Chapter 11 Rolling Contact Bearings

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1 Chapter 11 Rolling Contact Bearings 1

2 2 Chapter Outline

3 3 Overview The term rolling bearing is used to describe class of bearing in which the main load is transferred through elements in rolling contact rather than in sliding contact. Rolling Contact Bearings load is transferred through rolling elements such as balls, straight and tapered cylinders and spherical rollers.

4 4 Overview Frictional characteristics of a rolling bearing are affected by: Load Speed Operating viscosity of lubricant Bearings are manufactured to take: Pure radial loads Pure thrust loads Combination of the two kinds of loads

5 5 Bearing Types Figure 11 1: Nomenclature of a ball bearing

6 Bearing Types Figure 11 2: Various types of ball bearings 6

7 Bearing Types 7 Thrust Self aligning

8 8 Bearing Types will take radial load as well as some thrust load. Balls are inserted into the grooves by moving the inner ring to an eccentric position. Balls are separated after loading, and the separator is then inserted.

9 9 Bearing Types Use of a filling notch in inner and outer rings enables a greater number of balls to be inserted, thus increasing the load capacity. Thrust capacity is decreased Filling Notch

10 10 Bearing Types Angular-contact bearing provides a greater thrust capacity. Angular Contact

11 11 Bearing Types Figure 11 3: Types of roller bearings a. straight roller b. spherical roller, thrust c. tapered roller, Thrust Straight roller Spherical roller

12 12 Bearing Types Figure 11 3: Types of roller bearings d. Needle e. Tapered roller f. Steep-angle tapered roller Needle Type Tapered roller

13 Bearing Types Figure 11 3: Types of roller bearings Straight roller bearings will carry a greater radial load than ball bearings of same size

13 13 Bearing Types Figure 11 3: Types of roller bearings Straight roller bearings will carry a greater radial load than ball bearings of same size because of greater contact area. A slight misalignment will cause rollers to skew and get out of line. Straight roller bearings will not take thrust loads.

14 14 Bearing Types Figure 11 3: Types of roller bearings Spherical-roller thrust bearing is useful where heavy loads and misalignment occur. The spherical elements have the advantage of increasing their contact area as the load is increased.

15 15 Bearing Types Figure 11 3: Types of roller bearings Needle bearings are very useful where radial space is limited. They have a high load capacity when separators are used Needle Type

16 Bearing Life When ball or roller of rolling-contact bearings rolls, contact stresses occur on: inner ring rolling element outer ring

17 Bearing Life Common life measures: Number of revolutions of inner ring (outer ring stationary) until first tangible evidence of fatigue Number of hours of use at a standard angular speed until first tangible evidence of fatigue

18 Bearing Life Fatigue failure consists of spalling of the load carrying surfaces American Bearing Manufacturers Association (ABMA) standard: failure criterion is the first evidence of fatigue Timken Fatigue criterion: spalling or pitting of an area of 0.01 in 2

19 Bearing Life The rating life of a group of nominally identical ball or roller bearings is defined as number of revolutions (or hours at a constant speed) that 90% of a group of bearings will achieve or exceed before failure criterion develops. Minimum life, L 10 life, and B 10 life are also used as synonyms for rating life. Rating life is the 10 th percentile location of the bearing group s revolutions-to-failure distribution.

20 Bearing Life Median life is the 50 th percentile life of a group of bearings. Median life is between 4 & 5 times L 10 life. Most commonly used rating life is 10 6 revs Timken Company is rating its bearings at 3000 hours at 500 rpm ( revs)

21 Bearing Load Life at Rated Reliability When nominally identical groups are tested to the life-failure criterion at different loads, the data are plotted on a graph as depicted in Fig a = 3 for ball bearings a = 10/3 for roller bearings (cylindrical and tapered roller)

22 Bearing Load Life at Rated Reliability Catalog load rating = radial load that causes 10% of a group of bearings to fail at bearing manufacturer s rating life. C 10 : catalog load rating If manufacturer s rating life is 10 6 rev, Catalog load rating is often referred to as: Basic Dynamic Load Rating Basic Load Rating

23 Bearing Load Life at Rated Reliability Radial load that would be necessary to cause failure at such a low life would be unrealistically high. Thus, Basic Load Rating should be viewed as a reference value, and not as an actual load to be achieved by a bearing.

24 Bearing Load Life at Rated Reliability In selecting a bearing for a given application, it is necessary to relate desired load & life requirements to catalog load rating corresponding to catalog rating life. Units of L R and L D are revolutions Subscripts R & D stand for Rated & Desired

25 Bearing Load Life at Rated Reliability

26 26 EXAMPLE 11 1 Consider SKF, which rates its bearings for 1 million revolutions. If you desire a life of 5000 h at 1725 rpm with a load of 400 lbf with a reliability of 90%, for which catalog rating would you search in an SKF catalog?

27 Reliability Reliability: probability of survival of the design s function Reliability method of design is one in which: We obtain distribution of stresses & distribution of strengths Relate these two in order to achieve an acceptable success rate

28 Reliability The statistical measure of the probability that a mechanical element will not fail in use is called the reliability of that element. p f is probability of failure, given by number of instances of failures per total number of possible instances. 0 R 1.

29 Reliability R = 0.90: there is a 90 % chance that the part will perform its proper function without failure Failure of 6 parts out of every 1000 manufactured might be considered an acceptable failure rate for a certain class of products. This represents a reliability of

30 Reliability Consider a shaft with two bearings having reliabilities of 95 % & 98 %. The overall reliability of the shaft system is

31 Example Select a deep groove ball bearing for a desired life of 5000 hours at 1725 rpm with 90% reliability. The bearing radial load is 400 lb. 31

32 32 Bearing Reliability If a machine is assembled with 4 bearings, each having a reliability of 90%, then reliability of the system is (.9) 4 = 0.65 Select bearings with higher than 90% reliability Mechanical Engineering Dept.

33 Bearing Reliability The distribution of bearing failure can be best approximated by two and three parameter Weibull distribution. 33 C 10 C 10 is catalog basic dynamic load L R hours of life at speed of n R rpm

Example 34 Ken Youssefi Select a deep groove ball bearing for a desired life of 5000 hours at 1725 rpm with 99% reliability. The bearing radial load is 400 lb.

34 Example 34 Ken Youssefi Select a deep groove ball bearing for a desired life of 5000 hours at 1725 rpm with 99% reliability. The bearing radial load is 400 lb. For 90% reliability C 10 = 14.3 kn 30 mm Bore deep groove bearing Use 99% reliability, R =.99 = 23.7 kn Select a 35 mm bearing instead of 30 mm for 90% reliability

35 Combined Radial and Thrust Loading F a = axial thrust load F r = radial load F e = equivalent radial load that does the same damage as the combined radial & thrust loads together V = rotation factor V = 1 when inner ring rotates V = 1.2 when outer ring rotates Two dimensionless groups: F e /V F r and F a /V F r

36 Combined Radial and Thrust Loading e is defined by the intersection of the two lines. Equations for the two lines Figure 11 6: relationship of dimensionless group Fe/(VFr) & Fa/(VFr)

37 Combined Radial and Thrust Loading X & Y factors depend upon geometry & construction of specific bearing. Table 11 1: representative values of X 1, Y 1, X 2, and Y 2 as a function of e, which in turn is a function of F a /C 0 C 0 = basic static load rating Load that will produce a total permanent deformation in the raceway and rolling element at any contact point of times diameter of the rolling element

38 11 6 Combined Radial and Thrust Loading Table 11

38 Combined Radial and Thrust Loading Table 11 1: Equivalent Radial Load Factors for Ball Bearings

39 11 6 Combined Radial and Thrust Loading Table 11 2: Dimensions & Load

39 Combined Radial and Thrust Loading Table 11 2: Dimensions & Load Ratings for Single-Row 02-Series Deep-Groove and Angular-Contact Ball Bearings

40 Combined Radial and Thrust Loading The rotation factor V is intended to correct for the rotating ring conditions. The factor of 1.2 for outer-ring rotation is simply an acknowledgment that the fatigue life is reduced under these conditions. For Self-aligning bearings, V = 1 for rotation of either ring. Straight or cylindrical roller bearings will take no axial load, or very little, the Y factor is always zero.

41 Combined Radial and Thrust Loading ABMA has established standard boundary dimensions for bearings, which define bearing bore, outside diameter (OD), width, and fillet sizes on the shaft and housing shoulders. The basic plan covers all ball and straight roller bearings in metric sizes. For a given bore, there is an assortment of widths & outside diameters. For a particular outside diameter, one can usually find a variety of bearings having different bores and widths.

42 11 6 Combined Radial and Thrust Loading Basic ABMA plan is illustrated in Fig.

42 Combined Radial and Thrust Loading Basic ABMA plan is illustrated in Fig Bearings are identified by a two-digit number called the dimension-series code 1 st number = width series, 0, 1, 2, 3, 4, 5, and 6 2 nd number = diameter series (outside) 8, 9, 0, 1, 2, 3, 4

43 Combined Radial and Thrust Loading Figure 11 7: Basic ABMA plan for boundary dimensions. Apply to ball bearings, straight roller bearings, and spherical roller bearings, but not to inch series ball bearings or tapered roller bearings.

44 11 6 Combined Radial and Thrust Loading Figure 11 8: Shaft & housing

44 Combined Radial and Thrust Loading Figure 11 8: Shaft & housing shoulder diameters d S & d H should be adequate to ensure good bearing support

45 11 6 Combined Radial and Thrust Loading Table 11 3:

45 Combined Radial and Thrust Loading Table 11 3: Dimensions & Basic Load Ratings for Cylindrical Roller Bearings

46 11 6 Combined Radial and Thrust Loading Table 11 4:

46 Combined Radial and Thrust Loading Table 11 4: Bearing-Life Recommendations for Various Classes of Machinery

47 11 6 Combined Radial and Thrust Loading Table 11 5: Load-Application Factors Use

47 Combined Radial and Thrust Loading Table 11 5: Load-Application Factors Use the load-application factors to increase the equivalent load before selecting a bearing

48 EXAMPLE 11 4 An SKF 6210 angular-contact ball bearing has an axial load F a of 400 lbf & a radial load F r of 500 lbf applied with the outer ring stationary. The basic static load rating C 0 is 4450 lbf & the basic load rating C 10 is 7900 lbf. Estimate the life at a speed of 720 rpm. 48

49 Selection of Ball & Cylindrical Roller Bearings EXAMPLE 11 7: The second shaft on a parallel-shaft 25-hp foundry crane speed reducer contains a helical gear with a pitch diameter of 8.08 in. Helical gears transmit components of force in the tangential, radial, and axial directions. The components of the gear force transmitted to the second shaft are shown in Fig , at point A. The bearing reactions at C and D, assuming simple-supports, are also shown. A ball bearing is to be selected for location C to accept the thrust, and a cylindrical roller bearing is to be utilized at location D. The life goal of the speed reducer is 10 kh, with a reliability factor for the ensemble of all four bearings (both shafts) to equal or exceed 0.96 for the Weibull parameters of Ex The application factor is to be 1.2.

50 EXAMPLE a f =1.2 T = 595(4.04) = 2404 lbf in F rd = F rc = R =

51 EXAMPLE C 10 = a f = Choose a mm series, or a mm series cylindrical roller bearing from Table (b) The ball bearing at C involves a thrust component. Assuming F a /(V F r ) > e, 1 Choose Y 2 from Table Find C 10 3 Identify a suitable bearing from Table 11 2, note C 0. 4 Using F a /C 0 enter Table 11 1 to obtain a new value of Y 2. 5 Find C If the same bearing is obtained, stop. 7 If not, take next bearing and go to step 4.

EXAMPLE 11 7 52 As a first approximation, take the middle entry from Table 11 1: X2 = 0.56 Y2 = 1.63. From Table 11 2, angular-contact bearing 02-60 mm has C10 = 55.

52 EXAMPLE As a first approximation, take the middle entry from Table 11 1: X2 = 0.56 Y2 = From Table 11 2, angular-contact bearing mm has C10 = 55.9 kn. C0 is 35.5 kn. which makes e from Table 11 1 approximately Now Fa/[V Fr ] = 344/[(1) 464.4] = 0.74, which is greater than 0.24, so we find Y2 by interpolation:

EXAMPLE 11 7 53 From Table 11 2 an angular contact bearing 02-65 mm has C10 = 63.7 kn and C0 of 41.5 kn.

53 EXAMPLE From Table 11 2 an angular contact bearing mm has C10 = 63.7 kn and C0 of 41.5 kn. making e approximately Now from before, Fa/V Fr = 0.74, which is greater than We find Y2 again by interpolation:

54 EXAMPLE From Table 11 2 an angular-contact mm is still selected, so the iteration is complete

55 Selection of Tapered Roller Bearings Components of a tapered roller bearing: 1. Cone (inner ring) 2. Cup (outer ring) 3. Tapered rollers 4. Cage (spacer-retainer)

56 Selection of Tapered Roller Bearings Assembled bearing consists of two separable parts: 1. Cone assembly: cone, rollers, and cage 2. Cup Bearings can be: single-row, two row, fourrow, and thrust-bearing assemblies Auxiliary components such as spacers and closures can be used

57 Selection of Tapered Roller Bearings Figure 11 13: Nomenclature of a tapered roller bearing. G = location of effective load center; use this point to estimate radial bearing load

58 Selection of Tapered Roller Bearings Even when an external thrust load is not present, radial Cup load will induce a thrust reaction within bearing because of taper. To avoid separation of the races & rollers, this thrust must be resisted by an equal and opposite force. One way of generating this force is to always use at least two tapered roller bearings on a shaft.

59 Indirect mounting Selection of Tapered Roller Bearings Direct & indirect mounting involve space and compactness needed or desired, but with same system stability Direct mounting

60 11 9 Selection of Tapered Roller Bearings Figure 11 15: Catalog

60 Selection of Tapered Roller Bearings Figure 11 15: Catalog entry of single-row straight-bore Timken roller bearings, in part.

61 61

62 Selection of Tapered Roller Bearings A radial load on a tapered roller bearing will induce a thrust reaction. The load zone includes about half the rollers and subtends an angle of approximately 180. F i = induced thrust load from a radial load with a 180 load zone, Timken provides the equation

63 Selection of Tapered Roller Bearings K factor is geometry specific = ratio of radial load rating to thrust load rating K can be first approximated with 1.5 for a radial bearing and 0.75 for a steep angle bearing in the preliminary selection process. After a possible bearing is identified, exact value of K for each bearing can be found in bearing catalog.

64 11 9 Selection of Tapered Roller Bearings Figure 11 16: Direct-mounted

64 Selection of Tapered Roller Bearings Figure 11 16: Direct-mounted tapered roller bearings, showing radial, induced thrust, and external thrust loads.

65 Selection of Tapered Roller Bearings F ra & F rb = radial loads, applied at effective force centers G A & G B. F ia & F ib = induced loads due to effect of radial loads F ae = externally applied thrust load on shaft

66 Selection of Tapered Roller Bearings Fe = X V F r + Y F a Timken recommends using X = 0.4 & V = 1 for all cases, and using the K factor for the specific bearing for Y. This gives an equation of the form

67 Selection of Tapered Roller Bearings F a is net axial load carried by bearing due to combination of induced axial load from the other bearing & external axial load. Only one of the bearings will carry the net axial load. Which one it is depends on: 1. Direction the bearings are mounted 2. Relative magnitudes of induced loads 3. Direction of external load 4. Whether shaft or housing is the moving part

68 Selection of Tapered Roller Bearings First, determine visually which bearing is being squeezed by the external thrust load, and label it as bearing A. Label the other bearing as bearing B. If there is no external thrust, then either bearing can arbitrarily be labeled as bearing A.

69 Selection of Tapered Roller Bearings Figure 11 17: Examples of determining which bearing carries the external thrust load. In each case, the compressed bearing is labeled as bearing A. a. External thrust applied to rotating shaft b. External thrust applied to rotating cylinder

70 Selection of Tapered Roller Bearings Figure 11 17

71 Selection of Tapered Roller Bearings Second, determine which bearing actually carries the net axial load. If induced thrust F ia from bearing A happens to be larger than the combination of external thrust & thrust induced by bearing B, then bearing B will carry the net thrust load.

72 Selection of Tapered Roller Bearings If equivalent radial load is ever less than original radial load, then original radial load should be used.

73 73 EXAMPLE 11 8 The shaft depicted in Fig a carries a helical gear with a tangential force of 3980 N, a radial force of 1770 N, and a thrust force of 1690 N at the pitch cylinder with directions shown. The pitch diameter of the gear is 200 mm. The shaft runs at a speed of 800 rpm, and the span (effective spread) between the direct-mount bearings is 150 mm. The design life is to be 5000 h and an application factor of 1 is appropriate. If the reliability of the bearing set is to be 0.99, select suitable single-row tapered roller Timken bearings.

74 74 EXAMPLE 11 8 Find reactions at A & B Trial 1: With direct mounting of bearings and application of external thrust to shaft, the squeezed bearing is bearing A.

75 75 EXAMPLE 11 8 Using K of 1.5 as initial guess for each bearing, the induced loads from the bearings are Since F ia is clearly less than F ib + F ae, bearing A carries the net thrust load, and Eq. (11 16) is applicable. R D =

76 76 EXAMPLE 11 8 From Fig , tentatively select type TS cone and cup, which will work: K A = 1.67, C 10 = N. For bearing B, from Eq. (11 7), the catalog entry C 10 should equal or exceed Tentatively select the bearing identical to bearing A, which will work: K B = 1.67, C 10 = N.

77 77 EXAMPLE 11 8 Trial 2: Repeat the process with K A = K B = 1.67 from tentative bearing selection. For bearing A, from Eq. (11 7) the corrected catalog entry C 10 should equal or exceed

78 78 EXAMPLE 11 8 Select cone and cup and 15245, respectively, for both bearing A and B. Effective load center is located at a = 5.8 mm, that is, 5.8 mm into the cup from the back. The shoulder-to-shoulder dimension = 150 2(5.8) = mm

79 Lubrication If relative velocity of sliding surfaces is high enough, then lubricant action is hydrodynamic Elastohydrodynamic lubrication (EHD) = phenomenon that occurs when a lubricant is introduced between surfaces that are in pure rolling contact.

80 Lubrication When a lubricant is trapped between two surfaces in rolling contact, a tremendous increase in pressure within the lubricant film occurs. Viscosity is exponentially related to pressure, A very large increase in viscosity occurs in the lubricant that is trapped between the surfaces

81 Lubrication Purposes of an antifriction-bearing lubricant: 1. Provide a film of lubricant between sliding & rolling surfaces 2. Help distribute & dissipate heat 3. Prevent corrosion of bearing surfaces 4. Protect the parts from entrance of foreign matter

82 11 11 Lubrication 82 Use Grease When Temperature 93 C Speed is low Unusual protection is required from entrance of foreign matter Simple bearing enclosures are desired Operation for long periods without attention is desired Use Oil When Temperatures are high Speed is high Oil tight seals are readily employed Bearing type is not suitable for grease lubrication Bearing is lubricated from a central supply

83 Mounting and Enclosure The housing bore & shaft outside diameter must be held to very close limits. One of the bearings usually has the added function of positioning or axially locating the shaft.

84 11 12 Mounting and Enclosure Figure 11 20: A common bearing

84 Mounting and Enclosure Figure 11 20: A common bearing mounting. Outer ring of right-hand bearing floats in the housing.

85 Mounting and Enclosure Fig : The function of shaft shoulder may be performed by: 1. retaining rings 2. hub of a gear or pulley 3. spacing tubes or rings The round nuts may be replaced by: 1. retaining rings 2. washers locked in position by screws 3. Cotters 4. taper pins

86 Mounting and Enclosure Fig : The housing shoulder may be replaced by: 1. a retaining ring 2. Outer ring of bearing may be grooved for a retaining ring 3. a flanged outer ring may be used 4. Force against outer ring of the left-hand bearing is usually applied by: a. cover plate b. retaining rings

87 11 12 Mounting and Enclosure Figure 11 21: An alternative bearing mounting to that in Fig.

87 Mounting and Enclosure Figure 11 21: An alternative bearing mounting to that in Fig Outer races are completely retained. If distance between bearings is great, temperature rise during operation may expand the shaft enough to destroy the bearings.

88 11 12 Mounting and Enclosure Figure 11 22: Two-bearing mountings

88 Mounting and Enclosure Figure 11 22: Two-bearing mountings The effect of mounting is to preload the bearings in an axial direction.

89 11 12 Mounting and Enclosure Figure 11

89 Mounting and Enclosure Figure 11 23: Mounting for a washing machine spindle.

90 Mounting and Enclosure When maximum stiffness & resistance to shaft misalignment is desired, pairs of angular contact ball bearings are often used in an arrangement called duplexing. Bearings manufactured for duplex mounting have their rings ground with an offset, so that when a pair of bearings is tightly clamped together, a preload is automatically established.

91 11 12 Mounting and Enclosure Figure 11 24: Arrangements of angular ball bearings a.

91 Mounting and Enclosure Figure 11 24: Arrangements of angular ball bearings a. Duplex Face-to-face mounting, DF b. Duplex Back to back mounting, DB c. Duplex Tandem mounting, DT

92 11 12 Mounting and Enclosure Figure 11 24: DF mounting DF

92 Mounting and Enclosure Figure 11 24: DF mounting DF mounting, will take heavy radial loads and thrust loads from either direction.

93 11 12 Mounting and Enclosure Figure 11 24: DB mounting DB mounting has the

93 Mounting and Enclosure Figure 11 24: DB mounting DB mounting has the greatest aligning stiffness Good for heavy radial loads thrust loads from either direction.

94 11 12 Mounting and Enclosure Figure 11 24: DT mounting DT, is used where thrust is

94 Mounting and Enclosure Figure 11 24: DT mounting DT, is used where thrust is always in same direction A preload, if required, must be obtained in some other manner

95 Mounting and Enclosure Bearings are usually mounted with the rotating ring a press fit. The stationary ring is then mounted with a push fit. This permits the stationary ring to creep in its mounting slightly, bringing new portions of the ring into the load-bearing zone to equalize wear.

96 11 12 Mounting and Enclosure Preloading The object of preloading is to: 1.

96 Mounting and Enclosure Preloading The object of preloading is to: 1. remove internal clearance usually found in bearings 2. increase fatigue life 3. decrease shaft slope at the bearing

97 Mounting and Enclosure Preloading Methods of Preloading straight roller bearings: 1. Mounting bearing on a tapered shaft or sleeve to expand the inner ring 2. Using an interference fit for the outer ring 3. Purchasing a bearing with the outer ring preshrunk over the rollers

98 11 12 Mounting and Enclosure Preloading Ball bearings are usually preloaded by the axial load built in during

98 Mounting and Enclosure Preloading Ball bearings are usually preloaded by the axial load built in during assembly. Bearings of Fig a and b are preloaded in assembly because of differences in widths of the inner & outer rings.

99 Mounting and Enclosure Alignment Permissible misalignment in bearings depends on: Type of bearing Geometric & material properties of specific bearing In general, cylindrical & tapered roller bearings require alignments that are closer than deepgroove ball bearings. Spherical ball bearings & self-aligning bearings are the most forgiving.

100 11 12 Mounting and Enclosure Alignmentm, Table 7 2: Typical Max Ranges for Slopes &

100 Mounting and Enclosure Alignmentm, Table 7 2: Typical Max Ranges for Slopes & Transverse Deflections Life of bearing decreases significantly when misalignment exceeds allowable limits.

101 11 12 Mounting and Enclosure Enclosures To exclude dirt and foreign matter and to

101 Mounting and Enclosure Enclosures To exclude dirt and foreign matter and to retain the lubricant, bearing mountings must include a seal. Figure 11 26: Typical sealing methods

102 11 12 Mounting and Enclosure Enclosures Used with grease lubrication when speeds are low Rubbing surfaces should have

102 Mounting and Enclosure Enclosures Used with grease lubrication when speeds are low Rubbing surfaces should have a high polish Felt seals should be protected from dirt by: placing them in machined grooves using metal stampings as shields

103 11 12 Mounting and Enclosure Enclosures An assembly consisting of rubbing element and, generally, a spring backing, which are retained in

103 Mounting and Enclosure Enclosures An assembly consisting of rubbing element and, generally, a spring backing, which are retained in a sheetmetal jacket. usually made by press fitting them into a counter bored hole in the bearing cover. They should not be used for high speeds

104 11 12 Mounting and Enclosure Enclosures Effective for high-speed May be used with either oil or grease.

104 Mounting and Enclosure Enclosures Effective for high-speed May be used with either oil or grease. At least three grooves should be used, and they may be cut on either bore or outside diameter. Clearance may vary from to in, depending upon speed and temperature.

105 105 3 rd Exam On Wednesday 20/11/2013 at 11:00 Tested Material: Chapter 11 Practice Problems: 14, 17, 19, 27, 28, 41

Chapter 11 Rolling Contact Bearings

Chapter 11 Rolling Contact Bearings 1 2 Chapter Outline Bearing Types Bearing Life Bearing Load Life at Rated Reliability Bearing Survival: Reliability versus Life Relating Load, Life, and Reliability