Rolling Contact Bearings

Rolling Contact Bearings
Unit 6
Dr. L.K. Bhagi
Associate Professor
School of Mechanical Engineering
Lovely Professional University
06-11-2023 1

Bearings
Bearings are used to support a load while permitting relative motion
between two elements of a machine.
The term rolling contact bearings refers to the wide variety of
bearings that use spherical balls cylindrical rollers, or some other
type of roller between the stationary and the moving elements.
06-11-2023
Design of Machine Elements II
(Dr. L K Bhagi)
2

Bearing Types
The functions of the bearing are as follows:
(i) The bearing ensures free rotation of the shaft or the axle with
minimum friction.
(ii) The bearing supports the shaft or the axle and holds it in the
correct position.
(iii) The bearing takes up the forces that act on the shaft or the axle
and transmits them to the frame or the foundation.
06-11-2023
(Dr. L K Bhagi)
3

Bearing Types
Bearings are classified in different ways.
Depending upon the direction of force that acts on them.
Classified into two categories
Radial Bearings
Thrust Bearings
06-11-2023
(Dr. L K Bhagi)
4
https://www.youtube.com/watch?app=desktop&v=kahXmbcAs04

Bearing Types
Radial Bearings - supports the load, which is perpendicular to the
axis of the shaft. Such loads are typical of those created by power
transmission elements on shafts such as spur gears, V-belt drives,
and chain drives.
06-11-2023
(Dr. L K Bhagi)
5

Bearing Types
Thrust Bearings - supports the load, which acts along the axis of the
shaft.
The axial components of the forces on helical gears, worms and
worm gears, and bevel gears are thrust loads. Also, bearings
supporting shafts with vertical axes are subjected to thrust loads due
to the weight of the shaft and the elements on the shaft as well as
from axial operating forces.
06-11-2023
(Dr. L K Bhagi)
6

06-11-2023
(Dr. L K Bhagi)
7
Comparison of Bearing Types

Bearing Types
The most important criterion to classify the bearings is the
type of friction between the shaft and the bearing surface.
Depending upon the type of friction, bearings are classified into two
main groups
Sliding Contact Bearings
06-11-2023
(Dr. L K Bhagi)
8

Bearing Types
06-11-2023
(Dr. L K Bhagi)
9

Bearing Types
also called Plain Bearings, Journal Bearings or
Sleeve Bearings.
In this case, the surface of the shaft slides over
the surface of the bush resulting in friction and
wear. In order to reduce the friction, these two
surfaces are separated by a film of lubricating oil.
06-11-2023
(Dr. L K Bhagi)
10

Bearing Types
also called Antifriction Bearings or simply Ball
Bearings.
Rolling elements, such as balls or rollers, are
introduced between the surfaces that are in
relative motion. In this type of bearing, sliding
friction is replaced by rolling friction.
06-11-2023
(Dr. L K Bhagi)
11

Introduction to Rolling Contact Bearings
>Nomenclature of a ball bearing
The components of a typical rolling contact bearing are
the inner race,
the outer race, and
the rolling elements.
06-11-2023
(Dr. L K Bhagi)
12

Introduction to Rolling Contact Bearings
Usually the outer race is stationary and is held by the housing of the
machine.
The inner race is pressed onto the rotating shaft and thus rotates
with it.
Then the balls roll between the outer and inner races. The spacing
of the balls is maintained by retainers or “cages.”
The load path is from the shaft, to the inner race, to the balls, to the
outer race, and finally to the housing.
06-11-2023
(Dr. L K Bhagi)
13

Types of Rolling Contact Bearings
>Deep Groove Ball Bearing
Although designed primarily for radial load-
carrying capacity, the deep groove allows it to
carry a fairly sizable thrust load. The thrust
load would be applied to one side of the inner
race by a shoulder on the shaft.
The radius of the ball is slightly smaller than
the radius of the groove to allow free rolling of
the balls.
06-11-2023
(Dr. L K Bhagi)
14

The contact between a ball and the race is
theoretically at a point, but it is actually a
small circular area because of the
deformation of the elements.
06-11-2023
(Dr. L K Bhagi)
15

Advantages
Due to relatively large size of the balls, deep
groove ball bearing has high load carrying
capacity
06-11-2023
(Dr. L K Bhagi)
16

Advantages
Deep groove ball bearing takes loads in the
radial as well as axial direction.
06-11-2023
(Dr. L K Bhagi)
17

Advantages
Due to point contact between the balls and
races, frictional loss and the resultant
temperature rise is less in this bearing.
Therefore, deep groove ball bearing gives
excellent performance, especially in high
speed applications.
06-11-2023
(Dr. L K Bhagi)
18

Advantages
Deep groove ball bearing generates less
noise due to point contact.
06-11-2023
(Dr. L K Bhagi)
19

Disadvantages
✓Deep groove ball bearing is not self-aligning.
Accurate alignment between axes of the
shaft and the housing bore is required.
✓Poor rigidity compared with roller bearing.
This is due to the point contact compared
with the line contact in case of roller bearing.
06-11-2023
(Dr. L K Bhagi)
20

>Double-Row, Deep-Groove Ball Bearing
Adding a second row of balls increases the
radial load-carrying capacity of the deep-
groove type of bearing compared with the
single-row design because more balls share
the load.
Thus, a greater load can be carried in the
same space, or a given load can be carried in
a smaller space.
06-11-2023
(Dr. L K Bhagi)
21

>Cylindrical Roller Bearing
will carry a greater radial load than ball bearings of
the same size because of the greater contact area.
The resulting contact stress levels are lower than
for equivalent-sized ball bearings, allowing smaller
bearings to carry a given load or a given size
bearing to carry a higher load.
06-11-2023
(Dr. L K Bhagi)
22

Thrust load capacity is poor because any thrust
load would be applied to the side of the rollers,
causing rubbing, not true rolling motion.
06-11-2023
(Dr. L K Bhagi)
23

However, Disadvantage of requiring almost perfect
geometry of the raceways and rollers. A slight
misalignment will cause the rollers to skew and get
out of line. For this reason, the retainer must be
heavy. Straight roller bearings will not, of course,
take thrust loads.
06-11-2023
(Dr. L K Bhagi)
24

>Angular Contact Bearing
In angular contact bearing, the grooves in inner
and outer races are so shaped that the line of
reaction at the contact between balls and races
makes an angle with the axis of the bearing.
Angular contact bearing can take both radial and
thrust loads.
06-11-2023
(Dr. L K Bhagi)
25

>Angular Contact Bearing
In angular contact bearing, one side of the groove
in the outer race is cut away to permit the insertion
of larger number of balls than that of deep groove
ball bearing. This permits the bearing to carry
relatively large axial and radial loads.
Therefore, the load carrying capacity of angular
contact bearing is more than that of deep groove
ball bearing.
06-11-2023
(Dr. L K Bhagi)
26

>Self-aligning Bearings
There are two types of self-aligning rolling contact
bearings,
Self-aligning ball bearing and
spherical roller bearing.
06-11-2023
(Dr. L K Bhagi)
27

>Self-aligning Bearings
The self-aligning ball
bearing consists of two
rows of balls, which roll
on a common spherical
surface in the outer race.
06-11-2023
(Dr. L K Bhagi)
28
Compared with the self-aligning ball bearing, the spherical roller bearing can
carry relatively high radial and thrust loads.

> Taper Roller Bearing
The taper roller bearing consists of rolling
elements in the form of a frustum of cone. They
are arranged in such a way that the axes of
individual rolling elements intersect in a common
apex point on the axis of the bearing.
06-11-2023
(Dr. L K Bhagi)
29

In taper roller bearing, the line of resultant
reaction through the rolling elements makes an
angle with the axis of the bearing.
Therefore, taper roller bearing can carry both
radial and axial loads. In fact, the presence of
either component results in the other, acting on the
bearing.
06-11-2023
(Dr. L K Bhagi)
30

Taper roller bearings are always used in pairs to
balance the thrust component.
Taper roller bearing has separable construction.
The outer ring is called ‘cup’ and
the inner ring is called ‘cone’.
The cup is separable from the remainder assembly
of the bearing elements including the rollers, cage
and the cone.
06-11-2023
(Dr. L K Bhagi)
31

Difference Between Spherical roller bearings And
cylindrical roller bearings
The main difference between these two types of roller bearings is the
surface area that comes into contact with the inner and outer rings.
Spherical roller bearings have a greater surface area than cylindrical roller
bearings. This gives them the ability to handle higher loads.
06-11-2023
(Dr. L K Bhagi)
32

SELECTION OF BEARING-TYPE
The selection of the type of bearing in a particular application depends
upon the requirement of the application and the characteristics of different
types of bearings.
06-11-2023
(Dr. L K Bhagi)
33

For low and medium radial loads,
ball bearings are used,
for heavy loads and large shaft diameters,
roller bearings are selected.
06-11-2023
(Dr. L K Bhagi)
34

For misalignment between the axes of the shaft and housing,
Self-aligning ball bearings and spherical roller bearings
Spherical roller bearings are self-aligning bearings designed for heavy
radial loading. The rollers are barrel shaped. These bearings automatically
compensate for large angular errors commonly called shaft misalignments.
06-11-2023
(Dr. L K Bhagi)
35

For misalignment between the axes of the shaft and housing,
Self-aligning ball bearings and spherical roller bearings
Spherical roller bearings are self-aligning bearings designed for heavy
radial loading. The rollers are barrel shaped. These bearings automatically
compensate for large angular errors commonly called shaft misalignments.
06-11-2023
(Dr. L K Bhagi)
36

for medium thrust loads
Thrust ball bearings are used
for heavy thrust loads,
cylindrical roller thrust bearings are recommended.
Double acting thrust bearings can carry the thrust load in either direction.
06-11-2023
(Dr. L K Bhagi)
37

When the load acting on the bearing consists of two components—radial
and thrust.
Deep groove ball bearings, angular contact bearings and spherical roller
bearings
06-11-2023
(Dr. L K Bhagi)
38

For high speed applications,
deep groove ball bearings, angular contact bearings and cylindrical roller
bearings are recommended.
06-11-2023
(Dr. L K Bhagi)
39

For rigidity of the system,
The line of contact in these bearings, as compared with the point of
contact in ball bearings, improves the rigidity of the system.
Double row cylindrical roller bearings or taper roller bearings are used.
06-11-2023
(Dr. L K Bhagi)
40

Bearing Materials
The load on a rolling contact bearing is exerted on a small area.
✓ The resulting contact stresses are quite high, regardless of the type of
bearing.
✓ Contact stresses of approximately 20000 Kgf/cm2 are not uncommon
in commercially available bearings.
✓ To withstand such high stresses, the balls, rollers, and races are made
from a very hard, high strength steel or ceramic.
06-11-2023
(Dr. L K Bhagi)
41

Bearing Materials
✓ The most widely used bearing material is AISI 52100 steel.
✓ Impurities are carefully minimized to obtain a very clean steel.
✓ The material is through-hardened to the range of 58–65 on the
Rockwell C scale to give it the ability to resist high contact stress.
06-11-2023
(Dr. L K Bhagi)
42

STATIC LOAD CARRYING CAPACITY
Static load is defined as the load acting on the bearing when the shaft is
stationary.
Static load produces permanent deformation in balls and races, which
increases with increasing load.
06-11-2023
(Dr. L K Bhagi)
43

Researchers found that a total permanent
deformation of 0.0001 of the ball or roller
diameter occurring at the most heavily
stressed ball and race contact, can be
tolerated in practice, without any
disturbance like noise or vibrations.
06-11-2023
(Dr. L K Bhagi)
44
The permissible static load depends upon the permissible magnitude of
permanent deformation.

06-11-2023
(Dr. L K Bhagi)
45
So, the static load carrying capacity of a bearing is defined as the static
load which corresponds to a total permanent deformation of balls and
races, at the most heavily stressed point of contact, equal to 0.0001 of the
ball diameter.

STRIBECK’S EQUATION
06-11-2023
(Dr. L K Bhagi)
46
Stribeck’s equation gives the static load capacity of bearing.
It is based on the following assumptions:
1) The races are rigid and retain their circular shape.
2) The balls are equally spaced.
3) The balls in the upper half do not support any load.

06-11-2023
(Dr. L K Bhagi)
47
Figure shows the forces acting on the inner race through the rolling
elements, which support the static load C0. It is assumed that there is a
single row of balls. Considering the equilibrium of forces in the vertical
direction,
Fig. Forces acting on Inner Race Fig. Deflection of Inner Race

06-11-2023
(Dr. L K Bhagi)
48
Co = P1 + 2P2 cos β + 2P3 cos (2β) + ......
As the races are rigid, only balls are deformed. Suppose δ1 is the
deformation at the most heavily stressed Ball No.1. Due to this
deformation, the inner race is deflected with respect to the outer race
through δ1.
the centre of the inner ring moves from O to Oʹ through the distance δ1
without changing its shape.

06-11-2023
(Dr. L K Bhagi)
49
Suppose δ1, δ2 … are radial deflections at the respective balls.
According to Hertz’s equation, the relationship between the load and
deflection at each ball is given by,

06-11-2023
(Dr. L K Bhagi)
50
Therefore,
In a similar way

06-11-2023
(Dr. L K Bhagi)
51
From eqn

06-11-2023
(Dr. L K Bhagi)
52
If z is the number of balls,
The values of M for different values of z are tabulated as follows:
It is seen from the table that
(z/M) is practically constant.
Stribeck suggested the value
for (z/M) as 5.

06-11-2023
(Dr. L K Bhagi)
53
Substituting this value in
From experimental evidence, it is found that the force P1 required to
produce a given permanent deformation of the ball is given by,
where d is the ball diameter and the factor k depends upon the radii of curvature
at the point of contact, and on the modulii of elasticity of materials.

06-11-2023
(Dr. L K Bhagi)
54
From eqn and
The above equation is known as Stribeck’s equation.

DYNAMIC LOAD CARRYING CAPACITY
06-11-2023
(Dr. L K Bhagi)
55
The dynamic load carrying capacity of the bearing is based on the fatigue
life of the bearing.
Life of a bearing is defined as the number of revolutions that the bearing
can make before it fails.
It is denoted in million revolutions (106 revolutions)
e.g. 1000 hrs at 200 rpm means (200 x 60 x 1000) x 10-6 million rev

06-11-2023
(Dr. L K Bhagi)
56
The dynamic load carrying capacity of the bearing is based on the fatigue
life of the bearing.
The life of an individual ball bearing is defined as the number of
revolutions (or hours of service at some given constant speed), which the
bearing runs before the first evidence of fatigue crack in balls or races.

06-11-2023
(Dr. L K Bhagi)
57
Life of a single bearing is difficult to predict so, it is necessary to define
the life in terms of the statistical average performance of a group of
bearings.
Bearings are rated on one of the two criteria
✓ the average life of a group of bearings or
✓ the life, which 90% of the bearings will reach or exceed (mainly used in
bearing industry)

06-11-2023
(Dr. L K Bhagi)
58
Rated life (L10 or L90): Number of revolutions that at least 90% of bearings
run before failure.
Average life (L50): Number of revolutions that at least 50% of bearings run
before failure.
Average Life is approximately five times the rated life.
This means that for the majority of bearings, the actual life is considerably more
than the rated life.
L50 = 5 x L10 or L90

06-11-2023
(Dr. L K Bhagi)
59
The rating life of a group of apparently identical ball bearings is defined as
the number of revolutions that 90% of the bearings will complete or
exceed before the first evidence of fatigue crack.
There are a number of terms used for this rating life.
They are minimum life, catalogue life, L10 life or B10 life.
These terms are synonyms for rating life.

> EQUIVALENT BEARING LOAD
06-11-2023
(Dr. L K Bhagi)
60
In actual applications, the force acting on the bearing has two
components
Radial and Thrust
It is therefore necessary to convert the two components acting on the
bearing into a single hypothetical load, fulfilling the conditions applied to
the dynamic load carrying capacity.

> EQUIVALENT BEARING LOAD
06-11-2023
(Dr. L K Bhagi)
61
The expression for the equivalent dynamic load is
P = XVFr + YFa
P = equivalent dynamic load (N)
Fr = radial load (N)
Fa = axial or thrust load (N)
V = race-rotation factor
X and Y are radial and thrust factors
V = 1 when the inner race rotates while the outer
race is held stationary in the housing.
V = 1.2 when the outer race rotates with respect
to the load, while the inner race remains
stationary.
When the bearing is subjected to pure radial
load
P = Fr
When the bearing is subjected to pure thrust
load
P = Fa

> LOAD-LIFE RELATIONSHIP
06-11-2023
(Dr. L K Bhagi)
62
The relationship between the dynamic load carrying capacity, the
equivalent dynamic load, and the bearing life is given by,
L10 = rated bearing life (in million revolutions)
C = dynamic load capacity (N), and
p = 3 (for ball bearings)
p = 10/3 (for roller bearings)

> LOAD-LIFE RELATIONSHIP
06-11-2023
(Dr. L K Bhagi)
63
The relationship between life in million revolutions and life in working
hours is given by
L10h = rated bearing life (hours)
n = speed of rotation (rpm)

>Solved Problem
06-11-2023
(Dr. L K Bhagi)
64
In a particular application, the radial load acting on a ball bearing is 5 kN
and the expected life for 90% of the bearings is 8000 h. Calculate the
dynamic load carrying capacity of the bearing, when the shaft rotates at
1450 rpm.

>Solved Problem
06-11-2023
(Dr. L K Bhagi)
65
A taper roller bearing has a dynamic load capacity of 26 kN. The desired
life for 90% of the bearings is 8000 h and the speed is 300 rpm. Calculate
the equivalent radial load that the bearing can carry.

>Solved Problem
06-11-2023
(Dr. L K Bhagi)
66
GATE-1987
The expected life of a ball bearing subjected to a load of 9800N and working at
1000RPM is 3000 hours. What is the expected life of the same bearing for a
similar load of 4900 N and a speed of 2000 rpm?
A. Unchanged B. 12,000 hours C. 1,500 hours D. 6,000 hours

>Solved Problem
06-11-2023
(Dr. L K Bhagi)
67
GATE-2007
A ball bearing operating at a load F has 8000 hours of life. The life of the
bearing, in hours, when the load is doubled to 2F is
A. 8000 B. 6000 C. 4000 D.1000

Selection of Bearing Life From Manufacturer Catalogue
06-11-2023
(Dr. L K Bhagi)
68

06-11-2023
(Dr. L K Bhagi)
69

06-11-2023
(Dr. L K Bhagi)
70

06-11-2023
(Dr. L K Bhagi)
71

06-11-2023
(Dr. L K Bhagi)
72

06-11-2023
(Dr. L K Bhagi)
73

06-11-2023
(Dr. L K Bhagi)
74

06-11-2023
(Dr. L K Bhagi)
75

06-11-2023
(Dr. L K Bhagi)
76

06-11-2023
(Dr. L K Bhagi)
77

06-11-2023
(Dr. L K Bhagi)
78

06-11-2023
(Dr. L K Bhagi)
79

06-11-2023
(Dr. L K Bhagi)
80

06-11-2023
(Dr. L K Bhagi)
81

06-11-2023
(Dr. L K Bhagi)
82

06-11-2023
(Dr. L K Bhagi)
83

06-11-2023
(Dr. L K Bhagi)
84

06-11-2023
(Dr. L K Bhagi)
85

06-11-2023
(Dr. L K Bhagi)
86

Rolling Contact Bearings

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Rolling Contact Bearings

Similar to Rolling Contact Bearings (20)

More from Dr. L K Bhagi

More from Dr. L K Bhagi (16)

Recently uploaded

Recently uploaded (20)

Rolling Contact Bearings