Furnace Brazing

Brazing is a joining technique for metals or ceramics using a metal with a lower melting point than either of the materials to be joined to make the joint. Technically, only processes using a metal that melts above 450°C is brazing; below that is characterized as soldering. In furnace brazing the whole assembly is heated to a temperature where the braze alloy melts and flows into the joint. On subsequent cooling it freezes making a solid joint. In Furnace brazing operations many thousands of joints can be made at the same time.

Figure 1: Belt conveyor brazing furnace

HTG is a pioneer and specialist in the field of furnace brazing.

There are many heating methods available to accomplish brazing operations. The most important factor in choosing a heating method is achieving efficient transfer of heat throughout the joint and doing so within the heat capacity of the individual base metals used. The geometry of the braze joint is also a crucial factor to consider, as is the rate and volume of production required. The easiest way to categorize brazing methods is to group them by heating method. Here are some of the most common:

• Torch brazing
• Furnace brazing [Exothermic, Hydrogen, Argon and Vacuum Atmospheres]
• Induction brazing
• Dip brazing
• Resistance brazing
• Infrared brazing
• Blanket brazing
• Electron beam and laser brazing
• Braze welding

Furnace Brazing - Process

Furnace brazing defines a process of joining metallic materials using a molten filler metal. The filler metal permeates into the joint by the dynamics of capillary action [attraction]. The filler metal is generally preplaced on the parts before the parts are carefully placed onto the furnace belt. The filler metal has a lower melting point than the parent materials. Furnace brazing is considered best for mass production of parts.

The following additional considerations must be made in order to produce a brazed product with high braze joint integrity:

The effect of temperature and time on the quality of brazed joints is considered with all applications. As the temperature of the braze alloy is increased, the alloying and wetting action of the filler metal increases as well. In general, the brazing temperature selected must be above the melting point of the filler metal.

Advantages and Disadvantages of Furnace Brazing

Furnace Brazing has many advantages over other metal-joining techniques, such as induction or torch brazing and welding. The Furnace Brazing does not melt the base metal of the joint. The process yields tighter control over tolerances and produces clean parts and brazes joints without the need for secondary finishing. Additionally, dissimilar metals and non-metals can be brazed. In general, furnace brazing also produces less thermal distortion than welding due to the uniform heating of a brazed piece. Complex and multi-part assemblies can be brazed cost-effectively.

Furnace brazing is easily adapted to mass production and it is easy to automate because the individual process parameters are less sensitive to variation.

One of the main disadvantages is: that brazed joints require a high degree of base-metal cleanliness. And, all braze applications require design and manufacturing considerations prior to the manufacturing of both the components [pieces and parts] and the final assembly.

Figure 2: Schematic of furnace brazing process