Bearings and their Mechanical Applications
TABLE OF CONTENTS
|
Sr.No |
Title |
|
1 |
What are Bearings |
|
2 |
Types of
Bearings |
|
3 |
Rolling Contact Bearings |
|
4 |
Sliding
Contact Bearings |
|
5 |
Magnetic Bearings |
|
6 |
Flexure
Bearings |
|
7 |
Jewel Bearings |
|
8 |
References |
What are Bearings
A bearing is a machine element which supports another moving
machine element. It permits a relative motion between the contact surfaces of
the members, while carrying the load. A little consideration will show that due
to the relative motion between the contact surfaces, a certain amount of power
is wasted in overcoming frictional resistance and if the
rubbing surfaces are in direct contact, there will be rapid
wear. Bearings are a crucial component of many types of
machinery and exist in a variety of forms and shapes. They are components that
support or permit only a specific type of motion in a system that may be under
static or dynamic loading.
Top
Bearing manufacturing companies in India
1. Schaeffler India Ltd
The Company Incorporated in the Year 1962, Schaeffler with
four plants and 19 sales offices has a significant presence in India with three
majors widely known product brands – FAG, INA, and LuK. It is the largest
Bearing Manufacturing Company in India.
2. SKF Bearings India
SKF India Ltd was incorporated in the year 1961 as a result
of a collaboration between AB SKF, Associated Bearing Company limited and
Investment Corporation of India Ltd. In 1965, the first manufacturing plant was
commissioned in Pune.
3. Timken India Limited (TIL)
Timken India Limited (TIL) was incorporated in 1987 as Tata
Timken Limited (TTL), a joint venture between Tata Iron and Steel Company
(TISCO) and The Timken Company, a world leader.
Timken India Limited, a Timken Company subsidiary, started
manufacturing bearings in India nearly three decades ago and today has
state-of-the-art manufacturing plants in Jamshedpur and Raipur to serve local
bearing market needs and beyond.
4. NRB Bearings Ltd
Founded in 1965, NRB was the first company to manufacture needle roller bearings in India. For over 40 years NRB has pioneered the leading edge of bearing technology, and today over 90% of vehicles on Indian roads run on NRB parts
Types of Bearings
Depending upon the direction of force the bearings
are further classified as:
Rolling Contact Bearings
For starting conditions and at moderate speeds, the
frictional losses in rolling contact bearing are lower than that of equivalent
hydrodynamic journal bearing. This is because the sliding contact is replaced
by rolling contact resulting in low coefficient of friction. Therefore, rolling
contact bearings are called ‘antifriction’ bearings. However, this is a
misnomer. There is always friction at the contacting surfaces between the
rolling element and the inner and outer cage
There are specific materials for the parts of rolling contact
bearings:
The chromium
steel contains 1 per cent carbon and 1.5 per cent chromium. The balls and races
are through-hardened to obtain a minimum hardness of 58 Rockwell C and the
rollers are case carburized to obtain a surface hardness of 58 Rockwell C.
Depending upon the type of rolling element, the bearings are
classified as ball bearing, cylindrical roller bearing, taper roller bearing
and needle bearing.
A.
Ball
bearings
Ball bearings are one of the most common types of bearing
classes used. It consists of a row of balls as rolling elements. They are
trapped between two annular shaped metal pieces. These metal pieces are known
as races. The inner race is free to rotate while the outer race is stationary.
Ball bearings provide very low friction during rolling but have limited
load-carrying capacity. This is because of the small area of contact between
the balls and the races. They can support axial loads in two directions besides
radial loads. Ball bearings are used for controlling oscillatory and rotational
motion. For example, in electrical motors where the shaft is free to rotate but
the motor housing is not, ball bearings are used to connect the shaft to the
motor housing.
Depending upon their applications, we have a wide range of
ball bearings to choose from. They are:
a. Deep Groove Ball Bearing
The most frequently used bearing is the deep groove ball
bearing. Bearing found in almost all kinds of products in general mechanical
engineering. In this type of bearing, the radius of the ball is slightly less
than the radius of curvature of the grooves in the races.
|
Rolling element |
Row
of balls as rolling elements. |
|
Design |
They
are trapped between two annular shaped metal pieces. These metal pieces are
known as races. The inner race is free to rotate while the outer race is
stationary. |
|
Specifications |
1. The radius of the ball is
slightly less than the radius of curvature of the grooves in the races.
Kinematically, this gives a point contact between the balls and the races.
Therefore, the balls and the races may roll freely without any sliding. 2. Due
to relatively large size of the balls, deep groove ball bearing has high load
carrying capacity 3.
Generate less noise due to point of contact 4. They are not self-aligning and
have poor rigidity compared to roller bearings. 5. Give excellent performance in
high-speed applications. |
|
Type of load |
Radial
and (limited) axial load. |
|
Applications |
Electric
motors, compressors, fans, and conveyors. |
b. Angular Contact Ball
Bearing
In angular contact bearing, the grooves in inner and outer races are so shaped that the line of reaction at the contact between balls and races makes an angle with the axis of the bearing. This reaction has two components— radial and axial.
|
1.
Can carry radial as well as axial loads. 2.
Assembled with some magnitude of preload. |
|
Rolling element |
Row
of balls as rolling elements. |
|
Design |
The
grooves in inner and outer races are so shaped that the line of reaction at
the contact between balls and races makes an angle with the axis of the
bearing. This reaction has two components— radial and axial. |
|
Specifications |
1. Often used in pairs, either
side by side or at the opposite ends of the shaft, 2. Require
initial pre loading. 3. Load carrying
capacity is more than deep groove ball bearings |
|
Type of load |
Radial
and axial load. |
|
Applications |
Materials
Handling, Machine Tool, Steel Mill, and Wind Energy industries. |
c. Self-aligning Bearings
There are two types of self-aligning rolling contact
bearings:
1.
Self-aligning ball bearing
The self-aligning ball bearing consists of two rows of
balls, which roll on a common spherical surface in the outer race. In this
case, the assembly of the shaft, the inner race and the balls with cage can
freely roll and adjust itself to the angular misalignment of the shaft.
2.
Spherical roller bearing.
There is a similar arrangement in the spherical roller
bearing, where balls are replaced by
two rows of spherical rollers, which run on a common
spherical surface in the outer race.
|
Self-aligning ball
bearings |
Spherical roller
bearings |
|
|
|
|
|
|
Rolling elements are
balls |
Rolling elements are
rollers |
|
|
Consists of two rows of balls, which roll on a common
spherical surface in the outer race. |
Two rows of spherical rollers, which run on a common spherical
surface in the outer race. |
|
|
Can carry relatively
less radial and trust loads compared to self-aligning ball bearings |
Can carry relatively
high radial and thrust loads compared to self-aligning ball bearings |
|
|
Permit minor angular misalignment of the shaft relative to the
housing and They are used in agricultural machinery, ventilators, and railway
axle-boxes |
||
d. Thrust Ball Bearing
A thrust ball bearing consists of a row of balls running between two rings—the shaft ring and the housing ring. Thrust ball bearing carries thrust load in only one direction and cannot carry any radial load. The use of a large number of balls results in high thrust load carrying capacity in smaller space. This is the major advantage of thrust bearing.
|
Rolling element |
Row
of balls as rolling elements. |
|
Design |
Row of balls running between two rings—the
shaft ring and the housing ring. |
|
Specifications |
1. Not self-aligning 2.Cannot
tolerate mis-alignment. 3.Operate
better on vertical shafts compared to horizontal shafts. 4.
bearings give poor service because the balls are subjected to centrifugal
forces and gyroscopic couple. |
|
Type of load |
Only
Thrust load in one direction and cannot carry radial load. |
|
Applications |
Worm
gear boxes and crane hooks. |
B. Roller Bearings
Roller
bearings contain cylindrical rolling elements instead of balls as load carrying
elements between the races. An element is considered a roller if its length is
longer than its diameter. Since they are in line contact with the inner and
outer races instead of point contact as in the case of ball bearings, they can
support greater loading.[1]
Cylindrical Roller Bearing
When
maximum load carrying capacity is required in a given space, the point contact
in
ball bearing is replaced by the line contact of roller
bearing. A cylindrical roller bearing consists of relatively short rollers that
are positioned and guided by the cage.
|
1.
Very high radial load carrying capacity. 2.
More rigid than ball bearings 3.
Cannot take thrust load. |
|
Rolling Element |
Rollers
|
|
Design |
Consists of relatively short
rollers that are positioned and guided by the cage. |
|
Specifications |
1. When
maximum load carrying capacity is required in a given space, the point
contact in ball bearing is replaced by the line contact of roller bearing. 2.Not
self-aligning 3.Cannot
tolerate mis-alignment 4.Generate
more noise. |
|
Type of load |
High
Radial load carrying capacity and cannot carry thrust load. |
|
Applications |
Wind
turbines. |
C. Taper
Roller Bearing
The taper roller bearing consists of rolling elements in the
form of a frustum of cone. They are arranged in such a way that the axes of
individual rolling elements intersect in a common apex point on the axis of the
bearing. In kinematics’ analysis, this is the essential requirement for pure
rolling motion between conical surfaces. In taper roller bearing, the line of
resultant reaction through the rolling elements makes an angle with the axis of
the bearing. Therefore, taper roller bearing can carry both radial and axial
loads. In fact, the presence of either component results in the other, acting
on the bearing. In other words, a taper roller bearing subjected to pure radial
load induces a thrust component and vice versa. Therefore, taper roller
bearings are always used in pairs to balance the thrust component. Taper roller
bearing has separable construction. The outer ring is called ‘cup’ and the
inner ring is called ‘cone’. The cup is separable from the remainder assembly
of the bearing elements including the rollers, cage and the cone.
|
Rolling Element |
Rollers
in the form of frustum of a cone |
|
Design |
The outer ring is called ‘cup’ and
the inner ring is called ‘cone’. The cup is separable from the remainder
assembly of the bearing elements including the rollers, cage and the cone. |
|
Specifications |
1.the
axes of individual rolling elements intersect in a common apex point on the
axis of the bearing. In kinematics’ analysis, this is the essential
requirement for pure rolling motion between conical surface. The line of
resultant reaction through the rolling elements makes an angle with the axis
of the bearing. 2.are
always used in pairs to balance the thrust component. 3.Have
greater rigidity. 4.can be easily assembled and
disassembled due to separable parts. |
|
Type of load |
Radial
and Thrust (a
taper roller bearing subjected to pure radial load induces a thrust component
and vice versa) |
|
Applications |
Used
in Bevel gears. Cars and trucks, propeller shafts and differentials, railroad
axle boxes. |
D. Needle roller bearing
Needle bearings are characterized by cylindrical rollers of
very small diameter and relatively long length. They are also called quill bearings.
The length to diameter ratio of needles is more than four. Needle bearings are
used with or without inner and outer races. Very often, needle bearings are
used without the races. In some cases, the needles run directly on the surface
of the shaft. Needle bearings are ideally suited for applications involving
oscillatory motion such as piston pin bearings, rocker arms and universal
joints.
Static load carrying capacity
Static load is defined as the load acting
on the bearing when the shaft is stationary.
It produces permanent deformation in balls and races, which increases with
increasing load. The permissible static load, therefore, depends upon the
permissible magnitude of permanent deformation.
Where conditions of friction, noise and
smoothness are not critical, a much higher permanent deformation can be
tolerated and consequently static loads up to four times the static load
carrying capacity may be permissible. On the other hand, where extreme
smoothness of operation is desired, a smaller permanent deformation is
permitted
Dynamic Load carrying capacity
The dynamic load carrying capacity of a
bearing is defined as the radial load in radial bearings (or thrust load in
thrust bearings) that can be carried for a minimum life of one million
revolutions. The minimum life in this definition is the L10 life, which 90% of
the bearings will reach or exceed before fatigue failure. The dynamic load
carrying capacity is based on the assumption that the inner race is rotating
while the outer race is stationary. However, the manufacturer’s catalogues
give ready-made values of dynamic load capacities of bearings.
Equivalent
Bearing load
The force acting on the bearing has two
components—radial and thrust. It is therefore necessary to convert the two
components acting on the bearing into a single hypothetical load, fulfilling
the conditions applied to the dynamic load carrying capacity. Then the
hypothetical load can be compared with the dynamic load capacity. The
equivalent dynamic load is defined as the constant radial load in radial
bearings, which if applied to the bearing would give same life as that which
the bearing will attain under actual condition of forces. The expression for
the equivalent dynamic load is written as,
Where,
P = equivalent dynamic load (N)
Fr = radial load (N)
Fa = axial or thrust load (N)
V = race-rotation factor X and Y are
radial and thrust factors respectively and their values are given in the
manufacturer’s catalogues.
Elements of V is 1 when the inner race
rotates while the outer race is held stationary in the housing. The value of V
is 1.2 when the outer race rotates with respect to the load, while the inner
race remains stationary. In most of the applications, the inner race rotates
and the outer race is fixed in the housing.
Assuming V as unity, the general equation
for equivalent dynamic load is given by,
In this chapter, we will use the above
equation for calculating equivalent dynamic load. The effect of V should be
considered in special cases, where the outer race rotates and the inner race is
stationary.
When the bearing is subjected to pure
radial load Fr,
When the bearing is subjected to pure
thrust load Fa,
A rolling contact bearing is usually
designated by three or four digits. The meaning of these digits is as follows:
(i)
The last two
digits indicate the bore diameter of the bearing in mm (bore diameter divided
by 5)
(ii)
For example,
XX07 indicates a bearing of 35 mm bore diameter.
(iii)
The third digit
from the right indicates the series of the bearing.
(iv)
For example, X307
indicates a medium series bearing with a bore diameter of 35 mm.
(iv) The fourth digit and sometimes fifth
digit from the right specifies the type of rolling contact bearing. For
example, the digit 6 indicates deep groove ball bearings.
The first step is to safely and correctly
remove a failed bearing. For three factors, pullers and presses designed for
this purpose are the best options: protection, time savings, and minimizing
damage to the shaft and housing during the operation. As the threaded post,
which is balanced on the end of the shaft, is tightened, two- and three-jaw
mechanical pullers pull uniformly on the outer ring.
The separator or knife type of removal
tool, which has two plates placed behind the bearing, is another choice.
Hydraulic-assisted rams are used in heavy-duty pullers to make removal easier.
The shaft and housing can be destroyed if the bearing is removed with a
high-speed, cut-off tool that is used carelessly.
Thermal removal,
installation and methods.
Another technique for removing and
installing bearings is to lower or raise the temperature of the bearing, shaft,
and/or housing within specified limits. All of the warnings about mechanical
removal methods often refer to thermal removal methods. Both the shaft and the
housing should be free of nicks and burrs. Allow time to test and check that
the shaft and housing are within tolerances.
Sliding
Contact Bearings
|
What is lubrication Lubrication is the
science of reducing friction by application of a suitable substance called
lubricant between the rubbing surfaces of bodies having relative motion. Used to reduce
friction, carry away heat generated due to friction, protect journal and
bearing from corrosion and prevent wear. |
A.
Thick
Film Bearings
Thick film lubrication describes a condition of lubrication, where two surfaces of the bearing in relative motion are completely separated by a film of fluid.
Thick film lubrication is further divided into two groups:
1.
Hydrodynamic
Hydrodynamic lubrication is defined as a system of lubrication in which the load-supporting fluid film is created by the shape and relative motion of the sliding surfaces.
A.
Journal Bearing
(supports radial load)
A journal bearing is a sliding contact bearing working on hydrodynamic lubrication and which supports the load in radial direction. The portion of the shaft inside the bearing is called journal and hence the name ‘journal’ bearing.
a.
Full
In full journal bearing, the angle of contact of the bushing with the journal is 360°. Full journal bearing can take loads in any radial direction. Most of the bearings used in industrial applications are full journal bearings.
b.
Partial
In partial bearings, the angle of contact between the bush and the journal is always less than 180°. Most of the partial bearings in practice have 120° angle of contact. Partial bearing can take loads in only one radial direction. Partial bearings are used in railroad-cars.
B.
Thrust bearing
(supports axial load)
a.
Footsteps
The footstep bearing
or simply ‘step’ bearing is a thrust bearing in which the end of the shaft is
in contact with the bearing surface.
b.
Collar
The collar bearing is a thrust bearing in which a collar
integral with the shaft is in contact with the bearing surface.
2.
Hydrostatic
lubrication.
Hydrostatic lubrication is defined as a system of
lubrication in which the load supporting fluid film, separating the two
surfaces is created by an external source, like a pump, supplying sufficient
fluid under pressure. Since the lubricant is supplied under pressure, this type
of bearing is called externally pressurised bearing
B.
Thin
Film Bearings
Thin film lubrication, which is also called boundary
lubrication, is defined as a condition of lubrication where the lubricant film
is relatively thin and there is partial metal to metal contact. This mode of
lubrication is seen in door hinges and machine tool slides. The conditions
resulting in boundary lubrication are excessive load, insufficient surface area
or oil supply, low speed and misalignment
C.
Elastohydrodynamic
Bearings
There is a particular mode of lubrication known as
elastohydrodynamic lubrication. When the fluid film pressure is high and the
surfaces to be separated are not sufficiently rigid, there is elastic
deformation of the contacting surfaces. This elastic deflection is useful in
the formation of the fluid film in certain cases. Since the hydrodynamic film
is developed due to elastic deflection of the parts, this mode of lubrication
is called elastohydrodynamic lubrication. This type of lubrication occurs in
gears, cams and rolling contact bearings.
D.
Zero
film Bearings
Zero film bearing is a bearing which operates without any lubricant, that is without any film of lubricating oil.
Applications of Fluid Bearings:
•
Fluid bearings are frequently used in high
load, high speed or high precision applications where ordinary ball bearings
would have short life or cause high noise and vibration. They are also used
increasingly to reduce cost.
•
For example, hard disk drive motor fluid
bearings are both quieter and cheaper than the ball bearings they replace.
Applications are very versatile and may even be used in complex geometries such
as leadscrews
Magnetic Bearings
A magnetic bearing is a type of bearing that supports a load
using magnetic levitation. Magnetic bearings support moving parts without
physical contact. For instance, they are able to levitate a rotating shaft and
permit relative motion with very low friction and no mechanical wear.
Types:
1. Active Magnetic Bearing (AMB)
A
type of magnetic bearing in which non-contact support of a shaft is achieved by
using closed-loop control.
2. Passive Magnetic Bearing
A
type of magnetic bearing that does not require active control.
3. Electromagnetic (EM) Biased Magnetic Bearing
A
type of AMB in which the magnetic field has two components – a constant bias
field and a variable control field, with the bias magnetic field being
generated by an electrical current in a coil.
4. Radial Magnetic Bearing
Magnetic
Bearing in which magnetic forces produce radial support for the shaft in two
orthogonal axes.
5. Axial Magnetic Bearing
Magnetic Bearing in which magnetic forces produce axial support for the shaft
Its applications are
1.
Magnetic bearings are commonly used in watt-hour
meters by electric utilities to measure home power consumption.
2.
They are also used in energy storage or
transportation applications and to support equipment in a vacuum.
3.
Magnetic bearings are also used in some
centrifugal compressors for chillers with a shaft made up of magnetic material
lies between magnetic bearings.
4. A new application of magnetic bearings is in artificial hearts
Flexure
Bearings
A flexure bearing is a category of flexure which is engineered to be compliant in one or more angular degrees of freedom. Flexure bearings are often part of compliant mechanisms. Flexure bearings serve much of the same function as conventional bearings or hinges in applications which require angular compliance.
1.
Pin flexure
A thin bar or cylinder of material, constrains 3 degrees of
freedom when geometry matches a notch cutout.
2.
Blade flexure
Thin sheet of material, constrains 3 degrees of freedom.
3.
Notch flexure
Thin cutout on both sides of a thick piece of material,
constrains 5 degrees of freedom.
|
ADVANTAGES |
DISADVANTAGES |
|
•
Flexure bearings have the advantage over most other bearings that they
are simple and thus inexpensive. They are also often compact, lightweight,
have very low friction, and are easier to repair without specialized
equipment. |
•
Flexure bearings have the disadvantages that the range of motion is
limited, and often very limited for bearings that support high loads. |
Jewel
Bearings
A
jewel bearing is a plain bearing in which a metal spindle turns in a
jewel-lined pivot hole. The hole is typically shaped like a torus and is
slightly larger than the shaft diameter. The jewels are typically made from the
mineral corundum, usually either synthetic sapphire or synthetic ruby. Jewel
bearings are used in precision instruments where low friction, long life, and
dimensional accuracy are important. Their largest use is in mechanical watches.
The other major use of jeweled bearings is in sensitive mechanical measuring
instruments.
|
The other major use of jewel bearings is in sensitive mechanical measuring instruments: galvanometers, compasses, gyroscopes, gimbals, dial indicators, dial calipers, and turbine flow meters galvanometers, compasses, gyroscopes, gimbals, dial indicators, dial calipers, and turbine flow meters |
References
•
https://www.researchgate.net/publication/280722544_A_STUDY_OF_BEARING_AND_ITS_TYPES
•
Design of Machine Elements – V.B BHANDARI
Very informative!
ReplyDeleteReally nice content! Would love to read more of such stuff!
ReplyDeleteGreat content … very informative
ReplyDeleteVery well written!!
ReplyDeleteVery informative, great blog!
ReplyDeleteCovers all aspects , good job
ReplyDeleteGreat Work 🙌
ReplyDeleteToo much knowledge on a single blog !
ReplyDelete