Objective of bearing is to provide relative positioning and rotational freedom while transmitting a load between two parts

1. GANDHINAGAR INSTITUTE OF
TECHONOLOGY(012)
SUBJECT : Machine Design
(2171909)
Active Learning Assignment on the topic of
“Rolling Contact Bearing”
BE Mechanical Sem:7 A3
Prepared By:

2. Introduction
 Objective of bearing is to provide relative positioning and rotational
freedom while transmitting a load between two parts.
 In rolling contact bearings as the name implies the friction is of rolling
type.
 It is much smaller than the sliding type

3. Types of Bearings
 Rolling Contact Bearings:
 load is transferred through rolling elements such as balls,
straight and tapered cylinders and spherical rollers.
 Journal (sleeve) Bearings:
 load is transferred through a thin film of lubricant (oil).

4. Rolling Contact Bearings
 Rolling contact bearing is also known as antifriction bearing.
 The load, speed, and operating viscosity of the lubricant affect
the friction characteristics of a rolling bearing.
 This type of bearings provide coefficient of friction between
0.001 to 0.002
 The designer must deal with such matters as fatigue, friction,
heat, lubrication, kinematics problems, material properties,
machining tolerances, assembly, use and cost etc.

5. Element of RCB
The rolling contact bearings are composed of four elements.
 Outer race
 Inner race
 Rolling element
 Cage of retaining ring

6. Construction Diagram

7. Classification of RCB
 Classified into two types:
1) Ball Bearing
 Deep groove (Conrad) bearing
 Filling notch ball bearing
 Angular contact bearings (AC)
2) Roller Bearing
Cylindrical bearings
Needle bearings
Tapered bearings
Spherical bearings

8. Ball Bearing
 Angular contact Ball bearings (AC)
 The centerline of contact between the balls and the raceway is at
an angle to the plane perpendicular to the axis of rotation.
 Used for high radial and thrust
load applications.

9. Ball Bearing
 Deep groove bearing
 Single row of deep groove ball bearing can combinational of
radial and thrust load.
 Load capacity is limited by the number of balls
 Primarily designed to support radial loads, the thrust capacity is
about 70% of radial load capacity

10. Ball Bearing
 Filling notch ball bearings
 Bearings have the same basic radial construction as Conrad
type. However, a filling notch (loading groove) permits more
balls to be used.
 Radial load capacity is 20 – 40% higher than Conrad type.
 Thrust load capacity drops to 20% (2 directions) of radial
load capacity.

11. Roller Bearing
 Roller bearings have higher load capacity than ball bearings,
load is transmitted through line contact instead of point contact.
 Helical rollers are made by winding rectangular material into
roller. Due to inherent flexibility they are capable of taking
considerable misalignment.
 A roller with length much larger than diameter is known as
needle roller and are used where radial space is limited. Cage
may be absent in needle roller bearings.

12. Roller Bearing

13. Bearing life
 Life number of revolution or hours of operation, at constant
speed, required for the failure criterion to develop
 defines the number of revolution or hours of operation, at constant
speed, in such a way that of the bearings tested (from the same group)
will complete or exceed before the first evidence of failure develops.
This is known as bearing life.
 For ball bearings and spherical bearings:
 L10 = 500 (hours) x 33.33 (rpm) x 60 = 106 = 1
million revolutions For tapered bearings
manufactured by Timken:
 L10 = 3000 (hours) x 500 (rpm) x 60 = 90 x 106
= 90 million revolutions
 Basic Dynamic Load Rating, C constant radial
load that a group of bearings can carry for L10 life.

14. Bearing Life
 Rating life:
L= (C/Pe)^3 * 10^6 cycle for ball bearings
L = (C/Pe)^10/3 * 10^6 cycle for roller bearings
 Equivalent Dynamic Load:
Pe = (XV Fr + YFa)^6
Where; X = radial factor
V = race rotation factor 1.00 for inner race 1.2 for outer race
Y = axial load factor
Fr, Fa = radial and axial load respectively
S = service factor
C = dynamic load for 10^6 cycles.
 Equivalent Static Load:
Po = XoFr * YoFn
Where; Xo and Yo are radial and axial load factors respectively

15. Materials & Manufacture
 Since the rolling elements and the races are subjected to
high local stresses of varying magnitude with each revolution
of the bearing, therefore the material of the rolling element) (i.e.
steel) should be of high quality. The balls are generally made
of high carbon chromium steel.
 The material of both the balls and races are heat treated to give
extra hardness and toughness.
 The balls are manufactured by hot forging on hammers
from steel rods. They are then heat treated, ground and polished.
The races are also formed by forging and then heat-treated,
ground and polished.

16. Lubrication of Ball and Roller Bearings
 Purposes :
To reduce friction and wear between the sliding parts of the
bearing,
1. 1)To prevent rusting or corrosion of the bearing surfaces,
2. 2)To protect the bearing surfaces from water, dirt etc., and
3. 3) To reduce friction and wear between the sliding parts of the
bearing,
4. 4)To dissipate the heat.
 In general, oil or light grease is used for lubricating ball and roller
bearings.
 Only pure mineral oil or a calcium-base grease should be used. If there
is a possibility of moisture contact, then potassium or sodium-base
greases may be used. Another additional advantage of the grease is that
it forms a seal to keep out dirt or any other foreign substance.
 The temperature should be kept below 90ºC and in no case a
bearing should operate above 150ºC.

17. Advantages
 Low starting and good operating friction torque
 Ability to withstand momentary shock loads
 Requiring less axial space
 Good low-temperature starting.
 Rapid replacement
 Accuracy of shaft alignment.
 Low cost of maintenance, as no lubrication is required while
in service
 Small overall dimensions.
 Cleanliness.

18. Disadvantages
 Low resistance to shock loading
 Greater diametric space.
 More severe alignment requirements.
 More noisy at very high speeds.
 Finite life due to eventual failure by fatigue.
 Poor damping ability
 More initial cost.
 Design of bearing housing complicated

19. Conclusion
 Composition, microstructure , hardness & case depth found
satisfactory.
 Fractographic features indicated that fatigue was the main failure
cause.
 Misalignment was observed which has caused failure.
 Formation of destructive pitting and spalling at one end was due to
load concentration at that area.

20. References
 Machine Design by R. S. Khurmi & J. K. Gupta
 Technical Publication

21. Thank You