Why buy a dedicated vacuum aluminum brazing furnace

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Why braze aluminum?

While many common metals such as copper, silver, brass and nickel-based alloys can be used to braze parts, aluminum offers a lightweight yet strong solution and can be used to braze a variety of other metal alloys.

Applications for aluminum brazing are ubiquitous in the field of gas-to-liquid heat exchangers, such as automotive radiators, intercoolers, air conditioning units or evaporators. In these heat exchangers, the complex geometry of the tubes and the winding back and forth along a strict path with a large surface area are well suited to the vacuum aluminum brazing process to ensure a complete seal in all bends and recesses throughout the part.

Vacuum aluminum brazing is also suitable for parts that require a high degree of cleanliness – aerospace components, medical devices or other high-precision parts. Once these parts are cleaned before the brazing process, the vacuum aluminum brazing process will not generate other oxides or other contaminants that can contaminate the parts.

When brazing aluminum in a vacuum furnace, one of the major issues that operators must be aware of is the buildup of magnesium oxide. Magnesium acts much like a flux as an additive to the aluminum brazing filler metal. Aluminum alloys containing magnesium have lower melting points than pure aluminum or other common alloys. As the brazing material heats, the released magnesium vaporizes and seeks out any remaining oxygen atoms in the vacuum furnace, moving them away from the brazing location. Magnesium also eats away the aluminum oxide on the aluminum surface to ensure that the remaining brazing material is evenly attached to the surface of the part.

As the furnace reaches and exceeds 570°C, these chemical reactions occur, creating a “magnesium explosion” – a peak in outgassing. A good vacuum design to handle this instantaneous large amount of outgassing requires an exhaust system powerful enough to maintain a vacuum of 10-4 to 10-5mbar at all times. As the vacuum furnace continues to pump out gas, this process can leave a degassing residue on the hot zone walls.

Dealing with magnesium oxide residue is very tricky because the chemical composition of this residue is similar to that of a hand-held flame torch. A large part of the maintenance time of aluminum brazing vacuum furnaces is spent cleaning these magnesium oxide deposits. The hot zone walls and hot zone shields must be scraped with a non-ferrous metal material to avoid sparks that ignite the oxide, which will burn rapidly. If the magnesium oxide accumulation is too thick to be scraped off, an air combustion cycle may be required to break up the larger magnesium oxide crystals. When most of the residue has been removed, a normal vacuum cleaning cycle can be performed to return the equipment to production. Diffusion pumps also need to be cleaned regularly according to the manufacturer’s specifications.

Why buy a dedicated vacuum aluminum brazing furnace?

In theory, vacuum aluminum brazing can be performed in almost any vacuum furnace with a metal hot zone, but we do not recommend performing aluminum brazing processes in ordinary vacuum furnaces. Dedicated vacuum aluminum brazing furnaces have special processes that are not available in standard vacuum furnaces and are difficult to achieve in standard vacuum furnaces.

Vacuum aluminum brazing is a tested and proven solution for joining metal parts with large undulating surfaces or complex geometries. Companies that perform vacuum aluminum brazing need a furnace that can provide high vacuum, precise temperature control and excellent temperature uniformity.

Compared with traditional vacuum furnaces, aluminum brazing processes require higher process control accuracy and temperature uniformity at lower temperatures. Using standard vacuum furnaces to handle conventional aluminum brazing processes, aluminum brazing requires lower temperatures and higher precision.

Aluminum Vacuum Brazing Furnace