SM Bearings December 10, 2012

7/28/2019 SM Bearings December 10, 2012

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Bearings

Teknocrats Academy of Automation & Control Technology 1

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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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:-

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SM Bearings December 10, 2012

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