ball bearing ppt mubai university

1. Machine Design I
BE Mechanical- Sem VI
(Academic Year 2022-23)
Sliding Contact Bearings
Prof. A. V. Gotmare
22 March 2023 1
Department of Mechanical Engineering

2. SCB
According to the nature of contact.
The bearings under this group are classified as:
(a) Sliding contact bearings,
(b) Rolling contact bearings.
In sliding contact bearings, as shown in the following Figure (a), the sliding
takes place along the surfaces of contact between the moving element and the
fixed element. The sliding contact bearings are also known as plain bearings
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Department of Mechanical Engineering

3. SCB
These bearings have certain advantages over the rolling contact bearings. They are:
1.The design of the bearing and housing is simple.
2.They occupy less radial space and are more compact.
3.They cost less.
4.The design of shaft is simple.
5.They operate more silently.
6.They have good shock load capacity.
7.They are ideally suited for medium and high speed operation.
The disadvantages are:
1.The frictional power loss is more.
2.They required good attention to lubrication.
3.They are normally designed to carry radial load or axial load only.
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Department of Mechanical Engineering

4. SCB
Hydrodynamic bearings
It is a lubricated journal bearing that uses fluid as lubricants to separate the
moving surfaces completely without an external pressure supply, required
pressure to support journal inside the bearing is generated from wedging action
inside the journal
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Department of Mechanical Engineering

5. SCB
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Department of Mechanical Engineering

6. SCB
Hydrostatic Bearings
It is also known as externally pressurized lubrication in which the pressurized
lubricant pumped into clearance of bearing and journal hence it can support
higher loads even at stationary conditions with very low starting friction
resulting very low tear an wear. But they are very expensive
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Department of Mechanical Engineering

7. SCB
Types of Sliding Contact Bearings
• The sliding contact bearings in which the sliding action is along the circumference of a circle or an arc of a
circle and carrying radial loads are known as journal or sleeve bearings. When the angle of contact of the
bearing with the journal is 360° as shown in the above figure (a), then the bearing is called a full journal
bearing. This type of bearing is commonly used in industrial machinery to accommodate bearing loads in any
radial direction.
• When the angle of contact of the bearing with the journal is 120°, as shown in figure 3 (b), then the bearing is
said to be partial journal bearing. This type of bearing has less friction than full journal bearing, but it can be
used only where the load is always in one direction. The most common application of the partial journal
bearings is found in rail road car axles. The full and partial journal bearings may be called as clearance
bearings because the diameter of the journal is less than that of bearing.
• When a partial journal bearing has no clearance i.e. the diameters of the journal and bearing are equal, then
the bearing is called a fitted bearing, as shown in figure 3 (c).
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Department of Mechanical Engineering

8. SCB
The following terms used in hydrodynamic journal bearing are important from
the subject point of view:
1. Diametral clearance. It is the difference between the diameters of the bearing
and the journal. Mathematically, diametral clearance,
c = D – d
2. Radial clearance. It is the difference between the radii of the bearing and the
journal. Mathematically, radial clearance,
C1=𝑅−𝑟=(𝐷−𝑑)/2=𝑐/2
3. Diametral clearance ratio. It is the ratio of the diametral clearance to the
diameter of the journal. Mathematically, diametral clearance ratio
=𝑐/𝑑=(𝐷−𝑑)/𝑑
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Department of Mechanical Engineering

9. SCB
4. Eccentricity. It is the radial distance between the center (O) of the bearing and the
displaced center (O ‘) of the bearing under load. It is denoted by e.
5. Minimum oil film thickness. It is the minimum distance between the bearing and the
journal, under complete lubrication condition. It is denoted by h0 and occurs at the line of
centers as shown in Fig.7. Its value may be assumed as c / 4.
6. Attitude or eccentricity ratio. It is the ratio of the eccentricity to the radial clearance.
Mathematically, attitude or eccentricity ratio,
𝜀=𝑒/𝑐1=(𝑐1−ℎ𝑜)/𝑐1=1−(ℎ𝑜/𝑐1) =1−(2ℎ𝑜/𝑐)
7. Short and long bearing. If the ratio of the length to the diameter of the journal (i.e. l /
d) is less than 1, then the bearing is said to be short bearing. On the other hand, if l / d is
greater than 1, then the bearing is known as long bearing.
Note:
When the length of the journal (l) is equal to the diameter of the journal (d), then the
bearing is called square bearing.
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Department of Mechanical Engineering

10. SCB
 Sommerfeld Number
The Sommerfeld number is also a dimensionless parameter used extensively in
the design of journal bearings. Mathematically,
 Heat Generated in a Journal Bearing
The heat generated in a bearing is due to the fluid friction and friction of the
parts having relative motion. Mathematically, heat generated in a bearing,
Qg = μ.W.V N-m/s or J/s or watts
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Department of Mechanical Engineering

11. • Bearing Pressure (P) ….. {If P is not given in quest., take 1.5N/mm2}
W = radial load
L = length of journal
D = diameter of bearing
• Operating temp of oil film - top
tb = bearing surface temp.
to= temp. rise in oil
Find tb,
Hg = Hd = h A t = h A (tb - tambient) PSG 7.34
Assume : h = 25 w/m2°C ; A = 25xLxD and tambient= 30 °C
After finding tb , calculate top
if top < 95 °C then selection is safe….PSG 7.35
if top > 95 °C pressure fed bearing is suggested.
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𝑃 =
𝑊
𝐿 𝑋 𝐷
top = tb+
to
2

12.  Coefficient of friction
can be taken from PSG 7.36 onwards and calculate 
 Oil flow rate (q)
4𝑞
𝐷𝐶𝑛′𝐿
can be taken from PSG 7.36 onwards and calculate 𝑞
 Side leakage rate (qs)
qs
𝑞
can be taken from PSG 7.36 onwards and calculate qs
 Selection of lubricating oil
Based on top and z’in centipoise, select grade of oil from PSG 7.41
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𝐷
𝐶

13. SCB
Q1. The radial load on a 360 degree hydro dynamically lubricated self contained
bearing is 20KN. The journal rotates at 1200rpm.
Assuming journal length by diameter ratio as 1 and suitable fit between journal
and bearing. Design the bearing for average clearance. Check the bearing for
heat dissipation. The bearing pressure should not exceed 1.5 N/mm2
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Department of Mechanical Engineering

14. SCB
Given :
Radial Load W : 20KN
Journal Speed N :1200rpm ; n : 20rps
L / D= 1
Allowable bearing Pressure [P ] = 1.5 N/mm2
D = 115.47 mm
Taking D = L = 120mm
P = 1.38N/mm2
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Department of Mechanical Engineering

15. SCB
Calculating diametrical clearance assuming suitable fit
Assuming Loose running fit of Fine type H8d8 Basic Size =120mm
Tolerance on hole (Bearing) ……PSG 3.9
120H8 120 +0.054
+0.000
Hmax = 120 + 0.054 Hmin = 120 + 0.000
Hmax = 120.054 mm Hmin = 120.000 mm
Tolerance on Shaft(Journal) ……PSG 3.7
120d8 120-0.120
-0.174
Smax = 120 - 0.120 Smin = 120 - 0.174
Smax = 119.88 mm Smin = 119.826 mm
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Department of Mechanical Engineering

16. SCB
Finding clearance
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Department of Mechanical Engineering

17. SCB
Performance parameters for 360 degree full Journal bearing PSG 7.36
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Department of Mechanical Engineering
Z’ X 20
Z’
Z’

18. SCB
Calculate Oil flow rate
From Flow variable
q = 57.879 X 103 mm3 / sec
q = 57.879 cc3 / sec
Calculate Side flow rate
From Side Leakage ratio
qs = 48.73 cc/sec
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Department of Mechanical Engineering

19. SCB
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Department of Mechanical Engineering

20. SCB
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Department of Mechanical Engineering
Friction power loss = heat
generated = Hg
Hg
Hg
Hg
Hg

21. SCB
Selection of Oil ……PSG7.41
Selecting SAE20 Oil to be on safer side
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Department of Mechanical Engineering

22. SCB
Q2. the following data is given for 360 degree hydrodynamic bearing
Radial Load : 10KN
Journal speed : 1450rpm
L/D ratio : 1 Bearing length : 50mm
Radial Clearance : 20microns Eccentricity : 15 microns
Sp.Gravity of Lubricant : 0.86 Sp.Heat of Lubricant : 2.09KJ/kgC
Calculate:
Minimum oil film thickness
Co-efficient of Friction
Power loss in Friction
Viscosity of lubricant in cp
Total oil flow rate in lpm
Side leakage
Average Temp of the oil if makeup oil is supplied at 30C
Select suitable grade of oil for the bearing.
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Department of Mechanical Engineering

23. SCB
Given:
360Degree Full Journal Bearing
Radial Load W : 10KN
Journal speed N: 1450rpm ; n: 24.16rps L/D ratio : 1
Bearing length L : 50mm
Radial Clearance Cr : 20microns Eccentricity e : 15 microns
Sp.Gravity of Lubricant : 0.86 Sp.Heat of Lubricant : 2.09KJ/kgC
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Department of Mechanical Engineering

24. SCB
Calculate the Diametral Clearance
C = 2Cr
C = 2 X 20 = 40microns
Performance parameters at the calculated attitude ..PSG7.36
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Department of Mechanical Engineering

25. From PSG 7.34
Finding value of s from PSG 7.36,
S= 0.0637
n’ = 1450 /60 = 24.17 rps
After calculating
Z’ = 6.747 X 10-9 Ns/mm2
= 6.747 Centipoise …….. As 1 cp = 10-9 Ns/mm2
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= 4 N/mm2

26. SCB
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Department of Mechanical Engineering

27. SCB
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Department of Mechanical Engineering

28. SCB
• Selection of Oil ……PSG7.41
Selecting SAE10 Oil to be on safer side
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Department of Mechanical Engineering

29. 22 March 2023 29
Department of Mechanical Engineering