Brazing is the process of joining metals using a metallic filler material to flow across the joints to create an invisible, resilient bond between the base metals. A perfect model for nearly all metalwork projects done in schools and colleges, brazing is also used in the industry for:
a) Tool-making,
b) Manufacturing of bicycle frames,
c) Fasten hard metal tips, such as carbide, ceramics, and cement to tools like saw blades.
Brazing vs. Soldering and Welding
Similar to soldering and welding, brazing forms a strong joint that can withstand a broad range of temperature and different motions, such as jolting, shuddering, and twisting.
However, brazing, soldering and welding use different metals and work on different temperatures. Brazing can be done using brazing rods, pipes, flat metals, or other shapes provided that the metal pieces can be mounted against each other without huge spaces or cavities. Welding creates spot welds on easier, straightforward, and uncomplicated shapes, whereas brazing can manage more unfamiliar and not-so-common configurations.
Brazing has more advantages over soldering and spot welding. A brazed coupling is smooth and complete that creates a sealed, flawless, and waterproof joint, which can easily be coated so the joint melts and vanishes. Brazing is the only process that can connect and bond divergent types of metals with different melting points, such as steel, bronze, aluminum, copper, and wrought iron.
How to Build a Brazing Hearth
A brazing hearth normally comprises of three vermiculite blocks with a 200-mm by 230-mm plate and insulation blanket. Thermalite and vermiculite are considered the best material to use in building a brazing hearth.
However, these blocks are difficult to find; hence, a firebrick can be used as a substitute as they are readily available from brick suppliers and companies selling stoves and fireplaces. Furthermore, firebricks are difficult to find and easily crack due to heat, it is recommended to purchase brazing hearth bricks for spare.
A homemade brazing hearth should be robust enough to withstand the high brazing temperature. Building a brazing hearth starts with building a jig, a fixture that is used to hold the metal pieces in its position while being assembled. A homemade brazing hearth is normally made of firebricks inside a steel enclosure that is welded on an angle. The brazing hearth bricks are simply held in friction and clamped in place using an angle iron. The strips are then welded so that they will not slide out.
Some people also use the big stones from pizza ovens as a replacement for vermiculite blocks and firebricks. A large brazing hearth can be constructed by purchasing extra briquette.
A lot of people also prefer mobile brazing hearths that they can use outdoors. Mobile brazing hearths are usually made of steel angle and sheets with a hood that catches and extracts fumes. These types of brazing hearths are lightweight so that they can easily be transported. These mobile brazing hearths are not more than 18 inches deep, which can pass through a standard door.
The Brazing Process
The brazing process normally comprises five steps: cleaning the mating surfaces, fluxing the metal pieces, assembly of parts for brazing, brazing the assembly, and cleaning the brazed joint.
1. Cleaning the surfaces of the metal pieces:
Capillary action does not work properly on filthy surfaces; hence, the whole area where the metal pieces will be joined should be cleaned to avoid clumping of the melted braze mixture. If the surfaces are contaminated with oil, dirt, or grease, the brazing filler metals will not hold and an inconsistent joint will form.
2. Applying flux to the base metals:
It is highly recommended to wash the surfaces of the material before applying the melted flux. Flux is a chemical compound, usually in the form of liquid or paste, which removes the oxides and prevents more oxidation that occurs during brazing. Additionally, flux smoothens the surface of the metal pieces to facilitate uniform flow of braze throughout the joint.
3. Aligning and supporting metal parts:
Before heating and brazing the parts, they need to be aligned and supported. The best allowance between two metal pieces that will be brazed is usually 0.001 inch to 0.003 inch, generally not more than 0.005 inch. During assembly, it is necessary to ensure that the first metal piece is fully inserted to the other metal piece before brazing them together.
4. Brazing the metal pieces for assembly
The actual brazing process consists of two parts: heating the base metal pieces and applying the filler metal to the connection. Regardless of the heating apparatus utilized, make sure that both metals are extensively and equally heated. The heating equipment can be a brazing torch that uses acetylene or hydrogen that will help create a very high brazing temperature. The standard RF80 brazing torch usually gets hot between 800°F and 2000°F, but low enough not to melt the base metals.
The joint is completed by brazing a tube to a fixture or connector. After the brazing torch has heated the base metals, bring the brazing rod to the hot base metals until the braze melts and flows around the joint, penetrating the entire junction. The brazing rods melt at a lower temperature than the metal so it forms a molten liquid, which flows along the joint between the two metal parts. When the joint solidifies and cools completely, the junction becomes permanent as long as the brazing process is done correctly.
5. Cleaning the brazed joint
While flux was applied to the metal pieces before brazing them, it is necessary to remove the flux residues after performing the brazing process, by brushing or swabbing the flux using hot water. More stubborn flux residues can be removed using wire brush.
Some Products: –
Flame fast have developed brazing hearth DS320 where brazing and forging can take place in the one part in the combination unit sections. This unit is an improved version of the brazing hearth units DS430S and DS430D that have individual brazing and forging areas.
Brazing Hearth Safety
The brazing process itself and utilizing a brazing hearth are potentially dangerous. When reached a very high temperature, it can result to serious burns; hence, safety procedures should always be observed and never ignored. It is highly recommended to observe the following safety tips when working with brazing hearth:
- Always face the brazing hearth when using it.
- Remember to wear goggles to shield the eyes against hot splashes of flux, which could cause permanent damage to the eyes.
- Wear leather aprons and gloves for protection against hot metals.
- Use tongs to handle the heated material.
- Allow the substance to cool on a block or steel plate before moving it to another place in the workshop. The steel plate will absorb the heat from the metal but not trying to cool it too quickly.
- Turn the brazing torch on slowly and carefully but never turn the brazing torch around, which is highly dangerous.
- Focus on the brazing process while heating the base metals, and place the brazing torch back to its place after using.
Keep in mind that to be successful in brazing or any kind of metalworking, safety should be considered a priority.
