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 round 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 may be used in static applications or in dynamic applications where there is relative motion between the parts and the O-ring. Dynamic examples include rotating pump shafts and hydraulic cylinder pistons. Static applications of O-rings may include fluid or gas sealing applications in which: (1) the O-ring is compressed resulting in zero clearance, (2) the O-ring material is vulcanized solid such that it is impermeable to the fluid or gas, and (3) the O-ring material is resistant to degradation by the fluid or gas.[1]

O-rings are one of the most common seals used in machine design because they are inexpensive, easy to make, reliable and have simple mounting requirements. They have been tested to seal up to 5000 psi (35 megapascals) of pressure.[2] The maximum recommended pressure of an O-ring seal depends on the seal hardness and gland clearance.[3]

O ring
Typical O-ring and application

Manufacturing

O-rings can be produced by extrusion, injection molding, pressure molding or transfer molding.[4]

History

The first patent for the O-ring, is dated May 12, 1896 as a Swedish patent. J. O. Lundberg, the inventor of the O-ring, received the patent.[5] The US patent[6] for the O-ring was filed in 1937 by a then 72-year-old Danish-born machinist, Niels Christensen.[7] Soon after migrating to the United States in 1891, he patented an air brake system for streetcars (trams). Despite his legal efforts, his intellectual property rights were passed from company to company until they ended up at Westinghouse.[7] During World War II, the US government commandeered the O-ring patent as a critical war-related item and gave the right to manufacture to other organizations. Christensen received a lump sum payment of US$75,000 for his efforts. Litigation resulted in a $100,000 payment to his heirs in 1971, 19 years after his death.[8]

Theory and design

O-ring
O-ring mounting for an ultra-high vacuum application. Pressure distribution within the cross-section of the O-ring. The orange lines are hard surfaces, which apply high pressure. The fluid in the seams has lower pressure. The soft O-ring bridges the pressure over the seams.

O-rings are available in various metric and inch standard sizes. Sizes are specified by the inside diameter and the cross section diameter (thickness). In the US the most common standard inch sizes are per SAE AS568C specification (e.g. AS568-214). ISO 3601-1:2012 contains the most commonly used standard sizes, both inch and metric, worldwide. The UK also has standards sizes known as BS sizes, typically ranging from BS001 to BS932. Several other size specifications also exist.

Typical applications

Successful O-ring joint design requires a rigid mechanical mounting that applies a predictable deformation to the O-ring. This introduces a calculated mechanical stress at the O-ring contacting surfaces. As long as the pressure of the fluid being contained does not exceed the contact stress of the O-ring, leaking cannot occur. The pressure of the contained fluid transfers through the essentially incompressible O-ring material, and the contact stress rises with increasing pressure. For this reason, an O-ring can easily seal high pressure as long as it does not fail mechanically. The most common failure is extrusion through the mating parts.

The seal is designed to have a point contact between the O-ring and sealing faces. This allows a high local stress, able to contain high pressure, without exceeding the yield stress of the O-ring body. The flexible nature of O-ring materials accommodates imperfections in the mounting parts. But it is still important to maintain good surface finish of those mating parts, especially at low temperatures where the seal rubber reaches its glass transition temperature and becomes increasingly crystalline. Surface finish is also especially important in dynamic applications. A surface finish that is too rough will abrade the surface of the O-ring, and a surface that is too smooth will not allow the seal to be adequately lubricated by a fluid film.

Vacuum applications

In vacuum applications, the permeability of the material makes point contacts quite useless. Instead, higher mounting forces are used and the ring fills the whole groove. Also, round back-up rings are used to save the ring from excessive deformation [9][10][11] Because the ring feels the ambient pressure and the partial pressure of gases only at the seal, their gradients will be steep near the seal and shallow in the bulk (opposite to the gradient of the contact stress [12] See: Vacuum flange#KF.2FQF. High-vacuum systems below 10−9 Torr use copper or nickel O-rings. Also, vacuum systems that have to be immersed in liquid nitrogen use indium O-rings, because rubber becomes hard and brittle at low temperatures.

High temperature applications

In some high-temperature applications, O-rings may need to be mounted in a tangentially compressed state, to compensate for the Gow-Joule effect.

Sizes

O-rings come in a variety of sizes. Society of Automotive Engineers (SAE) Aerospace Standard 568 (AS568)[13] specifies the inside diameters, cross-sections, tolerances, and size identification codes (dash numbers) for O-rings used in sealing applications and for straight thread tube fitting boss gaskets. British Standard (BS) which are imperial sizes or metric sizes. Typical dimensions of an O-ring are internal dimension (id), outer dimension (od) and thickness / cross section (cs)

Metric O-rings are usually defined by the internal dimension x the cross section. Typical part number for a metric O-ring - ID x CS [material & shore hardness] 2x1N70 = defines this O-ring as 2mm id with 1mm cross section made from Nitrile rubber which is 70Sh

BS O-rings are defined by a standard reference.

Material

O-rings
Some small O-rings

O-ring selection is based on chemical compatibility, application temperature, sealing pressure, lubrication requirements, durometer, size and cost.[14]

Synthetic rubbers - Thermosets:

  • Butadiene rubber (BR)
  • Butyl rubber (IIR)
  • Chlorosulfonated polyethylene (CSM)
  • Epichlorohydrin rubber(ECH, ECO)
  • Ethylene propylene diene monomer (EPDM): good resistance to hot water and steam, detergents, caustic potash solutions, sodium hydroxide solutions, silicone oils and greases, many polar solvents and many diluted acids and chemicals. Special formulations are excellent for use with glycol-based brake fluids. Unsuitable for use with mineral oil products: lubricants, oils, or fuels. Peroxide-cured compounds are suitable for higher temperatures.[15]
  • Ethylene propylene rubber (EPR)
  • Fluoroelastomer (FKM): noted for their very high resistance to heat and a wide variety of chemicals. Other key benefits include excellent resistance to aging and ozone, very low gas permeability and the fact that the materials are self-extinguishing. Standard FKM materials have excellent resistance to mineral oils and greases, aliphatic, aromatic and chlorinated hydrocarbons, fuels, non-flammable hydraulic fluids (HFD) and many organic solvents and chemicals. Generally not resistant to hot water, steam, polar solvents, glycol-based brake fluids and low molecular weight organic acids. In addition to the standard FKM materials, a number of specialty materials with different monomer compositions and fluorine content (65% to 71%) are available that offer improved chemical or temperature resistance and/or better low temperature performance.[15]
  • Nitrile rubber (NBR, HNBR, HSN, Buna-N): a common material for o-rings because of its good mechanical properties, its resistance to lubricants and greases, and its relatively low cost. The physical and chemical resistance properties of NBR materials are determined by the acrylonitrile (ACN) content of the base polymer: low content ensures good flexibility at low temperatures, but offers limited resistance to oils and fuels. As the ACN content increases, the low temperature flexibility reduces and the resistance to oils and fuels improves. Physical and chemical resistance properties of NBR materials are also affected by the cure system of the polymer. Peroxide-cured materials have improved physical properties, chemical resistance and thermal properties, as compared to sulfur-donor-cured materials. Standard grades of NBR are typically resistant to mineral oil-based lubricants and greases, many grades of hydraulic fluids, aliphatic hydrocarbons, silicone oils and greases and water to about 80 °C. NBR is generally not resistant to aromatic and chlorinated hydrocarbons, fuels with a high aromatic content, polar solvents, glycol-based brake fluids and non-flammable hydraulic fluids (HFD). NBR also has low resistance to ozone, weathering and aging. HNBR has considerable improvement of the resistance to heat, ozone and aging, and gives it good mechanical properties.[15]
  • Perfluoroelastomer (FFKM)
  • Polyacrylate rubber (ACM)
  • Polychloroprene (neoprene) (CR)
  • Polyisoprene (IR)
  • Polysulfide rubber (PSR)
  • Polytetrafluoroethylene (PTFE)
  • Sanifluor (FEPM)
  • Silicone rubber (SiR): noted for their ability to be used over a wide temperature range and for excellent resistance to ozone, weathering and aging. Compared with most other sealing elastomers, the physical properties of silicones are poor. Generally, silicone materials are physiologically harmless so they are commonly used by the food and drug industries. Standard silicones are resistant to water (to 100 °C), aliphatic engine and transmission oils and animal and plant oils and fats. Silicones are generally not resistant to fuels, aromatic mineral oils, steam (short term to 120 °C is possible), silicone oils and greases, acids or alkalis. Fluorosilicone elastomers are far more resistant to oils and fuels. The temperature range of applications is somewhat more restricted.[15]
  • Styrene-butadiene rubber (SBR)

Thermoplastics:

  • Thermoplastic elastomer (TPE) styrenics
  • Thermoplastic polyolefin (TPO) LDPE, HDPE, LLDPE, ULDPE
  • Thermoplastic polyurethane (TPU) polyether, polyester: Polyurethanes differ from classic elastomers in that they have much better mechanical properties. In particular they have a high resistance to abrasion, wear and extrusion, a high tensile strength and excellent tear resistance. Polyurethanes are generally resistant to aging and ozone, mineral oils and greases, silicone oils and greases, nonflammable hydraulic fluids HFA & HFB, water up to 50 °C and aliphatic hydrocarbons.[15]
  • Thermoplastic etheresterelastomers (TEEEs) copolyesters
  • Thermoplastic polyamide (PEBA) Polyamides
  • Melt Processible Rubber (MPR)
  • Thermoplastic Vulcanizate (TPV)

Chemical Compatibility:

  • Air, 200 - 300 °F – Silicone
  • Beer - EPDM
  • Chlorine Water – Viton (FKM)
  • Gasoline – Buna-N or Viton (FKM)
  • Hydraulic Oil (Petroleum Base, Industrial) – Buna-N
  • Hydraulic Oils (Synthetic Base) – Viton
  • Water – EPDM
  • Motor Oils – Buna-N

[16]

Other seals

Orings Xrings
O-ring and other sealing profiles

For sealings, there are variations in cross-section design other than circular. The shape can have different profiles, an x-shaped profile, commonly called the X-ring, Q-ring, or by the trademarked name Quad Ring. When squeezed upon installation, they seal with 4 contact surfaces—2 small contact surfaces on the top and bottom. This contrasts with the standard O-ring's comparatively larger single contact surfaces top and bottom. X-rings are most commonly used in reciprocating applications, where they provide reduced running and breakout friction and reduced risk of spiraling when compared to O-rings.

There are also rings with a square profile, commonly called square-cuts, lathe cuts,tabular cut or Square rings. When O-rings were selling at a premium because of the novelty, lack of efficient manufacturing processes and high labor content, Square rings were introduced as an economical substitution for O-rings. The square ring is typically manufactured by molding an elastomer sleeve which is then lathe-cut. This style of seal is sometimes less expensive to manufacture with certain materials and molding technologies (compression molding, transfer molding, injection molding), especially in low volumes. The physical sealing performance of square rings in static applications is superior to that of O-rings, however in dynamic applications it is inferior to that of O-rings. Square rings are usually used only in dynamic applications as energizers in cap seal assemblies. Square rings can also be more difficult to install than O-rings.

Similar devices with a non-round cross-sections are called seals, packings or gaskets. See also washers.[17]

Automotive cylinder heads are typically sealed by flat gaskets faced with copper.

Knife edges pressed into copper gaskets are used for high vacuum.

Elastomers or soft metals that solidify in place are used as seals.

Failure modes

O-ring materials may be subjected to high or low temperatures, chemical attack, vibration, abrasion, and movement. Elastomers are selected according to the situation.

There are O-ring materials which can tolerate temperatures as low as -200 C or as high as 250+ C. At the low end, nearly all engineering materials become rigid and fail to seal; at the high end, the materials often burn or decompose. Chemical attack can degrade the material, start brittle cracks or cause it to swell. For example, NBR seals can crack when exposed to ozone gas at very low concentrations, unless protected. Swelling by contact with a low viscosity fluid causes an increase in dimensions, and also lowers the tensile strength of the rubber. Other failures can be caused by using the wrong size of ring for a specific recess, which may cause extrusion of the rubber.

Elastomers are sensitive to ionizing radiation. In typical applications, O-rings are well protected from less penetrating radiation such as ultraviolet and soft X-rays, but more penetrating radiation such as neutrons may cause rapid deterioration. In such environments, soft metal seals are used.

There are a few common reasons for O-Ring Failure:

1. Installation Damage – This is caused by improper installation of the O-ring.

2. Spiral Failure – Found on long-stroke piston seals and – to a lesser degree – on rod seals. The seal gets “hung up” at one point on its diameter (against the cylinder wall) and slides and rolls at the same time. This twists the O-ring as the sealed device is cycled and finally causes a series of deep spiral cuts (typically at a 45 degree angle) on the surface of the seal.

3. Explosive Decompression - An O-ring embolism, also called gas expansion rupture, occurs when high pressure gas becomes trapped inside the elastomeric seal element. This expansion causes blisters and ruptures on the surface of the seal.

Challenger disaster

The failure of an O-ring seal was determined to be the cause of the Space Shuttle Challenger disaster on January 28, 1986. A crucial factor was cold weather prior to the launch. This was famously demonstrated on television by Caltech physics professor Richard Feynman, when he placed a small O-ring into ice-cold water, and subsequently showed its loss of flexibility before an investigative committee.

The material of the failed O-ring was FKM, which was specified by the shuttle motor contractor, Morton-Thiokol. When an O-ring is cooled below its Tg (glass transition temperature), it loses its elasticity and becomes brittle. More importantly, when an O-ring is cooled near, but not beyond, its Tg, the cold O-ring, once compressed, will take longer than normal to return to its original shape. O-rings (and all other seals) work by creating positive pressure against a surface thereby preventing leaks. On the night before the launch, exceedingly low air temperatures were recorded. On account of this, NASA technicians performed an inspection. The ambient temperature was within launch parameters, and the launch sequence was allowed to proceed. However, the temperature of the rubber O-rings remained significantly lower than that of the surrounding air. During his investigation of the launch footage, Feynman observed a small out-gassing event from the Solid Rocket Booster (SRB) at the joint between two segments in the moments immediately preceding the disaster. This was blamed on a failed O-ring seal. The escaping high temperature gas impinged upon the external tank, and the entire vehicle was destroyed as a result.

The rubber industry has gone through its share of transformation after the accident. Many O-rings now come with batch and cure date coding, as in the medicine industry, to precisely track and control distribution. For aerospace and military/defense applications, O-rings are usually individually packaged and labeled with the material, cure date, and batch information. O-rings can, if needed, be recalled off the shelf.[18] Furthermore, O-rings and other seals are routinely batch-tested for quality control by the manufacturers, and often undergo Q/A several more times by the distributor and ultimate end users.

As for the SRBs themselves, NASA and Morton-Thiokol redesigned them with a new joint design, which now incorporated three O-rings instead of two, with the joints themselves having onboard heaters that can be turned on when temperatures drop below 50 °F (10 °C). No O-ring issues have occurred since Challenger, and they did not play a role in the Space Shuttle Columbia disaster of 2003.

Future

An O-ring is one of the simplest, yet highly critical, precision mechanical components ever developed. But, there are new advances that may take some of the burden of critical sealing away from the O-ring. There are cottage industries of elastomer consultants assisting in designing O-ring-less pressure vessels. Nano-technology-rubber is one such new frontier. Presently, these advancements are increasing the importance of O-rings. Since O-rings encompass the areas of chemistry and material science, any advancement in nano-rubber will affect the O-ring industry.

Already, there are elastomers filled with nano-carbon and nano-PTFE and molded into O-rings used in high-performance applications. For example, carbon nanotubes are used in electrostatic dissipative applications and nano-PTFE is used in ultra pure semiconductor applications. The use of nano-PTFE in fluoroelastomers and perfluoroelastomers improves abrasion resistance, lowers friction, lowers permeation, and can act as clean filler.

Using conductive carbon black or other fillers can exhibit the useful properties of conductive rubber, namely preventing electrical arcing, static sparks, and the overall build-up of charge within rubber that may cause it to behave like a capacitor (electrostatic dissipative). By dissipating these charges, these materials, which include doped carbon-black and rubber with metal filling additives, reduce the risk of ignition, which can be useful for fuel lines.

Standards

ISO 3601 Fluid power systems — O-rings

See also

References

  1. ^ Whitlock, Jerry (2004). "The Seal Man's O-Ring Handbook" (PDF). EPM, Inc. - The Seal Man.
  2. ^ Pearl, D.R. (January 1947). "O-Ring Seals in the Design of Hydraulic Mechanisms". S.A.E. Annual Meeting. Hamilton Standard Prop. Div. of United Aircraft Corp.
  3. ^ "Frequently Asked O-ring Technical Questions". Parker O-Ring & Engineered Seals Division. Retrieved December 7, 2018.
  4. ^ http://www.oringsusa.com/html/factory_tour.html
  5. ^ "O-Ring - Who Invented the O-Ring?". Inventors.about.com. 2010-06-15. Archived from the original on 2009-03-15. Retrieved 2011-03-25.
  6. ^ US patent 2180795, Niels A. Christensen, issued 1939-11-21
  7. ^ a b "No. 555: O-Ring". Uh.edu. 2004-08-01. Retrieved 2011-03-25.
  8. ^ "Sealing system eliminates O-rings: News from John Crane". Engineeringtalk.com. 2001-07-16. Retrieved 2011-03-25.
  9. ^ http://n-c.com/Page.asp?NavID=397
  10. ^ "MDC Vacuum Products-Vacuum Components, Chambers, Valves, Flanges & Fittings". Mdc-vacuum.com. Retrieved 2011-03-25.
  11. ^ "O-ring". Glossary.oilfield.slb.com. Retrieved 2011-03-25.
  12. ^ http://www.dhcae.com/FEA.htm).
  13. ^ "AS568: Aerospace Size Standard for O-Rings - SAE International". www.sae.org. Retrieved 2018-02-20.
  14. ^ "O-ring Design, O-ring Design Guide, O-ring Seal Design -Mykin Inc". Mykin.com. Retrieved 2011-03-25.
  15. ^ a b c d e "Type details". O-ring elastomer. Dichtomatik Americas. 2012. Retrieved 9 April 2013.
  16. ^ "Chemical Compatibility". The O-Ring Store LLC.
  17. ^ "John Crane seals measure up to API standards: News from John Crane EAA". Processingtalk.com. 2005-12-09. Retrieved 2011-03-25.
  18. ^ "What is O-Ring Shelf Life?". Oringsusa.com. Retrieved 2011-03-25.

External links

2007 Bombardier Dash 8 landing gear incidents

In September 2007, two separate accidents due to similar landing gear failures occurred within four days of each other on Bombardier Dash 8 Q400 aircraft operated by Scandinavian Airlines (SAS). A third incident, again with a SAS aircraft, occurred in October 2007, leading to the withdrawal of the type from the airline's fleet.

BDORT

The Bi-Digital O-Ring Test (BDORT), characterized as a form of applied kinesiology, is a patented alternative medicine diagnostic procedure in which a patient forms an 'O' with his or her fingers, and the diagnostician subjectively evaluates the patient's health according to the patient's finger strength as the diagnostician tries to pry them apart.BDORT has been cited and characterized at length by the American Institute for Technology and Science Education as a specific and noteworthy example of pseudoscientific quackery.BDORT was invented by Yoshiaki Omura, along with several other related alternative medicine techniques. They are featured in Omura's self-published Acupuncture & Electro-Therapeutics Research, The International Journal, of which Omura is founder and editor-in-chief, as well as in seminars presented by Omura and his colleagues.Omura is registered to practice acupuncture in New York State.In the only known full, formal independent evaluation of BDORT or of any other BDORT-related treatment and technique by a mainstream scientific or medical body, the Medical Practitioners Disciplinary Tribunal of New Zealand ruled, in two separate cases brought before it in 2003, that Richard Warwick Gorringe, MB, ChB of Hamilton, New Zealand, who used BDORT (which he also called "Peak Muscle Resistance Testing", or "PMRT") to the exclusion of conventional diagnoses on his patients, was guilty of malpractice. In the first case, the Tribunal found it "is not a plausible, reliable, or scientific technique for making medical decisions" and "there is no plausible evidence that PMRT has any scientific validity".

In the second case the Tribunal ruled Gorringe again relied on BDORT to the exclusion of traditional diagnoses, which ultimately led to the death of a patient. As a result of these findings and conclusions, Gorringe was fined and stripped of his license to practice medicine.

Buddy breathing

Buddy breathing is a rescue technique used in scuba diving "out of gas" emergencies, when two divers share one demand valve, alternately breathing from it. Techniques have been developed for buddy breathing from both twin-hose and single hose regulators, but to a large extent it has been superseded by safer and more reliable techniques using additional equipment, such as the use of a bailout cylinder or breathing through a secondary demand valve on the rescuer's regulator.

Running out of breathing gas most commonly happens as a result of poor gas management. It can also happen due to unforeseen exertion or breathing equipment failure. Equipment failure resulting in the loss of all gas could be caused by failure of a pressure retaining component such as an O-ring or hose in the regulator or, in cold conditions, a freezing of water in the regulator resulting in a free flow from the demand valve.

Groove (engineering)

In manufacturing or mechanical engineering a groove is a long and narrow indentation built into a material, generally for the purpose of allowing another material or part to move within the groove and be guided by it. Examples include:

A canal cut in a hard material, usually metal. This canal can be round, oval or an arc in order to receive another component such as a boss, a tongue or a gasket. It can also be on the circumference of a dowel, a bolt, an axle or on the outside or inside of a tube or pipe etc. This canal may receive a circlip an o-ring or a gasket.

A depression on the entire circumference of a cast or machined wheel, a pulley or sheave. This depression may receive a cable, a rope or a belt.

A longitudinal channel formed in a hot rolled rail profile such as a grooved rail. This groove is for the flange on a train wheel.

Hydraulic machinery

Hydraulic machines are machinery and tools that use liquid fluid power to do simple work, operated by the use of hydraulics, where a liquid is the powering medium. In heavy equipment and other types of machine, hydraulic fluid is transmitted throughout the machine to various hydraulic motors and hydraulic cylinders and becomes pressurised according to the resistance present. The fluid is controlled directly or automatically by control valves and distributed through hoses and tubes.

The popularity of hydraulic machinery is due to the very large amount of power that can be transferred through small tubes and flexible hoses, and the high power density and wide array of actuators that can make use of this power.

Lineshaft roller conveyor

A lineshaft roller conveyor or line-shaft conveyor is, as its name suggests, powered by a shaft beneath rollers. These conveyors are suitable for light applications up to 50 kg such as cardboard boxes and tote boxes.

A single shaft runs below the rollers running the length of the conveyor. On the shaft are a series of spools, one spool for each roller. An elastic polyurethane o-ring belt runs from a spool on the powered shaft to each roller. When the shaft is powered, the o-ring belt acts as a chain between the spool and the roller making the roller rotate. The rotation of the rollers pushes the product along the conveyor. The shaft is usually driven by an electrical motor that is generally controlled by an electronic PLC (programmable logic controller). The PLC electronically controls how specific sections of the conveyor system interact with the products being conveyed.

Advantages of this conveyor are quiet operation, easy installation, moderate maintenance and low expense. Line-shaft conveyors are also extremely safe for people to work around because the elastic belts can stretch and not injure fingers should any get caught underneath them. Moreover, the spools will slip and allow the rollers to stop moving if clothing, hands or hair gets caught in them. In addition, since the spools are slightly loose on the shaft, they act like clutches that slip when products are required to accumulate (stop moving and bump up against each other. i.e. queue up). With the exception of soft bottomed containers like cement bags, these conveyors can be utilized for almost all applications.

A disadvantage of the roller lineshaft conveyor is that it can only be used to convey products that span at least three rollers, but rollers can be as small as 17mm in diameter and as close together as 18.5mm. For items shorter than 74mm, the conveyor belt system is generally used as an alternative option.

O-ring chain

The o-ring chain is a specialized type of roller chain used in the transmission of mechanical power from one sprocket to another.

O-ring theory of economic development

The O-ring theory of economic development is a model of economic development put forward by Michael Kremer in 1993, which proposes that tasks of production must be executed proficiently together in order for any of them to be of high value. The key feature of this model is positive assortative matching, whereby people with similar skill levels work together.

The name comes from the 1986 Challenger shuttle disaster, a catastrophe caused by the failure of a single O-ring.

Kremer thinks that the O-ring development theory explains why rich countries produce more complicated products, have larger firms and much higher worker productivity than poor countries.

Plug (jewellery)

A plug (sometimes earplug or earspool), in the context of body modification, is a short, cylindrical piece of jewellery commonly worn in larger-gauge body piercings. Modern western plugs are also called flesh tunnels. Because of their size—which is often substantially thicker than a standard metal earring—plugs can be made out of almost any material. Acrylic glass, metal, wood, bone, stone, horn, glass, silicone or porcelain are all potential plug materials.

Plugs are commonly, and have historically, been worn in the ears. They can, however, be inserted into any piercing.

In order for a plug to stay put within a piercing, the ends of its cylindrical shape are often "flared out," or the plug is fastened in place by o-rings. Combinations of these two methods may also be used.

A double-flared (or saddle) plug, flares outward at both ends, and is thinner towards the middle. No o-rings are needed to keep the plug in the piercing, but the fistula needs to be wide enough to accommodate the flare when the plug is initially put in.

A single flared plug has one flared end, usually worn on the front of the piercing, and one end with no flare. The no flare end is held in place by an o-ring and may or may not be grooved. These plugs give the aesthetic of double-flared plugs without requiring that the wearer's fistulas be large enough to accommodate flares.

A straight plug (or no-flare plug) is a typical-looking cylinder, without flares, and is kept in place by sliding o-rings against both ends of the plug. A grooved plug is a variation on the straight plug, with grooves carved in the material to hold the o-rings snug.

Roger Boisjoly

Roger Mark Boisjoly ( boh-zhə-LAY; April 25, 1938 – January 6, 2012) was an American mechanical engineer, fluid dynamicist, and an aerodynamicist. He is best known for having raised strenuous objections to the launch of the Space Shuttle Challenger months before the loss of the spacecraft and its crew in January 1986. Boisjoly correctly predicted, based on earlier flight data, that the O-rings on the rocket boosters would fail if the shuttle launched in cold weather.

Rogers Commission Report

The Rogers Commission Report was created by a Presidential Commission charged with investigating the Space Shuttle Challenger disaster during its 10th mission, STS-51-L. The report, released and submitted to President Ronald Reagan on 9 June 1986, both determined the cause of the disaster that took place 73 seconds after liftoff, and urged NASA to improve and install new safety features on the shuttles and in its organizational handling of future missions.

STS-51-L

STS-51-L was the 25th mission of the United States Space Shuttle program, the program to carry out routine transportation for Earth-to-orbit crew and cargo; as well as the final flight of Space Shuttle Challenger.

Planned as the first Teacher in Space Project in addition to observing Halley's Comet for six days, the mission never flew past orbit; a structural failure during its ascent phase 73 seconds after launch from Kennedy Space Center Launch Complex 39 on January 28, 1986, killed all seven crew members—Commander Dick Scobee, Pilot Michael J. Smith, Mission Specialists Ellison S. Onizuka, Judith A. Resnik and Ronald E. McNair, and Payload Specialists Gregory Jarvis and Christa McAuliffe—and destroyed the orbiter.

Immediately after the disaster, NASA convened the Rogers Commission to determine the cause of the explosion. The failure of an O-ring seal on the starboard Solid Rocket Booster (SRB) was determined to have caused the shuttle to break-up in flight. Space Shuttle flights were suspended for 32 months while the hazards with the shuttle were addressed. The Space Shuttle program resumed with STS-26, launched two years after the accident.

Seal (mechanical)

A mechanical seal is a device that helps join systems or mechanisms together by preventing leakage (e.g. in a plumbing system), containing pressure, or excluding contamination. The effectiveness of a seal is dependent on adhesion in the case of sealants and compression in the case of gaskets.

A stationary seal may also be referred to as 'packing'.

Seal types:

Induction sealing or cap sealing

Adhesive, sealant

Bodok seal, a specialized gas sealing washer for medical applications

Bonded seal, also known as Dowty seal or Dowty washer. A type of washer with integral gasket, widely used to provide a seal at the entry point of a screw or bolt

Bridgman seal, a piston sealing mechanism that creates a high pressure reservoir from a lower pressure source

Bung

Compression seal fitting

Diaphragm seal

Ferrofluidic seal

Gasket or Mechanical packing

Flange gasket

O-ring

O-ring boss seal

Piston ring

Glass-to-metal seal

Glass-ceramic-to-metal seals

Heat seal

Hose coupling, various types of hose couplings

Hermetic seal

Hydrostatic seal

Hydrodynamic seal

Inflatable seal Seals that inflate and deflate in three basic directions of operation: the axial direction, the radial-in direction, and the radial-out direction. Each of these inflation directions has their own set of performance parameters for measurements such as the height of inflation and the center-line bend radius that the seal can negotiate. Inflatable seals can be used for numerous applications with difficult sealing issues.

Labyrinth seal A seal which creates a tortuous path for the liquid to flow through

Lid (container)

Rotating face mechanical seal

Face seal

Plug

Radial shaft seal

Trap (plumbing) (siphon trap)

Stuffing box (mechanical packing)

Wiper seal

Dry gas seal

Smoke ring

A smoke ring is a visible vortex ring formed by smoke in a clear atmosphere.

Smokers may blow smoke rings from the mouth, intentionally or accidentally. Smoke rings may also be formed by sudden bursts of fire (such as lighting and immediately putting out a cigarette lighter), by shaking a smoke source (such as an incense stick) up and down, by firing certain types of artillery, or by the use of special devices, such as vortex ring toys. The head of a mushroom cloud is a large smoke ring.

A smoke ring is commonly formed when a puff of smoke is suddenly injected into clear air, especially through a narrow opening. The outer parts of the puff are slowed down by the still air (or by edges of the opening) relative to the central part, imparting it the characteristic poloidal flow pattern.

The smoke makes the ring visible, but does not significantly affect the flow. The same phenomenon occurs with any fluid, creating vortex rings which are invisible but otherwise entirely similar to smoke rings.

Space Shuttle Challenger disaster

On January 28, 1986, the NASA shuttle orbiter mission STS-51-L and the tenth flight of Space Shuttle Challenger (OV-99) broke apart 73 seconds into its flight, killing all seven crew members, which consisted of five NASA astronauts, one payload specialist and a civilian school teacher. The spacecraft disintegrated over the Atlantic Ocean, off the coast of Cape Canaveral, Florida, at 11:39 a.m. EST (16:39 UTC). The disintegration of the vehicle began after a joint in its right solid rocket booster (SRB) failed at liftoff. The failure was caused by the failure of O-ring seals used in the joint that were not designed to handle the unusually cold conditions that existed at this launch. The seals' failure caused a breach in the SRB joint, allowing pressurized burning gas from within the solid rocket motor to reach the outside and impinge upon the adjacent SRB aft field joint attachment hardware and external fuel tank. This led to the separation of the right-hand SRB's aft field joint attachment and the structural failure of the external tank. Aerodynamic forces broke up the orbiter.

The crew compartment and many other vehicle fragments were eventually recovered from the ocean floor after a lengthy search and recovery operation. The exact timing of the death of the crew is unknown; several crew members are known to have survived the initial breakup of the spacecraft. The shuttle had no escape system, and the impact of the crew compartment at terminal velocity with the ocean surface was too violent to be survivable.The disaster resulted in a 32-month hiatus in the shuttle program and the formation of the Rogers Commission, a special commission appointed by United States President Ronald Reagan to investigate the accident. The Rogers Commission found NASA's organizational culture and decision-making processes had been key contributing factors to the accident, with the agency violating its own safety rules. NASA managers had known since 1977 that contractor Morton-Thiokol's design of the SRBs contained a potentially catastrophic flaw in the O-rings, but they had failed to address this problem properly. NASA managers also disregarded warnings from engineers about the dangers of launching posed by the low temperatures of that morning, and failed to adequately report these technical concerns to their superiors.

Approximately 17 percent of Americans witnessed the launch live because of the presence of high school teacher Christa McAuliffe, who would have been the first teacher in space. Media coverage of the accident was extensive: one study reported that 85 percent of Americans surveyed had heard the news within an hour of the accident. The Challenger disaster has been used as a case study in many discussions of engineering safety and workplace ethics.

Vendhar TV

Vendhar TV (Tamil: வேந்தர் தொலைக்காட்சி) (also known as Vendhar) is a Tamil television channel launched on 24 August 2014 by SRM group.The channel features a number of shows, such as Oru sol khealir, Vendhar veetu kalyanam, Sundharakandam, Bharathi Kannamma, Mudivalla Arambam, Suryavamsam, Iruvar, Ninaithala innikum, Kollywood roundup, Puthumputhu kaalai, Ring O Ring, Thinnai,.

X-ring chain

The X-ring chain is a specialized type of sealed roller chain used to transfer mechanical power. Like the O-ring chain it is used in high performance motorcycles. It uses X-ring seal to keep lubricant(usually grease) in place.

It has higher performance (in terms of durability, lifetime, and power loss) than non-O-ring chain as it has less friction than O-ring chain which also increases reliability. It can last twice as long as the O-ring chain.

Yamaha AG100

The Yamaha AG100 is a Yamaha motorcycle introduced in 1973 for use in agriculture, humanitarian aid and other rural professional use. Its is only marketed in select regions, and is popular in Africa, Latin America, Australia, and New Zealand. Initial advertisements described it as, "built tough for tough Australian farm use". The bike has a single-cylinder two stroke engine, with five gears, and weighs 99 kg (218 lb) dry.The motorbike has many features designed for hard rural use, including a full-enclosed O-ring chain drive, autolube, kick start, both left and right kickstands for parking on sloped ground, and generally being a simple bike to maintain and repair. New Zealand's Farm Trader describes it as, "the best all-round performer in the low-budget farm bike sector". The New Zealand Herald describes the bike as "King of the two strokes".

Basic terminology
Main components
Valvetrain
Aspiration
Fuel system
Ignition
Electrics and engine
management
Exhaust system
Engine cooling
Other components
ISO standards by standard number
1–9999
10000–19999
20000+

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