An ideal vacuum is the absence of vapors, particles, gases or other matter. The absence of these
materials would constitute an absolute pressure of zero. While this "absolute zero" is impossible,
it is possible to get very close. Normally when the word vacuum is used it refers to any absolute
pressure below that of normal atmospheric pressure. Atmospheric pressure is defined as 14.6
psia or 760 torr. Any pressure less than this is considered a vacuum.
The heat treating process takes place inside a vessel that is airtight. The entire heat treating
process can take place under vacuum or precisely controlled atmospheres can be introduced.
Heat treating under vacuum can: prevent surface reactions, such as oxidation or decarburization;
remove surface contaminants such as oxide films and residual traces of lubricants; add a
substance to the surface layers of the work; remove dissolved contaminating substances from
metals by means of degassing.
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 1100–1500°C (2000–2800°F)
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.