Rolling contact bearings are used to support rotating shafts. There are different types including radial ball bearings, radial roller bearings, thrust ball bearings, and thrust roller bearings. The basic dynamic load rating or load carrying capacity depends on factors like the bearing geometry, materials, and accuracy of manufacture. Dynamic equivalent load accounts for variable operating loads over the life of the bearing. Proper selection involves calculating forces, selecting the bearing type, checking the dynamic load capacity, and ensuring it meets the expected life. Lubrication is also important to reduce friction and wear, prevent corrosion, and dissipate heat.

1. Lecture 4
Unit-4: Machine Design(RME-603)
Rolling Contact Bearing
By:
Dr. Ashish Gupta
(Associate Prof., Department of Mechanical Engineering)
G.L Bajaj Institute of Technology and Management, Greater Noida-
201306, India

2. Basic Dynamic Load Rating or load carrying capacity (C)
1. For radial ball bearings,
When balls are not larger than 25.4 mm in diameter.
for balls larger than 25.4 mm in diameter,
fc = A factor, depending upon the geometry of the
bearing components, the accuracy of manufacture and
the material used.

3. 2. For radial roller bearings,
3. For thrust ball bearings,
4. For thrust roller bearings,

4. Dynamic Equivalent Load (W)

7. Load-Life
relationship

8. Service factor
(Ks)
• The dynamic radial load is multiplied by the service factor (KS) to get
the basic dynamic radial load . The service factor for the ball
bearings is shown in the following table.

9. Selection of bearing
or
Design steps for bearing

10. I. Calculate the radial and axial forces
acting on the bearing and determine
the diameter of the shaft where the
bearing is to be fitted.
II. Select the type of bearing for the given
application.
III. Determine the values of X and Y, the
radial and thrust factors, from the
catalogue.
IV. Calculate the equivalent dynamic load
from the equation.
V. Make a decision about the expected
bearing life and express the life L10 in
million revolutions.
VI. Calculate the dynamic load capacity
VII. Check whether the selected bearing of
series 60 has the required dynamic
capacity.
Suppose it is required to select a single-row
deep groove ball bearing, for a shaft that is
75 mm in diameter and which rotates at
125 rpm. The bearing is subjected to a
radial load of 21 kN and there is no thrust
load. The expected life of the bearing is 10
000 hours. Select the type of bearing for
the given application.

11. Equivalent Dynamic Load for Rolling
Contact Bearings under Variable
Loads
Consider a rolling contact bearing subjected to variable loads W1,
W2, W3 etc. for successive n1, n2, n3 etc. number of revolutions
respectively. If the bearing is operated at the constant load W1,
then its life is given by

12. for equivalent load
From equation (i) and (ii)
and also

13. Reliability (Probability of
survival)
• The reliability (R) is defined as the ratio of the number of bearings which
have successfully completed L million revolutions to the total number of
bearings under test.
According to Wiebull, the relation between the bearing life and the
reliability is given as

15. Lubrication of Ball and Roller Bearings
 To reduce friction and wear between the sliding parts of the bearing,
 To prevent rusting or corrosion of the bearing surfaces,
 To protect the bearing surfaces from water, dirt etc., and
 To dissipate the heat.
Lubrications used:
 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.