In this post, you will learn what brazing is and how it is done. It’s working principle, Applications, Advantages, types of brazing, and more.
What is a Brazing?
Brazing is a process of joining two pieces of metal in which a non-ferrous alloy is introduced in a liquid state between the pieces of metal to allow the joining to solidify.
The melting temperature of the filler material is about 600°c but lower than the melting temperature of the parent metal. The filler metal is distributed between the surface by capillary action.
Brazing is the same as soldering but gives a much stronger joint than soldering. The principal difference is the use of harder filler material, commercially known as a speller, which fuses at some temperature above red heat, but below the melting temperature of the parts to be joined.
What is a Brazing Process?
One of the most important processes in the metal joining process is cleaning the base metal surfaces. Both wire brushes and emery cloth work well for removing impurities.
The brazing process starts with arranging the assembly correctly after calculating joint gaps for the liquid filler metal to achieve surface tension with the workpiece.
Typically, a torch is used to gradually raise the filler metal’s temperature and the metal surface of the workpiece to the brazing temperature.
As the filler metal evaporates, capillary action allows it to travel through the tight crevices, forming a strong connection with the base metals’ surfaces. When the assembly cools down, the brazed joints form.
Types of Filler Metal Used in Brazing
Filler metals used in this process may be divided into two classes:
- Copper-base alloys.
- Silver-based alloys.
There are many different alloys in each class, but brasses (copper and zinc), sometimes with up to 20% tin are mostly used.
They have a melting range from 850 to 250°C and are used mainly for brazing ferrous metals.
Silver alloys (silver and copper or silver, copper, and zinc) having a melting range of 600 to 850°C are suitable for brazing any metals capable of being brazed. They give a clean finish and a strong ductile joint.
Like welding and soldering, The parts joined by brazing are cleaned of oil, dirt, or oxides, and clearances between mating surfaces are very small. The flux is applied and the pieces are applied together with proper clearances for filling the filler metal.
They are then heated at about 600°c. The molten is allowed to flow by capillary action into the space between the parts and then cooled slowly. Borax, either alone or in combination with other salts is commonly used in a flux.
The advantages of joining metals by brazing are that dissimilar metals and parts having a thin section can be joined easily. Brazing is used for the fastening of pipe fittings, and tanks, credible tips on tools, radiators, heat exchangers, and the repair of castings.
Types of Brazing Process
The following are the common types of brazing process:
- Torch brazing
- Induction brazing
- Resistance brazing
- Furnace brazing
- Silver brazing
- Braze welding
- Cast iron welding
- Vacuum brazing
- Dip brazing
#1. Torch Brazing.
Torch brazing is the most common method used in mechanized brazing. It is used in small production versions or special operations and some countries. There are three main classifications of torch brazing in use:
- Manual torch brazing
- Machine torch brazing
- Automatic torch brazing
#2. Induction Brazing.
In these types of brazing, high-frequency alternating current is fed into a coil to heat the workpiece and melt the filler material.
#3. Resistance Brazing.
This type of brazing generates heat due to the electrical resistance of the brazing alloy, making it ideal for highly conductive metals. This heating process works best for making simple metal joins.
#4. Furnace Brazing.
Furnace brazing is a semi-automatic process that is widely used in industrial brazing operations due to its flexibility for mass production and the use of unskilled labor.
One of the main advantages of furnace brazing is the ease with which it can produce a large number of small parts that are easily toothed or self-detecting.
This process has a controlled heat cycle (permitting the use of parts that may be deformed under localization heating).
#5. Silver Brazing.
Silver brazing also known as hard soldering, is brazed utilizing a silver alloy-based filler. These silver alloys contain many different percentages of silver and other metals, such as copper, zinc, and cadmium.
#6. Braze Welding.
Brake welding is the use of a bronze or brass filler rod coated with flux to attach the steel workpiece. The equipment required for braze welding is the same as the equipment used in brazing.
Since brake welding usually requires more heat than brazing, acetylene or methylacetylene-propylene (MAP) gas fuel is commonly used. Brake welding has several advantages over fusion welding.
#7. Cast Iron Welding.
Welding of cast iron is usually a brazing operation, in which mainly nickel filler rods are made, although true welding with cast iron rods is also possible.
The purpose behind this process is to use electricity with copper to hold underground climate pipes warm in cold climates.
#8. Vacuum Brazing.
Vacuum brazing is a material joining method that gives vital benefits such as extremely clean, superior, flux-free brake joints of high integrity and strength. This process is expensive because it must be done inside a vacuum chamber vessel.
The temperature uniformity is maintained at room temperature when heated in a vacuum, reducing residual stresses due to slow heating and cooling cycles.
#9. Dip Brazing.
Dip brazing is particularly suited to aluminum brazing because air is excluded, thus preventing the formation of oxides. Joining parts are fixtures and brazing complexes applied to mate surfaces, usually in slurry form.
Difference Between Brazing, Soldering & Welding
Brazing connects dissimilar metal surfaces by use of capillary action. It uses a technique known as wetting, in which molten filler material is used to connect the base metals together. The melting point of the brazing filler metal is higher than 450 °C.
Soldering makes use of filler metals with melting points lower than 450 °C. While brazing and soldering share the same basic idea, the strength of the joint produced by each technique differs mostly due to different operating temperatures.
Welding melts both the workpieces and the filler metal. Compared to brazing, this enables the formation of stronger connections. Stick welding, MIG, TIG, and other processes use far greater temperatures.
Advantages of Brazing
The following are the advantages of brazing:
- Dissimilar metals and parts having a thin section can be easy.
- brazing may avoid metallurgical damage to the base metal.
- The strong joint can be obtained by brazing.
- Properly brazed joints are pressure-tight.
- It is an economical and quick process.
- Less heating is required than for welding.
Disadvantages of Brazing
The following are the disadvantages of brazing:
- Reduction of joint strength compared to a welded joint due to the soft filler metals used.
- The strength of the brazed joint is less than that of base metal but is more likely to be higher than filler metal.
- The brazed joints can be destroyed under high service temperatures.
- Brazed joints need high-metal cleaning when done in an industrial setting.
- The joint color is usually different from the base metal, creating an aesthetic disadvantage.
Applications of Brazing
Following are the applications of brazing:
- It is used in vacuum interrupters.
- It is used in transport applications.
- Used in constructions.
- It is helpful in medical equipment.
- Used in art and jewelry.