What Is Brazing and How To Braze Metal?

What is Brazing?

Brazing is a type of metal-joining method which joins two or more metal items together by melting and flowing a filler metal into the joint. The filler metal has a lower melting temperature than the adjoining metal. It differs from welding because, in brazing, the workpieces do not melt.

Brazing differs from soldering in that it uses higher temperature and much closer fitting parts than in soldering.

In the brazing process, the filler metal flows into the gap between the close-fitting parts by capillary action. Usually, the filler metal is raised slightly above its melting (liquidus) temperature, while protected by a proper atmosphere, usually a flux.

The filler metal then flows over the base metal (wicking) and then is cooled in order to join the workpieces. One of the main benefits of brazing is the ability to join the same or different metals with significant strength.

Key Takeaway

Brazing is the process of joining two independent pieces of metal to form one strong load-bearing joint.

• Brazing is similar to soldering but is performed at a higher temperature.
• Use the right material for the brazing rod with respect to the metal used in your project.
• The heat from the metal parts you are joining should melt the brazing rod, not the flame of the torch.
• Use a flame with a lot of intensity, from a torch.

Brazing Rods Materials

• Copper, brass, bronze: Copper Phosphorous Brazing & Welding Rods
• Steel, stainless steel, nickel alloys, copper alloys, cast iron, tungsten carbide: Nickel Silver Brazing & Welding Rods
• Cast iron, galvanized, nickel, steel, malleable iron: Bronze Brazing & Welding Rods
• Aluminum: Bernzomatic AL3 Aluminum Brazing & Welding Rods

How To Braze Metal?

Brazing is a joining process normally used for metals (but also for ceramics) in which molten filler metal (the braze alloy) flows into the joint.

Steps by step:

• Utilize either the wire brush or emery cloth to clean or scuff the surface of the metal. After, clean the surfaces with soapy water or with a degreaser.
• Once the cleaning is completion, set the pieces of metal to position the way you want them. The majority of the time, an overlapped joint is better and will braze together easier than a gapped joint. If necessary, use clamps to hold the pieces in a position.
• Heat the joint where the two different pieces of metal will meet until the joint glows.
• After the joint as glowed, apply the brazing rod to the joint while still heating the metal surfaces. For larger areas, heat portions of the joint to temperature then move to the next adjacent area.
• Once brazing is complete, use the wire brush to clean the brazed surface from oxidation or residue.

The filler metal has a melting point above 450 °C but always below the melting point of the materials being joined. This differentiates it from welding, which describes a process that must melt the metals being joined at high temperature.

The filler metal is heated just above the melting point; as the filler melts, it is protected by a suitable atmosphere, generally a flux. The molten wetted filler metal then solidifies, thereby joining the parts together establishing a good join between similar or dissimilar metals.

Brazing can use all forms of atmospheres: air, combusted fuels gas, ammonia, nitrogen, hydrogen, noble gases, inorganic vapours, and a vacuum and use of variety of heat sources, torch, furnace and induction coils.

There are two aspects that must be achieved in order to create a good brazed join two different types of aspect in the filler and base material are metallurgically compatible, and you have a joint design that has provided a gap in the joint where molten braze filler can be drawn or spread by capillary action.

The gap required is a flexible range and can vary depending on a number of factors including brazing temperature, brazing atmosphere, brazing base materials and braze alloy composition.

Brazing is suitable for joining dissimilar metals and is a commercial accepted process in many areas of applications and industries.

Brazing is a process that can take advantage of flexibility and high integrity and an important aspect of ensuring these joints can be achieved and be dependable in important and non-important applications. It is one of the most used methods of joining materials.

What Are the Different Methods of Brazing?

Brazing, which employs a broad spectrum of heat sources, is frequently categorized by the method of heating. Certain methods heat locally (only the joint area) to bring about brazing temperatures, while others heat the entire assembly (diffuse heating).

Some of the more commonly used methods are summarized below:

Localized Heating Techniques

1. Torch Brazing

Within this process, the heat needed to melt and flow the filler metal is obtained from a fuel gas flame. The fuel gas can be acetylene, hydrogen, or propane, and a flame is produced when the fuel gas is combined with oxygen or air.

The torch brazing process is easy to automate and requires low capital investment. It is important to note torch brazing utilizes flux and therefore a post-braze clean may be required.

2. Induction Brazing

Brazing with high-frequency induction heating is clean and very quick, provides good control of temperature, and good control of the location of heat. Heat is created by a rapidly alternating electrical current, that is induced to flow in the workpiece by an induction coil adjacent to it.

3. Resistance Brazing

Resistance heating is the process of generating heat from resistance to electrical current flowing in a circuit that includes all of the workpieces (as is the case for induction brazing). It typically applies to fairly simple joints in metals that have high electrical conductivity.

Diffuse Heating Techniques

1. Furnace Brazing

Furnace brazing has two main advantages: working in a protective atmosphere (the high-purity gases or vacuum eliminate the need for flux) and the ability to control each step of the heating and cooling cycles accurately. Heating is by either element, or gas firing.

2. Dip Brazing

The process consists of submerging the entire assembly of parts into a bath of molten flux or molten braze alloy. In both instances, the bath temperature is below the solidification point of the parent metal and above the melting point of the filler metal.

Brazing vs. Welding

AWS classifications have also classified Brazing as a bonding process of the liquid-solid phase. Liquid means the filler metal is molten. Solid means that either of the base material (or materials) does not undergo melting.

Welding is a process with the workpieces are melted, while brazing does not. The key difference is the heat source.

Brazing can be applied by using a torch, furnace, induction, dipped, or resistance wherein the minimum heat temperature is reached is above 840°F (450°C) while arc welding uses electricity as a heat source for melting materials reaching about 10,000 degrees Fahrenheit.

Brazing vs. Soldering

The only distinction between brazing and soldering is in the temperature that governs each process. While soldering occurs at a temperature below 840°F (450°C), brazing occurs at a temperature above 840°F (450°C).

Advantages of Brazing and Soldering

Some advantages of brazing and soldering as compared to other methods of joining include the following:

• Low temperature
• Maybe permanently or temporarily joined
• Dissimilar materials can be joined
• Speed of joining
• Less chance of damaging parts
• A slow rate of heating and cooling
• Parts of varying thicknesses can be joined
• Easy realignment

Both brazing and soldering processes have many unique benefits of joining materials and are no doubt the most overlooked joining process when select a process.

The ability to join lots of different materials with a limited number of fluxes and filler metals reduces the need for a huge range of materials, and potential savings for a small business, home shop, or a farm can be great.

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