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CONTENTS
1. Basics of Bearingsa. Introductionb. Principles of Frictionc. Types of Motion / Bearing design & function
2. Rolling Element Bearing Classifications3. Rolling Element Bearings & Tolerances4. Principles of Operation5. Bearing Loads6. Bearing Life7. Bearing Applications8. Materials & Manufacturing
a. Standard Bearing Components
b. Optional Bearing Componentsc. Outer Ring Modificationsd. Inner Ring Modificationse. Basic Boundary Dimensionsf. Load carrying Surfacesg. Load Zone & Contact Points
9. Bearing Types / Selection Process10.Bearing Materials11.Bearing Terminologies / Nomenclature12.Bearing Failures analysis, Causes13.Bearing Lubrication & Contamination14.Bearings for special applications in railways Traction Motor Bearings
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1. Basics of Bearingsa. Introduction:- A bearing is a device to allow constrained relative motion between
two or more parts, typically rotation or linear movement. Bearings may be classifiedbroadly according to the motions they allow and according to their principle of
operation as well as by the directions of applied loads they can handle.
Bearings are used primarily to support rotating shafts in mechanical equipment.
They can be found in the smallest electric motors to the largest pieces of industrial
equipment. They are of simple design and can be precision manufactured in mass
production quantities. They can support heavy loads over a wide speed range and do it
virtually friction free. They come in many different sizes and shapes, are relatively
inexpensive, and require little or no maintenance. They have predictable design lives
and operating characteristics and are truly a valuable asset to the rotating equipment
industry.
b. Principle of Friction:- That is because when things slide, the friction between themcauses a force that tends to slow them down. But if the two surfaces can roll over each
other, the friction is greatly reduced.
Bearings reduce friction by providing smooth metal balls or rollers, and a smooth
inner and outer metal surface for the balls to roll against. These balls or rollers "bear"
the load, allowing the device to spin smoothly
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c. Types of Motion / Bearing Design & Function:-
i.
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ii.
iii.
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iv.
v.
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vi.
vii.
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viii.
ix.
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x.
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2. Rolling Element Bearing Classifications:-
Ball Cylindrical Needle Tapered Spherical
3. Rolling Element Bearings & Tolerances:-
Tapered Spherical
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4. Principles of Operation:- There are at least six common principles of operation:
1. Plain Bearing, also known by the specific styles: bushings, journal bearings, sleeve bearings, rifle
bearings2. Rolling-Element Bearings such as ball bearings and roller bearings
3. Jewel Bearings, in which the load is carried by rolling the axle slightly off-center
4. Fluid Bearings, in which the load is carried by a gas or liquid
5. Magnetic Bearings, in which the load is carried by a magnetic field
6. Flexure Bearings, in which the motion is supported by a load element which bends.
Plain Bearing:- A plain bearing is the simplest type of bearing, comprising just a bearing surface and
no rolling elements. Therefore the journal (i.e., the part of the shaft in contact with the bearing) slides over
the bearing surface. The simplest example of a plain bearing is a shaft rotating in a hole. A simple linear
bearing can be a pair of flat surfaces designed to allow motion; e.g., a drawer and the slides it rests onor theways on the bed of a lathe.
Plain bearings, in general, are the least expensive type of bearing. They are also compact and lightweight,
and they have a high load-carrying capacity.
A linear table with four linear bearings (1)
The design of a plain bearing depends on the type of motion the bearing must provide. The three types of
motions possible are:
Journal (friction, radial or rotary) bearing: This is the most common type of plain bearing; it is
simply a shaft rotating in a bearing. In locomotive applications ajournal bearing specificallyreferred to the plain bearing once used at the ends of the axles of railroad wheel sets, enclosed
byjournal boxes.
Linear bearing: This bearing provides linear motion; it may take the form of a circular bearing and
shaft or any other two matching surfaces (e.g., a slide plate).
Thrust bearing: A thrust bearing provides a bearing surface for forces acting axial to the shaft .
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Integral
Integral plain bearings are built into the object of use. It is a hole that has been prepared into a bearing surface.
Industrial integral bearings are usually made from cast iron or babbitt and a hardened steelshaft is used in the
bearing.
Integral bearings are not as common because bushings are easy to accommodate and if they wear out then they
are just replaced. Depending on the material an integral bearing may be less expensive but it cannot be replaced.
If an integral bearing wears out then the item may be replaced or reworked to accept a bushing. Integral bearings
were very common in 19th-century machinery, but became progressively less common as interchangeable
manufacture permeated the industry.
An example of a common integral plain bearing is the hinge, which is both a thrust bearing and a journal bearing.
Bushing
A bushing, also known as a bush, is an independent plain bearing that is inserted into a housing to provide
a bearing surface for rotary applications; this is the most common form of a plain bearing. Common designs
include solid(sleeve andflanged), split, and clenchedbushings. A sleeve, split, or clenched bushing is only a
"sleeve" of material with an inner diameter (ID), outer diameter (OD), and length. The difference between the
three types is that a solid sleeved bushing is solid all the way around, a split bushing has a cut along its length,
and a clenched bearing is similar to a split bushing but with a clench across the cut. A flanged bushing is a sleeve
bushing with a flange at one end extending radially outward from the OD. The flange is used to positively locate
the bushing when it is installed or to provide a thrust bearing surface.
Sleeve bearings of inch dimensions are almost exclusively dimensioned using the SAE numbering system. The
numbering system uses the format -XXYY-ZZ, where XX is the ID in sixteenths of an inch, YY is the OD in
sixteenths of an inch, and ZZ is the length in eights of an inch. Metric sizes also exist.
A linear bushing is not usually pressed into a housing, but rather secured with a radial feature. Two such
examples include two retaining rings, or a ring that is molded onto the OD of the bushing that matches with a
groove in the housing. This is usually a more durable way to retain the bushing, because the forces acting on the
bushing could press it out.
The thrust form of a bushing is conventionally called a thrust washer.
A solid sleeve bushing A flanged bushing A clenched bushing
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Two-piece
Two-piece plain bearings, known asfull bearings in industrial machinery, are commonly used for larger diameters,
such as crankshaft bearings. The two halves are called shells. There are various systems used to keep the shells
located. The most common method is a tab on the parting line edge that correlates with a notch in the housing to
prevent axial movement after installation. For large, thick shells a button stop or dowel pin is used. The button stop is
screwed to the housing, while the dowel pin keys the two shells together. Another less common method uses a dowel
pin that keys the shell to the housing through a hole or slot in the shell.
The distance from one parting edge to the other is slightly larger than the corresponding distance in the housing so that
a light amount of pressure is required to install the bearing. This keeps the bearing in place as the two halves of the
housing are installed. Finally, the shell's circumference is also slightly larger than the housing circumference so that
when the two halves are bolted together the bearing crushes slightly. This creates a large amount of radial force
around the entire bearing which keeps it from spinning. It also forms a good interface for heat to travel out of the
bearings into the housing.
Crankshaft plain bearing shells
Rolling Element Bearing:- A rolling-element bearing, also known as a rolling bearing, is a bearing which
carries a load by placing round elements between two bearing rings. The relative motion of the pieces causes the
round elements to roll with very little rolling resistance and with little sliding.
One of the earliest and best-known rolling-element bearings are sets of logs laid on the ground with a large stone
block on top. As the stone is pulled, the logs roll along the ground with little sliding friction. As each log comes out
the back, it is moved to the front where the block then rolls on to it. It is possible to imitate such a bearing by placing
several pens or pencils on a table and placing an item on top of them.
A rolling element rotary bearing uses a shaft in a much larger hole, and cylinders called "rollers" tightly fill the space
between the shaft and hole. As the shaft turns, each roller acts as the logs in the above example. However, since the
bearing is round, the rollers never fall out from under the load.
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Rolling-element bearings have the advantage of a good tradeoff between cost, size, weight, carrying capacity,
durability, accuracy, friction, and so on. Other bearing designs are often better on one specific attribute, but worse in
most other attributes, although fluid bearings can sometimes simultaneously outperform on carrying capacity,
durability, accuracy, friction, rotation rate and sometimes cost. Only plain bearings are used as widely as rolling-
element bearings.
A sealed deep groove ball bearing
Design
Typical rolling-element bearings range in size from 10 mm diameter to a few metres diameter, and have load-carrying
capacity from a few tens of grams to many thousands of tonnes.
A particularly common kind of rolling-element bearing is the ball bearing. The bearing has inner and
outer races between which balls roll. Each race features a groove usually shaped so the ball fits slightly loose. Thus, in
principle, the ball contacts each race across a very narrow area. However, a load on an infinitely small point would
cause infinitely high contact pressure. In practice, the ball deforms (flattens) slightly where it contacts each race much
as a tire flattens where it contacts the road. The race also yields slightly where each ball presses against it. Thus, the
contact between ball and race is of finite size and has finite pressure. Note also that the deformed ball and race do notroll entirely smoothly because different parts of the ball are moving at different speeds as it rolls. Thus, there are
opposing forces and sliding motions at each ball/race contact. Overall, these cause bearing drag.
Jewel Bearing::::---- Ajewel bearing is a plain bearing in which a metal spindle turns in a jewel-lined pivot hole.
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The hole is typically shaped like a torus and is slightly larger than the shaft diameter. The jewel material is usually
some form of synthetic sapphire, such as ruby. Jewel bearings are used in precision instruments, but their largest use is
in mechanical watches.
Ruby jewel bearings used for a balance wheel in a mechanical watch movement.
Cross section of a jewel bearing in a mechanical watch
In wheels where friction is critical, a capstone is added on the end to prevent the shoulder of the shaft from bearing against the face
of the jewel.
Uses
The largest use for jewel bearings is in mechanical watches, where their low and predictable friction improves watch
accuracy as well as improving bearing life. Manufacturers listed the number of jewels prominently on the watch face
or back, as an advertising point. A typicalfully jeweledtime-only watch has 17 jewels: two cap jewels, two pivot
jewels, an impulse jewel for the balance wheel, two pivot jewels, two pallet jewels for the pallet fork, and two pivot
jewels each for the escape, fourth, third, and center wheels. In modern quartz watches, the timekeeper is a quartz
crystal in an electronic circuit, so accuracy of timekeeping is not dependent on low friction of the mechanical parts,
and jewels are not used much.
The other major use of jewelled bearings is in sensitive measuring instruments. They are typically used for delicate
linkages that must carry very small forces, in instruments such as; galvanometers, compasses, gyroscopes, gimbals,
and turbine flow meters. Bearing bores are typically less than 1 mm and typically support loads of under the weight of
1 gram, although they are made as large as 10 mm and support loads up to about the weight of 500 g.
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Fluid Bearings:-Fluid bearings are bearings which support the bearing's loads solely on a thin layer of
liquid or gas.
They can be broadly classified into two types: fluid dynamic bearings and hydrostatic bearings. Hydrostatic
bearings are externally pressurized fluid bearings, where the fluid is usually oil, water or air, and the pressurization is
done by a pump. Hydrodynamic bearings rely on the high speed of the journal (the part of the shaft resting on the
fluid) to pressurize the fluid in a wedge between the faces.
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.
Hydrodynamic bearing demonstration rig.
Operation:- Fluid bearings use a thin layer of liquid or gas fluid between the bearing faces, typically sealed
around or under the rotating shaft.
There are two principal ways of getting the fluid into the bearing:
In fluid static, hydrostatic and many gas or air bearings, the fluid is pumped in through an orifice or through a
porous material.
In fluid-dynamic bearings, the bearing rotation sucks the fluid on to the inner surface of the bearing, forming a
lubricating wedge under or around the shaft.
Hydrostatic bearings rely on an external pump. The power required by that pump contributes to system energy loss
just as bearing friction otherwise would. Better seals can reduce leak rates and pumping power, but may increase
friction.
Hydrodynamic bearings rely on bearing motion to suck fluid into the bearing and may have high friction and short life
at speeds lower than design or during starts and stops. An external pump or secondary bearing may be used for startup
and shutdown to prevent damage to the hydrodynamic bearing. A secondary bearing may have high friction and short
operating life, but good overall service life if bearing starts and stops are infrequent.
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A hydrostatic bearing has two surfaces which has a fluid forced, via a restrictive orifice, in between the surfaces so that it keeps
them apart. If the gap between the surfaces reduces then the outflow via the edges of the bearing is reduced and the pressure goes
up, forcing the surfaces apart again very strongly, giving excellent control of the gap and giving low friction
Some fluid bearings
Foil bearings
Foil bearings are a type of fluid dynamic air bearing that was introduced in high speed turbine applications in the
1960s by Garrett AiResearch. They use a gas as the working fluid, usually air and require no external pressurisation
system.
Journal bearings
Pressure-oiled journal bearings appear to be plain bearings but are arguably fluid bearings For example, journal
bearings in gasoline (petrol) and diesel engines pump oil at low pressure into a large-gap area of the bearing. As the
bearing rotates, oil is carried into the working part of the bearing, where it is compressed, with oil viscosity preventing
the oil's escape. As a result, the bearing hydroplanes on a layer of oil, rather than on metal-on-metal contact as it may
appear.
This is an example of a fluid bearing which does not use a secondary bearing for start/stop. In this application, a large
part of the bearing wear occurs during start-up and shutdown, though in engine use, substantial wear is also caused by
hard combustion contaminants that bridge the oil film.
Air bearings
Unlike contact-roller bearings, an air bearing (or air caster) utilizes a thin film of pressurized air to provide an
exceedingly low friction load-bearing interface between surfaces. The two surfaces don't touch. Being non-contact, air
bearings avoid the traditional bearing-related problems of friction, wear, particulates, and lubricant handling, and offer
distinct advantages in precision positioning, such as lacking backlash and stiction, as well as in high-speed
applications.
The fluid film of the bearing is air that flows through the bearing itself to the bearing surface. The design of the air
bearing is such that, although the air constantly escapes from the bearing gap, the pressure between the faces of the
bearing is enough to support the working loads.
Examples
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Air hockey is a game based on an aerostatic bearing which suspends the puck and player's paddles to provide low
friction and thus fast motion. The bearing uses a flat plane with periodic orifices which deliver air just over ambient
pressure. The puck and paddles rest on air.
Another example of a fluid bearing is ice skating. Ice skates form a hydrodynamic fluid bearing where the skate and
ice are separated by a layer of water caused by entropy
Magnetic Bearings:-
A magnetic bearing
A magnetic bearing is a bearing that supports a load using magnetic levitation. Magnetic bearings support
moving machinery 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. Magnetic bearings support the highest speeds of
any kind of bearing and have no known maximum relative speed
Magnetic bearings are difficult to design using permanent magnets due to the limitations described
by Earnshaw's theorem while techniques using diamagnetic materials are relatively undeveloped. As a result,
most magnetic bearings require continuous power input and an active control system to hold the load stable.
Magnetic bearings often use permanent magnets to carry the static load, while a power input is only used when
the levitated object deviates from its optimum position. Magnetic bearings typically require a back-up bearing inthe case of power or control system failure and during initial start-up conditions.
Magnetic bearings are used in several industrial applications such as electrical power generation, petroleum
refinement, machine tool operation, and natural gas pipelines. They are also used in the Zippe-typecentrifuge
used for uranium enrichment. Magnetic bearings are used in turbomolecular pumps, where oil-lubricated
bearings would be a source of contamination.
Design:-
Basic operation for a single axis
An active magnetic bearing (AMB) works on the principle of electromagnetic suspension and consists of
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an electromagnet assembly, a set of power amplifiers which supply current to the electromagnets, a controller,
and gap sensors with associated electronics to provide the feedback required to control the position of the rotor
within the gap. The power amplifier supplies equal bias current to two pairs of electromagnets on opposite sides
of a rotor. This constant tug-of-war is mediated by the controller which offsets the bias current by equal and
opposite perturbations of current as the rotor deviates from its center position.
The gap sensors are usually inductive in nature and sense in a differential mode. The power amplifiers in a
modern commercial application are solid state devices which operate in a pulse width modulation (PWM)
configuration. The controller is usually a microprocessor or DSP.
Active bearings have several advantages: they do not suffer from wear, have low friction, and can often
accommodate irregularities in the mass distribution automatically, allowing them to spin around their centre of
mass with very low vibration.
Two types of instabilities are typically present in magnetic bearings. Attractive magnets produce an unstable
static force that decreases with increasing distance and increases at decreasing distances. This can cause the
bearing to become unbalanced. Secondly, because magnetism is a conservative force, it provides little damping,
oscillations may cause loss of successful suspension if any driving forces are present.
Electrodynamic Bearings:-
An axial homopolar electrodynamic bearing
Electrodynamic bearings (EDB) are a novel type of bearing that is a passive magnetic technology. EDBs do notrequire any control electronics to operate. They work by the electrical currents generated by motion causing a
restoring force.
Applications
Magnetic bearing advantages include very low and predictable friction, and the ability to run without lubrication
and in a vacuum. Magnetic bearings are increasingly used in industrial machines such as compressors, turbines,
pumps, motors and generators. Magnetic bearings are commonly used in watt-hour meters by electric utilities to
measure home power consumption. Magnetic bearings are also used in high-precision instruments and to
support equipment in a vacuum, for example in flywheel energy storage systems. A flywheel in a vacuum has
very low wind resistance losses, but conventional bearings usually fail quickly in a vacuum due to poorlubrication. Magnetic bearings are also used to support maglev trains in order to get low noise and smooth ride
by eliminating physical contact surfaces. Disadvantages include high cost, and relatively large size.
A new application of magnetic bearings is their use in artificial hearts. The use of magnetic suspension in
ventricular assist devices was pioneered by Prof. Paul Allaire and Prof. Houston Wood at the University of
Virginia culminating in the first magnetically suspended ventricular assist centrifugal pump (VAD) in 1999
Future advances
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With the use of an induction-based levitation system present in maglev technologies such as
the Inductrack system, magnetic bearings could be used instead of complex control systems by using Halbach
Arrays and simple closed loop coils. These systems gain in simplicity, but are less advantageous with regard
to eddy current losses. For rotating systems it is possible to use homopolar magnet designs instead of multipole
Halbach structures, which reduces losses considerably. An example of this - that has bypassed the Earnshaw's
theorem issues - is the homopolar electrodynamic bearings invented by Dr Torbjrn Lembke.
Flexure Bearings:-
A flexure bearing is a bearing which allows motion by bending a load element.
A typical flexure bearing is just one part, joining two other parts. For example, a hinge may be made by attaching a
long strip of a flexible element to a door and to the door frame. Another example is a rope swing, where the rope is
tied to a tree branch.
A living hinge (a type of flexure bearing), on the lid of a Tic Tac box
Flexure bearings have the advantage over most other bearings that they are simple and thus inexpensive. They are also
often compact, light weight, 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.
A flexure bearing relies on the bearing element being made of a material which can be repeatedly flexed without
disintegrating. However, most materials fall apart if flexed a lot. For example, most metals will fatigue with repeated
flexing, and will eventually snap. Thus, one part of flexure bearing design is avoiding fatigue. Note, however, that
fatigue is important in other bearings. For example, the rollers and races in a rolling-element bearing fatigue as they
flatten against each other.
Flexure bearings can give very low friction and also give very predictable friction. Many other bearings rely on sliding
or rolling motions, which are necessarily uneven because the bearing surfaces are never perfectly flat. A flexure
bearing operates by bending of materials, which causes motion at microscopic level, so friction is very uniform. For
this reason, flexure bearings are often used in sensitive precision measuring equipment.
Flexure bearings are not limited to low loads, however. For example, the drive shafts of some sports cars replace
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cardan universal joints with an equivalent joint called a rag joint which works by bending rubberized fabric. The
resulting joint is lighter yet is capable of carrying hundreds of kilowatts, with adequate durability for a sports car.
Many flexure bearings are combined with other elements. For example, many motor vehicles use leaf springs. The
spring both holds the position of the axle as the axle moves (flexure bearing) and provides force to support the vehicle
(springing). In many cases it is not clear where flexure bearing leaves off and something else takes up. For
example, turbines are often supported on flexible shafts so an imperfectly balanced turbine can find its own center and
run with reduced vibration. Seen one way, the flexible shaft includes the function of a flexure bearing; seen another,
the shaft is not a "bearing".
5. Bearing Loads:- Bearings typically have to deal with two kinds of loading, radial and thrust. Depending
on where the bearing is being used, it may see all radial loading, all thrust loading or a combination of both.
The bearings in the electric motor and the pulley pictured above face only a radial load. In this case, most of theload comes from the tension in the belt connecting the two pulleys.
The bearing above is like the one in a barstool. It is loaded purely in thrust, and the entire load comes from the
weight of the person sitting on the stool.
The bearing above is like the one in the hub of your car wheel. This bearing has to support both a radial load and
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a thrust load. The radial load comes from the weight of the car, the thrust load comes from the cornering forces
when you go around a turn.
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6. Bearing Life:-
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Fluid and magnetic bearings
Fluid and magnetic bearings can have practically indefinite service lives. In practice, there are fluid bearings
supporting high loads in hydroelectric plants that have been in nearly continuous service since about 1900 and which
show no signs of wear.
Rolling element bearings
Rolling element bearing life is determined by load, temperature, maintenance, lubrication, material defects,
contamination, handling, installation and other factors. These factors can all have a significant effect on bearing life.
For example, the service life of bearings in one application was extended dramatically by changing how the bearings
were stored before installation and use, as vibrations during storage caused lubricant failure even when the only load
on the bearing was its own weight; the resulting damage is often false brinelling. Bearing life is statistical: several
samples of a given bearing will often exhibit a bell curve of service life, with a few samples showing significantly
better or worse life. Bearing life varies because microscopic structure and contamination vary greatly even where
macroscopically they seem identical.
Plain bearings
For plain bearings some materials give much longer life than others. Some of the John Harrison clocks still operate
after hundreds of years because of the lignum vitae wood employed in their construction, whereas his metal clocks are
seldom run due to potential wear.
Flexure bearings
Flexure bearings rely on elastic properties of material.Flexure bearings bend a piece of material repeatedly. Some
materials fail after repeated bending, even at low loads, but careful material selection and bearing design can make
flexure bearing life indefinite.
Short-life bearings
Although long bearing life is often desirable, it is sometimes not necessary. Harris describes a bearing for a rocket
motor oxygen pump that gave several hours life, far in excess of the several tens of minutes li fe needed.
L10 life
Bearings are often specified to give an "L10" life (outside the USA, it may be referred to as "B10" life.) This is the life
at which ten percent of the bearings in that application can be expected to have failed due to classical fatigue failure
(and not any other mode of failure like lubrication starvation, wrong mounting etc.), or, alternatively, the life at which
ninety percent will still be operating.The L10 life of the bearing is theoretical life and may not represent service life of
the bearing. Bearings are also rated using C0 (static loading) value. This is the basic load rating as a reference, and not
an actual load value.
External factors
The service life of the bearing is affected by many parameters that are not controlled by the bearing manufactures. For
example, bearing mounting, temperature, exposure to external environment, lubricant cleanliness and electrical
currents through bearings etc.
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7. Bearing Applications:-In general, ball bearings are used in most applications that involve moving parts. Some of these applications have
specific features and requirements:
Hard drive bearings used to be highly spherical, and were said to be the best spherical manufactured shapes,
but this is no longer true, and more and more are being replaced with fluid bearings.
German ball bearing factories were often a target of allied aerial bombings during World War II; such was
the importance of the ball bearing to the German war industry.
In horology, the company Jean Lassale designed a watch movement that used ball bearings to reduce the
thickness of the movement. Using 0.20 mm balls, the Calibre 1200 was only 1.2 mm thick, which still is the
thinnest mechanical watch movement.
Aerospace bearings are used in many applications on commercial, private and military aircraft including
pulleys, gearboxes and jet engine shafts. Materials include M50 tool steel (AMS6491), Carbon chrome steel
(AMS6444), the corrosion resistant AMS5930, 440C stainless steel, silicon nitride (ceramic) and titanium
carbide-coated 440C.
Skateboarding. The wheels in a skateboard contain two bearings in each of the four wheels. Most commonly
bearing 608-2Z is used (a deep groove ball bearing from series 60 with 8 mm bore diameter)
Yo-Yos, there are ball bearings in the center of high quality Yo-Yos.
8. Materials & Manufacturing:-a. Standard Ball Bearing Components:-
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b. Optional Bearing Components:-
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c. Outer Ring Modifications
d. Inner Ring Modifications
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e. Basic Boundary DimensionsThese are also referred as bearings envelope dimensions. These consists of Outside
Diameter(D), Inside Diameter(d) & Width(B) of the bearing. Along with these, the
Chamfer ( r ) also referred, i.e. the corner (edge) formed when outside surface of outer ring
intersects the edge surface (face) of outer ring. It also refers to the corner formed when inside
surface of inner ring intersects the edge surface of the inner ring.
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f. Load Carrying Surfaces:-
g. The Load Zone & Contact Points:-When the bearing is supporting to the radial load, the load is distributed through
approximately 1/3rd
portion of the bearing, at any given time. This area is called as
bearing load zone.
Every point or surface of the bearing that supporting to the load, are called as load
carrying contact points or surfaces. These include the outer ring (OD), inner ring
(ID), the adjacent surfaces that form the right angles to each other raceways & rolling
elements.
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9. Bearing Types / Selection Processes:-
Hydrodynamic bearings are bearings where an oil-film separates metal to metal contact
between the bearing and the shaft.
The hydrodynamic bearings are used for high rotational speeds and momentary overloads and
impact.
Rolling element bearings are bearings where balls or rollers are sandwiched between two
rings or races; one racethe inner race houses the shaft.
Rolling element bearings are good for applications with high starting loadsrail car axles
on a locomotive, for example. Starting friction is relatively low.
Rolling element bearings are typically nosier than hydrodynamic bearings.
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The two types of rolling element bearings:
1. Ball bearings2. Roller bearings
Ball bearings can handle higher speeds, while roller bearings can handle higher loads.
Rolling element bearings are classed according to the types of loads they can carry:
1. Radial (directed along the radius)2. Thrust or Axial (directed along the longitudinal axis of the shaft)3. Angular contact (radial + axial)
Double Row
Angular Contact
Thrust
Assembly ofDeep Groove (Conrad type) ball bearings
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If filling notches are added, more balls can be pushed in and greater loads can be handled
(20-40% increase in radial load capacitybut thrust load capacity is greatly reduced and
sensitivity to misalignment is increased).
Roller bearings are classified by their roller configuration
1. Cylindrical2. Spherical3. Tapered4. Needle
Spherical Roller Bearings
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Cylindrical Roller Bearings
Needle Bearings
Good at increasing radial space.
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Bearing Design
The trick is to maximize contact area to carry load, but minimize sliding and friction.
Studying stresses on bearings requires understanding how the ball contacts the races (surface
patch contact). Elastic deflection of the ball due to loading, makes the patch area difficult to
analyze. Deflection increases contact area (carry bigger loads), but increases sliding and
friction.
Inner raceway radius of curvature is slightly larger than the radius of
the ball
Outer raceway radius of curvature is larger than the radius of curvature of the inner
raceway
Bearing Selection
Bore is same size O.D. of bearings is same size
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Vendor information
Bearing Basic Number
Seriesmultiply last 2 digits by 5 to get bore diameter
L08 Extra light series 40 mm bore
316 - Medium series 80 mm bore
Bore diameter
Outside diameter
Width of race, w
Corner radius, r
Shaft diameter, ds
Housing diameter, dh
Further the bearings are classified as:-
Sleeve Bearings
Also called "plain" or "plane" bearings, they allow smooth, low-friction motion between two surfaces. The
load is supported through the sliding motion of one solid surface against another.
Ball and Roller Bearings
Support loads using balls or rollers. Since they operate with less friction than plain or sleeve bearings,
they're often called anti-friction bearings.
Mounted Bearings
Mounted in a housing to make installation a snap. Choose from base or flange mounted. Includes ball,
needle-roller, spherical, and sleeve bearings.
Thrust Bearings
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Handles thrust loads, also called an axial or side load, which is a load parallel to a shaft. Facilitates smooth
rotation between surfaces like other rotary bearings, but their design supports higher thrust loads. Choose
from plain and ball bearing designs.
Turntables
Ball bearings contained in a circular race for revolving capability. Perfect for displays, industrial
assemblies, and many other lazy Susan applications, these incredibly versatile bearings let you put a spin on
just about anything. Choose a load capacity from l ight duty to more than 200,000 lbs.
Rod Ends
Used to build control linkages and shaft connections. Includes rod ends, ball joint rod ends, clevises, and
ball joint swivel bearings.
Linear Bearings
Allows motion along a straight line. Includes linear plain and linear ball bearings.
Linear Guide Blocks and Rails
Compared to linear bearings, guide blocks and rails generally offer better load carrying capacity and handle
unbalanced and off-centered loads more easily due to their high rigidity, plus you only need to use one in a
linear motion system.
Ball and Roller Bearings Overview
991 products match your selections
Type Ball Bearings
Ball Bearing Style
OpenHave exposed bearing balls that run cooler than sealed and shielded bearings and are easy to lubricate.
FlangedEasy to install, the flange provides precise positioning during installation so you don't need a snap ring.
Double SealedHave seals on both sides that block out contaminants, preserve lubricants, and reduce noise.
Double ShieldedHave shields on both sides to keep lubricants in and protect bearings from contaminants that cause damage and reduce life.
Extended Inner RingProvides improved performance when used with shaft collars. The collar mates with the inner ring and doesn't touch moving parts.
Retaining RingAids in positioning during installation.
Open Flanged Open Double Sealed Flanged Double Sealed
Double Shielded
Double Shielded with Extended Inner
Ring Flanged Double Shielded
Flanged Double Shielded with Extended
Inner Ring
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Double Shielded with Retaining Ring
Double Shielded with Retaining Ring
and Extended Inner Ring
Ball Bearing Type
General Purpose
Suitable for most applications.
Available in varying levels of
precision.
Maintenance-Free
Plastic bearings don't require
lubrication, which means less
downtime for maintenance. Run light,
quiet, are smooth running, and
corrosion resistant.
Clean-Wearing
An ultra-thin film coating reduces
metal particles generated from normal
wear and adds corrosion resistance.
Ideal for clean room environments.
Perma-Lube
A lubricant fills the space between the
balls and the race, virtually eliminating
the need for maintenance. Lubricant
blocks out water and dust, extending
the life of the bearing.
Self-Aligning
A sphere-shaped raceway and two
rows of balls give these bearings a
high load capacity and the ability to
compensate for misalignment. Low-
friction design allows bearings to run
cooler at higher speeds.
Dual-Load Angular-Contact
The 40 contact angle of these bearings
enables them to accept combined
thrust and radial loads.
Angular-Contact
Also known as machine tool spindle
bearings, these 15 contact angle
bearings are made to meet super-tight
ABEC standards and can handle very
high speeds.
Ultra-Thin Multi-Load
Unique internal geometry contacts the
ball at four points enabling these
bearings to resist any combination of
radial, thrust, and moment loads
(torque-type forces off the axial and
radial plane).
System of Measurement
Inch|Metric
Bearing Dimensions
Select For Shaft Diameter:
Select Outside Diameter:
Select Width:
ABEC Precision Bearing Rating
ABECBearing dimensions are rated for precision by the Annular Bearing Engineers Committee (ABEC). The higher the ABEC number, the more precise the bearing and
the less it will deviate from its (ideal) stated dimensions. For example: ABEC-5 bearings have tighter tolerances than ABEC-1 bearings.
ABEC-1FAre thinner which makes them ideal for tight spaces.
ABEC-1
|ABEC-1F
|ABEC-3
|ABEC-5
|ABEC-7
|Not Rated
Bearing Trade Number
Select Bearing Trade Number:
Dynamic Radial Load Capacity Range, lbs.
Radial Load refers to a load that's perpendicular to the shaft that a bearing can withstand for one million revolutions.
6 to 250 lbs.|251 to 500 lbs.|501 to 1,000 lbs.|1,001 to 1,500 lbs.|1,501 to 3,000 lbs.|3,001 to 5,000 lbs.|5,001 to 7,500 lbs.|7,501 to 10,000 lbs.|10,001 to 30,000lbs.
Maximum rpm Range
The top speed a bearing can handle at low loads.
250 to 3,000|3,001 to 7,500|7,501 to 15,000|15,001 to 30,000|30,001 to 60,000|Above 60,000
Bearing Material
Steel
Extremely strong, but not as corrosion resistant as
stainless steel.
Stainless Steel
As strong as steel plus offers excellent corrosion
resistance.
Delrin
Adds wear and chemical resistance. Compared to
conventional metal bearings, this material is lighter,
quieter, smoother running, and corrosion resistant.
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Accessories
Bearing Shim Rings: Use around the outer race of your ball bearings for a tight fit in a stamped, cast, molded, or worn housing. They
operate like a spring, compressing and expanding to create tension between the bearing and housing and hold the bearing in place. Dampens
vibration and compensates for some thermal expansion between the housing and the bearing. They eliminate the need for keys, pins, and
adhesives so you can install parts easily. Ideal for use in motors, pumps, and pulleys.
Specifications Met
American Bearing Manufacturers Association 26.2 (ABMA)|Not Rated
Shafts Types
Your search returned products in the following categories.
Precision Shafts
Shafts transmit linear or rotary motion for power transmission applications.
Aluminum
Aluminum alloys are strong, naturally soft, lightweight, ductile and malleable. They are easy to machine, fabricate, join and work. Aluminum is non-toxic and electrically
and thermally conductive.
Brass
Brass resists atmospheric corrosion, water, and many salt water solutions. A high percentage of zinc makes it stronger and more durable than copper and bronze. It is easy
to manufacture and maintains higher electrical characteristics.
Bronze
This copper and tin alloy is generally ductile and malleable. Its high copper content makes it more corrosion resistant than brass. It is also harder and stronger than copper.
Copper
Copper is corrosion resistant and highly ductile. Great for electrical applications.
Iron
Iron is soft, ductile and malleable. It is supplied oversize "as cast" to allow for final finishing to the sizes listed.
Nickel
Nickel features outstanding oxidation and chemical resistance. Commonly used in chemical processing, marine components and heat exchangers. Includes Monel, Inconel,
and Hastelloy alloys and mu-metal foils.
Stainless Steel
Stainless steel alloys are generally more corrosion resistant than steel. Includes 300 series, 400 series, 15-5 PH, 17-4 PH, 17-7 PH, Nitronic 60 and A286 stainless steels.
Steel
Steel is composed mainly of iron, carbon, and other alloying elements that offer a wide range of characteristics including high strength, shock resistance, and machinability.
Titanium
Very strong yet lightweight, titanium has excellent corrosion resistance and a melting point of 3000 F. Cut it with sharp tooling and ample cutting fluid at slow speeds and
high feed rates.
Tungsten Carbide and Tungsten Alloys
Tungsten has good hardness and provides strong abrasion resistance.
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10.Bearing Materials:-Plain bearings must be made from a material that is durable, low friction, low wear to the bearing and shaft, resistant
to elevated temperatures, and corrosion resistant. Often the bearing is made up of at least two constituents, where one
is soft and the other is hard. The hard constituent supports the load while the soft constituent supports the hard
constituent. In general, the harder the surfaces in contact the lower the coefficient of friction and the greater the
pressure required for the two to seize.
Babbitt
Babbitt is usually used in integral bearings. It is coated over the bore, usually to a thickness of 1 to 100 thou (0.025 to
2.5 mm), depending on the diameter. Babbitt bearings are designed to not damage the journal during direct contact
and to collect any contaminants in the lubrication.
Bi-material
Split bi-material bushings: a metal exterior with an inner plastic coating
Bi-material bearings consist of two materials, a metal shell and a plastic bearing surface. Common combinations
include a steel-backed PTFE-coated bronze and aluminum-backed Frelon. Steel-backed PTFE-coated bronze
bearings are rated for more load than most other bi-metal bearings and are used for rotary and oscillating motions.Aluminum-backed frelon are commonly used in corrosive environments because the Frelon is chemically inert.
Bronze
A common plain bearing design utilizes a hardened and polished steel shaft and a softer bronze bushing. The bushing
is replaced whenever it has worn too much.
Common bronze alloys used for bearings include: SAE 841, SAE 660 (CDA 932), SAE 863, and CDA 954.
Cast iron
A cast iron bearing can be used with a hardened steel shaft because the coefficient of friction is relatively low. The
cast iron glazes over therefore wear becomes negligible.
Graphite
In harsh environments, such as ovens and dryers, a copper and graphite alloy, commonly known by the trademarked
name graph alloy, is used. The graphite is a dry lubricant, therefore it is low friction and low maintenance. The
copper adds strength, durability, and provides heat dissipation characteristics.
Unalloyed graphite bearings are used in special applications, such as locations that are submerged in water.
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Jewels
Known asjewel bearings, these bearings use jewels, such as sapphire, ruby, and garnet.
Plastic
Solid plastic plain bearings are now increasingly popular due to dry-running lubrication-free behavior. Solid polymer
plain bearings are low weight, corrosion resistant, and maintenance free. After studies spanning decades, an accurate
calculation of the service life of polymer plain bearings is possible today. Designing with solid polymer plain
bearings is complicated by the wide range, and non-linearity, of coefficient of thermal expansion. These materials
can heat rapidly when used in applications outside the recommended pV limits.
Solid polymer type bearings are limited by the injection molding process. Not all shapes are possible with this
process and the shapes which are possible are limited to what is considered good design practice for injection
molding. Plastic bearings are subject to the same design cautions as all other plastic parts: creep, high thermal
expansion, softening (increased wear/reduced life) at elevated temperature, brittle fractures at cold temperatures,
swelling due to moisture absorption. While most bearing-grade plastics/polymers are designed to reduce these design
cautions, they still exist and should be carefully considered before specifying a solid polymer (plastic) type.
Plastic bearings are now everywhere from photocopy machines to the tills in the super market. Other applications
include farm equipment, textile machinery, medical devices, food and packaging machines, car seating, marine
equipment and many more.
Common plastics include nylon, polyacetal, polytetrafluoroethylene (PTFE), ultra-high-molecular-weight
polyethylene (UHMWPE), rulon, PEEK, urethane, and vespel (a high-performance polyimide).
Others
Ceramic bearings are very hard and sand and other grit which enter the bearing are simply ground to a fine powder
which does not inhibit the operation of the bearing.
Lubrite
Lignum vitae is a self lubricating wood and in clocks it gives extremely long life.
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11.Bearing Terminologies / Nomenclature:-
Bearing Nomenclature
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You can learn a lot about a bearing just from its part number.
A typical bearing is the 6203ZZ bearing. This part number can be divided into it's
components:
6203ZZ
which means:
Type Code
Series
Bore
Suffix
The type code indicates the type of bearing. While each manufacturer uses their own
numbers, there are a few numbers that could be considered standard in the industry.
1
Self-Aligning Ball Bearing
This kind of ball bearing has a
spherical outer race, allowing the
axis of the bearing to "wander
around". This is important
because misalignment is one of
the big causes of bearing failure.
2 Spherical Roller Bearing
3
Double-Row Angular Contact
Ball Bearing
Designed to take axial as well as
radial loads.
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4Double-Row Ball Bearing
Designed for heavy radial loads.
5
Thrust Ball Bearing
Intended for exclusively axial
loads.
6
Single-Row Deep Groove Ball
Bearing
Typical ball bearing. Handles
light axial loads as well as radial
loads.
7
Single-Row Angular Contact
Bearing
For axial (one direction only!) as
well as radial loads.
8
Felt Seal
To assure that the entire inside
edge of the seal touches the inner
ring, the inner ring is enlarged. If
a bearing of more normal
proportions is required, the outerring is also enlarged, and the
bearing is referred to as a "wide
cup" bearing.
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32
Tapered Roller Bearing
This is the kind of wheel bearings
used in cars. The rollers are not
cylindrical, but conical. Theyhandle large raidal and axial
loads.
R Inch (Non-Metric) Bearing Varies
N
Cylindrical Roller Bearing
Instead of balls, cylindrical rollers
are used. These bearings can
handle much more radial load, but
can handle much less axial load,
than ball bearings.
NN
Double-Row Roller Bearing
Handles greater radial loads than
standard cylindrical roller
bearings.
NA
Needle Roller Bearing
Needle bearings are basically
roller bearings, but the rollers are
much smaller, making the bearing
more compact.
Varies
Type 6, "single-row deep groove", is perhaps the most common type of bearing.
If the bearing is an inch bearing (the first digit in the number is an R), then the size is the
digit or digits immediately following the R, in 16ths of an inch. An R8-2RS bearing, for
example, has an 8/16th or 1/2 inch bore.
If the first digit is a number, however, it is a metric bearing, and the second digit is the
series, which reflects the robustness of the bearing. The series are, from lightest to heaviest:
8 Extra thin section
9 Very thin section
0 Extra light
1 Extra light thrust
2 Light
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3 Medium
4 Heavy
Yes, they go in that order. Gotta keep things simple, you know.
Each of these series also establishes a relationship between the bore size, outer diameter, and
thickness of the bearing, in accordance with ISO standards. I have no idea what they are.
The third and fourth digits indicate the bore size in millimeters. Except for 0 through 3, the
bore size is simply five times the third and fourth digits together. 0 through 3, however, are
different:
00 10mm
01 12mm
02 15mm
03 17mm
If there is no fourth digit - for example, a 608 bearing, a common roller skate bearing - then
the size is the last digit in millimeters.
The last letters indicate something special about the bearing. For example:
Z Single shielded
ZZ Double shielded
RS Single sealed
2RS Double sealed
V Single non-contact seal
VV Double non-contact seal
DDU Double contact seals
NR Snap ring and groove
M Brass cage
And then there are the completely off-the-wall bearing numbers, like 499502H. I have no
idea what that number is supposed to mean, but it applies to what is basically an R10-2RS
bearing, only a bit thicker and with a groove and snap ring.
12.Bearing Failure, Causes, Maintenance Practices, Mounting & Dis-mounting:-
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Rolling-element bearings often work well in non-ideal conditions, but sometimes minor problems cause
bearings to fail quickly and mysteriously. For example, with a stationary (non-rotating) load, small vibrations
can gradually press out the lubricant between the races and rollers or balls (false brinelling). Without lubricant
the bearing fails, even though it is not rotating and thus is apparently not being used. For these sorts of reasons,
much of bearing design is about failure analysis.
There are three usual limits to the lifetime or load capacity of a bearing: abrasion, fatigue and pressure-induced
welding. Abrasion is when the surface is eroded by hard contaminants scraping at the bearing materials.
Fatigue is when a material breaks after it is repeatedly loaded and released. Where the ball or roller touches the
race there is always some deformation, and hence a risk of fatigue. Smaller balls or rollers deform more
sharply, and so tend to fatigue faster. Pressure-induced welding is when two metal pieces are pressed together
at very high pressure and they become one. Although balls, rollers and races may look smooth, they are
microscopically rough. Thus, there are high-pressure spots which push away the bearing lubricant. Sometimes,
the resulting metal-to-metal contact welds a microscopic part of the ball or roller to the race. As the bearing
continues to rotate, the weld is then torn apart, but it may leave race welded to bearing or bearing welded to
race.
Although there are many other apparent causes of bearing failure, most can be reduced to these three. For
example, a bearing which is run dry of lubricant fails not because it is "without lubricant", but because lack of
lubrication leads to fatigue and welding, and the resulting wear debris can cause abrasion. Similar events occurin false brinelling damage. In high speed applications, the oil flow also reduces the bearing metal temperature
by convection. The oil becomes the heat sink for the friction losses generated by the bearing.
Some of the reasons for bearing failure are:-
a. Excessive Loads: Excessive loads usually cause premature fatigue. Tight fits, brinelling & improper preloading can
also bring about early failure
The solution is to reduce the load or redesign using a bearing with greater capacity
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b. Overheating: Symptoms are discoloration of rings, balls & cages from gold to blue
Temperature in excess of 400F can anneal the ring & ball materials
The resulting loss in hardness reduces the bearing capacity causing early failure
In extreme cases, balls & rings will deform. The temperature rise can also degrade or destroy the
lubricant
Excessive roller end heat Advance metal flow due to excessive heat
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c. True Brinelling:-
Brinelling occurs when load exceed the elastic limit of ring material
Brinell marks results in indentation in raceways which further increases thevibrations & noise in the bearings
Any static overload or impact results in brinelling
d. False Brinelling:-
False brinelling elliptical wear marks in axial direction at each ballposition, with a bright finish & sharp demarcation, often by a ring of brown
debris indicates excessive internal vibration
Correct by isolating bearing from external vibration & using greases withantiwear additives
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e. Normal Fatigue Failure:- Fatigue failure fracture of running surfaces & subsequent removal of small
discrete particles of material
Fatigue can occur on inner ring, outer ring or balls
Progressive type of damage, normally accompanied with marked increase invibrations
f. Reverse Loading:- Normally observed in angular contact bearings when loaded in opposite
direction
Results in excessive stress & increase in temperature
Can be avoided by installing the bearing correctly
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g. Contamination:-
One of the leading cause of bearing failure
Symptoms are the denting of bearing raceways & balls resulting in highvibrations & wear
Clean work areas, tools, fixtures can help to avoid / reduce contamination &to avoid the failure
h. Lubricant Failure:-
Discoloration of ball raceways as well as balls due to this
Results in overheating & subsequent catastrophic failure Further increase in temperature cause to destroy the lubricant
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i. Corrosion:-
Results in red / brown areas on ball race ways, cages or bands of ballbearings
Occurred due to exposing the bearings to the corrosive environment
In extreme cases, results in early fatigue failures
j. Misalignment:-
Can be detected on raceways of non-rotating ring by a ball wear path whichis not parallel to raceway edges
Results in abnormal temperature rise in bearings / housings & heavy wear incage-ball pockets
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k. Loose Fits:-
Results in relative motion in mating parts
Continuation results in fretting i.e. generation of fine metal particles whichfurther turned in to brown color due to oxidation
This material is abrasive & aggravate the looseness further
l. Tight Fits:-
A heavy ball wear path in the bottom of the raceway around entirecircumference of inner ring & outer ring is resulted due to tight fits
The balls gets heavily loaded if the interference fits exceed the radialclearances at operating temperature
Due to this heavy torque develops suddenly with sudden rise in temperature& resulting in bearing failure
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Grease Types
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Types of Oil
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Lubrication of oil bearings
Centrifugal (or splash)lubrication
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Bearing Puller & Accessories:-