Sintering Furnaces

Vacuum Brazing Furnaces

While sintering is a process for forming solid objects below their melting point, brazing is a process for joining solid objects below their melting point through use of a separate material that does melt. A common alternative to welding (which requires object melting), brazing is readily adapted to mass production procedures. This is because large numbers of components can be simultaneously joined in one furnace load. Use of a vacuum furnace to prevent metal oxidation allows elimination of the flux used in atmosphere or torch brazing. This improves braze quality, reduces post-braze processing, and increases production yields.

Vacuum brazing is commonly used to join two or more metallic components, but may also be used to join ceramic materials, either to other ceramics or to metals. Since ceramics are not readily wet by most molten metals, brazing to ceramics requires the addition of a highly reactive component to the braze alloy. Often referred to as active metal brazes, these alloys typically contain titanium, or some other highly reactive metal that will bond with the non-metallic atoms in the ceramic (like oxygen, nitrogen, boron, or carbon atoms).

These metals are designated as highly reactive because they readily react with and bond to oxygen and other light elements. Processing these materials at elevated temperatures requires low oxygen partial pressures in the environment to minimize premature bonding of the reactive metal to atmospheric oxygen.

Vacuum brazing furnaces provide the ideal environment for this processing. The addition of a turbomolecular high vacuum pump to a basic rotary vane mechanical pumped vacuum system allows ready attainment and maintenance of 10-4 mbar vacuum levels or lower. This is a seven order of magnitude reduction from 10+3 atmospheric pressure levels. This 99.99999% reduction in oxygen partial pressures is comparable to inert gas with less than 1 ppm impurity levels. While inert gas with these impurity levels can be readily purchased (at considerable cost), outgassing of furnace components, workload, and melting braze alloys inevitably contaminates the furnace environment and reduces gas purity levels. Vacuum brazing furnaces are continually being pumped to removed outgassed constituents, always providing a lower oxygen partial pressure and a superior braze environment. In addition, vacuum gauges used on all vacuum furnaces provide an instantaneous and continuous measurement of total impurity pressure level. They assure constant monitoring and appropriate oxygen partial pressure levels.

The following figure show a cross-section of the RD-M benchtop metallic heat zone turbomolecular pumped vacuum brazing furnace. It is rated to 1200°C, which is widely used for brazing diamonds to tungsten carbide, molybdenum, and steel cutting tools. Diamond brazing is an excellent application for vacuum brazing furnaces. This is because diamond requires very low oxygen partial pressures at elevated temperatures to prevent a phase change conversion from diamond to graphite.

RD-G Vacuum Furnace

RD-M Vacuum Brazing Furnace (cross-section)