cryogenic seal

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.[http://dmrcryogenics.com/aboutus.aspx Some Cryogenic History] {{webarchive|url=https://web.archive.org/web/20111125063809/http://dmrcryogenics.com/aboutus.aspx |date=2011-11-25 }}

Applications which utilize cryogenic seals include:[http://www.statebourne.com/cryogenic_applications.html Applications for Stored Liquefied Cryogenic Gases] {{webarchive|url=https://web.archive.org/web/20111102170803/http://www.statebourne.com/cryogenic_applications.html |date=2011-11-02 }}

• Magnetic resonance imaging (MRI)
• Chromatography
• Dilution Refrigeration Units
• Cooled Detectors
• Optical Windows
• Infrared Detectors
• Centrifugal Cryogenic Pumps
• Unmanned Aerial Vehicle Systems
• Missile Warning Receivers
• Satellite Tracking Systems
• Infrared Telescopes

Advantages of indium cryogenic seals:

• Established/proven design techniques for indium seal assembly[http://www.chemistry.nmsu.edu/Instrumentation/G200_Vserv.html Vacuum Service for a Gemini 200 NMR] {{webarchive|url=https://web.archive.org/web/20110928103351/http://www.chemistry.nmsu.edu/Instrumentation/G200_Vserv.html |date=2011-09-28 }}[http://lennon.astro.northwestern.edu/DesIssue/SPindium.html Indium and Vacuum Seals]
• Option for disassembly and re-assembly
• Indium can be reformed into useful seals after use
• 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[http://blogs.indium.com/blog/carol-gowans/indium-wire-and-cryogenic-sealing Indium Wire and Cryogenic Sealing]
• Seal integrity remains following thermal shock from room temperature to immersion in cryogenic bath[http://plosjournal.deepdyve.com/lp/spie/compact-indium-seal-for-cryogenic-optical-windows-S73S61i0R1 Compact indium seal for cryogenic optical windows]
• Seal quality is independent of the mating surface composition, for instance ceramic, germanium, metal, or glass.[http://www.mtm-inc.com/reduce_project_risk/demountable_cryogenic_seal_options/ Demountable Cryogenic Seal Options]
• 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.{{Cite web |url=http://www.indium.com/_dynamo/download.php?docid=15 |title=Indium for Sealing |access-date=2011-08-29 |archive-date=2011-09-25 |archive-url=https://web.archive.org/web/20110925200411/http://www.indium.com/_dynamo/download.php?docid=15 |url-status=dead }}

In spite of their advantage, indium cryogenic seals have a few disadvantages:

bulky mechanical structures are required to compress indium between the flanges,

and pulsating loads cause creep of indium seals which loosens the bolt tension and thereby reducing the quality of the seal.

Clean, oxide-free indium will cold weld to itself. The mating ends of a wire seal will weld together under compression.{{Cite web |url=http://www.indium.com/_dynamo/download.php?docid=466 |title=Indium Cold Welding |access-date=2011-08-29 |archive-date=2011-09-29 |archive-url=https://web.archive.org/web/20110929034720/http://www.indium.com/_dynamo/download.php?docid=466 |url-status=dead }}

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.

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.{{cite journal| doi=10.1016/S0042-207X(79)80644-2 | bibcode=1979Vacuu..29..231N | volume=29 | issue=6–7 | title=Pressure-made soft-metal vacuum seals for glass and ceramics | year=1979 | journal=Vacuum | pages=231–235 | last1 = Neuhauser | first1 = Robert G}}

Using vacuum-cast materials for indium cryogenic seals can prevent outgassing.

• Helium leak tests
• Cryogenic temperature shock testing

• 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

{{Reflist}}

• [http://www.indium.com/_dynamo/download.php?docid=358 Physical Constants of Pure Indium] {{Webarchive|url=https://web.archive.org/web/20110925201445/http://www.indium.com/_dynamo/download.php?docid=358 |date=2011-09-25 }}
• [http://www.sciencedirect.com/science/article/pii/S0011227509001532 A reusable, low-profile, cryogenic wire seal]
• [http://blogs.indium.com/blog/amanda-hartnett/corrosion-of-indium-base-solders Corrosion of Indium-Base Solders]
• [http://blogs.indium.com/blog/amanda-hartnett/indium-compressed-into-hermetic-seals- Indium Compressed into Hermetic Seals]
• [http://groups.physics.umn.edu/zudovlab/manuals/cryogenics/HelioxTL_Generic_Manual.pdf HelioxTL System Operator's Handbook - Generic System Manual]
• [http://www.cryogenicsociety.org/ Cryogenic Society of America, Inc.]
• [http://www.cmr-direct.com/how-to-make-indium-seals VIDEO showing how to make an indium seal on a cryogenic system]

Category:Cryogenics