In this article, we’ll discuss the different types of brazing, their applications, advantages, and disadvantages.
What is Brazing?
Brazing is the process of joining two metals together using a molten filler metal. The filler metal will melt at a lower temperature than the two metals being joined.
Brazing Process
Cleaning the base metal surfaces is one of the most important steps in the metal joining process. Emery cloth and wire brushes are both the best tools for removing contaminants.
There are many different methods for brazing. There are two main types of heating: localized heating, which heats only the joint area, and diffuse heating, which heats the entire object.
During the brazing process, the joining metal is melted and filled into the joint between the two parent metals by capillary action—the ability of liquids to flow in narrow spaces without the assistance of gravity. A flux shields the liquid metal from oxidation while it is still in the liquid state. The pieces are then joined together by cooling the liquid metal.
What is a flux?
The braze alloy must be protected by a flux unless the brazing procedure is carried out in a contained space, such as a furnace. A flux is a substance that prevents the metal from oxidizing while it is still in the liquid state. During the joining process, flux flows into the joint and is typically made of a substance like borax that hinders the formation of oxides.
Filler Materials in Brazing
In brazing, filler metal refers to the alloy (or element metal) that forms the joint.
- It is placed between two (or more) components (the parent materials) and is melted and allowed to solidify, forming a joint within a brazing assembly.
- The various types of alloys are used as brazing filler materials.
- The selection is based on the material’s capacity to melt at a lower temperature than the base metal, to withstand service conditions, and to wet base metals.
Depending on the application, the filler is either placed at the desired locations or applied during the cycle.
The following are some examples of filler materials:
- Aluminium
- Cast iron
- Magnesium
- Copper and copper alloys
- Silver
Filler metal requirements
- Once the molten flux and filler metal have solidified, the brazed joint should have the expected mechanical properties.
- Brazing temperatures must be sufficient to ensure proper liquid flow from the molten brazing alloy into the joints.
- In order to form strong bonds, filler metals must be wetted properly.
Types of Brazing Method
Brazing employs a variety of heating methods to suit a wide range of purposes and applications. Heat can be applied directly to a joint (localized heating) or to the entire workpiece (diffuse heating).
Localised Heating Techniques
Torch brazing – Burning acetylene, propane, or hydrogen with oxygen to heat and melt the filler metal produces combusted fuel gas. This method calls for flux in order to protect the joint, which necessitates post-cleanup. Torch brazing is most commonly used for small production assemblies with unequal metal weights. The procedure is frequently carried out using gas welding equipment.
Induction brazing – In this types of brazing method, to achieve brazing temperature, a high-frequency alternating current is supplied into a coil, which heats the workpiece and melts the filler material.
Resistance brazing – The electrical resistance of the brazing alloy, which is ideal for highly conductive metals, produces heat. This heating method is best suited for making simple metal joints.
Diffuse Heating Techniques
Furnace brazing – In this types of brazing method, the furnace is heated to the desired temperature using gas firing or heating elements. The brazing filler metal is applied to the surfaces to be joined before the entire assembly is placed in the furnace and brought to brazing temperature. Furnace brazing allows for precise control of metal heating and cooling cycles. To protect the braze alloy from environmental factors, the procedure is frequently carried out in a vacuum. Additionally, this eliminates the requirement for flux protection.
Dip brazing – When brazing with molten filler metal or molten salt, the workpiece or assembly is submerged in a bath of molten metal (chemical bath dip brazing). The parts are covered in brazing flux to stop oxidation. Once the molten brazing filler metal has cooled and hardened, the assembly can be removed.
Difference Between Welding ,Soldering and Brazing
| WELDING | SOLDERING | BRAZING |
|---|---|---|
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Welding joints are the strongest joints used to support the load. Usually, the welded portion of the joint has strength greater than the base metal. |
Soldering joints are the weakest of the three types of joints. Not intended to support the weight. Generally used to create electrical contacts. |
Brazing joints are less strong than welding joints but more strong than soldering joints. This can be used to support the load to some extent. |
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For welding joints, a temperature of 3800 degrees Celsius is required. |
In soldering joints, a temperature requirement of up to 450 degrees Celsius is required. |
In brazing joints, temperatures can reach 600 degrees Celsius. |
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Work pieces that are to be joined must be heated until they reach their melting point. |
It is not necessary to heat the work pieces. |
The work pieces are heated, but not to the point of melting. |
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The mechanical properties of the base metal may change at the joint due to heating and cooling. |
There is no change in mechanical properties after joining. |
There may be a change in the mechanical properties of the joint, but it is almost negligible. |
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Heat costs are involved, and a high level of skill is required. |
Low cost and skill requirements are involved. |
The cost involved and the skill required are in between the other two. |
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Heat treatment is usually required to remove the undesirable effects of welding. |
Heat treatment is not necessary. |
There is no need for heat treatment after brazing. |
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The workpiece does not need to be preheated before welding, as it is carried at a high temperature. |
Preheating workpieces before soldering improves the quality of the joint. |
Since brazing is carried at a relatively low temperature, preheating is preferred to create a strong joint. |
Advantages
- Can combine different metals, unlike most welding techniques.
- High production rates.
- Uses less energy than welding.
- Produces cleaner joints than most other welding processes.
- Base metals maintain their mechanical characteristics and shape by not melting.
Disadvantages
- Poorer results when compared to welded joints.
- It is impossible to join components that operate at high temperatures.
- In order to achieve capillary action, joint gaps must be uniformly tight.
- Leaky joints may be brought on by unclean or contaminated metals.
Applications of Brazing
Brazing has the following applications:
- It is used in construction.
- It’s utilized in vacuum interrupters.
- It is utilized in transportation applications.
- It is used in art and jewelry.
- It is useful in medical equipment.