1. Chapter 13 Rolling-contact Bearings
Key Terms:
rolling-contact bearing
ball bearing
roller bearing
thrust bearing

2. radial load
thrust load
basic dynamic load rating
basic static load rating
equivalent load
the rated life
expected life

4. 13.1 Types of Rolling-contact Bearings and the Representing Code
1. Construction
width
Materials:
GCr15、GCr15SiMn 58~65HRC
outer ring D
inner ring
Retainer d
rolling element
outer ring race

5. 2. Parameters Contact angle Load angle Limiting speed
Misalignment Capacity:
allowable angular deviation 

9. 3. Types of Rolling-contact Bearing
According to loading direction:
radial bearings
thrust bearings
angular contact bearings
According to rolling element shapes:
ball bearings
roller bearings

10. 4. Types Double-row angular contact bearings

11. Double-row tapered roller bearings35

12. Double-row self-align ball bearings1

13. Double-row self-align roller bearings2

14. Self-align thrust bearings2

15. Tapered roller bearings3

16. Double-row deep groove bearings4

17. Thrust bearings 5

19. Deep groove bearings 6

20. Angular contact bearings7

21. Thrust roller bearings8

22. Roller bearings N

23. Double-row roller bearingsNN

24. Needle bearings NA

25. Four points contact bearingsQJ

27. 5. Numbers of Rolling-contact Bearings(GB/T272-93)
Bearing Designation:
71206AC/P6/C2
pre-symbol
basic number
post number

28. First & second: inner diameter number d=065=30mm
Basic Number
First & second: inner diameter number 　　
　　　　　　　d=065=30mm
Third: diameter number 　　　　　　　
1－extra-light series
2－light series
3－medium series
4－heavy series

29. Fourth: width number 　　　　　　　
0－narrow series (omitted )
1－normal series
2－wide series
Fifth: Type number
　see table 13.1　　　　

30. First: Internal configuration number
Post Number
First: Internal configuration number
70000：
C：=150
AC：=250
B：=400
Fourth: Tolerance lever
/P2：2
/P4：4
/P5：5
/P6：6
/P6x－6x
/P0－0(omitted) -

31. sixth: free clearance number
/C0: 0(omitted)
/C3: 3
/C4: 4
/C5: 5 +
Pre-symbol
Partial symbol of the bearing, e.g. L, K, R, etc.

32. Example Explain the following bearing codes: 6308 ，7211C/P5 Solution
6308－
Tolerance 0, 0 Group Clearance
For the diameter of 40mm,
deep groove ball bearings, in the series,
7211C/P5 － The inside diameter is 55mm, the angle contact ball bearing, light series, angle of contact =150,5 level common difference, 0 group of windage

33. 6. The Choices of the Bearing Types
Load
Limiting Speed
Misalignment Capacity
Mount and Dismount

34. 13.2 The Forces and Failures
1. The loading analysis

35. Fig. 13.5 the force changing procedure

36. 2. The Failure types of rolling-contact bearing
1) Pitting

37. 2) Plastic deformation

38. 3) wear

39. 4) breakage

41. 5) burning

43. 3. Design Criterion
1）for revolution bearings:
calculate the fatigue life
2）for static or low revolution speed bearings:
calculate the static strength

44. 13.3 The Selection of Rolling-contact Bearings
1. The fatigue life of rolling-contact bearings
1)Life
The life is the working revolutions or hours before the pitting occurs on the bearing.
2) Rated life L10 , Lh
The rated life is the life that 90% of the bearings would achieve successfully under a rated load.

45. Rated Life of Different Reliability

46. 3) Basic dynamic load rating C
The basic dynamic load rating is the load to which the bearings can be subjected while achieving a rated life of 106r.
Cr or Ca
4) Basic static load rating C0
The basic static load rating is the load that the bearings can withstand without permanent deformation of any component.
C0r or C0a

47. 5) Load/life relationship
P/kN
L10 /(106r) 3 10 1 C
=3, for ball bearings;
=10/3, for roller bearings.

48. C——basic dynamic load rating P——equivalent load
—— check formula
Lh——the rated life
C——basic dynamic load rating
P——equivalent load
n——rotational speed (rpm)
——3 or 10/3

49. C——basic dynamic load rating P——equivalent load
—— design formula
L'h——the expected life
C——basic dynamic load rating
P——equivalent load
n——rotational speed (rpm)
——3 or 10/3

50. 2. Equivalent load of bearings
1)Concept
2)Calculation
For radial load only: P=fpR
For thrust load only: P=fpA

51. For radial and thrust load: P= fp(xR+yA)
P——equivalent load;
R——applied radial load;
A——applied thrust load;
fp——load coefficient, table 13.4
x——radial factor, table 13.3
y——thrust factor, table 13.3

53. 3. Determination of radial load R
According to force equilibrium principle:

54. =3000N

56. 4. Determination of thrust load A —for angular ball bearings and tapered roller bearings
(1) Two mountings of angular contact bearings:
Face to face
Back to back

57. (2) According to equilibrium condition:S1 S2
Derived axial load S

58. (3) Calculation of applied thrust load for angular contact bearings

59. (4) Procedure
1) Draw directions of derived axial load and compute its magnitude;
2) According to direction of resultant axial forces on shaft, judge moving tendency of shaft, judge “loosen bearing” and “pressed bearing”;
3) The applied thrust load of “loosen bearing” is equal to its own derived axial load;
4) The applied thrust load of “pressed bearing” is equal to algebraic sum of other thrust loads (except for its own derived axial load ).

60. Example
As shown below, R1=10000N, R2=5000N, FA=2000N, S=0.68R. Find: A1=? A2=? 1 2
Solution

61. —for deep groove ball bearings
Determination of thrust load A
—for deep groove ball bearings
Regarding the gulley ball bearing, its axial loading A decided by the external influence on axis axial force FA, aims the bearing, its withstands axial force A is the external influence on axis axial force (A=FA), another bearing withstands the axial force is zero.

62. Procedure for Bearing Selection
Determine the design life L'h
Determine the equivalent load
P=xR+yA
Calculate the required basic dynamic load
Select a bearing with C( > Creq’d) and a bore that closely matches the shaft diameter.

63. Procedure for Bearing Life Check
Determine the basic dynamic load rating
Determine the equivalent load
P=xR+yA
Calculate the expected life
Check the bearing life

64. 1.The angular contact bearings (7207C) are shown below, they are subjected to radial loads R1=1500N, R2=875N, the applied external thrust load FA=400N, the derived load S=eR. Compute the applied thrust loads A1, A2 .

65. 2. The tapered roller bearings are shown below，the external applied load FA=1030N, FR=6000N, n=1000r/min, load coefficient fp=1, the basic dynamic load rating C=34000N， Find：
1) The equivalent dynamic loads P1, P2；
2) The rated life of bearings.

66. 3. Two angular contact bearings 7207AC are mounted back to back on the shaft, the applied loads on the gears as know that is Ft=2200N, Fr=900N, Fa=400N, the reference diameter d=314mm, the rotational speed n=520rpm, medium shock, Find the rated life of bearings.

67. 13.4 Mounting of Bearings 1. Tolerance and Fit The Basic Hole System
interference fit
Shaft tolerances:
k6, m6, n6, etc.
The Basic Shaft System
clearance fit
Hole tolerance:
H7, J7, Js7, etc

69. “walks the inner loop” the scratch

70. Heat crack

71. Hot adhesion

72. “walks the addendum circle” the scratch

73. 1, in forbids to rap the addendum circle directly with the iron hammer!
2, forbids through the rolling body transmission installment strength!

79. 2. Dimensions
The shoulder is lower than the inner loop altitude highly!

80. Dismount of bearings

83. 3. Axial Retaining of bearings
1) inner race retaining
(a) (b) (c)
Retaining ring
End cap
Locknut

84. 2) outer race retaining
(a) (b)
a) Retaining ring
b) End cap

85. 4. Mount Types
1) Two bearings retained in one direction

87. C=0.2~0.4mm

88. 2) One bearing retained in two directions, one bearing float
The inner loop is fixed, the addendum circle is not fixed!

90. At the same time inner loop, addendum circle fixed!

95. 3) Two bearings float

96. 13.5 Practical Considerations in Application of Bearings
1. Lubrication
Function:
1.Provide a low-friction film;
2.Protect the bearing components from corrosion;
3.Carry heat away from the bearing unit;
4.Dispel contaminants and moisture from the bearing;
Lubricant:
grease and oil: table 13.5

97. 2. Bears’ Preloading

98. 3. Sealing
1) Contact sealing
a) Felt circle seal

99. b) Lip Seal

100. 2) Non-contact Sealing
a) Groove seal
b) Labyrinth seal

101. 4. Modify Clearance 1) By shim Attention: The bevel gear must adjust
the shafting the axial location.
method: Between adjustment retainer
cup end surface and bearing seat end
surface filling piece thickness.

102. 2) By screw

103. 3) By locknut

104. 5. Stiffness

105. Derived Axial Load S
Direction:

106. Magnitude of Derived Axial Load
Tapered Roller Bearing
Angular Contact Ball Bearing
70000C(a=15°)
70000AC(a=25°)
70000B(a=40°)
S=R/(2Y)
S=eR
S=0.68R
S=1.14R

107. a) face to face

108. b) Back to back

110. Typical Shapes of a Roller

111. Radial Bearing : (a)、(b) =00
Thrust Bearing: (c) 、(d) =45~900
Angular Contact Bearing: (e)、(f) =0~450

117. Life Distribution Chart1 90
Amount of no failure /%

122. Angular contact bearings 7

123. The end Thanks!