Cryogenic seal

Cryogenic seal

Cryogenic seals provide a mechanical containment mechanism for materials held at cryogenic temperatures, such as cryogenic fluids. Various techniques, including soldering and welding are available for creating seals, however specialized materials and processes are necessary to hermetically entrap cryogenic constituents under vacuum-tight conditions. Most commonly used are liquid helium and liquid nitrogen, which boil at very low temperatures, below −153 °C (120 K), as well as hydrocarbons with low freezing points and refrigerating mixtures.[1] [2] Pure indium wire or solder preform washers are accepted as the most reliable low temperature sealing materials. When correctly formed, indium will afford leak rates of less than 4.0x10 -9 mbar- liter/sec.[3] Alternative cryogenic seal materials include silicone grease conical seals, and Pb/Sn (lead-tin) wire seals.[4]

Contents

Applications

Applications which utilize cryogenic seals include:[5]

Advantages

Advantages of indium cryogenic seals:

  • Established/proven design techniques for indium seal assembly[6] [7]
  • Option for disassembly and re-assembly[3]
  • Indium can be reformed into useful seals after use[7]
  • Soft and pliable at room temperature, due to the low melting temperature of indium, so it fills imperfections. This creates an impervious bond between the mating surfaces, crafting a hermetic seal which remains malleable at cryogenic temperatures[1]
  • Seal integrity remains following thermal shock from room temperature to immersion in cryogenic bath[8]
  • Seal quality is independent of the mating surface composition, for instance ceramic, germanium, metal, or glass.[9]
  • Indium forms a self-passivating oxide layer, 80-100Ǻ thick. This layer is easy to remove with an acid etch, and the underlying, exposed indium metal can be compressed to form a tight, hermetic bond.[10]

Disadvantages

  • Bulky mechanical structure required to compress indium between the flanges.[8]
  • Pulsating loads cause creep of indium seals, which loosens the bolt tension, thereby reducing the quality of the seal.[3]

Process information for indium seals

  • Mating surfaces should be kept as clean as possible, and may be cleaned using acetone.[8]
  • Clean, oxide-free indium will cold weld to itself. The mating ends of a wire seal will weld together under compression.[11]
  • A more reliable alternative to a seal made from indium wire is a seal that uses an indium washer. Washers minimize the risk of seal degradation and cryogenic leaks by eliminating the interface between connected butt ends of wire. Washers are manufactured as a continuous ring with no breaks.[8]
  • As many fasteners as possible should be used to clamp the indium seal.[8]
  • Indium material used must be ultra-pure (99.9 minimum purity) to prevent hardening of the material at sub-zero temperatures, as well as to restrict impurities of elements with low vapor-pressure.[12]
  • Material used for indium cryogenic seals should be manufactured from vacuum-cast material to prevent outgassing after fixturing in the assembly.

Reliability testing

  • Helium leak tests[3]
  • Cryogenic temperature shock testing[8]

Types

  • Compact indium seal
  • Compressible hermetic seal
  • Compression seal
  • Cryogenic vacuum seal
  • Demountable cryogenic seal
  • Indium cryogenic vacuum seal
  • Indium o-ring flange seals
  • Indium seal
  • Indium wire o-ring
  • Indium wire seal
  • Low profile indium seal
  • Low temperature seal
  • Reusable cryogenic vacuum seal
  • Reusable indium wire seal
  • Reusable, low-profile, cryogenic wire seal
  • Soft metal seal
  • Vacuum compatible seal
  • Vacuum compatible seal at cryogenic temperature
  • Corner joint seal
  • Face joint seal

History

Fundamental cryogenic processing began in the 1940s, albeit primitive. Steel cutting tools were immersed in liquid nitrogen to enhance their service life.

Mechanical processes utilizing cryogenics were documented well in the 1950s and by the 1980s cryogenic fluids began to be considered for storage and use in modern devices.

Today, cryogenic seals are a necessity in high-tech commercial, medical, and military applications to encapsulate the cryogenic fluids critical for device resolution and function.[13]

Manufacturers

Indium Corporation
Garlock Helicoflex
AIM
ESPI Metals
Sealwise
Kapton®
Mylar®
Indium Wire Extrusion

External links

Physical Constants of Pure Indium
A reusable, low-profile, cryogenic wire seal
Corrosion of Indium-Base Solders
Indium Compressed into Hermetic Seals
HelioxTL System Operator's Handbook - Generic System Manual
Cryogenic Society of America, Inc.

References


Wikimedia Foundation. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • Cryogenic nitrogen plant — Nitrogen, as an element of great technical importance, can be produced in a cryogenic nitrogen plant with a purity of more than 99.9999%. Air inside a distillation column is separated at cryogenic temperatures (about 100K/ 173°C) to produce high… …   Wikipedia

  • List of Bobobo-bo Bo-bobo characters — The universe of the anime and manga series Bobobo bo Bo bobo is a home to a wide array of fictional characters. Contents 1 Main characters 1.1 Bobobo bo Bo bobo 1.2 Beauty 1.3 …   Wikipedia

  • Rebreather — A fully closed circuit electronic rebreather (Ambient Pressure Diving Inspiration) Acronym CCUBA (Closed Circuit Underwater Breathing Apparatus); CCR (Closed circuit rebreather), SCR (Semi closed rebreather) Uses Breathing set …   Wikipedia

  • Valve — This article is about the flow control device. For the game developer, see Valve Corporation. For the electronic component, see Vacuum tube. For other uses, see Valve (disambiguation). These water valves are operated by handles. A valve is a… …   Wikipedia

  • Liquefied natural gas — Not to be confused with Natural Gas Liquids (NGL). Liquefied natural gas or LNG is natural gas (primarily methane, CH4) that has been converted to liquid form for ease of storage or transport. Liquefied natural gas takes up about 1/600th the… …   Wikipedia

  • Staged combustion cycle (rocket) — Staged combustion rocket cycle. Usually, all of the fuel and a portion of the oxidizer are fed through the pre burner (fuel rich) to power the pumps. An oxygen rich circuit is possible also, but less common because of the metallurgy required. The …   Wikipedia

  • India — /in dee euh/, n. 1. Hindi, Bharat. a republic in S Asia: a union comprising 25 states and 7 union territories; formerly a British colony; gained independence Aug. 15, 1947; became a republic within the Commonwealth of Nations Jan. 26, 1950.… …   Universalium

  • food preservation — Any method by which food is protected against spoilage by oxidation, bacteria, molds, and microorganisms. Traditional methods include dehydration, smoking, salting, controlled fermentation (including pickling), and candying; certain spices have… …   Universalium

  • Vacuum flask — Thermos redirects here. For other uses, see Thermos (disambiguation). This article is about the vacuum insulated flask. For the flask used in filtration under vacuum, see Büchner flask. Domestic vacuum flask, used for maintaining the temperature… …   Wikipedia

  • Former Maruhage Empire villains — This is a list of villains in the anime/manga, Bobobo bo Bo bobo, that are from the Maruhage Empire of 100 yrs. ago.BackgroundOne century before the start of the series, the Maruhage Empire was one of many countries on planet Earth: a small… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”