Vacuum chamber
Overview
 
A vacuum chamber is a rigid enclosure from which air and other gases are removed by a vacuum pump
Vacuum pump
A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke.- Types :Pumps can be broadly categorized according to three techniques:...

. The resulting low pressure, commonly referred to as 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...

, allows researchers to conduct physical experiments or to test mechanical devices which must operate in outer space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....

 (for example). Chambers are typically made of metals which may or may not shield applied external magnetic fields depending on wall thickness, frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

, resistivity
Resistivity
Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. The SI unit of electrical resistivity is the ohm metre...

, and permeability
Permeation
Permeation, in physics and engineering, is the penetration of a permeate through a solid, and is related to a material's intrinsic permeability...

 of the material used.
Discussions
Encyclopedia
A vacuum chamber is a rigid enclosure from which air and other gases are removed by a vacuum pump
Vacuum pump
A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke.- Types :Pumps can be broadly categorized according to three techniques:...

. The resulting low pressure, commonly referred to as 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...

, allows researchers to conduct physical experiments or to test mechanical devices which must operate in outer space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....

 (for example). Chambers are typically made of metals which may or may not shield applied external magnetic fields depending on wall thickness, frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

, resistivity
Resistivity
Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. The SI unit of electrical resistivity is the ohm metre...

, and permeability
Permeation
Permeation, in physics and engineering, is the penetration of a permeate through a solid, and is related to a material's intrinsic permeability...

 of the material used. Only some materials
Materials for use in vacuum
Materials for use in vacuum are materials showing very low rate of outgassing in vacuum, and, where applicable, tolerant to the bake-out temperatures. The requirements grow increasingly stringent with the desired degree of vacuum achievable in the vacuum chamber.The materials can produce gas by...

 are suitable for vacuum use.

Chambers often have multiple ports, covered with vacuum flange
Vacuum flange
A vacuum flange is a flange at the end of a tube used to connect vacuum chambers, tubing and vacuum pumps to each other.-Vacuum flange types:...

s, 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
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...

 o-ring
O-ring
An O-ring, also known as a packing, or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a disc-shaped cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface.The O-ring...

s. In higher vacuum applications, the flanges have hardened steel knives welded onto them, which cut into a copper gasket
Gasket
thumb|sright|250px|Some seals and gaskets1. [[o-ring]]2. fiber [[Washer |washer]]3. paper gaskets4. [[cylinder head]] [[head gasket|gasket]]...

 when the flange is bolted on.

A type of vacuum chamber frequently used in the field of spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

 engineering is a Thermal Vacuum Chamber
Thermal vacuum chamber
A thermal vacuum chamber is a vacuum chamber in which the radiative thermal environment is controlled.Typically the thermal environment is achieved by passing liquids or fluids through thermal shrouds for cold temperatures or through the application of thermal lamps for high temperatures.Thermal...

, which provides a thermal environment representing what a spacecraft would experience in space.

Degassing Mold Making and Casting Materials

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 straight forward. The casting or molding material is mixed according to the manufacturers directions.

The Process

Since the material will expand 4-5 times under a vacuum, the mixing container must be large enough to hold a volume of four-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
Foam
-Definition:A foam is a substance that is formed by trapping gas in a liquid or solid in a divided form, i.e. by forming gas regions inside liquid regions, leading to different kinds of dispersed media...

). When the material falls it will plateau and not rise any more. The vacuuming is continued for another 2-3-minute 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 and the material is removed and ready to pour into the mold.

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 to flow freely into the box or mold cavity. This method will usually not introduce any new bubbles into the vacuumed material. To insure that the material is totally devoid of air bubbles you can place the entire mold/mold box into the chamber for an additional few minutes. This will assist the material to flow into difficult areas of the mold/mold box.

High Altitude Vacuuming

Though a vacuum of 29-inches of mercury is desired for de-airing most mold making and casting materials, it cannot be achieved at higher elevations. It is a sea level target. For example, in Denver (The mile-high city) only about 24-inches of mercury can be achieved even with the most efficient vacuum pump. In those instances, vacuuming will be required for a longer period to achieve proper de-gassing.

See also

  • Bell jar
    Bell jar
    A bell jar is a piece of laboratory equipment used for creating vacuums.http://www.belljar.net/about.htm It can be similar in shape to a bell, and can be manufactured out of a variety of materials . A bell jar is placed on a base which is vented to a hose fitting, which can be connected via a hose...

  • Optical window
    Optical window
    The meaning of this term depends on the context:* In astronomy, the optical window is the optical portion of the electromagnetic spectrum that passes through the atmosphere all the way to the ground...

  • Thermal Vacuum Chamber
    Thermal vacuum chamber
    A thermal vacuum chamber is a vacuum chamber in which the radiative thermal environment is controlled.Typically the thermal environment is achieved by passing liquids or fluids through thermal shrouds for cold temperatures or through the application of thermal lamps for high temperatures.Thermal...

  • Vacuum engineering
    Vacuum engineering
    Vacuum engineering deals with technological processes and equipment that use vacuum to achieve better results than those run under atmospheric pressure...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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