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Ask the Expert: Can I Use my Conventional Vacuum Furnace for Aluminum Brazing?

Ask the Expert

Short answer: No. Aluminum should only be brazed in vacuum furnaces specifically built for aluminum brazing.

When aluminum brazing is performed in a vacuum furnace, it is considered fluxless brazing. Due to the vacuum furnace’s clean environment, flux is not needed. Magnesium is used as an additive, or getter, in the vacuum aluminum brazing process.

By nature, vapor pressure aids in the depletion of magnesium and parent aluminum alloys in high vacuum, depositing magnesium onto the hot zone and into the shielding.

A conventional furnace can braze aluminum until it reaches a point of aluminum saturation and stops pumping due to water vapor retention, because it is not specifically designed for this process.

Ipsen Vacuum Aluminum Brazing (VAB) Furnace

Proper vacuum aluminum brazing requires special components that standard vacuum furnaces generally do not have, including:

  • Stainless steel hot zone insulation and Nichrome heating elements
  • Multi-sided heating zones for precise temperature control
  • Specialized hot water chamber re-circulating system, set at 140 °F (60 °C), to prevent magnesium build-up on the cold walls
  • Larger pumping system designed to handle magnesium burst during the brazing process (poor vacuum = poor braze quality)
  • Vacuum gauge filter vapor traps
  • Multi zone proportional integral derivative (PID) control loop design to adjust to different part sizes and weights
  • Shielding for prevention of magnesium build up on door O-ring and main valve poppet ring
  • Double door for ease of maintenance.

The heating element ceramic insulator design and spacing is also different on a vacuum aluminum brazing furnace, which allows it to run for longer periods of time before replacement is needed.

What if I try it anyway? 

  • Aluminum and magnesium will contaminate the furnace.
  • A burn out will push contaminants further into the hot zone and cold wall of the furnace vessel.
  • Trace amounts of aluminum or magnesium may react negatively with other production materials and parts.
  • Aluminum can cause black spotting and eutectic related melting problems.

If you’re thinking about brazing aluminum in a standard vacuum furnace, you should first consider the possible negative effects it may have on future processes and the life span of your furnace.

About the Author
Jim Grann, Technical Director, started with Ipsen in 1978 where he has also held roles in quality control, technical support and instruction. He is an industry veteran who supports sales, engineering and Ipsen’s worldwide customer base. His 42 years of experience allow him to provide excellent solutions for troubleshooting and process-related issues. Jim has presented at conferences, written technical papers, and contributed to industry publications. He is a graduate of Council Rock High School and Bucks County Community College in Pennsylvania. Jim is married with two daughters, a grandson and enjoys camping, hiking and hunting in his free time.


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