Vacuum furnaces are most often used to braze to heat treat materials with very stable oxides that cannot be brazed in atmosphere furnaces. Vacuum brazing is also used heavily with refractory materials and other exotic alloy combinations unsuited to atmosphere furnaces. Due to the absence of flux or a reducing atmosphere, the part cleanliness is critical when brazing in a vacuum. Hi TecMetal Group utilizes vacuum furnaces of a cold-wall design. Typical vacuum levels for brazing range from pressures of 1.3 to 0.13 Pascal’s (10−2 to 10−3 Torr) to 0.00013 Pa (10−6Torr). Vacuum furnaces are batch-type and they are suited to medium and high production volumes.
Furnace Brazing - Process
Furnace brazing defines a process of joining metallic materials using a molten filler metal. The filler metal permeates into the joint by the dynamics of capillary action [attraction]. The filler metal is generally preplaced on the parts before the parts are carefully placed onto the furnace belt. The filler metal has a lower melting point than the parent materials. Furnace brazing is considered best for mass production of parts.
The following additional considerations must be made in order to produce a brazed product with high braze joint integrity:
The effect of temperature and time on the quality of brazed joints is considered with all applications. As the temperature of the braze alloy is increased, the alloying and wetting action of the filler metal increases as well. In general, the brazing temperature selected must be above the melting point of the filler metal.
Advantages and Disadvantages of Furnace Brazing
Furnace Brazing has many advantages over other metal-joining techniques, such as induction or torch brazing and welding. The Furnace Brazing does not melt the base metal of the joint. The process yields tighter control over tolerances and produces clean parts and brazes joints without the need for secondary finishing. Additionally, dissimilar metals and non-metals can be brazed. In general, furnace brazing also produces less thermal distortion than welding due to the uniform heating of a brazed piece. Complex and multi-part assemblies can be brazed cost-effectively.
Furnace brazing is easily adapted to mass production and it is easy to automate because the individual process parameters are less sensitive to variation.
One of the main disadvantages is: that brazed joints require a high degree of base-metal cleanliness. And, all braze applications require design and manufacturing considerations prior to the manufacturing of both the components [pieces and parts] and the final assembly.