BHEL is India's largest engineering and manufacturing company in the energy and infrastructure sector. It was established over 40 years ago with its first plant in Bhopal, kickstarting India's indigenous heavy electrical equipment industry. BHEL caters to key sectors like power, transportation, and telecommunications. It has 14 manufacturing divisions, regional centers, and offices across India and abroad. Bearings are crucial components that support rotating shafts in machines. They experience friction which generates heat, so proper lubrication and cooling is required. BHEL manufactures various types of bearings used in products like turbines, compressors, and generators. Careful consideration is given to bearing design factors such as load capacity, clearances, and lubrication flow

1. By
Mr. B . SIVA PRADEEP

2. BHEL - AN OVER VIEW
 BHEL is the largest engineering and manufacturing enterprise in
India in the energy related in fracture sector today. BHEL was
established more than 40 years ago ,when its first plant was set up
in Bhopal ushering in the indigenous Heavy Electrical Equipment
industry in India, a dream that has been more than realized with
a well-recognized tract record of performance. It has been
earning profits continuously since 1971-72 and achieved a sales
turnover of Rs. 7482.3 crores with a profit before tax of Rs. 802.4
crores in 2002 – 2003.

 BHEL caters to core sectors of the Indian Economy Viz., Power
Generation &
Transmission, Industry, Transportation, Telecommunication, Ren
ewable Energy, Defence etc., The wide network of BHEL’S 14
manufacturing divisions, four Power Sector regional centers, eight
service centers and 18 regional offices and a large number of
project sites spread all over India and abroad enables the
company to promptly serve its customers and provide them with
suitable products, systems and services efficiently and at
competitive prices. BHEL has already attained ISO 9000 and
all the major units/divisions of BHEL have been upgraded to the
latest ISO-9001: 2000 version quality standard version quality
standard certification for quality management.

3. B.H.E.L….HYDERABAD
 Currently there are nine important products being
manufactured at R.C.PURAM.
 1)Gas turbines 8)heat exchangers
 2)Steam turbines 9)oil filled equipment.
 3)Compressors
 4)generators and exciters
 5)pumps
 6)pulverizers
 7)switch gears
 *Bearings for all these products are also designed and
manufactured by BHEL.

5. Bearings and their necessity..
 Bearings are used to support a rotating shaft in a machine. The relative
motion between the rotating shaft (journal) & stationary bearing
generates frictional losses, which are converted into heat energy
leading to the temperature rise of the bearing.

 The most important objectives of a bearing design is to reduce
frictional losses, insure stable running of the rotor system in the
extreme and normal condition ensuring long life of the bearing, and
particularly no wear to the rotating journal etc.

 There are different types of bearings used for different speeds and
applications. A quick review of various type bearings and their field of
application is made. But the main focus of this project work is on
journal bearings.

 As it is possible to reduce the weight of the machines, by increasing
the speeds, it is not a common practice to go in for high-speed
machines. These high-speed machines naturally need suitable bearings
to withstand high dynamic faces and seven operating condition like
misalignment, axial thrust etc. Lubrication also plays an important role
in the bearing design and application. Hence lubrication aspects have
also presented in this project work.

6. TYPES OF BEARINGS
 Based on the principle of operation, the bearings are
divided into two main categories.
 These are:
 Anti-friction bearings(rolling element bearings)
 Sliding contact bearings

 Anti-friction bearings are further divided into:
 i) Ball bearing
 ii) Cylindrical roller bearings
 iii) Taper roller bearings
 iv) Spherical roller bearings
 v) Needle roller bearings

7. TYPES OF BEARINGS
 Sliding contacts bearings are further divided into:
 i) Journal bearing
 ii) Thrust bearing

 Journal bearings are further sub divided into
 (i) Cylindrical journal bearings
 (ii) Two-lobe journal bearings (Elliptical bearings)
 (iii) Three-lobe journal bearings
 (iv) Pivoted (Tilting) pad journal bearings

 Thrust bearings are sub divided into
 (i) Flat-land thrust bearings
 (ii) Taper-land thrust bearings
 (iii) Pivoted shoe thrust bearings
 (iv) Spring mounted flexible plate thrust bearings

8. Types of bearings .

9. DESIGN PROCEDURE
 INTRODUCTION TO DESIGN PROCEDURE:

 The primary requirements of good bearing design are:

 (i) The specific bearing pressure shall be with in limits.
 (ii) The operating temperature of the bearing shall be
well below the safe limits of the material used(Babbitt
plasticity temperature limit). This means that sufficient oil
flow must be there to take away the heat developed by the
frictional losses and keep the bearing cool.
 (iii) The stiffness of the bearing oil film (together with the
support and foundation stiffness) shall be such that, the
natural frequency of the rotor bearing system is away from
the operating speed.

10. TWO LOBE BEARINGS AND THEIR
DESIGN

11. ROTOR SHAFT
TWO LOBE BEARING FOR
ROTOR SHAFT TO COUPLE WITH
TURBINE.

12. 1 ) SPECIFIC BEARING PRESSURE
 . This is the static load per unit area of the projected surface of the
bearing

 P = (Wb) / (L x D) Kg/cm2 …………………………………………...........2.1

 Where, Wb= is the load on the bearing in kg
 L = is the length of the bearing in cm
 D = is the diameter of the bearing in cm

 If specific bearing pressure is too high, the oil film will be very
thin and there may be a chance of occasional metal to metal contact. If
the specific pressure is too low, the oil film will be very thick and the
rotor will be just floating on the oil film. The rotor will not be stable and
for any small disturbance, the rotor becomes unstable. More over lightly
loaded condition leads to a phenomenon called HALF FREQUENCY
WHRIL.

 For journal bearings, the guide line for the limits of specific bearing pressure
is about 8-25 kg/cm2
 If the specific bearing pressure is less than 5 kg/cm2, the bearing will be
unstable.


13. 2) L/D RATIO
 Generally in journal bearings, the L/D ratio of bearing
is maintained in the range of 0.6-1.0. For bearings in
the speed range about 3000 rpm, generally L/D ratio is
taken as 0.8.
Peripheral velocity:
The peripheral velocity of the journal
in the bearing is given by the equation
u = (3.14 x D’ x n)/60
meters/sec2
where,
D’ is the diameter of
the journal in meters.
N is the speed in rpm.

14. 3 BEARING CLEARANCES AND
CLEARANCE RATIO:
 (i)Cylindrical bearing
 Diametrical clearance = Bearing inner diameter - journal diameter

 Cd = Db - Dj

 In cylindrical bearings, the diametrical clearance is generally maintained
0.15-0.2% of the journal diameter.
 (ii)Elliptical bearings (two-lobe bearings)
 In this case, the horizontal diameter of the bearing Dh is more than the
vertical diameter of the bearing Dv. Generally the following values are
maintained.

 Vertical clearance = Cv= Dv – Dj
 Horizontal clearance = Ch = Dh – Dj

 From practical point of view (measurement point of view), half the value of
horizontal clearance is called SIDE CLEARANCE. During assembly of the
bearing and during inspections, when the journal is stationary, the journal will
be resting in the bearing The bearing clearances are measured as TOP and SIDE
CLEARANCES and compared with the design values

15. 4 ECCENTRICITY AND ECCENTRICITY RATIO:
 Eccentricity is the distance between the bearing center and the journal
center. The eccentricity depends on the load on the bearing, viscosity
and peripheral velocity of the journal. This is denoted by e.

 ECCENTRICITY RATIO:
 It is a dimensionless quantity, which is the ratio of eccentricity to the
radial clearance.

 N = ((e)/(c/2)) = ((2e)/c)

 ELLIPTICITY RATIO:

 (Horizontal diameter -Vertical diameter)/ Horizontal diameter
CLEARANCE RATIO
This is the ratio of diametrical clearance to the bearing diameter. This is a
non dimensional quantity.
m =Cd/D.
This acts as a guide line for selecting the clearance for different journal
diameters of any particular type of bearing

16. 5) FRICTIONAL LOSSES IN A BEARING:
 The frictional losses in a bearing are given by

 P = {frictional force on the rotor} x {distance traveled by
the rotor journal in one sec}

 Frictional force on the rotor = u x Wb

 Where
 Ø u =coefficient of friction of hydrodynamic film
 Ø Wb =load on the bearing in kg
 Ø D’ = diameter of the journal in meters.
 Ø N’ = Speed of the journal in rps

17. 6) Quantity of oil flow required
 The quantity of oil flow required shall be such that, the oil
should be adequate to carry away the frictional heat
generated in the bearing and keep the bearing temperature
with in the limits.Maximum allowable temperature for
Babbitt is 120ºC. In the process of cooling the bearing, the
temperature of oil increases. The rate of flow is dependent
on

 (i) Heat generated due to frictional losses.
 (ii) The specific heat of oil
 (iii) The temp rise allowed for the oil
Flow rate requirement of lubricating oil =P/(r x n x )…
Where,
P -Frictional losses in KW
r -Density of oil on gm/cm2
n -Specific heat of oil
 -Temperature rise allowed for oil.

18. 7)BEARING STIFFNESS AND
DAMPING COEFFICIENTS:
 In actual practice the journal is supported on an oil film of
the bearing, and the bearing itself is supported bearing
pedestal (or simply called the support) which in turn rest on
the foundation. So in addition to the oil film stiffness, there
are stiffness of support and stiffness of foundation in series.

 The rotor natural frequency (critical speed) is influenced
by the combined stiffness of the oil film + support +
foundation.

 The representation of the rotor bearing system as
mass, spring and damper elements .

19. BABBITTING OF BEARING SHELLS:
 Babbitt metal is most commonly used as a thin surface layer in a
complex, multi-metal structure. Babbitt metal is soft and easily
damaged, which suggests that it might be unsuitable for
a bearing surface.
 However, its structure is made up of small hard crystals dispersed in a
softer metal, which makes it a metal matrix composite. As the bearing
wears, the softer metal erodes somewhat, which creates paths for
lubricant between the hard high spots that provide the actual bearing
surface.
 When tin is used as the softer metal, friction causes the tin to melt and
function as a lubricant, which protects the bearing from wear when
other lubricants are absent.
 There are many Babbitt alloys in addition to Babbitt's original. Some
common compositions are:
 90% tin, 10% copper
 89% tin, 7% antimony, 4% copper
 80% lead, 15% antimony, 5% tin
 76% copper, 24% lead
 75% lead, 10% tin
 67% copper, 28% tin, 5% lead

20. PROBLEM
 In comparison with most other types of engineering design
work, the design procedure for bearings is unusual in that the
theory cannot be used to produce a design. The reason for this
that bearing theory and practice are, in a sense, diametrically
opposed to each other.
 In bearings the rotor rotates continuously thus generating a lot
of heat. We circulate cooling oil in a way to dissipate heat. It is
one of the vulnerable practical problems in oil ingress. Primary
requirement is to avoid leakage of oil and thus reduce the loss of
oil and improve the aesthetics of the machine.
 Oil leakage occurs due to
 (i). Pressure variation:
 Due to rotation of the shaft, the heat is developed and vaporizes
the lubricating oil. Thus vapor pressure is developed and this
vapor pressure is greater, that outside atmospheric pressure
causing oil ingress.
 (ii). Surface tension:
 The liquid surface exerts tension upon the adjacent portions of
the surface with which they are in contact. Oil due to the surface
tension is carried away along with the rotor.

21. REMEDY

 To reduce the vapor pressure developed, two holes are
provided on either side of the pedestal. For any
substance, generally the flow takes place from the high-
pressure side to the low-pressure side. So the vapor forces the
oil outside.
 To avoid this leakage, we provide a sealing ring in addition to
the knife edge scrapper fins that are available with a number of
pins. If there is a contact between the rotor and the sealing
rings, vibrations are produced. In order to avoid this small
clearances of the order of few microns are provided between
the and the rings. But some oil is found to leak through the
clearances provided.
 ` Initially a plastic sealing is provided on the pedestal. This
results in vibrations. Then sealing with felt is provided. Felt has
very less durability i.e. Worn out and influences the insulation.
A suction pipe is provided on both sides, into the holes and
vapor pressure is sucked out. The vapor pressure is then

22. .
 Another improvement in the above arrangement is to
provide a annular groove in the sealing ring. A tapping
of high-pressured air from open fan zone have been
extracted and connected to the annular ring thus
providing circular air sealing.
 This sealing proved to be effective and around 95% of
oil entering was slotted.

23. Thank you!
 .