Definition of Vacuum Furnace Process

A vacuum furnace is a type of furnace that can heat materials, typically metals, to very high temperatures and carry out processes such as brazing, sintering and heat treatment with high consistency and low contamination.

In a vacuum furnace the product in the furnace is surrounded by a vacuum. The absence of air or other gases prevents heat transfer with the product through convection and removes a source of contamination.

Some of the benefits of a vacuum furnace are:

• Uniform temperatures in the range 2000–2800°F (1100–1500°C)
• Temperature can be controlled within a small area
• Low contamination of the product by carbon, oxygen and other gases
• Quick cooling (quenching) of product.
• The process can be computer controlled to ensure metallurgical repeatability.

Heating metals to high temperatures normally causes rapid oxidation, which is undesirable. A vacuum furnace removes the oxygen and prevents this from happening.

An inert gas, such as Argon, is typically used to quickly cool the treated metal back to non-metallurgical levels (below 400 °F) after the desired process in the furnace.  This inert gas can be pressurized to two times atmosphere or more, then circulated through the hot zone area to pick up heat before passing through a heat exchanger to remove heat. This process is repeated until the desired temperature is reached.
References
http://en.wikipedia.org/wiki/Vacuum_furnace