Heat treatments for metal can be performed with different types of heating equipment. The most popular types of heating equipment for brazing are:
- Torches (handheld and machine operated)
- Vacuum furnaces
- Continuous furnaces
Of these types of equipment, the latter offers the most versatility, as it can handle the majority of production requirements. There are, however, some instances where continuous furnaces are not the best heating equipment for brazing. To put their usefulness in context, below is a list of their basic benefits and drawbacks:
Ideal for Uniform Heating
The furnaces are ideal for heating metal that distorts easily under localized heat. Instead of being heated in the vicinity of its joints, the assembly is heated in its entirety, preventing distortion that can compromise the strength and appearance of the finished product.
Can be too Small for Large Assemblies
Some assemblies are too large to fit inside the furnaces. In such instances, an acetylene torch is used instead. Although the door size of heating equipment can be a legitimate concern for large assemblies, instances where assemblies are too large to fit through the door of the largest equipment are rather rare.
Can Create Controlled Atmospheres
The furnaces can be outfitted with design elements (e.g. curtain boxes and directional flow control valves) that result in a controlled heating atmosphere-a requirement for brazing stainless steel. By preserving an atmosphere of nitrogen, hydrogen, or a mixture of the two, they can prevent the chromium in the metal from oxidizing under heat.
Ideal for Large Production Runs
Continuous furnace brazing involves the constant movement of assemblies through the heating chamber on a conveyor belt. This style of operation makes it possible to complete large volumes of assemblies in a short period of time. In comparison, a vacuum furnace requires assemblies to sit stationary in the heating chamber.
Not Suitable for all Assembly Requirements
If an assembly has an extremely low tolerance for oxidization, a vacuum model may be preferred over a continuous model. This is because the former applies a vacuum to the heating chamber that removes all gases, whereas the latter uses special design elements to “control” the atmosphere in the chamber.
The level of oxidation prevention is superior in each case, but a vacuum furnace is considered the best choice for assemblies that require the most assurance against the formation of an oxide layer between the filler metal and base metal (e.g. assemblies for aerospace equipment that will endure heavy g-forces).
Ideal for Timely Production Runs
As mentioned above, the furnaces can produce a large number of assemblies in a short period of time. In addition to making them valuable for large production runs, this capability makes them ideal for producing a production run of any size on short notice.
Conclusion
Continuous furnace brazing brings numerous benefits to the brazing process, particularly: uniform heating, expedited production, and atmosphere control for stainless steel brazing. Although not ideal for treating all types of assemblies, continuous furnaces can accommodate the majority of work requirements.
Source by Brian Figlioli
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