Rolling Element BearingsFigure 11-1, Mechanical Engineering Design, Juvinall& MarshekBearing Terminology•Tapered Bore:Seat the bearing onto a tapered shaft or to accommodatea tapered sleeve which can be used to fix a bearing to a shaft.•Shields or Seals:Between the inner and outer rings to capture lubricating grease around the balls and prevent intrusion ofcontaminants.( Z-shield ,RS-seal)-eg-61814-2RS1-two contact seals(NRB)•Self Aligning:The inner ring can pivot so that the bore of the inner ring is not aligned with that of the outer ring, this accommodates shaftswhich are not perfectly aligned (concentric) with the outer ring of thebearing.Bearing Terminology•Pure Radial and Pure Axial Loads:This indicates a bearing’s ability to sustain each of these kinds of loads in isolation.•Combined Loads:Ability to sustain a radial and an axial load at the same time.•Moment Load:This indicates a bearing’s ability to support a moment at right angles to the longitudinal shaft axis.•High Running Accuracy and High Stiffness: Some applications require a bearing which maintains the center of rotation of the shaft with extreme accuracy even when large loads are applied.Bearing Terminology•Locating:If the inner ring of a bearing is axially “locked” to the shaft and the outer ring is axially “locked” to the housing, then the bearing is said to be locating since it prevents the shaft from moving axially w.r.t.the housing.•Non-Locating:If either the inner or outer ring is not axially locked, the bearing cannot prevent the axial movement of the shaft.•Axial Displacement:In some bearings, the inner and outer races are free to move axially w.r.t. each other. This kind of bearing cannot be used in a locating arrangement.Bearing TerminologyFig 122-124, Ball andRoller BearingsAngle Of Contact•Figure 122a,bBearing Classification Bearing ClassificationBearing Types & LoadsDeep Groove Ball Bearing Pictures Courtesy of SKF General Catalogue, and SKF Rolling Bearings in Industrial GearboxesDeep Groove Ball BearingsMax axial load =.25*C o --.5*C0Bearing Types & LoadsCylindrical Roller Bearing Pictures Courtesy of SKF General Catalogue, and SKF Rolling Bearings in Industrial GearboxesCylindrical Roller BearingAxial load is governed by load capabilityOf sliding contact on flange –function oflubricant, operating temp. and heatremoval.Bearing Types & LoadsSpherical Roller Bearing Pictures Courtesy of SKF General Catalogue, and SKF Rolling Bearings in Industrial GearboxesBearing Types & LoadsTapered Roller Bearing Pictures Courtesy of SKF General Catalogue, and SKF Rolling Bearings in Industrial GearboxesBearing Types & LoadsAngular Contact Ball Bearing Pictures Courtesy of SKF General Catalogue, and SKF Rolling Bearings in Industrial GearboxesBearing Types & LoadsThrust Taper Roller BearingPictures Courtesy of SKF General Catalogue, and SKF Rolling Bearings in Industrial GearboxesBearing Types & LoadsDouble-Row Angular ContactBall BearingPictures Courtesy of SKF General Catalogue, and SKF Rolling Bearings in Industrial GearboxesBearing Types & LoadsFour-Point Angular ContactBall BearingPictures Courtesy of SKF General Catalogue, and SKF Rolling Bearings in Industrial GearboxesBearing Types & LoadsCARB Bearing•Very high radial load carryingcapacity•No axial load carrying capacity•Accommodates both axial motion andangular misalignmentPictures Courtesy of SKF General Catalogue, and SKF Rolling Bearings in Industrial GearboxesLBasic Bearing Life Rating 10•Norton fig 10-22(10^6 revolutions)LBasic Bearing Life Rating10•The L10rating life of a sufficiently large number of dimensionally identical bearings is expressed by the number of revolutions or number of hours at constant speed reached or exceeded by 90% of this bearing group before the firstsigns of material fatigue appear.If design on L10life chance of 10% failure at design life.Can one do better.a 99% life rating =.21*L10 LifeThe Life EquationL 10= Basic Life Rating in [revolutions x 106]C = Basic Dynamic Load Rating . This is the max. load at which 90% of the tested bearings will show no fatigue damage after 106revolutions. This value is given in the bearing catalogue for every bearing type.Note:If a bearing is subjected to a basic dynamic load of “C” then there is a 90% confidence that it will survive to 106cycles (L 10=1)P (upper-case) = Equivalent Dynamic Bearing Load . This is a measure of the combined radial and axial load on the bearing.p (lower-case) = Exponent for Life Equation . 3 for ball bearings, 10/3 for roller bearings.The Life EquationThe Basic Life Rating can also be expressed in hours of operation:where, n, is the rotational speed in rpmpP C L ⎟⎠⎞⎜⎝⎛=10ph P C n L ⎟⎠⎞⎜⎝⎛=6010610Dynamic Bearing LoadsP = Equivalent Dynamic Bearing LoadF r = the Actual Radial Load on the bearing F a = the Actual Axial Load on the bearingX = the Radial Load Factor for the bearing Y = the Axial Load Factor for the bearingar YF XF P +=Equivalent Dynamic Bearing Loads •Y will be LARGE for bearings which are unsuitable for axial loads. For example, SKF self-aligning ball bearings have values of Y as large as6.1•Y will be SMALL for bearings which are suited to carry axial loads. For example, SKF taper roller bearings usually have Y values of 1.0ar YF XF P +=Applicable Values of X and Y or Where, e, is a reference value which depends on bearing type and load magnitudes (see tables of specifications for bearings in SKF catalogue)e F F r a >e F Fra<Applicable Values of X and YExampleA self-aligning bearing is needed for a 20mm dia shaft. The shaft speedis 1200rpm and the bearing must operate for 3000hrs without maintenance. The radial load is 3000N and the axial load is 600N. Choose a bearing for this application.ExampleExampleSelf-Aligning Ball Bearings, (SKF Catalogue Pg. 155)Equivalent Dynamic Bearing Loadswhere when a r F Y F P 1+=eF F ra≤eF Fra>a r F Y F P 265.0+=ExampleExample ExampleExampleSpherical Roller Bearings, (SKF Catalogue Pg. 245)Equivalent Dynamic Bearing Loadswhere when a r F Y F P 1+=eF F ra≤eF Fra>a r F Y F P 267.0+=ExampleExample ExampleTo make copy of SKF catalogue.---open up“easy CD creator” on machine next to scanner in DAPR Lab.open file “SKFCAT” then click on directory “SKFIEC”Make sure you copy with “smart burn” presets .Note-don’t reconfigure each time if making more than1 copy.To run catalogue , go to SKFIEC directory and clickon SKFCD2 .NOTE –ALL THE FITS LISTED IN BEARING BOOKS ARE CALCULATED FROMCSA/ISO STANDARDS FOR “FITS OF MATING PARTS”Note-page 542 text-”rollingelement bearings are intended tohave inner and outer races pres-fitted to shaft and housing”page 9 SKF Cat.925—As ageneral rule ,ball bearings shouldhave an operational clearancewhich is virtually zero ,or theremay be a slight preload .Cylindricaland spherical rollers should alwayshave some residual clearance.-design-assembly –maintenance –life-runningaccuracy-all may result invaried clearance or pressfits.Snap RingsBearing ArrangementsFloating / Locating Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig. 295a-f, Pg. 250Picture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig. 295a-f, Pg. 250Floating / Locating Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig. 295a-f, Pg. 250Floating / Locating Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig. 295a-f, Pg. 250Floating / Locating Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 295a-f, Pg. 250Floating / Locating Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig. 295a-f, Pg. 250Floating / Locating Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig. 296 -Fig 301, Pg. 250Adjustable Bearing ArrangementsExampleTaper rollersNote –these equations are only valid when Bearings are adjusted against each other with practically zero clearance , but without preload If you preload the bearings the axial forces will have to be determined. Best bet Call SKF To determine best coarse of action.Picture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig. 296 -Fig 301, Pg. 250Adjustable Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig. 296 -Fig 301, Pg. 250Adjustable Bearing ArrangementsAdjustable Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 333, Pg. 294Floating Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 302a-c, Pg. 254Floating Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 302a-c, Pg. 254Floating Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 302a-c, Pg. 254Floating Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 334, Pg. 294Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 396, Pg. 326 Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 397, Pg. 326Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 470, Pg. 374 Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 477, Pg. 390Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 499, Pg. 428 Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 502, Pg. 433Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 503, Pg. 433 Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 503, Pg. 433Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 503, Pg. 433 Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 503, Pg. 433Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 503, Pg. 433 Bearing ArrangementsPicture courtesy: Ball and Roller Bearing Arrangements, Theory Design and Application.Fig 503, Pg. 433。
