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What Is Brazing?

Brazing is a technique used to join two metal components using a filler metal (the brazing alloy) with a lower melting point than the base materials. Unlike welding, the base metals do not melt—only the filler metal does.

The method has been used for more than 5,000 years, dating back to ancient Egypt, where craftsmen applied it in the production of weapons, tools, artifacts, and jewelry. Today, brazing remains an essential joining technology used across modern industries including electronics, tooling, plumbing (HVAC), and the automotive sector.

 
 
Lodning af kobber- og stålrør
Lodning af kobber- og stålrør

Brazing Categories

Brazing can generally be divided into three main categories:

< 450°C

Soft soldering

Soft soldering is characterized by a soldering temperature below 450°C, where the filler metal typically consists of a tin-based alloy—commonly referred to as soldering tin—and is applied using either a soldering iron or a gas flame.

450-850°C

Brazing

Brazing is characterized by a soldering temperature between 450°C and 850°C, where the filler metal typically consists of a silver–copper alloy. Heating is applied using a gas flame, induction coil, or electrical resistance.

> 850°C

High-Temperature Brazing

High-temperature brazing is characterized by a soldering temperature above 850°C, where the filler metal typically consists of brass, copper, or nickel. Heating is generally performed in a brazing furnace.

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Surface Preparation

Successful brazing requires thorough cleaning of the metal components before the process to remove dust, grease, oil residues, and the naturally occurring oxide layer that forms when metals are exposed to air.

Impurities on the metal surface can prevent the filler metal from forming a proper metallic bond (diffusion) between the components.

Cleaning must also continue during the brazing process. This is typically done using a flux, a chemical agent that binds with oxides. Flux is available in various forms such as powder, paste, liquid, flux cores, or coatings on the filler metal.

For furnace brazing, a protective atmosphere of gas (hydrogen, argon, helium) or a vacuum can be used instead. There are also self-fluxing filler metals (silver/copper/phosphorus alloys) that allow copper-to-copper joints without additional flux.

After brazing, flux residues may need to be removed using sandblasting, acid treatment, or hot water, as many fluxes are corrosive and can lead to rusting of the joint.

Why Choose Brazing?

Before starting a brazing process, it is important to consider whether brazing is the most suitable joining method. There are many alternative techniques for joining metals, including welding (laser, TIG, MIG), adhesive bonding, and mechanical fasteners such as bolts.

The main advantage of brazing over other joining methods is its ability to join metals with different melting points, which is not possible with welding. Additionally, brazed joints offer long-term reliability and durability compared to mechanical fasteners.

Brazed_joint_1 Engelsk

Ready to Advise and Assist

If brazing has been selected as the preferred joining method, it is essential to carefully consider the following factors:

  • Choice of filler metal

  • Selection of heating method

  • Choice of flux

  • Design of the brazed joint

  • Compatibility of base materials (is joining feasible?)

  • Requirements for the finished assembly (strength, corrosion resistance, etc.)

  • Applicable standards (e.g., lead-free solder for potable water piping)

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