Definition, Use, Types of beariings, Types of Journal bearing, Materials for journal bearing, Failures of journal bearing, Design terms for journal bearing, Types of roller contact bearing, applications of roller contact bearing, Designation of roller contact bearing, Design terms for roller contact bearing, comparison between journal and roller bearings, characteristics of bearings, selection procedure of bearings

1. A Pedagogy Session on
Fundamentals and Selection
Procedure for Bearings.
Gaurav Mistry
Assistant Professor
Diwaliba Polytechnic, UTU.

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❑ Fundamentals of Journal Bearing
❖ What is Bearing?
A bearing is a machine element which support another moving machine element like
shaft (also known as journal) and axle.
❖ Why is Bearing used? (Functions of Bearing)
• The forces are transmitted from shaft and axle to the bearings, and from bearings to
the housing (i.e. it bears the load)
• A bearing permits controlled direction of motion (i.e. locate the moving parts in
correct position)
• It provides free motion to parts with minimum possible friction and wear.
• In some cases to carry away the heat generated (with the help of lubrication*
provided).
• The bearing plays an important role in the machine assembly to transmit motion
with minimum possible vibrations.
*The lubricant used to separate the journal and bearing is usually a mineral oil refined
from petroleum, but vegetable oils, silicon oils, greases etc., may be used.

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❖ Classification of Bearing
Though the bearings may be classified in many ways, yet the following are important
from the subject point of view:
❑ Fundamentals of Journal Bearing

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❖ Classification of Bearing
Depending upon the nature of contact. The bearings under this group are classified as :
(a) Sliding contact bearings, and (b) Rolling contact bearings.
In sliding contact bearings fig (a), the sliding takes place along the surfaces of contact between the
moving/rotating element (journal) and the fixed element (bearing). The sliding contact bearings are also
known as plain bearings. They are used in various subsystems in engines and power trains, for example
for support of both crankshaft and camshaft.
In rolling contact bearings fig (b), the steel balls or rollers, are interposed between the moving and fixed
elements. The balls offer rolling friction at two points for each ball or roller. They are widely used in
Machine Tools, Textile Machineries, Gear Boxes, Construction Machineries and in variety of
machines.
(b) Rolling contact bearings
(a) Sliding contact bearings
❑ Fundamentals of Journal Bearing

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❖ Classification of Bearing
❑ Fundamentals of Journal Bearing

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❖ Classification of Sliding Contact Bearing
▪ 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. Between the journal and bearing a film of lubricant is maintained.
• Different types of sliding contact bearings are:
1. Full journal bearing.
2. Partial journal bearing.
3. Fitted journal bearing.
4. Footstep or Pivoted bearing.
5. Collar bearing
6. Thick film bearing/ hydrodynamic lubricated bearing.
7. Thin film bearing/ boundary lubricated bearing.
8. Zero film bearing.
9. Hydrostatic or externally pressurized lubricated bearing.
❑ Fundamentals of Journal Bearing

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❖ Classification of Sliding Contact Bearing
1. Full journal bearing: When the angle of contact of the bearing with the journal is 360° as
shown in Fig. (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.
2. Partial journal bearing: When the angle of contact of the bearing with the journal is 120°, as
shown in Fig. (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.
3. Fitted journal 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.
❑ Fundamentals of Journal Bearing

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❖ Classification of Sliding Contact Bearing
4. Footstep/ Pivoted bearing: When shaft is in vertical position, the weight of shaft along with
gears, pinions, pulleys, etc. are supported by footstep or pivot bearing. The end of the shaft rests
inside a bearing which bears the load as well as prevents unnecessary movement of shaft. Steel
washer is fitted with the shaft, rotates on the brass washer which is at the bottom of the bearing.
5. Collar bearing: It is a thrust
bearing and normally used in
horizontal shaft. The solid collars
are made on the shaft and no. of
collars depends upon the amount
of load applied. The thrust pad
which is generally made of brass
or bronze fitted in the housing
and bears the load through
collars.
❑ Fundamentals of Bearing

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❖ Classification of Sliding Contact Bearing
▪ The sliding contact bearings, according to the thickness of layer of the lubricant
between the bearing and the journal, may also be classified as follows :
6. Thick film bearing/ hydrodynamic lubricated bearing: The thick film bearings are those in
which the working surfaces are completely separated from each other by the lubricant. Such
type of bearings are also called as hydrodynamic lubricated bearings.
7. Thin film bearing/ boundary lubricated bearing: The thin film bearings are those in which,
although lubricant is present, the working surfaces partially contact each other at least part of
the time. Such type of bearings are also called boundary lubricated bearings.
❑ Fundamentals of Journal Bearing

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❖ Classification of Sliding Contact Bearing
8. Zero film bearing: The zero film bearings are those which operate without any lubricant
present.
9. Hydrostatic or externally pressurized lubricated bearing: The hydrostatic bearings are those
which can support steady loads without any relative motion between the journal and the
bearing. This is achieved by forcing externally pressurized lubricant between the members.
❑ Fundamentals of Journal Bearing

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Ratio of bearing length to journal diameter (L/d ratio).
a. 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.
b. On the other hand, if L / d is greater than 1, then the bearing is known as long bearing.
c. When the length of the journal (L) is equal to the diameter of the journal (d), then the
bearing is called square bearing.
❑ Fundamentals of Journal Bearing

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❖ Types of bearing materials for Sliding bearing and their important properties.
• Many metals, alloys and non-metallic materials are used as bearing materials depending on
the external load on the bearing and working conditions. Certain basic properties are
necessary for the bearing materials. Some commonly used bearing materials and their
properties are discussed as follows:
1. Ferrous Metal:
a. Cast Iron
b. Steel (with lining)
2. Non Ferrous Metal:
a. Aluminum
b. Brass
c. Bronze
d. Tin base babbit
e. Lead bronse
f. Copper lead
g. Phosphor bronze
3. Non Metals:
a. Carbon graphite
b. Molded plastic
c. Wood
d. Teflon
e. Hard and soft rubber
f. Nylon
❑ Fundamentals of Journal Bearing

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❖ Properties of metallic bearing materials.
❑ Fundamentals of Journal Bearing

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❖ Bearing Failure.
• The failure of the plain bearing/ sliding bearings may occur due to one or more of the
following:
1. Excessive wear: During working, the bearing and journal surfaces are in contact with
relative motion between them. In the absence of lubricating film, there will be high friction
causing excessive wear. This will increase the bearing clearance and reduce the bearing
performance. Large amount of heat is generated, and this may cause the damage in the
bearing.
2. Cracking: When the bearings are subjected to excessive loads or impact or shocks, large
stresses may be induced which may cause the crack generation in the bearing. Use of high
endurance strength material and maintaining layer of thick film between the contact
surfaces, will prevent the formation of the crack.
3. Overheating: Constant overload and absence of layer of lubricating film between the
contact surfaces in the bearing, will be responsible to produce large friction. This large
friction is converted into high heat generated causing over heating of the bearing. Over
heating leads to thermal expansion of the bearing, which can cause seizure of the bearing.
Proper lubrication and the arrangement for heat dissipation can prevent the over heating of
the bearing.
❑ Fundamentals of Journal Bearing

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❖ Factors affecting the design of sliding Bearings
1. Viscosity of lubricant.
2. Rubbing speed/ relative speed between bearing and journal.
3. Specific pressure.
4. Heat dissipation.
5. Provision of cooling.
6. Selection of lubricant and its quantity.
7. Selection of bearing material.
❑ Fundamentals of Journal Bearing

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❖ Main terms used for the design of Sliding Bearings
❑ Design of Journal Bearing
Let D = Diameter of the bearing,
d = Diameter of the journal, and
L = Length of the bearing.
1. Diametral clearance. It 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,
3. Diametral clearance ratio. It is the ratio of the diametral clearance to the diameter of the
journal. Mathematically, diametral clearance ratio
4. Average bearing pressure (p):
“Due to external load on the bearing, the load per unit projected area of the bearing is known as
average bearing pressure.”
Where, p = average bearing pressure,
W = load acting on bearing,
d = Diameter of the journal, and
L = Length of the bearing.
p=
𝑊
𝐿𝑑

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❖ Main terms used for the design of Sliding Bearings
5. Bearing Characteristic Number (BCN):
“It is the unit less number having its value =
It helps to predict the performance of a bearing.
6. Sommerfeld Number: It is a dimensionless
number generally used for design of long bearing
without side leakage.
𝑍𝑁
𝑝
❑ Design of Journal Bearing

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❖ Main terms used for the design of Sliding Bearings
7. Coefficient of Friction:
Its value is obtained from McKee's Equation:
8. Heat Generated: 𝑯 𝒈= 𝝁𝑾𝒗 ; 𝑾𝒂𝒕𝒕
Where, v = rubbing velocity, m/sec and W = load on bearing, N.
❑ Design of Journal Bearing

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❖ Main terms used for the design of Sliding Bearings
9. Heat Dissipated: 𝑯 𝒅
It depends on projected area and the temperature difference between bearing surface and
surroundings.
Generally value of K is taken as 0.484
Note: If the Heat Generated is greater than Heat Dissipated then artificial cooling is
required.
❑ Design of Journal Bearing

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❖ Rolling contact/ Anti-friction bearing:
In rolling contact bearings, the elements of the bearing have a rolling contact. These
have following four main parts:
1. Outer Race/ Ring.
2. Inner Race/ Ring.
3. Balls/Rollers
4. Retainers/ Separator
❑ Fundamentals of Rolling Contact Bearing

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❖ Classification of Rolling contact/ Anti-friction bearing:
❑ Fundamentals of Rolling Contact Bearing

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❖ Classification of Rolling contact/ Anti-friction bearing:
a. Single Row Deep Groove Ball Bearing: are used for supporting
shafts in the gearbox.
b. Single Row Angular Contact Bearing: are used in supporting
wheel hubs, shafts of differential gear and steering gears like rack
and pinion.
c. Double Row Angular Contact Ball Bearing: are used to support
shafts with worm gears, angled spur gears, bevel gears etc.
d. Self Aligning Ball Bearings: are used in applications where
chances of shaft bending, mounting inaccuracies, misalignment
etc. are there e.g. transmissions, agricultural machinery, convening
machinery etc.
e. Cylindrical Roller Bearings: are used in electric motors,
gearboxes, rail car axles etc.
❑ Fundamentals of Rolling Contact Bearing

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❖ Classification of Rolling contact/ Anti-friction bearing:
f. Needle Roller Bearings: are used for supporting connecting rods,
swivel arms, rocker shafts, spindles etc.
g. Taper Roller Bearings: are used for shafts having worm and bevel
gears, machine tool spindles, cable pulleys and wheel hubs.
h. Spherical Roller Bearings: are used for cable pulleys, propelling
shafts, heavy wheels, crankshafts etc.
i. Single Row Thrust Ball Bearing: are used for injection pump
governor linkage steering boxes and other applications for supporting
thrust loads.
❑ Fundamentals of Rolling Contact Bearing

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❖ Standard Designation for Rolling contact/ Anti-friction bearing:
Bearing designation are standardized in different countries according to their own requirements.
1. The standard related to bearing are published by the S.K.F company.
• Bearing are designed with the help of numerical digits.
• First two/three digits specify the type of bearings
• The last two digits in multiple of five indicate the bearing bore excluding first three.
• E.g. 6006: It indicates that it is deep grove ball bearing of medium series having bore (06 x 5
= 30) of 30 mm.
• The complete details of bearings are available from catalogues.
• https://www.nationalprecision.com/ball-bearings/6000-series/
2. According to I.S specifications, bearings are designated with the help of alphabets and
numerical digits.
• The First two/three digits indicate the bore of the bearing.
• Next alphabetical characters indicate the type of bearing.
• The last two digits shows the duty (capacity) of the bearing.
• E.g. 30 BC 03: 30 mm - bearing bore, BC – deep groove ball bearing, 03 – medium duty
capacity.
• 25 BA 02: 25 mm – bearing bore, BA – single row angular contact bearing, 02 – light duty
capacity.
❑ Standard Designation of Roller Contact Bearing

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❖ Standard Designation for Rolling contact/ Anti-friction bearing:
❑ Standard Designation of Roller Contact Bearing

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❖ Standard Designation for Rolling contact/ Anti-friction bearing:
❑ Standard Designation of Roller Contact Bearing

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❑ Design of Roller Contact Bearing

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❖ Equivalent Load Calculation: (P)
• Normally Rolling contact bearings are subjected to both radial and axial loads (i.e. combined
load). In such case considering the effect of both, the equivalent radial load is determined
from the following equation:
P = S (X*V*Fr + Y*Fa)
Where, P = equivalent load,
S = service factor,
X = radial factor,
Y = thrust/axial factor,
V = rotation factor, 1 – when inner rate rotates, 1.2 – when outer race rotates.
Fr = radial load
Fa = thrust/axial load
❖ Basic Dynamic Load Rating/Dynamic Capacity: (C)
• The constant stationary radial load which a group of identical bearings with stationary outer
race can withstand for rating life of one million (106) revolution of inner race.
(X and Y is determined from the standard catalogue)
❑ Design of Roller Contact Bearing

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❖ Relation between Equivalent Load (P), Basic Dynamic Capacity (C) and Rating life
(L10)
Where, C = Basic Dynamic Capacity/ Dynamic load rating, N.
P = Equivalent load, N.
L = Expected bearing life in million revolutions.
L10 = Rating life, in one million revolution (106).
K = bearing constant,
K = 3 – for ball bearing,
K = 10/3 – for roller bearing.
𝐂
𝐏
= [
𝐋
L10
]
𝟏
𝐊
❑ Design of Roller Contact Bearing

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❖ Comparison of Antifriction bearing and Journal/Sliding bearing:
Sr.
No.
Journal Bearing Rolling Contact Bering
1 Starting torque is high. Less starting torque.
2 Hydrodynamic bearings remains
silent at high speeds.
Makes noise at high speeds.
3 Occupies less radial space and more
axial space.
Occupies less axial space and more radial
Space.
4 Sudden failure may take place and
create accident.
Makes noise prior to failure.
5 Simple journal bearings capable to
sustain both radial and axial load is
difficult to design.
Certain bearings can be designed to sustain
both radial and axial load.
6 More clearance is required compared
to rolling contact bearings.
Less clearance required comparatively.
7 Maintenance and lubrication is to be
done carefully.
Maintenance and lubrication is economical
and relatively easy.
❑ Comparison of Bearings

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❑ Characteristics of Bearings
❖ Main Features/ Characteristics of Bearings.

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❑ Selection Procedure of Bearings
❖ SELECTION OF BEARING.
Following are the different parameters for selecting a bearing :
LOAD :
(a) Amount of load : Extra light to heavy load
(b) Direction : Radial, axial or combined load
(c) Type : Regular or interrupted
SPEED : Low to high speed
TYPE OF MOTION :
(a) Rotary
(b) Reciprocating
TEMPERATURE : Low to High
ENVIRONMENT :
(a) Clean
(b) Dusty
TYPE OF MACHINE :
(a) Rough machine
(b) Precision machine
CLEARANCE : The amount of clearance between machine parts.
MOUNTING : Horizontal or Vertical mounting
ALIGNMENT : Fixed alignment or Self alignment type
METHOD OF LUBRICATION : The way through which machine will be lubricated
TYPE OF LUBRICANTS USED : Oil, grease or some different types of lubricants

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REFERENCES:
1. A textbook of Machine design, R. S. Khurmi, S. Chand.
2. Design of Machine Elements, S. B. Soni, Atul prakashan.
3. www.google.com