Vacuum brazing is a material joining technique that offers significant advantages: extremely clean, superior, flux-free braze joints of high integrity and strength. The process can be expensive because it must be performed inside a vacuum chamber vessel.
BENEFITS OF BRAZING PROCESS
●No oxidation eliminating the necessity for flux
●Minimized residual stress and distortion
●No heat-affected zones
●Allows performing certain heat-treating operations in the same cycle to save time and money
VACUUM BRAZING PROCESS CAPABILTIES
◆Length or diameter up to 3800 mm
◆Width/Height/Diameter up to 1100 mm
VACUUM BRAZING SHEET
Brazing sheet is a carefully designed sandwich material composed of a core alloy, with a cladding layer on one or both sides of a different aluminum alloy with a different melting point. During brazing, only the cladding alloy melts, while the core alloys stay solid.
Core alloys: AA3003, 6060,6061,6063,6951
Cladding alloys (Brazing alloys): AA4004, AA4104
●Air coolers, intercoolers, oil coolers
Overview: What’s brazing?
The basics of vacuum brazing
Vacuum brazing is a material joining technique that offers significant advantages: extremely clean, superior, flux-free braze joints of high integrity and strength. The process can be expensive because it must be performed inside a vacuum chamber vessel. Temperature uniformity is maintained on the work piece when heating in a vacuum, greatly reducing residual stresses due to slow heating and cooling cycles. This, in turn, can significantly improve the thermal and mechanical properties of the material, thus providing unique heat treatment capabilities. One such capability is heat-treating or age-hardening the workpiece while performing a metal-joining process, all in a single furnace thermal cycle.
Products that are most commonly vacuum-brazed include aluminum cold plates, plate-fin heat exchangers, and flat tube heat exchangers.
Vacuum brazing is often conducted in a furnace; this means that several joints can be made at once because the whole workpiece reaches the brazing temperature. The heat is transferred using radiation, as many other methods cannot be used in a vacuum.
Vacuum brazing is brazing in a furnace using a vacuum atmosphere. Brazing is broadly defined as a group of joining processes that occur above 400°Cand below the melting point of the base metal.
How does vacuum brazing work
Brazing is a method of joining two or more metals by melting a filler metal, or the brazing alloy.
When alloys are used instead of a pure metal for the process in a vacuum furnace, they do not contain fluxes, there is therefore no need to remove the slag by mechanical methods and the weld appears clean. The alloy must not include elements that can sublimate or evaporate, since the desired joint characteristics will not be achieved and the furnace could be contaminated.
In general alloys do not fuse together at a well-defined temperature as do pure metals, but within a range. When possible therefore eutectic alloys should be sought. These have a similar behavior to pure metals, where the solid and liquid elements co-exist only at the eutectic temperature.
There are a significant number of filler metalsfor vacuum brazing available. In some alloys, generally with high temperature uses, there are still in many cases a situation of a “solidus” and “liquidus” phase being present at a single temperature, made up of more than two forms of metal. Other alloys, commonly used in vacuum furnaces, nevertheless show a broad intermediate “solidus-liquidus” phase with a temperature rise between the two important phases. In this case the time for a complete fusion increases as this takes place at a higher temperature, which will be the brazing process temperature.