Enclosure with very low air pressure used for experiments and testing
A large vacuum chamber.
A small vacuum chamber for studio or lab use in de-airing materials such as mold rubbers and resins.
Vacuum chamber for testing leaks in
packaging
A
vacuum chamber
is a rigid enclosure from which
air
and other
gases
are removed by a
vacuum pump
. This results in a low-
pressure
environment within the chamber, commonly referred to as a
vacuum
. A vacuum environment allows researchers to conduct physical experiments or to test mechanical devices which must operate in
outer space
(for example) or for processes such as
vacuum drying
or
vacuum coating
. Chambers are typically made of metals which may or may not
shield
applied external
magnetic fields
depending on wall thickness,
frequency
,
resistivity
, and
permeability
of the material used. Only
some materials
are suitable for vacuum use.
Chambers often have multiple ports, covered with
vacuum flanges
, to allow instruments or windows to be installed in the walls of the chamber. In low to medium-vacuum applications, these are sealed with
elastomer
o-rings
. In higher vacuum applications, the flanges have knife edges machined onto them, which cut into a copper
gasket
when the flange is bolted on.
A type of vacuum chamber frequently used in the field of
spacecraft
engineering is a
thermal vacuum chamber
, which provides a thermal environment representing what a spacecraft would experience in space.
Vacuum chamber materials
[
edit
]
Vacuum chambers can be constructed of many materials. "Metals are arguably the most prevalent vacuum chamber materials."
[1]
The strength, pressure, and permeability are considerations for selecting chamber material.
Common materials are:
- Stainless Steel
- Aluminum
- Mild Steel
- Brass
- High density ceramic
- Glass
- Acrylic
- Hardened steel
Vacuum degassing
[
edit
]
"Vacuum is the process of using vacuum to remove gases from compounds which become entrapped in the
mixture when mixing the components."
[2]
To assure a bubble-free mold when mixing resin and silicone rubbers and slower-setting harder resins, a vacuum chamber is required. A small vacuum chamber is needed for de-airing (eliminating air bubbles) for materials prior to their setting. The process is fairly straightforward. The casting or molding material is mixed according to the manufacturers directions.
Process
[
edit
]
Since the material may expand 4?5 times under a vacuum, the mixing container must be large enough to hold a volume of four to five times the amount of the original material that is being vacuumed to allow for the expansion; if not, it will spill over the top of the container requiring clean-up that can be avoided. The material container is then placed into the vacuum chamber; a vacuum pump is connected and turned on. Once the vacuum reaches
29 inches
(at sea level) of mercury, the material will begin to rise (resembling
foam
). When the material falls, it will plateau and stop rising. The vacuuming is continued for another 2 to 3 minutes to make certain all of the air has been removed from the material. Once this interval is reached, the vacuum pump is shut off and the vacuum chamber release valve is opened to equalize air pressure. The vacuum chamber is opened, the material is removed and is ready to pour into the mold.
Though a maximum vacuum one can theoretically achieve at sea level is 29.921 inches of mercury (Hg,) this will vary significantly as altitude increases. For example, in
Denver, Colorado
, at one mile (1.6 km) above sea level, it is only possible to achieve a vacuum on the mercury scale of 24.896 Hg.
To keep the material air-free, it must be slowly poured in a high and narrow stream starting from the corner of the mold box, or mold, letting the material flow freely into the box or mold cavity. Usually, this method will not introduce any new bubbles into the vacuumed material. To ensure that the material is totally devoid of air bubbles, the entire mold/mold box may be placed in the chamber for an additional few minutes; this will assist the material in flowing into difficult areas of the mold/mold box.
Vacuum drying
[
edit
]
Water and other liquids may accumulate on a product during the production process. "Vacuum is often employed as a process for removing bulk and absorbed water (or other solvents) from a product. Combined
with heat, vacuum can be an effective method for drying."
[3]
[4]
World's largest vacuum chamber
[
edit
]
NASA
's
Space Power Facility
houses the world's largest vacuum chamber. It was built in 1969 and stands 122 feet (37 m) high and 100 feet (30 m) in diameter, enclosing a
bullet
-shaped space. It was originally commissioned for nuclear-electric power studies under vacuum conditions, but was later decommissioned. Recently, it was recommissioned for use in testing
spacecraft propulsion
systems. Recent uses include testing the airbag landing systems for the
Mars Pathfinder
and the
Mars Exploration Rovers
, Spirit and Opportunity, under simulated Mars atmospheric conditions.
Each arm of the
LIGO
detectors in
Livingston
,
Louisiana
, and
Hanford
,
Washington
, is a vacuum chamber 4 kilometres (2.5 mi) long, making them the longest vacuum chambers in the world.
See also
[
edit
]
References
[
edit
]
- ^
Danielson, PHil.
"Choosing the Right Vacuum Materials"
(PDF)
. The Vacuum Lab. Archived from
the original
(PDF)
on July 24, 2012
. Retrieved
February 10,
2012
.
- ^
"Vacuum Degassing Epoxy & Silicone"
(PDF)
. LACO Technologies, Inc
. Retrieved
February 10,
2012
.
- ^
"Vacuum Drying"
(PDF)
. LACO Technologies, Inc
. Retrieved
February 10,
2012
.
- ^
Danielson, Phil.
"Desorbing Water in Vacuum Systems: Bakeout or UV?"
(PDF)
. The Vacuum Lab. Archived from
the original
(PDF)
on May 16, 2011
. Retrieved
February 10,
2012
.