Brazing

• Brazing process uses the principle of capillary action to spread the molten filler metal between the surface of base metals. For the efficient working of brazing process, the capillary action should work properly and that requires clearance between the base metals.
  
  
• Base metals surface should be uncontaminated and oxide free to ensure sound brazed joints of uniform tensile strength. Some common contaminants found at the metal surfaces are grease, dirt, oil, oxides, etc.
  
  
• Cleaning should be done chemically or mechanically. They may be wire brushed, abraded or filed to remove oxide or scale and to expose clean metal.
  
  

Step 2: Fluxing the parts
Flux is a chemical compound applied to the joint surfaces. The use of flux is significant for brazing. This is because when the metals are heated, oxide formation get faster. The oxides are formed due to chemical reaction between the metals and the atmospheric oxygen. The oxides form a thin layer on the surface of metals and inhibit the brazing filler metal from wetting and bonding to the surfaces.

How Does Fluxing Helps?
The coating of flux on the joint area of metal surfaces shields the surfaces from the air, thus checking oxide formation. Flux is also capable of dissolving and absorbing any oxides that are formed during heating or that were not entirely removed in the cleaning process.
Types of Flux
The selection of flux should be based on specific metals, temperatures and conditions of your brazing application. A number of fluxes meeting practically every need are available:

• Fluxes for brazing at very high temperatures (2000°F/1093°C)
• Fluxes for metals with refractory oxides
• Fluxes for long heating cycles
• Fluxes for dispensing by automated machines

Step 3: Assembly For Brazing
Just after the proper cleaning of metal surfaces and fluxing, it is important to assemble them properly. They should be kept in correct alignment during the heating and cooling, so that the capillary action should perform their function efficiently. Gravitational power enables them to hold together properly, if their weight, shape and design allows.


Step 4: Heating of Metals & Application of Filler
This step involves heating the assembly and flowing the filler through the joints. In case of a small assembly, entire assembly can be heated to the flow point of the brazing filler metal. If the assembly is large and complicated, a broad area around the joint area is to be heated. Torch is the simplest method of heating used in brazing process.

Step 5: Cleaning the brazed joint
The last step, after brazing the joints properly, is cleaning. It is a two step process:

• Removal of the flux residues is a simple but an essential process. Flux residues are chemically corrosive and results in weakening of the joints if not removed properly.Removal of the flux residues is a simple but an essential process. Flux residues are chemically corrosive and results in weakening of the joints if not removed properly.
• Pickling is used to remove any oxide layer formed during the brazing process.

Generally, brazing fluxes are water soluble and hence can be easily washed out with hot water. The flux usually crack and flake off, but if they are a bit obstinate, they can be brushed gently while it is in hot water. Other complicated methods can also be used like an ultra-sonic cleaning tank to speed up the action of hot water or live steam.