Difference between revisions of "Bearing (mechanical)"

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{{Short description|Mechanism to constrain relative movement to the desired motion and reduce friction}}
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{{Use dmy dates|date=June 2013}}
 
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[[File:Ball Bearing2.jpg|thumb|[[Ball bearing]]]]
 
  
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A '''bearing''' is a [[machine element]] that constrains relative motion to only the desired motion, and reduces [[friction]] between [[moving parts]]. The design of the bearing may, for example, provide for free [[line (geometry)|linear]] movement of the moving part or for free [[rotation around a fixed axis]]; or, it may ''prevent'' a motion by controlling the [[vector (mathematics and physics)|vector]]s of [[normal force]]s that bear on the moving parts. Most bearings facilitate the desired motion by minimizing friction. Bearings are classified broadly according to the type of operation, the motions allowed, or to the directions of the loads (forces) applied to the parts.
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Rotary bearings hold rotating components such as [[shaft (mechanical engineering)|shaft]]s or [[axle]]s within mechanical systems, and transfer axial and radial loads from the source of the load to the structure supporting it. The simplest form of bearing, the ''[[plain bearing]]'', consists of a shaft rotating in a hole. [[Lubrication]] is used to reduce friction. In the ''[[ball bearing]]'' and ''[[roller bearing]]'', to reduce sliding friction, rolling elements such as rollers or balls with a circular cross-section are located between the races or journals of the bearing assembly. A wide variety of bearing designs exists to allow the demands of the application to be correctly met for maximum efficiency, reliability, durability and performance.
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The term "bearing" is derived from the verb "[[wikt:bear#Verb|to bear]]";<ref name="MWCD_online-headword_bearing">{{Citation |author=Merriam-Webster |author-link=Merriam-Webster |title=headwords "bearing" and "bear" |work=Merriam-Webster's Collegiate Dictionary, online subscription version |url=http://unabridged.merriam-webster.com/collegiate.htm }}</ref> a bearing being a machine element that allows one part to bear (i.e., to support) another. The simplest bearings are [[bearing surface]]s, cut or formed into a part, with varying degrees of control over the form, size, [[surface roughness|roughness]] and location of the surface. Other bearings are separate devices installed into a machine or machine part. The most sophisticated bearings for the most demanding applications are very [[accuracy and precision|precise]] devices; their manufacture requires some of the highest standards of [[high tech|current technology]].{{citation needed|date=July 2020}}
 
  
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==History==
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[[Image:Tapered steering head bearings.jpg|thumb|Tapered roller bearing]]
 
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[[Image:Шарикоподшипники.jpg|thumb|Drawing of [[Leonardo da Vinci]] (1452–1519) ''Study of a ball bearing'']]
 
  
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The invention of the rolling bearing, in the form of wooden rollers supporting, or bearing, an object being moved is of great antiquity and may predate the invention of a [[wheel]] rotating on a plain bearing used for transportation.
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= Bearing Standards =
  
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Though it is often claimed that the Egyptians used roller bearings in the form of [[tree trunk]]s under sleds,<ref name="guran">{{Citation | last = American Society of Mechanical Engineers | author-link = American Society of Mechanical Engineers | title = Transactions of the American Society of Mechanical Engineers | page = 441 | publisher = American Society of Mechanical Engineers | year = 1906 | volume = 27 | url = https://books.google.com/books?id=aWd1G50m8WEC&pg=RA1-PA441 }}</ref> this is modern speculation.<ref>{{cite book|last1=Bunch|first1=Bryan H.|last2=Hellemans|first2=Alexander|title=The History of Science and Technology: A Browser's Guide to the Great Discoveries, Inventions, and the People who Made Them, from the Dawn of Time to Today|url=https://books.google.com/books?id=MlQ7NK9dw7IC|year=2004|publisher=Houghton Mifflin|isbn=978-0-618-22123-3}}</ref> The Egyptians' own drawings in the tomb of [[Djehutihotep]] show the process of moving massive stone blocks on sledges as using liquid-lubricated runners which would constitute [[plain bearing]]s.<ref>{{cite book|last1=Bard|first1=Kathryn A.|last2=Shubert|first2=Steven Blake|title=Encyclopedia of the Archaeology of Ancient Egypt|url=https://books.google.com/books?id=PG6HffPwmuMC|year=1999|publisher=Routledge|isbn=978-0-415-18589-9}}</ref>
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=== Bearing Standards ===
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There are also Egyptian drawings of plain bearings used with [[hand drill]]s.<ref>{{Citation | last1 = Guran | first1 = Ardéshir | last2 = Rand | first2 = Richard H. | title = Nonlinear dynamics | page = 178 | publisher = World Scientific | year = 1997 | url = https://books.google.com/books?id=ttBQ1k8MYZ4C&pg=PA178  | isbn = 978-981-02-2982-5 }}</ref>
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ABMA/ANSI/ISO: A summary of each organization as they relate to the development of bearing standards.
  
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Wheeled vehicles using plain bearings [[Wheel#History|emerged between about 5000 BC and 3000 BC]].
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=== ABMA: American Bearing Manufacturers Association ===
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The American Bearing Manufacturers Association (ABMA), formerly the Anti-Friction Bearing Manufacturers Association, plays an important leadership role in an important industry. ABMA is the only U.S. trade organization representing manufacturers of bearings and bearing components. Through its headquarters in Washington, D.C., the ABMA defines national and international standards for bearing products; compiles market statistics; offers targeted educational programs; conducts industry conferences; and maintains contacts with elected officials and representatives from key government
  
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The earliest recovered example of a rolling element bearing is a wooden [[ball bearing]] supporting a rotating table from the remains of the [[Roman Republic|Roman]] [[Nemi ships]] in [[Lake Nemi]], [[Italy]]. The wrecks were dated to 40 BC.<ref>Purtell, John (1999/2001). Project Diana, chapter 10: [http://nemiship.multiservers.com/nemi.htm Wonders from the classical age]. {{Webarchive|url=https://web.archive.org/web/20100701192638/http://nemiship.multiservers.com/nemi.htm |date=1 July 2010 }}</ref><ref>{{Cite web|publisher= americanbearings.org| title = Bearing Industry Timeline | url = http://www.americanbearings.org/?page=bearing_timeline | access-date = 2012-10-21}}</ref>
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agencies.
  
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[[Leonardo da Vinci]] incorporated drawings of ball bearings in his design for a helicopter around the year 1500. This is the first recorded use of bearings in an aerospace design. However, [[Agostino Ramelli]] is the first to have published sketches of roller and thrust bearings.<ref name="guran"/> An issue with ball and roller bearings is that the balls or rollers rub against each other causing additional friction which can be reduced by enclosing the balls or rollers within a cage. The captured, or caged, ball bearing was originally described by [[Galileo Galilei|Galileo]] in the 17th century.{{citation needed|date=November 2010}}
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Membership in the ABMA is open to any firm in which a substantial part of its business includes the manufacture, in the United States, of bearings and major components used in those products.
  
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The first practical caged-roller bearing was invented in the mid-1740s by [[horology|horologist]] [[John Harrison]] for his H3 marine timekeeper. This uses the bearing for a very limited oscillating motion but Harrison also used a similar bearing in a truly rotary application in a contemporaneous regulator clock.{{citation needed|date=December 2017}}
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=== ABMA: National and International Standards ===
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ABMA cooperates with the American National Standards Institute (ANSI) in the development of bearing related standards. ABMA is an accredited standards developer through ANSI. ABMA develops industry standards, which are submitted to ANSI for approval as American National Standards. ABMA, as many other standards developers, have begun to adopt ISO standards as ANSI standards. Once adopted, they become ABMA/ANSI/ISO standards.
  
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===Industrial era===
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The ABMA is also responsible for developing and conveying the United States’ position on all proposals for the ISO’s Technical Committee 4 (TC4) concerning bearings.
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The first modern recorded [[patent]] on ball bearings was awarded to [[Philip Vaughan]], a [[United Kingdom|British]] inventor and [[ironmaster]] who created the first design for a ball bearing in [[Carmarthen]] in 1794. His was the first modern ball-bearing design, with the ball running along a groove in the axle assembly.<ref>{{cite web|url=http://www.intechbearing.com/5200Series-DoubleRowAngularContactBallBearings-SealsandShields-Shop.html|title=Double- Row Angular Contact Ball Bearings|url-status=dead|archive-url=https://web.archive.org/web/20130511155609/http://www.intechbearing.com/5200Series-DoubleRowAngularContactBallBearings-SealsandShields-Shop.html|archive-date=11 May 2013|df=dmy-all|publisher=intechbearing.com}}</ref>
 
  
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Bearings have played a pivotal role in the nascent [[Industrial Revolution]], allowing the new industrial machinery to operate efficiently. For example, they saw use for holding [[wheel and axle]] to greatly reduce friction over that of dragging an object by making the friction act over a shorter distance as the wheel turned.
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The U.S. Technical Advisory Committee (TAG) reviews all materials and submits a vote to ANSI which, in turn, is sent to the Secretariat of TC4
  
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The first plain and rolling-element bearings were [[wood]] closely followed by [[bronze]]. Over their history bearings have been made of many materials including [[ceramic]], [[sapphire]], [[glass]], [[steel]], [[bronze]], other metals and plastic (e.g., [[nylon]], [[polyoxymethylene]], [[polytetrafluoroethylene]], and [[UHMWPE]]) which are all used today.
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ABMA is the Secretariat of:
  
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Watch makers produce "jeweled" watches using sapphire plain bearings to reduce friction thus allowing more precise time keeping.
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* The ANSI Accredited National Standards Committee on Rolling Elements Bearings which is responsible for approval of bearing standards.
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* Three subcommittees of ISO’s Technical Committee 4 on Rolling Bearings and Spherical Plane Bearings, SC6, SC9, SC11.
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* The subcommittee on airframe bearings for ISO Technical Committee 20
  
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Even basic materials can have good durability. As examples, wooden bearings can still be seen today in old clocks or in water mills where the water provides cooling and lubrication.
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ABMA has published a complete set of bearing standards for ball and roller bearings and balls. More information on
  
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[[Image:Early Timken roller bearing.jpg|thumb|Early [[Timken Roller Bearing Company|Timken]] [[tapered roller bearing]] with notched rollers]]
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ABMA and their standards can be found at www.abma-dc.org
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The first [[patent]] for a radial style ball bearing was awarded to [[Jules Suriray]], a Parisian bicycle mechanic, on 3 August 1869. The bearings were then fitted to the winning bicycle ridden by [[James Moore (cyclist)|James Moore]] in the world's first bicycle road race, [[Paris–Rouen (cycle race)|Paris-Rouen]], in November 1869.<ref name="ibike%2Eorg">{{cite web|url=http://www.ibike.org/library/history-timeline.htm |title=Bicycle History, Chronology of the Growth of Bicycling and the Development of Bicycle Technology by David Mozer |publisher=Ibike.org |access-date=2013-09-30}}</ref>
 
  
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In 1883, [[Friedrich Fischer]], founder of [[Schaeffler Group|FAG]], developed an approach for milling and grinding balls of equal size and exact roundness by means of a suitable production machine and formed the foundation for creation of an independent bearing industry.
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=== ANSI: American National Standards Institute ===
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[[File:Wingquist patent PRV 25406 1907b.png|alt= Wingquist original patent|thumb|Wingquist original patent of self-aligning ball bearing]]
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Headquartered in Washington, D.C., ANSI is a private, non-profit organization that administers and coordinates the
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The modern, self-aligning design of ball bearing is attributed to [[Sven Wingquist]] of the [[SKF]] ball-bearing manufacturer in 1907, when he was awarded Swedish patent No. 25406 on its design.
 
  
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[[Henry Timken]], a 19th-century visionary and innovator in carriage manufacturing, patented the tapered roller bearing in 1898. The following year he formed a company to produce his innovation. Over a century the company grew to make bearings of all types, including specialty steel and an array of related products and services.
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U.S. voluntary standardization and conformity assessment system. The institute’s mission is to enhance both the
  
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Erich Franke invented and patented the [[wire race bearing]] in 1934. His focus was on a bearing design with a cross section as small as possible and which could be integrated into the enclosing design. After World War II he founded together with Gerhard Heydrich the company Franke & Heydrich KG (today Franke GmbH) to push the development and production of wire race bearings.
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global competitiveness of U.S. business and the U.S. quality of life by promoting and facilitating voluntary consensus
  
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Richard Stribeck’s extensive research<ref>{{cite journal|author=Stribeck, R. |title=Kugellager für beliebige Belastungen |journal=Zeitschrift des Vereines Deutscher Ingenieure|year= 1901|volume= 3|issue=45|pages=73–79}}</ref><ref>{{cite journal|author=Stribeck, R. |title=Kugellager (ball bearings)|journal= Glasers Annalen für Gewerbe und Bauwesen|date= 1 July 1901|volume= 577|pages=2–9}}</ref> on ball bearing steels identified the metallurgy of the commonly used 100Cr6 (AISI 52100)<ref>{{cite book|url=http://www.bam.de/de/ueber_uns/geschichte/adolf_martens.htm|author=Martens, A. |title=Schmieröluntersuchungen (Investigations on oils) |series=Mitteilungen aus den Königlichen technischen Versuchsanstalten zu Berlin, Ergänzungsheft III |year=1888|pages= 1–57|publisher=Verlag von Julius Springer|archive-url=https://web.archive.org/web/20120225142300/http://www.bam.de/de/ueber_uns/geschichte/adolf_martens.htm |archive-date=25 February 2012 |place= Berlin}}</ref> showing coefficient of friction as a function of pressure.
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standards and conformity assessment systems, and safeguarding their integrity.
  
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Designed in 1968 and later patented in 1972, Bishop-Wisecarver's co-founder Bud Wisecarver created vee groove bearing guide wheels, a type of linear motion bearing consisting of both an external and internal 90-degree vee angle.<ref name="vgroovebearings">{{Citation | last = Machine Design | author-link = Machine Design | title = Did You Know: Bud Wisecarver | page = 1 | publisher = Machine Design | year = 2007 | url = http://www.bwc.com/pdf/news/1737_MSD_BIWI_eprint_.pdf}}</ref>{{Better source needed|date=September 2010}}
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=== ANSI: National Standardization ===
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ANSI does not itself develop American National Standards; rather it facilitates the development by establishing
  
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In the early 1980s, Pacific Bearing's founder, Robert Schroeder, invented the first bi-material plain bearing which was size interchangeable with linear ball bearings. This bearing had a metal shell (aluminum, steel or stainless steel) and a layer of Teflon-based material connected by a thin adhesive layer.<ref>{{cite web|title=Design News Magazine – July 1995|url=http://www.designnews.com/article/9409-Prime_mover_in_custom_bearings.php}}{{Dead link|date=June 2019 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
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consensus among qualifying groups. Today there are approximately 14,650 American National Standards.
  
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Today ball and roller bearings are used in many applications which include a rotating component. Examples include ultra high speed bearings in dental drills, [[aerospace bearings]] in the Mars Rover, gearbox and wheel bearings on automobiles, flexure bearings in optical alignment systems, bicycle wheel hubs, and [[air bearings]] used in [[Coordinate-measuring machine]]s.
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=== ANSI: International Standardization ===
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ANSI promotes the use of U.S. standards internationally, advocates U.S. policy and technical positions in international
  
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==Common==
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and regional standards organizations. ANSI is the sole U.S. representative and dues paying member of the ISO.
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By far, the most common bearing is the [[plain bearing]], a bearing which uses surfaces in rubbing contact, often with a [[lubricant]] such as oil or graphite. A plain bearing may or may not be a [[wikt:discrete#Adjective|discrete]] device. It may be nothing more than the [[bearing surface]] of a hole with a shaft passing through it, or of a planar surface that [[wikt:bear#Verb|bears]] another (in these cases, not a discrete device); or it may be a layer of [[Babbitt (metal)|bearing metal]] either fused to the substrate (semi-discrete) or in the form of a separable sleeve (discrete). With suitable lubrication, plain bearings often give entirely acceptable accuracy, life, and friction at minimal cost. Therefore, they are very widely used.
 
  
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However, there are many applications where a more suitable bearing can improve efficiency, accuracy, service intervals, reliability, speed of operation, size, weight, and costs of purchasing and operating machinery.
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ANSI was a founding member of the ISO and plays an active role in its governance. ANSI participates in almost the
  
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Thus, there are many types of bearings, with varying shape, material, lubrication, principle of operation, and so on.
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entire technical program of the ISO (78%).
  
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==Types==
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In many instances, U.S. standards are taken forward, through ANSI, to the ISO where they are adopted as international
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[[Image:BallBearing.gif|thumb|Animation of ball bearing (Ideal figure without a cage). The inner ring rotates and the outer ring is stationary.]]
 
  
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There are at least 6 common types of bearing,<ref>{{cite web |title=6 Most Popular Types of Mechanical Bearings |url=https://www.craftechind.com/6-most-popular-types-of-mechanical-bearings/ |website=craftechind.com}}</ref> each of which operates on different principles:
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standards.
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*[[Plain bearing]], consisting of a shaft rotating in a hole. There are several specific styles: bushing, [[journal bearing]], sleeve bearing, rifle bearing, [[composite bearing]];
 
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*[[Rolling-element bearing]], in which rolling elements placed between the turning and stationary races prevent sliding friction.  There are two main types:
 
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**[[Ball bearing]], in which the rolling elements are spherical balls;
 
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**[[Roller bearing]], in which the rolling elements are cylindrical, taper or spherical rollers;
 
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*[[Jewel bearing]], a plain bearing in which one of the bearing surfaces is made of an ultrahard glassy jewel material such as [[sapphire]] to reduce friction and wear;
 
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*[[Fluid bearing]], a noncontact bearing in which the load is supported by a gas or liquid (i.e. [[air bearing]]);
 
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*[[Magnetic bearing]], in which the load is supported by a [[magnetic field]];
 
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*[[Flexure bearing]], in which the motion is supported by a load element which bends.
 
  
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==Motions==
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=== ISO: International Organization for Standardization ===
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Common motions permitted by bearings are:
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The ISO is a worldwide federation of national standards bodies from some 130 countries. The ISO’s mission is to
  
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*Radial rotation e.g. shaft rotation;
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promote the development of standardization and related activities in the world with a view to facilitating the international
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*linear motion e.g. drawer;
 
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*spherical rotation e.g. ball and socket joint;
 
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*hinge motion e.g. door, elbow, knee.
 
  
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==Friction==
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exchange of goods and services, and to developing cooperation in the spheres of intellectual, scientific, technological
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Reducing friction in bearings is often important for efficiency, to reduce wear and to facilitate extended use at high speeds and to avoid overheating and premature failure of the bearing. Essentially, a bearing can reduce friction by virtue of its shape, by its material, or by introducing and containing a fluid between surfaces or by separating the surfaces with an electromagnetic field.
 
  
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*'''By shape''', gains advantage usually by using spheres or [[Roller bearing|rollers]], or by forming flexure bearings.
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and economic activity.
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*'''By material''', exploits the nature of the bearing material used. (An example would be using plastics that have low surface friction.)
 
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*'''By fluid''', exploits the low viscosity of a layer of fluid, such as a lubricant or as a pressurized medium to keep the two solid parts from touching, or by reducing the normal force between them.
 
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*'''By fields''', exploits electromagnetic fields, such as magnetic fields, to keep solid parts from touching.
 
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*'''Air pressure''' exploits air pressure to keep solid parts from touching.
 
  
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Combinations of these can even be employed within the same bearing. An example of this is where the cage is made of plastic, and it separates the rollers/balls, which reduce friction by their shape and finish.
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=== ISO: Who does the work? ===
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The technical work of ISO is highly decentralized, carried out in a hierarchy of some 2,850 technical committees and
  
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==Loads==
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working groups. The major responsibility for administering a standards committee is accepted by one of the national
  
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Bearing design varies depending on the size and directions of the forces that they are required to support. Forces can be predominately [[radius|radial]], [[axis of rotation|axial]] ([[thrust bearing]]s), or [[bending moment]]s perpendicular to the main axis.
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standards bodies that make up the ISO membership. ANSI is one such member.
  
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==Speeds==
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The technical committee for bearings is “TC 4 Roller Bearings.” The scope of the committee is the standardization
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Different bearing types have different operating speed limits.  Speed is typically specified as maximum relative surface speeds, often specified ft/s or m/s. Rotational bearings typically describe performance in terms of the product ''DN'' where ''D'' is the mean diameter (often in mm) of the bearing and ''N'' is the rotation rate in revolutions per minute.
 
  
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Generally, there is considerable speed range overlap between bearing types.  Plain bearings typically handle only lower speeds, rolling element bearings are faster, followed by fluid bearings and finally magnetic bearings which are limited ultimately by centripetal force overcoming material strength.
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of all types and all sizes of bearing elements based on the principle of rolling motion, their accessories, application and
  
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==Play==
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identification and standardization of spherical plain bearings.
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Some applications apply bearing loads from varying directions and accept only limited play or "slop" as the applied load changes.  One source of motion is gaps or "play" in the bearing.  For example, a 10&nbsp;mm shaft in a 12&nbsp;mm hole has 2&nbsp;mm play.
 
  
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Allowable play varies greatly depending on the use.  As an example, a wheelbarrow wheel supports radial and axial loads.  Axial loads may be hundreds of [[newton (units)|newton]]s force left or right, and it is typically acceptable for the wheel to wobble by as much as 10&nbsp;mm under the varying load.  In contrast, a lathe may position a cutting tool to ±0.002&nbsp;mm using a ball lead screw held by rotating bearings. The bearings support axial loads of thousands of newtons in either direction and must hold the ball lead screw to ±0.002&nbsp;mm across that range of loads
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One of the standards committees SC’s for TC 4 is “TC4/SC 9 Tapered rolling bearings.” The Secretariat for this
  
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==Stiffness==
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committee is ANSI. The number of published ISO standards under the direct responsibility of the SC Secretariat is 4.
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A second source of motion is elasticity in the bearing itself. For example, the balls in a ball bearing are like stiff rubber, and under load deform from round to a slightly flattened shape.  The race is also elastic and develops a slight dent where the ball presses on it.
 
  
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The stiffness of a bearing is how the distance between the parts which are separated by the bearing varies with applied load.  With rolling element bearings this is due to the strain of the ball and race.  With fluid bearings it is due to how the pressure of the fluid varies with the gap (when correctly loaded, fluid bearings are typically stiffer than rolling element bearings).
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One of them, for example, is ISO 10317:1992 Rolling bearings – Metric tapered roller bearings – Designation system.
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==Service life==
 
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;Fluid and magnetic bearings
 
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{{Main|Fluid bearing|Magnetic bearing}}
 
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Fluid and magnetic bearings can have practically indefinite service lives.  In practice, there are fluid bearings supporting high loads in hydroelectric plants that have been in nearly continuous service since about 1900 and which show no signs of wear.{{citation needed|date=April 2018}}
 
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;Rolling element bearings
 
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Rolling element bearing life is determined by load, temperature, maintenance, lubrication, material defects, contamination, handling, installation and other factors.  These factors can all have a significant effect on bearing life.  For example, the service life of bearings in one application was extended dramatically by changing how the bearings were stored before installation and use, as vibrations during storage caused lubricant failure even when the only load on the bearing was its own weight;<ref name="Harris2001">{{cite book|last=Harris|first=Tedric A. |title=Rolling bearing analysis|url=https://books.google.com/books?id=Pt9SAAAAMAAJ|year=2001|publisher=Wiley|isbn=978-0-471-35457-4}}</ref>  the resulting damage is often [[false brinelling]].<ref>{{Citation|title=Time-dependent analyses of wear in oscillating bearing applications|last1=Schwack|first1=Fabian|last2=Byckov|first2=Artjom|work=Proceedings of the STLE/ASME International Joint Tribology Conference|last3=Bader|first3=Norbert|last4=Poll|first4=Gerhard|s2cid=201816405}}</ref>  Bearing life is statistical: several samples of a given bearing will often exhibit a [[Normal distribution|bell curve]] of service life, with a few samples showing significantly better or worse life.  Bearing life varies because microscopic structure and contamination vary greatly even where macroscopically they seem identical.
 
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===L10 life===
 
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Bearings are often specified to give an "L10" life (outside the USA, it may be referred to as "B10" life.) This is the life at which ten percent of the bearings in that application can be expected to have failed due to classical fatigue failure (and not any other mode of failure like lubrication starvation, wrong mounting etc.), or, alternatively, the life at which ninety percent will still be operating. The L10 life of the bearing is theoretical life and may not represent service life of the bearing. Bearings are also rated using C<sub>0</sub> (static loading) value. This is the basic load rating as a reference, and not an actual load value.
 
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;Plain bearings
 
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For plain bearings, some materials give much longer life than others. Some of the [[John Harrison]] clocks still operate after hundreds of years because of the ''[[lignum vitae]]'' wood employed in their construction, whereas his metal clocks are seldom run due to potential wear.
 
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;Flexure bearings
 
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Flexure bearings rely on elastic properties of a material. Flexure bearings bend a piece of material repeatedly.  Some materials fail after repeated bending, even at low loads, but careful material selection and bearing design can make flexure bearing life indefinite.
 
−
 
 
−
;Short-life bearings
 
−
Although long bearing life is often desirable, it is sometimes not necessary. {{harvnb|Harris|2001|p=}} describes a bearing for a rocket motor oxygen pump that gave several hours life, far in excess of the several tens of minutes life needed.<ref name="Harris2001"/>
 
−
 
 
−
'''Composite bearings'''
 
−
 
 
−
Depending on the customized specifications (backing material and PTFE compounds), [[composite bearing]]s can operate up to 30 years without maintenance.
 
−
 
 
−
'''Oscillating bearings'''
 
−
 
 
−
For bearings which are used in [[Oscillation|oscillating]] applications, customized approaches to calculate L10 are used.<ref>{{Cite journal|last1=Schwack|first1=F.|last2=Stammler|first2=M.|last3=Poll|first3=G.|last4=Reuter|first4=A.|date=2016|title=Comparison of Life Calculations for Oscillating Bearings Considering Individual Pitch Control in Wind Turbines|journal=Journal of Physics: Conference Series|volume=753|issue=11|pages=112013|doi=10.1088/1742-6596/753/11/112013|bibcode=2016JPhCS.753k2013S|doi-access=free|url=https://www.repo.uni-hannover.de/handle/123456789/2650}}</ref>
 
−
 
 
−
===External factors===
 
−
The service life of the bearing is affected by many parameters that are not controlled by the bearing manufacturers. For example, bearing mounting, temperature, exposure to external environment, lubricant cleanliness and [[shaft voltage|electrical currents through bearings]] etc. High frequency [[inverter drive|PWM inverter]]s can induce currents in a bearing, which can be suppressed by the use of [[ferrite choke]]s.
 
−
 
 
−
The temperature and terrain of the micro-surface will determine the amount of friction by the touching of solid parts.
 
−
 
 
−
Certain elements and fields reduce friction while increasing speeds.
 
−
 
 
−
Strength and mobility help determine the amount of load the bearing type can carry.
 
−
 
 
−
Alignment factors can play a damaging role in wear and tear, yet overcome by computer aid signaling and non-rubbing bearing types, such as magnetic levitation or air field pressure.
 
−
 
 
−
==Maintenance and lubrication==
 
−
Many bearings require periodic maintenance to prevent premature failure, but many others require little maintenance. The latter include various kinds of polymer, fluid and magnetic bearings, as well as rolling-element bearings that are described with terms including ''sealed bearing'' and ''sealed for life''. These contain [[seal (mechanical)|seals]] to keep the dirt out and the grease in. They work successfully in many applications, providing maintenance-free operation. Some applications cannot use them effectively.
 
−
 
 
−
Nonsealed bearings often have a [[grease fitting]], for periodic lubrication with a [[grease gun (tool)|grease gun]], or an oil cup for periodic filling with oil. Before the 1970s, sealed bearings were not encountered on most machinery, and oiling and greasing were a more common activity than they are today. For example, automotive chassis used to require "lube jobs" nearly as often as engine oil changes, but today's car chassis are mostly sealed for life. From the late 1700s through the mid-1900s, industry relied on many workers called [[oiler (occupation)|oilers]] to lubricate machinery frequently with [[oil can]]s.
 
−
 
 
−
Factory machines today usually have ''lube systems'', in which a central pump serves periodic charges of oil or grease from a reservoir through ''lube lines'' to the various ''lube points'' in the machine's [[bearing surface]]s, bearing journals, [[pillow block bearing|pillow blocks]], and so on. The timing and number of such ''lube cycles'' is controlled by the machine's computerized control, such as [[programmable logic controller|PLC]] or [[numerical control|CNC]], as well as by manual override functions when occasionally needed. This automated process is how all modern CNC [[machine tool]]s and many other modern factory machines are lubricated. Similar lube systems are also used on nonautomated machines, in which case there is a [[hand pump]] that a machine operator is supposed to pump once daily (for machines in constant use) or once weekly. These are called ''one-shot systems'' from their chief selling point: one pull on one handle to lube the whole machine, instead of a dozen pumps of an alemite gun or oil can in a dozen different positions around the machine.
 
−
 
 
−
The oiling system inside a modern automotive or truck engine is similar in concept to the lube systems mentioned above, except that oil is pumped continuously. Much of this oil flows through passages drilled or cast into the [[engine block]] and [[cylinder head]]s, escaping through ports directly onto bearings, and squirting elsewhere to provide an oil bath. The oil pump simply pumps constantly, and any excess pumped oil continuously escapes through a relief valve back into the sump.
 
−
 
 
−
Many bearings in high-cycle industrial operations need periodic lubrication and cleaning, and many require occasional adjustment, such as pre-load adjustment, to minimize the effects of wear.
 
−
 
 
−
Bearing life is often much better when the bearing is kept clean and well lubricated.  However, many applications make good maintenance difficult. One example is bearings in the conveyor of a [[crusher|rock crusher]] are exposed continually to hard abrasive particles.  Cleaning is of little use because cleaning is expensive yet the bearing is contaminated again as soon as the conveyor resumes operation.  Thus, a good maintenance program might lubricate the bearings frequently but not include any disassembly for cleaning. The frequent lubrication, by its nature, provides a limited kind of cleaning action, by displacing older (grit-filled) oil or grease with a fresh charge, which itself collects grit before being displaced by the next cycle. Another example are bearings in wind turbines, which makes maintenance difficult since the nacelle is placed high up in the air in strong wind areas. In addition, the turbine does not always run and is subjected to different operating behavior in different weather conditions, which makes proper lubrication a challenge.<ref name="SchwackBader2020">{{cite journal|last1=Schwack|first1=Fabian|last2=Bader|first2=Norbert|last3=Leckner|first3=Johan|last4=Demaille|first4=Claire|last5=Poll|first5=Gerhard|title=A study of grease lubricants under wind turbine pitch bearing conditions|journal=Wear|volume=454-455|year=2020|pages=203335|issn=0043-1648|doi=10.1016/j.wear.2020.203335|doi-access=free}}</ref>
 
−
 
 
−
===Rolling-element bearing outer race fault detection===
 
−
{{unreferenced section|date=May 2015}}
 
−
Rolling-element bearings are widely used in the industries today, and hence [[Maintenance, repair and operations|maintenance]] of these bearings becomes an important task for the maintenance professionals. The rolling-element bearings wear out easily due to metal-to-metal contact, which creates faults in the outer race, inner race and ball. It is also the most vulnerable component of a machine because it is often under high load and high running speed conditions. Regular [[diagnostics]] of rolling-element bearing faults is critical for industrial safety and operations of the machines along with reducing the maintenance costs or avoiding shutdown time. Among the outer race, inner race and ball, the outer race tends to be more vulnerable to faults and defects.
 
−
 
 
−
There is still room for discussion as to whether the rolling element excites the [[natural frequencies]] of bearing component when it passes the [[Fault (power engineering)|fault]] on the outer race. Hence we need to identify the bearing outer race natural frequency and its [[harmonics]]. The bearing faults create impulses and results in strong harmonics of the fault frequencies in the spectrum of vibration signals. These fault frequencies are sometimes masked by adjacent frequencies in the spectra due to their little energy. Hence, a very high spectral resolution is often needed to identify these frequencies during a [[FFT]] analysis. The [[natural frequencies]] of a rolling element bearing with the free boundary conditions are 3&nbsp;kHz. Therefore, in order to use the bearing component [[resonance]] bandwidth method to detect the bearing fault at an initial stage a high frequency range [[accelerometer]] should be adopted, and data obtained from a long duration needs to be acquired.  A fault characteristic frequency can only be identified when the fault extent is severe, such as that of the presence of a hole in the outer race. The harmonics of fault frequency is a more sensitive indicator of a bearing outer race fault. For a more serious detection of defected bearing faults [[waveform]], [[spectrum]] and [[envelope]] techniques will help reveal these faults. However, if a high frequency [[demodulation]] is used in the envelope analysis in order to detect bearing fault characteristic frequencies, the maintenance professionals have to be more careful in the analysis because of [[resonance]], as it may or may not contain fault frequency components.
 
−
 
 
−
Using spectral analysis as a tool to identify the faults in the bearings faces challenges due to issues like low energy, signal smearing, [[cyclostationarity]] etc. High resolution is often desired to differentiate the fault frequency components from the other high-amplitude adjacent frequencies. Hence, when the signal is sampled for [[FFT]] analysis, the sample length should be large enough to give adequate frequency resolution in the spectrum. Also, keeping the computation time and memory within limits and avoiding unwanted [[Aliasing (computing)|aliasing]] may be demanding. However, a minimal frequency resolution required can be obtained by estimating the bearing fault frequencies and other vibration frequency components and its harmonics due to shaft speed, misalignment, line frequency, gearbox etc.
 
−
 
 
−
===Packing===
 
−
Some bearings use a thick [[Grease (lubricant)|grease]] for lubrication, which is pushed into the gaps between the bearing surfaces, also known as ''packing''. The grease is held in place by a plastic, leather, or rubber gasket (also called a ''gland'') that covers the inside and outside edges of the bearing race to keep the grease from escaping.
 
−
 
 
−
Bearings may also be packed with other materials. Historically, the wheels on railroad cars used sleeve bearings packed with ''waste'' or loose scraps of cotton or wool fiber soaked in oil, then later used solid pads of cotton.<ref>{{White-Passenger-1985|volume=2|page=518}}</ref>
 
−
 
 
−
===Ring oiler===
 
−
{{Further|Ring oiler}}
 
−
Bearings can be lubricated by a metal ring that rides loosely on the central rotating shaft of the bearing. The ring hangs down into a chamber containing lubricating oil. As the bearing rotates, viscous adhesion draws oil up the ring and onto the shaft, where the oil migrates into the bearing to lubricate it. Excess oil is flung off and collects in the pool again.<ref>{{cite book|title=Steam Power Plant Engineering|first= George Frederick |last=Gebhardt| publisher= J. Wiley |date= 1917|page= [https://archive.org/details/steampowerplant02gebhgoog/page/n813 791] |url=https://archive.org/details/steampowerplant02gebhgoog}}</ref>
 
−
 
 
−
===Splash lubrication===
 
−
A rudimentary form of lubrication is [[splash lubrication]]. Some machines contain a pool of lubricant in the bottom, with gears partially immersed in the liquid, or crank rods that can swing down into the pool as the device operates. The spinning wheels fling oil into the air around them, while the crank rods slap at the surface of the oil, splashing it randomly on the interior surfaces of the engine. Some small internal combustion engines specifically contain special plastic ''flinger wheels'' which randomly scatter oil around the interior of the mechanism.<ref>{{cite book|title=The gasoline automobile|first1= George William |last1=Hobbs |first2= Ben George |last2=Elliott|first3= Earl Lester |last3=Consoliver|publisher=McGraw-Hill |date=1919 |pages= [https://archive.org/details/gasolineautomob00divigoog/page/n137 111]–114 |url=https://archive.org/details/gasolineautomob00divigoog}}</ref>
 
−
 
 
−
===Pressure lubrication===
 
−
For high speed and high power machines, a loss of lubricant can result in rapid bearing heating and damage due to friction. Also in dirty environments, the oil can become contaminated with dust or debris that increases friction. In these applications, a fresh supply of lubricant can be continuously supplied to the bearing and all other contact surfaces, and the excess can be collected for filtration, cooling, and possibly reuse. Pressure oiling is commonly used in large and complex [[internal combustion engines]] in parts of the engine where directly splashed oil cannot reach, such as up into overhead valve assemblies.<ref>{{cite journal|title=Pressure Lubricating Characteristics|first1= Paul |last1=Dumas|journal=Motor Age|volume= 42|publisher= Class Journal Co.|date= 14 Sep 1922 |url=https://books.google.com/books?id=S0AfAQAAMAAJ&q=engine+pressure+oiling&pg=RA10-PA22 }}</ref> High speed turbochargers also typically require a pressurized oil system to cool the bearings and keep them from burning up due to the heat from the turbine.
 
−
 
 
−
===Composite bearings===
 
−
Composite bearings are designed with a self-lubricating polytetrafluroethylene (PTFE) liner with a laminated metal backing. The PTFE liner offers consistent, controlled friction as well as durability whilst the metal backing ensures the composite bearing is robust and capable of withstanding high loads and stresses throughout its long life. Its design also makes it lightweight-one tenth the weight of a traditional rolling element bearing.<ref>{{cite news|last1=Gobain|first1=Saint|title=Saint-Gobain and Norco Get Celebrity Thumbs-Up|url=http://www.pddnet.com/news/2012/06/saint-gobain-and-norco-get-celebrity-thumbs?terms=saint-gobain|access-date=9 June 2016|date=1 June 2012}}</ref>
 
−
 
 
−
==Types==
 
−
There are many different types of bearings. Newer versions of more enabling designs are in development being tested, which will reduce friction, increase bearing load, increase momentum build-up, and speed.
 
−
 
 
−
{| class="wikitable"
 
−
|-
 
−
!Type
 
−
!Description
 
−
!Friction
 
−
![[Stiffness]]<sup>†</sup>
 
−
!Speed
 
−
!Life
 
−
!Notes
 
−
|-
 
−
![[Plain bearing]]
 
−
|Rubbing surfaces, usually with lubricant; some bearings use pumped lubrication and behave similarly to fluid bearings.
 
−
|Depends on materials and construction, PTFE has a coefficient of friction ~0.05–0.35, depending upon fillers added
 
−
|Good, provided wear is low, but some slack is normally present
 
−
|Low to very high
 
−
|Low to very high – depends upon application and lubrication
 
−
|Widely used, relatively high friction, suffers from [[stiction]] in some applications. Depending upon the application, the lifetime can be higher or lower than rolling element bearings.
 
−
|-
 
−
![[Rolling element bearing]]
 
−
|Ball or rollers are used to prevent or minimise rubbing
 
−
|Rolling coefficient of friction with steel can be ~0.005 (adding resistance due to seals, packed grease, preload and misalignment can increase friction to as much as 0.125)
 
−
|Good, but some slack is usually present
 
−
|Moderate to high (often requires cooling)
 
−
|Moderate to high (depends on lubrication, often requires maintenance)
 
−
|Used for higher moment loads than plain bearings with lower friction
 
−
|-
 
−
![[Jewel bearing]]
 
−
|Off-center bearing rolls in seating
 
−
|Low
 
−
|Low due to flexing
 
−
|Low
 
−
|Adequate (requires maintenance)
 
−
|Mainly used in low-load, high precision work such as clocks.  Jewel bearings may be very small.
 
−
|-
 
−
![[Fluid bearing]]
 
−
|Fluid is forced between two faces and held in by edge seal
 
−
|Zero friction at zero speed, low
 
−
|Very high
 
−
|Very high (usually limited to a few hundred feet per second at/by seal)
 
−
|Virtually infinite in some applications, may wear at startup/shutdown in some cases. Often negligible maintenance.
 
−
|Can fail quickly due to grit or dust or other contaminants. Maintenance free in continuous use. Can handle very large loads with low friction.
 
−
|-
 
−
![[Magnetic bearing]]
 
−
|Faces of bearing are kept separate by magnets ([[electromagnet]]s or [[eddy current]]s)
 
−
|Zero friction at zero speed, but constant power for levitation, eddy currents are often induced when movement occurs, but may be negligible if magnetic field is quasi-static
 
−
|Low
 
−
|No practical limit
 
−
|Indefinite. Maintenance free. (with [[electromagnet]]s)
 
−
|Active magnetic bearings (AMB) need considerable power. [[Electrodynamic bearing]]s (EDB) do not require external power.
 
−
|-
 
−
![[Flexure bearing]]
 
−
|Material flexes to give and constrain movement
 
−
|Very low
 
−
|Low
 
−
|Very high.
 
−
|Very high or low depending on materials and strain in application. Usually maintenance free.
 
−
|Limited range of movement, no backlash, extremely smooth motion
 
−
|-
 
−
|-
 
−
![[Composite bearing]]
 
−
|Plain bearing shape with PTFE liner on the interface between bearing and shaft with a laminated metal backing. PTFE acts as a lubricant.
 
−
|PTFE and use of filters to dial in friction as necessary for friction control.
 
−
|Good depending on laminated metal backing
 
−
|Low to very high
 
−
|Very high; PTFE and fillers ensure wear and corrosion resistance
 
−
|Widely used, controls friction, reduces stick slip, PTFE reduces static friction
 
−
|-
 
−
| colspan=7 | <sup>†</sup>Stiffness is the amount that the gap varies when the load on the bearing changes, it is distinct from the [[friction]] of the bearing.
 
−
|}
 
−
 
 
−
==See also==
 
−
{{div col}}
 
−
* {{annotated link|Axlebox}}
 
−
* {{annotated link|Ball bearing}}
 
−
* {{annotated link|Ball spline}}
 
−
* {{annotated link|Contact mechanics}}
 
−
* {{annotated link|Journal bearing}}
 
−
* {{annotated link|Hinge}}
 
−
* {{annotated link|Main bearing}}
 
−
* {{annotated link|Needle roller bearing}}
 
−
* {{annotated link|Pillow block bearing}}
 
−
* {{annotated link|Pitch bearing}}
 
−
* {{annotated link|Plain bearing}}
 
−
* {{annotated link|Race (bearing)}}
 
−
* {{annotated link|Rolamite}}
 
−
* {{annotated link|Rolling-element bearing}}
 
−
* {{annotated link|Scrollerwheel}}
 
−
* {{annotated link|Shock pulse method}}
 
−
* {{annotated link|Slewing bearing}}
 
−
* {{annotated link|Spherical bearing|Spherical plain bearing}}
 
−
* {{annotated link|Spherical roller bearing}}
 
−
* {{annotated link|Spiral groove bearing}}
 
−
{{div col end}}
 
−
 
 
−
==References==
 
−
{{Reflist|33em}}
 
−
 
 
−
==External links==
 
−
{{Commons category|Bearings}}
 
−
 
 
−
* [http://www.nsk.com.br/upload/file/nsk_cat_e728g_1.pdf ISO Dimensional system and bearing numbers]
 
−
* [https://web.archive.org/web/20190525010018/http://www.phase-trans.msm.cam.ac.uk/2011/Bearings/index.html Comprehensive review on bearings, University of Cambridge]
 
−
* [https://web.archive.org/web/20160104230339/http://www.timken.com/en-us/knowledge/glossary/pages/BearingTermsGlossary.aspx A glossary of bearing terms]
 
−
* [http://science.howstuffworks.com/bearing.htm How bearings work]
 
−
*[http://kmoddl.library.cornell.edu/index.php Kinematic Models for Design Digital Library (KMODDL)] – Movies and photos of hundreds of working mechanical-systems models at Cornell University. Also includes an [http://kmoddl.library.cornell.edu/e-books.php e-book library] of classic texts on mechanical design and engineering.
 
−
* [http://www.msm.cam.ac.uk/phase-trans/2010/types/index.html Types of bearings, Cambridge University]
 
−
 
 
−
{{Authority control}}
 
−
 
 
−
{{DEFAULTSORT:Bearing (Mechanical)}}
 
−
[[Category:Bearings (mechanical)| ]]
 
−
[[Category:Tribology]]
 

Latest revision as of 15:10, 11 February 2022

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Bearing Standards[edit | edit source]

Bearing Standards[edit | edit source]

ABMA/ANSI/ISO: A summary of each organization as they relate to the development of bearing standards.

ABMA: American Bearing Manufacturers Association[edit | edit source]

The American Bearing Manufacturers Association (ABMA), formerly the Anti-Friction Bearing Manufacturers Association, plays an important leadership role in an important industry. ABMA is the only U.S. trade organization representing manufacturers of bearings and bearing components. Through its headquarters in Washington, D.C., the ABMA defines national and international standards for bearing products; compiles market statistics; offers targeted educational programs; conducts industry conferences; and maintains contacts with elected officials and representatives from key government

agencies.

Membership in the ABMA is open to any firm in which a substantial part of its business includes the manufacture, in the United States, of bearings and major components used in those products.

ABMA: National and International Standards[edit | edit source]

ABMA cooperates with the American National Standards Institute (ANSI) in the development of bearing related standards. ABMA is an accredited standards developer through ANSI. ABMA develops industry standards, which are submitted to ANSI for approval as American National Standards. ABMA, as many other standards developers, have begun to adopt ISO standards as ANSI standards. Once adopted, they become ABMA/ANSI/ISO standards.

The ABMA is also responsible for developing and conveying the United States’ position on all proposals for the ISO’s Technical Committee 4 (TC4) concerning bearings.

The U.S. Technical Advisory Committee (TAG) reviews all materials and submits a vote to ANSI which, in turn, is sent to the Secretariat of TC4

ABMA is the Secretariat of:

  • The ANSI Accredited National Standards Committee on Rolling Elements Bearings which is responsible for approval of bearing standards.
  • Three subcommittees of ISO’s Technical Committee 4 on Rolling Bearings and Spherical Plane Bearings, SC6, SC9, SC11.
  • The subcommittee on airframe bearings for ISO Technical Committee 20

ABMA has published a complete set of bearing standards for ball and roller bearings and balls. More information on

ABMA and their standards can be found at www.abma-dc.org

ANSI: American National Standards Institute[edit | edit source]

Headquartered in Washington, D.C., ANSI is a private, non-profit organization that administers and coordinates the

U.S. voluntary standardization and conformity assessment system. The institute’s mission is to enhance both the

global competitiveness of U.S. business and the U.S. quality of life by promoting and facilitating voluntary consensus

standards and conformity assessment systems, and safeguarding their integrity.

ANSI: National Standardization[edit | edit source]

ANSI does not itself develop American National Standards; rather it facilitates the development by establishing

consensus among qualifying groups. Today there are approximately 14,650 American National Standards.

ANSI: International Standardization[edit | edit source]

ANSI promotes the use of U.S. standards internationally, advocates U.S. policy and technical positions in international

and regional standards organizations. ANSI is the sole U.S. representative and dues paying member of the ISO.

ANSI was a founding member of the ISO and plays an active role in its governance. ANSI participates in almost the

entire technical program of the ISO (78%).

In many instances, U.S. standards are taken forward, through ANSI, to the ISO where they are adopted as international

standards.

ISO: International Organization for Standardization[edit | edit source]

The ISO is a worldwide federation of national standards bodies from some 130 countries. The ISO’s mission is to

promote the development of standardization and related activities in the world with a view to facilitating the international

exchange of goods and services, and to developing cooperation in the spheres of intellectual, scientific, technological

and economic activity.

ISO: Who does the work?[edit | edit source]

The technical work of ISO is highly decentralized, carried out in a hierarchy of some 2,850 technical committees and

working groups. The major responsibility for administering a standards committee is accepted by one of the national

standards bodies that make up the ISO membership. ANSI is one such member.

The technical committee for bearings is “TC 4 Roller Bearings.” The scope of the committee is the standardization

of all types and all sizes of bearing elements based on the principle of rolling motion, their accessories, application and

identification and standardization of spherical plain bearings.

One of the standards committees SC’s for TC 4 is “TC4/SC 9 Tapered rolling bearings.” The Secretariat for this

committee is ANSI. The number of published ISO standards under the direct responsibility of the SC Secretariat is 4.

One of them, for example, is ISO 10317:1992 Rolling bearings – Metric tapered roller bearings – Designation system.

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