2. CONTENTS
Introduction
Terminology
Causes of failure
Assumptions
Problem statement
Design procedure and calculation
Graphs
Applications
Conclusion
References
3. INTRODUCTION
Bearings are machine elements that constrain
relative motion and reduce friction between
moving parts to only the desired motion.
In sliding contact bearing, surface of the shaft
slides over surface of the bush.
In order to reduce frictional resistance, wear
and to carry away the heat generated, a layer
of fluid i.e. lubricant is provided.
4. TERMINOLOGY
D= diameter of bearing
d= diameter of journal
l= length of bearing
c= radial clearance
e= eccentricity
h0 = minimum oil film
thickness.
ε= eccentricity ratio= e-
c
5. CAUSES OF FAILURE
Lubricant failure due to high operating
temperature.
Corrosion
Excessive loading
Misalignment
Improper mounting
7. ASSUMPTIONS
The bearing is subjected to static loads
only.
Bearing is assumed to be made of babbitt
material.
Lubricant carried away all the heat
generated during the operation.
The lubricant obeys Newton's law of
viscous flow.
The pressure is constant throughout the
film thickness.
8. The flow is one dimensional, i.e. the side
leakage is neglected.
The lubricant is incompressible.
The viscosity is constant throughout the
film.
There is continuous supply of lubricant.
No dynamic forces acting on both shaft
and bearing.
l=d
c=0.001r
h0 /c=0.6
9. PROBLEM STATEMENT
To design a full hydrodynamic journal bearing
with the following specification for high speed
machine tool application:[1]
• Journal diameter= 75mm
• Radial load=10kN
• Journal speed = 1440rpm
• Minimum oil film thickness=22.5microns
• Inlet temperature=400C
• Bearing material= Babbitt
Determine the length of the bearing and select a
suitable oil for this application.
10. DESIGN PROCEDURE
AND CALCULATION
Given: W=10kN, N=1440rpm, d=75mm,
h0= 22.5 microns, T= 40˚C
STEP 1: Length of bearing
For machine tool application , the
permissible bearing pressure, p=2N/mm²
l=W/(p*d) = 10000/(2*75) = 66.67mm
l/d= 66.67/75 =0.89 ≈1(standard value)
l=d=75mm
11. STEP 2: Selection of lubricant
p=W/(l*d)
=10000/(75*75)
= 1.78N/mm²
c=0.001r
=0.001*37.5
=0.0375mm
l/d=1 and h0/c = 0.0225/0.0375=0.6( high
speed application)
12. From table[1], for the above values,
S=0.264,
(r/c)f=5.79,
Q/(r*c*n*l)=3.99,
n=1440/60
=24rps
S=(r/c)²(µn/p)
0.264=(1000)²(µ*24/1.78)
µ=19.58cP
13. ∆t={8.3p(CFV)}/(FV)
= (8.3*1.78*5.79)/3.99
= 21.44˚C
We know that,
Average temperature=Ti + (∆t/2)
= 40+(21.44/2)
=50.72˚C
RESULT :
1) Length of bearing= 75mm
2)The viscosity of SAE-10 oil is 22cP at 50˚C
.So we select SAE-10 oil for this application from
the graph.
15. Fig 3: Variation between h0 and
frequency of rotation N [1],[6]
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35 40 45 50
h0(micron)-->
Ns (Revolution per second) -->
µ= 12.9 cP µ = 18.9 cP µ = 27.52 cP
16. Fig 4: Variation between temperature
and frequency of rotation N[1]
0
20
40
60
80
100
120
0 10 20 30 40 50 60 70
Temperature(°C)-->
Ns (Revolution per second) -->
Ti Tmax Tavg
19. CONCLUSION
From the graph it can be concluded
that it is in agreement with a numerical
solution. Further it can be used to
select lubricating oil for a particular
speed and permissible limit of
temperature rise.
20. REFERENCES
1. Bhandari V B , “Design of machine element” McGraw-Hill
third edition 2014
2. Thakar Dutt “Bearing failure its causes and
countermeasures” 2014
3. Pickering Steve, “ Tribology of journal bearing subjected to
boundary and mixed lubrication” Department of mechanical
& industrial engineering Northeastern university 2011
4. “Bearing failure causes and curses” by Wilcoxon Research
5. Temiz Vedat “sliding contact bearing” 1995
6. http://www.viscopedia.com/viscosity-tables/substances/iso-
viscosity-classification/
7. http://www.engineeringtoolbox.com/iso-grade-oil-
d_1207.html
8. tribolab.mas.bg.ac.rs/radovi/2005_02.pdf
9. https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&sourc
e=web&cd=1&cad=rja&uact=8&ved=0CB4QFjAA&url=http
%3A%2F%2Ffaculty.ksu.edu.sa%2Fessam%2FDocuments
%2FME301chapter12.pdf&ei=G7IZVZeHDYKjuQTPyIDAD
g&usg=AFQjCNHG1H5YGbDUxgWliwf43TtosWRA1A