Vacuum furnace
Encyclopedia
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:
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.
alloys. Many general heat treating applications involve the hardening and tempering of a steel part to make it strong and tough through service. Hardening involves heating the steel to a pre-determined temperature, then cooling it rapidly.
Vacuum furnaces are ideal for brazing
applications. Brazing is another heat-treating process used to join two or more base metal components by melting a thin layer of filler metal in the space between them.
A further application for vacuum furnaces is Vacuum Carburizing, also known as Low Pressure Carburizing or LPC. In this process, a gas (such as acetylene) is introduced as a partial pressure into the hot zone at temperatures typically between 1600F and 1950F. The gas disassociates into its constituent molecules (in this case carbon and hydrogen). The carbon is then diffused into the surface area of the part. This function is typically repeated, varying the duration of gas input and diffusion time. Once the workload is properly "cased", quench is induced typically using oil or high pressure gas (HPGQ) typically, nitrogen or for faster quench helium.
This process is also known as case hardening.
Furnace
A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...
that can heat materials, typically metals, to very high temperatures and carry out processes such as brazing
Brazing
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...
, sintering
Sintering
Sintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature...
and heat treatment
Heat treatment
Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass...
with high consistency and low contamination.
In a vacuum furnace the product in the furnace is surrounded by a vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
. The absence of air or other gases prevents heat transfer with the product through convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
and removes a source of contamination. Some of the benefits of a vacuum furnace are:
- Uniform temperatures in the range 1100–1500°CCelsiusCelsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
(2000–2800°FFahrenheitFahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...
) - Temperature can be controlled within a small area
- Low contamination of the product by carbon, oxygenOxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
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
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
, such as Argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
, 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
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
to remove heat. This process is repeated until the desired temperature is reached.
Common uses
A common use of a vacuum furnace is for the heat treatment of steelSteel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
alloys. Many general heat treating applications involve the hardening and tempering of a steel part to make it strong and tough through service. Hardening involves heating the steel to a pre-determined temperature, then cooling it rapidly.
Vacuum furnaces are ideal for brazing
Brazing
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...
applications. Brazing is another heat-treating process used to join two or more base metal components by melting a thin layer of filler metal in the space between them.
A further application for vacuum furnaces is Vacuum Carburizing, also known as Low Pressure Carburizing or LPC. In this process, a gas (such as acetylene) is introduced as a partial pressure into the hot zone at temperatures typically between 1600F and 1950F. The gas disassociates into its constituent molecules (in this case carbon and hydrogen). The carbon is then diffused into the surface area of the part. This function is typically repeated, varying the duration of gas input and diffusion time. Once the workload is properly "cased", quench is induced typically using oil or high pressure gas (HPGQ) typically, nitrogen or for faster quench helium.
This process is also known as case hardening.