Vacuum brazing is a term for various metal joining or brazing processes that take place in a chamber or retort below atmospheric pressure, otherwise known as a vacuum furnace. Vacuum brazing is brazing in a furnace using a vacuum atmosphere.
Brazing is broadly defined as a group of joining processes that occur above 840°F (400°C) and below the melting point of the base metal. Additionally, brazing produces coalescence by the melting and subsequent resolidification of a filler metal or brazing alloy in the very narrow space between surfaces to be joined. The brazing alloy or brazing filler metal must have a lower melting point than the material being joined, because in brazing the base metal does not melt. In conventional brazing, molten filler metal is distributed between closely fitted surfaces of the base metal joint by capillary action – even against gravity.
Most of the common metals can be brazed, but not necessarily with the same brazing filler metal equipment, method, or procedure.
A vacuum furnace is a furnace using low atmospheric pressures instead of a protective gas atmosphere like most heat treating furnaces. Furnaces are categorized as hot wall or cold wall, depending on the location of the heating and insulating components. Cold wall furnaces are used in vacuum brazing.
Assemblies are bright and clean (shiny) after vacuum brazing because the extremely low amount oxygen in a vacuum atmosphere prevents oxidation of parts. Vacuum brazing is particularly useful where base metals are processed that adversely react with other atmospheres, or where entrapped fluxes or gases are intolerable. Vacuum brazing is widely used to braze base metals of stainless steel, super alloys and carbon low alloy steels.
Vacuum brazing offers the combination of high cleanliness and uniform heating and cooling or rapid cooling. Vacuum brazing is ideal for oxidation sensitive materials such as those used in the aerospace industry.
Wall Colmonoy is the pioneer in furnace brazing of high-temperature base metals using nickel-based filler metals. Aerobraze Engineered Technologies, a division of Wall Colmonoy, has eight brazing/heat treating furnaces at their Cincinnati facility, including the world’s largest top-loading vacuum furnace at 120” dia. X 180” high. Since 1959, Aerobraze has specialized in hydrogen and vacuum furnace brazing and thermal processing of all types of metals. With furnaces handling workloads of up to 10 tons and quality assurance procedures to aerospace requirements, Aerobraze has the capabilities and experience to handle customer exact requirements.