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Ball bearing

Bearing (mechanical)From Wikipedia, the free encyclopedia

A bearing is a machine element that constrains relative motionto only the desired motion, and reduces friction between movingparts . The design of the bearing may, for example, provide forfree linear movement of the moving part or for free rotationaround a fixed axis; or, it may prevent a motion by controllingthe vectors of normal forces that bear on the moving parts. Manybearings also facilitate the desired motion as much as possible,such as by minimizing friction. Bearings are classified broadlyaccording to the type of operation, the motions allowed, or to thedirections of the loads (forces) applied to the parts.

The term "bearing" is derived from the verb "to bear";[1] abearing being a machine element that allows one part to bear(i.e., to support) another. The simplest bearings are bearingsurfaces, cut or formed into a part, with varying degrees ofcontrol over the form, size, roughness and location of the surface.Other bearings are separate devices installed into a machine or machine part. The most sophisticatedbearings for the most demanding applications are very precise devices; their manufacture requires someof the highest standards of current technology.

Contents

1 History1.1 Industrial era

2 Common3 Principles of operation4 Motions5 Friction6 Loads7 Speeds8 Play9 Stiffness10 Service life

10.1 L10 life10.2 External factors

11 Maintenance and lubrication11.1 Rolling­element bearing outer race fault detection11.2 Packing11.3 Ring oiler11.4 Splash lubrication11.5 Pressure lubrication

12 Types13 See also14 References15 External links

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Tapered roller bearing

Drawing of Leonardo da Vinci(1452­1519) Study of a ball bearing

History

The invention of the rolling bearing, in the form of wooden rollerssupporting, or bearing, an object being moved is of great antiquity, andmay predate the invention of the wheel.

Though it is often claimed that the Egyptians used roller bearings in theform of tree trunks under sleds,[2] this is modern speculation.[3] They aredepicted in their own drawings in the tomb of Djehutihotep [4] asmoving massive stone blocks on sledges with liquid­lubricated runnerswhich would constitute a plain bearing. There are also Egyptiandrawings of bearings used with hand drills.[5]

The earliest recovered example of a rolling element bearing is awooden ball bearing supporting a rotating table from the remainsof the Roman Nemi ships in Lake Nemi, Italy. The wrecks weredated to 40 BC.[6][7]

Leonardo da Vinci incorporated drawings of ball bearings in hisdesign for a helicopter around the year 1500. This is the firstrecorded use of bearings in an aerospace design. However,Agostino Ramelli is the first to have published sketches of rollerand thrust bearings.[2] An issue with ball and roller bearings isthat the balls or rollers rub against each other causing additional friction which can be prevented byenclosing the balls or rollers in a cage. The captured, or caged, ball bearing was originally described byGalileo in the 17th century.

The first practical caged­roller bearing was invented in the mid­1740s by horologist John Harrison forhis H3 marine timekeeper. This uses the bearing for a very limited oscillating motion but Harrison alsoused a similar bearing in a truly rotary application in a contemporaneous regulator clock.

Industrial era

The first modern recorded patent on ball bearings was awarded to Philip Vaughan, a British inventor andironmaster who created the first design for a ball bearing in Carmarthen in 1794. His was the firstmodern ball­bearing design, with the ball running along a groove in the axle assembly.[8]

Bearings played a pivotal role in the nascent Industrial Revolution, allowing the new industrialmachinery to operate efficiently. For example, they saw use for holding wheel and axle to greatly reducefriction over that of dragging an object by making the friction act over a shorter distance as the wheelturned.

The first plain and rolling­element bearings were wood closely followed by bronze. Over their historybearings have been made of many materials including ceramic, sapphire, glass, steel, bronze, othermetals and plastic (e.g., nylon, polyoxymethylene, polytetrafluoroethylene, and UHMWPE) which areall used today.

Watch makers produce "jeweled" watches using sapphire plain bearings to reduce friction thus allowingmore precise time keeping.

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Early Timken tapered roller bearingwith notched rollers

Even basic materials can have good durability. As examples, wooden bearings can still be seen today inold clocks or in water mills where the water provides cooling and lubrication.

The first patent for a radial style ball bearing was awarded toJules Suriray, a Parisian bicycle mechanic, on 3 August 1869.The bearings were then fitted to the winning bicycle ridden byJames Moore in the world's first bicycle road race, Paris­Rouen,in November 1869.[9]

In 1883, Friedrich Fischer, founder of FAG, developed anapproach for milling and grinding balls of equal size and exactroundness by means of a suitable production machine andformed the foundation for creation of an independent bearingindustry.

The modern, self­aligning design of ball bearing is attributed toSven Wingquist of the SKF ball­bearing manufacturer in 1907,when he was awarded Swedish patent No. 25406 on its design.

Henry Timken, a 19th­century visionary and innovator in carriage manufacturing, patented the taperedroller bearing in 1898. The following year he formed a company to produce his innovation. Over acentury the company grew to make bearings of all types, including specialty steel and an array of relatedproducts and services.

Erich Franke invented and patented the wire race bearing in 1934. His focus was on a bearing designwith a cross section as small as possible and which could be integrated into the enclosing design. AfterWorld War II he founded together with Gerhard Heydrich the company Franke & Heydrich KG (todayFranke GmbH) to push the development and production of wire race bearings.

Richard Stribeck’s extensive research [10][11] on ball bearing steels identified the metallurgy of thecommonly used 100Cr6 (AISI 52100) [12] showing coefficient of friction as a function of pressure.

Designed in 1968 and later patented in 1972, Bishop­Wisecarver's co­founder Bud Wisecarver createdvee groove bearing guide wheels, a type of linear motion bearing consisting of both an external andinternal 90­degree vee angle.[13]

In the early 1980s, Pacific Bearing's founder, Robert Schroeder, invented the first bi­material plainbearing which was size interchangeable with linear ball bearings. This bearing had a metal shell(aluminum, steel or stainless steel) and a layer of Teflon­based material connected by a thin adhesivelayer.[14]

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, bicyclewheel hubs, and air bearings used in Coordinate­measuring machines.

Common

By far, the most common bearing is the plain bearing, a bearing which uses surfaces in rubbing contact,often with a lubricant such asOIL or graphite. A plain bearing may or may not be a discrete device. Itmay be nothing more than the bearing surface of a hole with a shaft passing through it, or of a planar

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Animation of ball bearing (without acage). The inner ring rotates and theouter ring is stationary.

surface that bears another (in these cases, not a discrete device); or it may be a layer of bearing metaleither fused to the substrate (semi­discrete) or in the form of a separable sleeve (discrete). With suitablelubrication, plain bearings often give entirely acceptable accuracy, life, and friction at minimal cost.Therefore, they are very widely used.

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 operatingmachinery.

Thus, there are many types of bearings, with varying shape, material, lubrication, principle of operation,and so on.

Principles of operation

There are at least 6 common principles of operation:

Plain bearing, also known by the specific styles: bushing,journal bearing, sleeve bearing, rifle bearingRolling­element bearing such as ball bearings and rollerbearingsJewel bearing, in which the load is carried by rolling theaxle slightly off­centerFluid bearing, in which the load is carried by a gas orliquidMagnetic bearing, in which the load is carried by amagnetic fieldFlexure bearing, in which the motion is supported by aload element which bends.

Motions

Common motions permitted by bearings are:

axial rotation e.g. shaft rotationlinear motion e.g. drawerspherical rotation e.g. ball and socket jointhinge motion e.g. door, elbow, knee

Friction

Reducing friction in bearings is often important for efficiency, to reduce wear and to facilitate extendeduse at high speeds and to avoid overheating and premature failure of the bearing. Essentially, a bearingcan reduce friction by virtue of its shape, by its material, or by introducing and containing a fluidbetween surfaces or by separating the surfaces with an electromagnetic field.

By shape, gains advantage usually by using spheres or rollers, or by forming flexure bearings.By material, exploits the nature of the bearing material used. (An example would be usingplastics that have low surface friction.)By fluid, exploits the low viscosity of a layer of fluid, such as a lubricant or as a pressurizedmedium to keep the two solid parts from touching, or by reducing the normal force between them.By fields, exploits electromagnetic fields, such as magnetic fields, to keep solid parts fromtouching.

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Combinations of these can even be employed within the same bearing. An example of this is where thecage is made of plastic, and it separates the rollers/balls, which reduce friction by their shape and finish.

Loads

Bearings vary greatly over the size and directions of forces that they can support.

Forces can be predominately radial, axial (thrust bearings) or bending moments perpendicular to themain axis.

Speeds

Different bearing types have different operating speed limits. Speed is typically specified as maximumrelative surface speeds, often specified ft/s or m/s. Rotational bearings typically describe performance interms of the product DN where D is the mean diameter (often in mm) of the bearing and N is the rotationrate in revolutions per minute.

Generally there is considerable speed range overlap between bearing types. Plain bearings typicallyhandle only lower speeds, rolling element bearings are faster, followed by fluid bearings and finallymagnetic bearings which are limited ultimately by centripetal force overcoming material strength.

Play

Some applications apply bearing loads from varying directions and accept only limited play or "slop" asthe applied load changes. One source of motion is gaps or "play" in the bearing. For example, a 10 mmshaft in a 12 mm hole has 2 mm play.

Allowable play varies greatly depending on the use. As example, a wheelbarrow wheel supports radialand axial loads. Axial loads may be hundreds of newtons force left or right, and it is typically acceptablefor the wheel to wobble by as much as 10 mm under the varying load. In contrast, a lathe may position acutting tool to ±0.02 mm using a ball lead screw held by rotating bearings. The bearings support axialloads of thousands of newtons in either direction, and must hold the ball lead screw to ±0.002 mm acrossthat range of loads

Stiffness

A second source of motion is elasticity in the bearing itself. For example, the balls in a ball bearing arelike stiff rubber, and under load deform from round to a slightly flattened shape. The race is also elasticand develops a slight dent where the ball presses on it.

The stiffness of a bearing is how the distance between the parts which are separated by the bearingvaries with applied load. With rolling element bearings this is due to the strain of the ball and race. Withfluid bearings it is due to how the pressure of the fluid varies with the gap (when correctly loaded, fluidbearings are typically stiffer than rolling element bearings).

Service life

Fluid and magnetic bearings

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Fluid and magnetic bearings can have practically indefinite service lives. In practice, there are fluidbearings supporting high loads in hydroelectric plants that have been in nearly continuous service sinceabout 1900 and which show no signs of wear.

Rolling element bearings

Rolling element bearing life is determined by load, temperature, maintenance, lubrication, materialdefects, contamination, handling, installation and other factors. These factors can all have a significanteffect on bearing life. For example, the service life of bearings in one application was extendeddramatically by changing how the bearings were stored before installation and use, as vibrations duringstorage caused lubricant failure even when the only load on the bearing was its own weight;[15] theresulting damage is often false brinelling. Bearing life is statistical: several samples of a given bearingwill often exhibit a bell curve of service life, with a few samples showing significantly better or worselife. Bearing life varies because microscopic structure and contamination vary greatly even wheremacroscopically they seem identical.

L10 life

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 dueto classical fatigue failure (and not any other mode of failure like lubrication starvation, wrong mountingetc.), or, alternatively, the life at which ninety percent will still be operating.The L10 life of the bearingis theoretical life and may not represent service life of the bearing. Bearings are also rated using C0(static loading) value. This is the basic load rating as a reference, and not an actual load value.

Plain bearings

For plain bearings some materials give much longer life than others. Some of the John Harrison clocksstill 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.

Flexure bearings

Flexure bearings rely on elastic properties of material.Flexure bearings bend a piece of materialrepeatedly. Some materials fail after repeated bending, even at low loads, but careful material selectionand bearing design can make flexure bearing life indefinite.

Short­life bearings

Although long bearing life is often desirable, it is sometimes not necessary. Tedric A. Harris describes abearing for a rocket motor oxygen pump that gave several hours life, far in excess of the several tens ofminutes life needed.[15]

External factors

The service life of the bearing is affected by many parameters that are not controlled by the bearingmanufactures. For example, bearing mounting, temperature, exposure to external environment, lubricantcleanliness and electrical currents through bearings etc.

Maintenance and lubrication

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Many bearings require periodic maintenance to prevent premature failure, but many others require littlemaintenance. The latter include various kinds of fluid and magnetic bearings, as well as rolling­elementbearings that are described with terms including sealed bearing and sealed for life. These contain sealsto keep the dirt out and the grease in. They work successfully in many applications, providingmaintenance­free operation. Some applications cannot use them effectively.

Nonsealed bearings often have a grease fitting, for periodic lubrication with a grease gun, or an oil cupfor periodic filling with oil. Before the 1970s, sealed bearings were not encountered on most machinery,andOILING 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 carchassis are mostly sealed for life. From the late 1700s through mid 1900s, industry relied on manyworkers called oilers to lubricate machinery frequently with oil cans.

Factory machines today usually have lube systems, in which a central pump serves periodic charges ofoil or grease from a reservoir through lube lines to the various lube points in the machine's bearingsurfaces, bearing journals, pillow blocks, and so on. The timing and number of such lube cycles iscontrolled by the machine's computerized control, such as PLC or CNC, as well as by manual overridefunctions when occasionally needed. This automated process is how all modern CNC machine tools andmany other modern factory machines are lubricated. Similar lube systems are also used onnonautomated machines, in which case there is a hand pump that a machine operator is supposed topump once daily (for machines in constant use) or once weekly. These are called one­shot systems fromtheir chief selling point: one pull on one handle to lube the whole machine, instead of a dozen pumps ofan 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 systemsmentioned above, except that oil is pumped continuously. Much of this oil flows through passagesdrilled or cast into the engine block and cylinder heads, escaping through ports directly onto bearings,and squirting elsewhere to provide an oil bath. The oil pump simply pumps constantly, and any excesspumped oil continuously escapes through a relief valve back into the sump.

Many bearings in high­cycle industrial operations need periodic lubrication and cleaning, and manyrequire occasional adjustment, such as pre­load adjustment, to minimise the effects of wear.

Bearing life is often much better when the bearing is kept clean and well lubricated. However, manyapplications make good maintenance difficult. For example, bearings in the conveyor of a rock crusherare exposed continually to hard abrasive particles. Cleaning is of little use, because cleaning is expensiveyet the bearing is contaminated again as soon as the conveyor resumes operation. Thus, a goodmaintenance program might lubricate the bearings frequently but not include any disassembly forcleaning. The frequent lubrication, by its nature, provides a limited kind of cleaning action, bydisplacing older (grit­filled)OIL or grease with a fresh charge, which itself collects grit before beingdisplaced by the next cycle.

Rolling­element bearing outer race fault detection

Rolling­element bearings are widely used in the industries today, and hence maintenance of thesebearings becomes an important task for the maintenance professionals. The rolling­element bearingswear out easily due to metal­to­metal 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 highrunning speed conditions. Regular diagnostics of rolling­element bearing faults is critical for industrialsafety and operations of the machines along with reducing the maintenance costs or avoiding shutdowntime. Among the outer race, inner race and ball, the outer race tends to be more vulnerable to faults anddefects.

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There is still a room for discussion whether the rolling element excites the natural frequencies of bearingcomponent when it passes the fault on the outer race. Hence we need to identify the bearing outer racenatural frequency and its harmonics. The bearing faults create impulses and results in strong harmonicsof the fault frequencies in the spectrum of vibration signals. These fault frequencies are sometimesmasked by adjacent frequencies in the spectra due to their little energy. Hence, a very high spectralresolution is often needed to identify these frequencies during a FFT analysis. The natural frequencies ofa rolling element bearing with the free boundary conditions are 3 kHz. Therefore, in order to use thebearing component resonance bandwidth method to detect the bearing fault at an initial stage a highfrequency range accelerometer should be adopted, and data obtained from a long duration needs to beacquired. A fault characteristic frequency can only be identified when the fault extent is severe, such asthat of a presence of a hole in the outer race. The harmonics of fault frequency is a more sensitiveindicator 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 frequencydemodulation 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 ormay not contain fault frequency components.

Using spectral analysis as a tool to identify the faults in the bearings faces challenges due to issues likelow energy, signal smearing, cyclostationarity etc. High resolution is often desired to differentiate thefault frequency components from the other high­amplitude adjacent frequencies. Hence, when the signalis sampled for FFT analysis, the sample length should be large enough to give adequate frequencyresolution in the spectrum. Also, keeping the computation time and memory within limits and avoidingunwanted aliasing may be demanding. However, a minimal frequency resolution required can beobtained by estimating the bearing fault frequencies and other vibration frequency components and itsharmonics due to shaft speed, misalignment, line frequency, gearbox etc.

Packing

Some bearings use a thick grease for lubrication, which is pushed into the gaps between the bearingsurfaces, also known as packing. The grease is held in place by a plastic, leather, or rubber gasket (alsocalled a gland) that covers the inside and outside edges of the bearing race to keep the grease fromescaping.

Bearings may also be packed with other materials. Historically, the wheels on railroad cars used sleevebearings packed with waste or loose scraps of cotton or wool fiber soaked inOIL , then later usedsolid pads of cotton.[16]

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 adhesiondraws oil up the ring and onto the shaft, where the oil migrates into the bearing to lubricate it. Excess oilis flung off and collects in the pool again.[17]

Splash lubrication

Some machines contain a pool of lubricant in the bottom, with gears partially immersed in the liquid, orcrank rods that can swing down into the pool as the device operates. The spinning wheels fling oil intothe air around them, while the crank rods slap at the surface of the oil, splashing it randomly on the

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interior surfaces of the engine. Some small internal combustion engines specifically contain specialplastic flinger wheels which randomly scatter oil around the interior of the mechanism.[18]

Pressure lubrication

For high speed and high power machines, a loss of lubricant can result in rapid bearing heating anddamage due to friction. Also in dirty environments the oil can become contaminated with dust or debristhat increases friction. In these applications, a fresh supply of lubricant can be continuously supplied tothe bearing and all other contact surfaces, and the excess can be collected for filtration, cooling, andpossibly reuse. Pressure oiling is commonly used in large and complex internal combustion engines inparts of the engine where directly splashed oil cannot reach, such as up into overhead valveassemblies.[19] High speed turbochargers also typically require a pressurized oil system to cool thebearings and keep them from burning up due to the heat from the turbine.

Types

There are many different types of bearings.

Type Description Friction Stiffness† Speed Life Notes

Plainbearing

Rubbingsurfaces,usually withlubricant; somebearings usepumpedlubrication andbehavesimilarly tofluid bearings.

Depends onmaterials andconstruction,PTFE hascoefficient offriction ~0.05­0.35, dependingupon fillers added

Good,providedwear islow, butsomeslack isnormallypresent

Low tovery high

Low to very high­ depends uponapplication andlubrication

Widely used,relatively highfriction, suffersfrom stiction insomeapplications.Dependingupon theapplication,lifetime can behigher or lowerthan rollingelementbearings.

Rollingelementbearing

Ball or rollersare used toprevent orminimiserubbing

Rollingcoefficient offriction with steelcan be ~0.005(adding resistancedue to seals,packed grease,preload andmisalignment canincrease frictionto as much as0.125)

Good, butsomeslack isusuallypresent

Moderateto high(oftenrequirescooling)

Moderate to high(depends onlubrication, oftenrequiresmaintenance)

Used for highermoment loadsthan plainbearings withlower friction

Jewelbearing

Off­centerbearing rolls inseating

Low Low dueto flexing Low

Adequate(requiresmaintenance)

Mainly used inlow­load, highprecision worksuch as clocks.Jewel bearings

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may be verysmall.

Fluidbearing

Fluid is forcedbetween twofaces and heldin by edge seal

Zero friction atzero speed, low

Veryhigh

Veryhigh(usuallylimited toa fewhundredfeet persecondat/byseal)

Virtually infinitein someapplications,may wear atstartup/shutdownin some cases.Often negligiblemaintenance.

Can failquickly due togrit or dust orothercontaminants.Maintenancefree incontinuous use.Can handlevery largeloads with lowfriction.

Magneticbearings

Faces ofbearing arekept separateby magnets(electromagnetsor eddycurrents)

Zero friction atzero speed, butconstant powerfor levitation,eddy currents areoften inducedwhen movementoccurs, but maybe negligible ifmagnetic field isquasi­static

LowNopracticallimit

Indefinite.Maintenancefree. (withelectromagnets)

Activemagneticbearings(AMB) needconsiderablepower.Electrodynamicbearings (EDB)do not requireexternal power.

Flexurebearing

Material flexesto give andconstrainmovement

Very low LowVeryhigh.

Very high or lowdepending onmaterials andstrain inapplication.Usuallymaintenancefree.

Limited rangeof movement,no backlash,extremelysmooth motion

†Stiffness is the amount that the gap varies when the load on the bearing changes, it is distinct from thefriction of the bearing.

!knife edge bearings

See also

AxleboxBall bearingBall splineHertz contact stressHingeMain bearingNeedle roller bearingPillow block bearingRace (bearing)Rolamite

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References

Rolling­element bearingScrollerwheelShock Pulse MethodSlewing bearingSpherical plain bearingSpherical roller bearingSpiral groove bearing

1. Merriam­Webster, "headwords "bearing" and "bear" " (http://unabridged.merriam­webster.com/collegiate.htm), Merriam­Webster's Collegiate Dictionary, online subscription version.Paywalled reference work.

2. American Society of Mechanical Engineers (1906), Transactions of the American Society of MechanicalEngineers (http://books.google.com/books?id=aWd1G50m8WEC&pg=RA1­PA441) 27, American Society ofMechanical Engineers, p. 441.

3. Bryan Bunch, The history of science and technology.4. Steven Blake Shubert, Encyclopedia of the archaeology of ancient Egypt5. Guran, Ardéshir; Rand, Richard H. (1997), Nonlinear dynamics (http://books.google.com/books?

id=ttBQ1k8MYZ4C&pg=PA178&lpg=PA178), World Scientific, p. 178, ISBN 978­981­02­2982­5.6. Purtell, John (1999/2001). Project Diana, chapter 10: http://nemiship.multiservers.com/nemi.htm7. Bearing Industry Timeline (http://www.americanbearings.org/?page=bearing_timeline), retrieved 2012­10­21.8. "Double­ Row Angular Contact Ball Bearings" (http://www.intechbearing.com/5200Series­

DoubleRowAngularContactBallBearings­SealsandShields­Shop.html).9. "Bicycle History, Chronology of the Growth of Bicycling and the Development of Bicycle Technology by

David Mozer" (http://www.ibike.org/library/history­timeline.htm). Ibike.org. Retrieved 2013­09­30.10. R. Stribeck, Kugellager für beliebige Belastungen Zeitschrift des Vereins Deutscher Ingenieure, 1901, Nr. 3,

Band 45, p. 73­7911. N.N. (R. Stribeck), Kugellager (ball bearings), Glasers Annalen für Gewerbe und Bauwesen, 1901, No. 577,

p. 2­9, Published 01. July 190112. A. Martens, Schmieröluntersuchungen (Investigations onOILS ) Part I: Mitteilungen aus den Königlichen

technischen Versuchsanstalten zu Berlin, Ergänzungsheft III 1888, p. 1­37, Verlag von Julius Springer, Berlinand Part II: Mitteilungen aus den Königlichen technischen Versuchsanstalten zu Berlin, Ergänzungsheft V,1889, p. 1­57, Verlag von Julius Springer, Berlin, (Note: These files can be downloaded from the website ofBAM: http://www.bam.de/de/ueber_uns/geschichte/adolf_martens.htm)

13. Machine Design (2007), Did You Know: Bud Wisecarver(http://www.bwc.com/pdf/news/1737_MSD_BIWI_eprint_.pdf) (PDF), Machine Design, p. 1.

14. "Design News Magazine ­ July 1995" (http://www.designnews.com/article/9409­Prime_mover_in_custom_bearings.php).

15. Harris, Tedric A. (2000). Rolling Bearing Analysis (4th ed.). Wiley­Interscience. ISBN 0­471­35457­0.16. White, John H. (1985) [1978]. The American Railroad Passenger Car (http://books.google.com/books?

id=RAidPrpZUNQC) 2. Baltimore, MD: Johns Hopkins University Press. p. 518. ISBN 0801827477.OCLC 11469984 (https://www.worldcat.org/oclc/11469984).

17. Steam Power Plant Engineering, by George Frederick Gebhardt, published by J. Wiley & sons, Incorporated,1917, p 791 Google Books scanned ref (http://books.google.com/books?id=6QhMAAAAMAAJ&dq=ring%20oiler&pg=PA791#v=onepage&q=ring%20oiler&f=false)

18. The gasoline automobile, George William Hobbs b. 1887, Ben George Elliott, Earl Lester Consoliver,University of Wisconsin. University Extension Division, McGraw­Hill Book Company, Inc., 1919 ­ 483pages, pp 111­114 Google Books scanned ref (http://books.google.com/books?id=kWJVAAAAMAAJ&pg=PA114&dq=splash+lubrication&hl=en&sa=X&ei=qN1zT8qZCcbl0gG77uT_Ag&ved=0CFAQ6AEwBA#v=onepage&q=splash%20lubrication&f=false)

19. Pressure Lubricating Characteristics, by Paul Dumas, Motor age, Volume 42, Class Journal Co., 14 Sep 1922Google Books scanned ref (http://books.google.com/books?id=S0AfAQAAMAAJ&pg=RA10­PA22&dq=engine+pressure+oiling&hl=en&sa=X&ei=hZlzT­P5L6bt0gGhstH_Ag&ved=0CEUQ6AEwAA#v=onepage&q=engine%20pressure%20oiling&f=false)

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Wikimedia Commons hasmedia related to Bearings.

External links

Comprehensive review on bearings, University ofCambridge (http://www.msm.cam.ac.uk/phase­trans/2011/Bearings/index.html)How bearings work(http://science.howstuffworks.com/bearing.htm)Bearing lubricants (http://www.jaredzone.info/2014/03/bearing­lubricants.html)Early bearing failure detection (http://www.reliableplant.com/Read/260/bearing­failure­detection)How to measure a bearing (http://www.bearing­king.co.uk/how­to­measure­a­bearing.php)Choosing the correct bearing type (http://www.bearingboys.co.uk/Measuring_Bearings­15­a)Kinematic Models for Design Digital Library (KMODDL)(http://kmoddl.library.cornell.edu/index.php) ­ Movies and photos of hundreds of workingmechanical­systems models at Cornell University. Also includes an e­book library(http://kmoddl.library.cornell.edu/e­books.php) of classic texts on mechanical design andengineering.Types of bearings, Cambridge University (http://www.msm.cam.ac.uk/phase­trans/2010/types/index.html)

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