General Information About Bearings

7/29/2019 General Information About Bearings

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General Information About Bearings

One of the greatest invention of all time is "WHEEL". It was wheel which gave mobility to theancient civilization which led to the development of man kind.

But this mobility and progress was too slow because man was not able to overcome the forcecalled friction---Force which opposes motion.

The most successful and practical solution for eliminating the friction was use of BEARINGS---

a device which reduces friction and enhances the motion between objects. The use of bearing is

so much prominent in today's modern life that we can see its usage in furniture's, instruments,Computers, Rockets, Robots, Automobiles and what not..

The exact origin of Bearings is not known, but the principle on which they operate has been

applied by man for thousands of years, Before "Rolling Elements" bearing, efforts were made touse plain type bearings.

Since than, continuous efforts were made to develop suitable Bearing, which can minimizefrictional losses. In Europe, the application of such bearing was found in the late 18th Century.

On top of church, a weather cock weighing about 180 Kgs. was supported by a thrust bearingconsisting rollers, races and cage.

Since then Bearing is under constant development. In modern world of today, it is the pioneering

works of Professor Stribeck, a German scientist, that led to development of bearings which werehaving less friction, high load bearing capacity, accurate dimensions etc.


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What is a Bearing:

A bearing is a component used to decreasing of friction which could

be caused from any elements related rotation, in order to reach themaximum efficiency of the power, which could have been converted

from torque power into heat power, so the main function for thebearings is decreasing the "converted to heat" power.

A great variety of rolling bearing types and designs are known, themanifolds of the bearings is justified by their various purpose of

application.

Technical Information About Bearings:

Every form of antifriction Bearing consists of four basic parts:-

1. An Inner Ring2. An Outer Ring3. Rolling Elements4. A Cage

1.An Inner Ring:- This is the smaller of the two bearing rings and gets its name from theposition it holds. It has a groove on its outside diameter to form a path for the balls. The surface

of this path is precision finished to extremely tight tolerances and is honed to a very smooth,mirror-like surface finish. The inner ring is mounted on the shaft and is usually the rotating

element.

2. An Outer Ring:- This is the larger of the two rings and, like its counterpart the inner ring, its

name is derived from the position it holds. Conversely, there is a groove on its inside diameterto form a pathway for the balls. This surface also has the same high precision finish of the inner

ring. The outer ring is normally placed into a housing and is usually held stationery.

3. Rolling Elements:- These are the rolling elements that separate the inner and outer ring andpermit the bearing to rotate with minimal friction. The ball radius is slightly smaller than the

grooved ball track on the inner and outer rings. This allows the balls to contact the rings at asingle point, appropriately calledpoint contact. Ball dimensions are controlled to very tight

tolerances. Ball roundness, size variations, and surface finish are very important attributes andare controlled to a micro inch level

(1 micro inch = 1/1,000,000th, or one-millionth of an inch). Rolling elements can be eitherBalls, Cylindrical Rollers, Spherical Rollers, Tapered Rollers and Oil in case of Journal type of

Bearings.

4. The Cage:-The main purpose of the cage is to separate the balls, maintaining an even andconsistent spacing, to accurately guide the balls in the paths, orraceways, during rotation, and

to prevent the balls from falling out. Cage may be of Steel, Brass, Bronze, or Phenoliccomposition, depending upon the type and application of the bearings.


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The parts of a Bearing in general is illustrated in the figure.

Bearings are designed in such a way that they offer following advantages:-

1. Low Friction--Particularly low starting friction.2. The ability to support both radial and thrust load and high speeds of rotation.3. Accurate performance under changing load and speed.4. High Load Carrying capacity5. Operating ability under extreme conditions of speed and performance.6. Practically no wear in running.7. Simple methods of Lubrication.8. Inherently Precision Mechanisms.

The above advantages clearly justify the ubiquitous presence of Bearings in our life.


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Fri Nov 19 2010 09:47:32 GMT+0530 (India Standard Time) Types of Bearings

In the most general classification; Bearing can be divided

into two main categories:-

Journal Bearings (Oil filmed Bearings)

o Hydro Static Bearings

o Hydro Dynamic Bearings

Types of Anti Friction Bearings

o Single Row Deep Groove Ball Bearings

o Double Row Deep Groove Ball Bearings

o Magneto Type Ball Bearing

o Angular Contact Ball Bearing

o Double Row Angular Contact Ball Bearings

o Double Row self Aligning Ball Bearingso Cylindrical Roller Bearings

o Self Aligning Spherical Roller Bearings

o Taper Roller Bearing

o Needle Roller Bearing

o Thrust Ball Bearing

o Spherical Roller Thrust Bearings

o Power Transmission Unit

o Shafer Bearings for Fertilizers and Chemical Units

o Single Row Radial Wide Bearing

Plastic Bearings


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hydrodynamic journal bearings

Types of Bearings

Single Row Deep Groove Ball Bearings:This bearing consists of inner and outer rings with deep symmetrical ball race, ways, separatorand complement of Balls. This beading is designed primarily for radial load but due to it's design

features it is capable of carrying equal amount of thrust load in either direction and is capable ofoperating at high speed too.

This bearing has the lowest frictional losses and therefore, it is the most widely used among alltypes of bearings.

Double Row Deep Groove Ball Bearings:Double row deep groove bearing embodied the same design principle as that of the single row

deep groove ball bearings.The bearing has a lower axial displacement than it occurs in the single row deep groove ballbearing. These bearings are capable of carrying substantial thrust loads in either direction and

due to double rows of ball they are also capable of carrying high radial loads too.


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Types of Bearings.

Magneto Type Ball Bearings:

In this type of bearings the inner ring is same to that of deep groove ball bearings but the track onouter race has one shoulder.

At the deepest position the groove track merges into the cylindrical track and therefore thisbearing has a character of separable outer race.

Magneto type bearings may be loaded radially and in one direction axially, generally they aremounted in pairs and adjusted against each other with a small amount of end play. Usually these

bearings are available in smaller size only.

Angular Contact Ball Bearings:

Angular contact bearings are single row ball bearings but designed insuch a way that the central line of the contact between balls and race

ways is at an angle. This angle is called a contact angle and as per themanufactured design these vary between 15

o, 25

o,45

o

In this type of bearings contact angles between balls and tracks havebeen swung to an angle between 20

oto 40

oto the radial plane.

These bearings are capable of carrying higher axial loads than thecorresponding deep groove ball bearings, but in one direction only.

These bearings are eminently suitable where heavy thrust loads areencountered at high speeds.Usually these bearings are mounted in pairs and adjusted axially

against each other so that they may support combination of heavyradial and thrust loads.

Types of Bearings

Double Row Angular Contact Ball Bearings:

The design of these bearings corresponds to a pair of single row angular contact. These bearings

are available either with no axial play or with limited amount of axial play.Double row angular contact bearings are characterized by a high load carrying capacity. They

can carry substantial amount of radial load as well as axial load. These bearings are particularlysuitable where rigid axial location of rotating mechanism is necessary.


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Double Row Self Aligning Ball Bearings:

In this type of bearings the track on the outer race is ground spherical and its this feature whichgives these bearings the property of self alignment. Due to the character of self alignment these

bearings are not affected by the shaft deflection and mounting errors and a shaft deflection up to4

ois automatically adjusted without damaging the bearings.

These bearings are chiefly designed for carrying radial loads but at the same time they arecapable to carry small thrust load in both directions. Load carrying capacity of these bearings are

slightly less than that of a single row deep groove ball bearings of same dimensions.

Cylindrical Roller Bearings:In this type of bearings, the rollers race tracks are essentially cylindrical, however they may be

ground slightly curved in order to achieve thereby small degree of flexibility.The rollers are guided between two lips on either the inner race or the outer race. Other types

provided with either no lip, one lip or two lips, according to the function which the bearing has toperform. Ball Bearings have a point contact on the races whereas all types of cylindrical roller

bearings have a line contact.Due to line contact the cylindrical roller bearings have a very high radial load carrying capacity

as compared to ball bearings of the same size. Due to their separable design, cylindrical rollerbearings are more convenient for mountings than ball bearings.

Self Aligning Spherical Roller Bearings:

This type of bearing consists of spherical outer race and inner race with two tracks, a cage, and acomplement of spherical shaped rollers. Just like double row self aligning ball bearings too are

not sensitive to misalignment and they can adjust themselves to shaft deflections.Due to the principle, sizes and shaft of rollers and accuracy with which they are guided thesebearings have un axial capacity. The design of this bearing permits radial load and heavy thrust

load in either direction.


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Taper Roller Bearings:

Taper roller bearings consists of two main units, a cup and a cone. The cup is on the outer racewhereas the cone consists of inner race, the separator and compliment of taper rollers. The taper

rollers are guided by the high load on the inner race. The taper roller bearings are manufacturedwith interchangeable cups and cone on the shaft separately.

These bearings are capable of carrying both the radial and axial loads and permit fine adjustmentfor end play. Greater care is required to ensure the proper alignment of bearings and maintenance

of proper axial clearance is essential to avoid bearing failure. Due to more development in thedesign of the taper roller bearings, these are also available with 2 rows and 4 rows.

Needle Roller Bearings:

Needle roller bearings comprise of special form of cylindrical roller bearings in which the rollers

are of a very small diameter and comparatively long therefore they have the advantage of a verysmall difference bet

These bearings are detachable and suitable for carrying only radial loads. Various designs ofneedle roller bearings are available and depending upon the designs of the bearing assembly.

Needle roller bearings may be used either without an inner race or outer race or even without anyraces merely using a set of needle rollers. In all these cases the shaft or the housing should be

strictly of the same qualities as of the bearings races( Hardness, Accuracy and finish); Needleroller bearings are found applicable where space is restricted and mostly where the units are

oscillating.


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Thrust Ball Bearings:

Thrust bearings are available mainly in two types, such as single and double thrust. Single thrust

bearings consists of two rings and a set of balls in a retainer.

Double thrust bearings consist of one rotating ring in the middle with two ball tracks, two sets ofballs in a retainer and two stationary rings.Tracks of balls are ground in such a way that the forces between the balls and tracks are parallel

to the axis of the shaft. Single thrust bearings are designed for carrying load in one directiononly. Whereas double thrust can take in both directions. But these bearings can never carry any

radial loads. On account of the centrifugal forces on the balls , these bearings have a limitation inthe speed of outer operation.

Spherical Roller Thrust Bearings:

This type of bearing is characterized by its high axial load carrying capacity. It can also absorbconsiderable radial loads because the direction of contact is inclined to the axis of the shaft. The

track of the housing washer is spherical, and the rolling bodies are barrel shaped. This makes thebearing self-aligning and therefore insensitive to misalignment.

Power Transmission Unit:

This unit consists of bearing with pillow block. The bearing is having self color for the gripwhich cannot loosen and the spherical outer race provides self- alignment in any direction. The

pillow block is having oil hole on the top for re-lubrification and bolt hole at the base to fixstandard bolt. Complete Unit can attach with machinery frames on a straight shaft with slip fit.

The pre lubricated bearings with the felt seals enable the unit to install even in dustyenvironment.


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Shafer Bearings for Fertilizers and Chemical Unit:

Shafer bearing in a block is a special unit consisting of double row taper bearing with concaverollers. This is designed for heavy thrust as well as radial loads with with shocks.

The micro lock washer on an extended inner ring provides fast adjoinment and resists vibration.Due to special "Z" Housing seals dirt stays out and grease stays in even under severest

conditions.

Single Row Radial Wide Type Bearings:

Wide type bearings are similar to single row deep groove ball bearings, having standard bore andoutside diameter, but thickness is same as double row bearings of corresponding sizes in inch

dimensions. Extra thickness in this bearing provides layer support area for shaft and housingcontact and also space for pre packed lubricant which has sufficient place for grease expansion

under agitation.Due to wide play seal these bearings are suitable for electric motors where it simplifies housing

design. Bearings are also available in mechanic seals.

Plastic Bearings

Plastic Bearings are Lightweight, Low Friction, Lube Free, and Can be Run In Liquids. BearingRings Can Be Molded To Integrate With Customer Applications. Specials Made In Low/High

Quantities. Services Include Prototyping, Pilot Runs & Custom Designs.

Many different types of plastics have properties which make them suitable for bearingapplications, the most commonly used are phenolics, acetals, UHMWPE, and nylon. The major

limitations involved in the use of plastics have to do with high temperatures and possible coldflow under heavy loads.


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Technical Specifications: Click on any of the links below to have detailed information

about that particular heading.

Load Bearing Capacity of a Bearing

Tolerance in a Bearing

Radial Clearance

Life of Bearing

Manufacturing of Bearing

Bearings Numbering System

LOAD CARRYING CAPACITY OF A BEARING

The illustration below shows a shaft mounted fan driven by a belt and powered by a motor.Two bearings support the shaft and are subjected to loads as follows:

Radial loads originate from the:

A. Weight of the shaftB. Weight of the pulleyC. Tension of the beltD. Weight of the propellerE. Propeller rotation

Note: Radial loads exerted on the ends of the shaft, outside of the two bearings supporting the

load (i.e. the belt tension, pulley weight and propeller weight), are compounded by a leveraffect and are referred to as overhung loads.

Axial loads originate from the wind (E) induced by the propeller rotation.

Combination loads are the result of both radial load(s) and axial load(s) being combined andexerted on a single bearing.


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To ensure a define load carrying capacity of ball and roller bearings for a given application, it is

essential to have a clear idea about the running speed, the size and direction of the loads and thedesigned expectation of life.

The magnitude of load is always influenced by the running speed. For every bearing number itsmaximum load carrying capacity is specified, corresponding to various running speeds. This

load carrying capacity is considered to be valid only for the bearing having normal dimensionaland running accuracy, proper methods of lubrication and a speed which yields a life expectance

of approximately 5000 running hours.

The Balls (3)

Balls have been defined previously as one ofthe essential bearing components. They are

subjected to the full brunt of the load carriedby the bearing. If ball and roller bearings are

subjected to high temperatures in service, theirload capacity is reduced as a result of

softening of the race rings and rollingelements. Once it occurs, the effect is

permanent, as the material does not regain itsoriginal hardness even if the temperature

drops.

Cages (4)

Under normal conditions, cages carry verylittle load. However, when a bearing is not

installed properly, is subjected to loads andspeeds higher than recommended by the

manufacturer, does not maintain properlubrication, etc., the cage then may be

subjected to loads far beyond what it is able tocarry. These conditions can lead to premature

cage failure.

The Raceways (5)Raceways are the large, honed (highly

polished), track surfaces on the inside of theouter ring (referred to as the outer raceway)

and the outside of the inner ring (the innerraceway), that form a closed circle around the

circumference of the ring. As the bearingrotates the rolling elements run on these

surfaces.


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Considering the other factors, the load should always be determined as accurately as possible,particularly with respect to its magnitude and direction. Because it exerts a decisive influence

on the life of the bearing, it is very important to take into account of all the force acting on thebearing.

The Load Zone and Contact Points

When a bearing is supporting a radial load, the load is distributed through only a portion of the

bearingapproximately one-third (1/3)at any given time. This area supporting the load iscalled the bearing load zone.

Radial ball bearings are probably the most

widely used and most recognized ball bearing.These bearings have one row of balls (referred

to as asingle row), that revolves around theball path. This feature provides another name

for the bearings; they are commonly calleddeep groove ball bearings. Although designed

to primarily carry radial loads, a radial ballbearings raceways are deep enough that it can

also carry reasonable thrust loads. (However, ifthrust loads are excessive, an alternative type

of bearing should be considered.)

TOLERANCE OF A BEARING

TOLERANCES You will find interesting to note that so as to get bearing'Perfect'. The scientists

have now succeeded in space in their sky-lab 1st mission (ie. in 0 gravity) by the help ofAstronauts.

The term bearing tolerances refers to the very close dimensional limits of bore, outside diameter

and width of a bearing.

Tolerances of boundary dimension are internationally standardized and are maintained in orderto ensure accurate mounting of the bearing on the shaft and in the housing; these tolerances alsoensure precise operations of the equipment in which the bearings are used.

One main factor must be noted that average dimension of any standard bearings are always on

Minus side. This means that if you take the measurement of bore, outside diameter or width of


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any kind of bearings, then it should be measured from eight different points and the average ofall the eight reading will always be on Minus side.

RADIAL CLEARANCE OF A BEARING

In order to freely rotate, a ball bearing must have a certain amount of internal freedom ofmovement (internal clearance, or the space between the raceway and ball). Without this internal

clearance, the bearing can be difficult to rotate or may even freeze-up and be impossible torotate. On the other hand, too much internal clearance will result in an unstable bearing that may

generate excessive noise or allow the shaft to wobble. The internal clearance is measured interms of the direction of the load (radial internal clearanceand axial internal clearance).

1.Radial Clearance 2.Axial Clearance 3.Moment Clearance

In our country radial clearance of the bearings known as 'dug' or 'play' and certain class of people

do not prefer to use the bearings having radial clearance. But for most of the application radialclearance is a must. This statement is supported by the following arguments. Infact, redial

clearance in the bearing is an important factor.

Measuring Radial Internal Clearance

The example shows a radial ball bearing, so the radial internal clearance is measured. Thebearing is grasped at one point on the inner ring and at another point on the outer ring, directly

opposite (see large arrows). The bearing is held together to assure radial contact between theinner raceway, balls, and outer raceway. This allows measurement of the bearings internal

clearance at a point on the opposite side of the bearing--180-- from where the points of contactare being made. The small gap between the top ball and the raceway represents the bearings


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radial internal clearance.

Measuring Radial Clearance Clearance Standard

There is a designation system for indicating the radial clearance of bearings. Following

designation indicates the magnitudes and clearance.

DESIGNATION MAGNITUDE OF CLEARANCE

C I *radial clearance smaller than c2

'0' or c2 =radial clearance smaller than Normal

'00' or cn =normal radial clearance

'000' or c3 =radial clearance greater than normal

'0000' or c4 =radial clearance greater than c3


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LIFE OF BEARING

DEFINITIONS

LIFE : For an individual rolling bearing, the number of revolutions which one of the bearing rings

(or washers) makes in relation to the other rings (or washers) under the prevailing workingconditions before the first evidence of fatigue develops in the material of one of the rings (or

washers) or rolling elements.

RELIABILITY: For a group of apparently identical rolling bearings, operating under the same conditions,

the percentage of the group that is expected to attain or exceed a specified life.

Basis for Calculation

Bearing life is defined as the length of time, or the number of revolutions, until a fatigue spell of

a specific size develops.This spell size, regardless of the size of the bearing, is defined by an areaof 0.01 inch

2(6 mm)

2. This life depends on many different factors such as loading, speed,

lubrication, fitting, setting, operating temperature, contamination, maintenance, plus many otherenvironmental factors. Due to all these factors, the life of an individual bearing is impossible to

predict precisely. Also, bearings that may appear to be identical can exhibit considerable life


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scatter when tested under identical conditions. Remember also that statistically the life ofmultiple rows will always be less then the life of any given row in the system.

L10 LifeL10 life is the life that 90 percent of a group of apparently identical bearings will complete or

exceed before the area of spalling reaches the defined 0.01 inch2

(6 mm2

size criterion. Ifhandled, mounted, maintained, lubricated and used in the right way, the life of your tapered

roller bearing will normally reach and even exceed the calculated L10 life.

If a sample of apparently identical bearings is run under specific laboratory conditions, 90

percent of these bearings can be expected to exhibit lives greater than the rated life. Then, only10 percent of the bearings tested would have lives less than this rated life.

Bearing Life Equation

As you will see it in the following, there is more than just one bearing life calculation method,but in all cases the bearing life equation is :

L10 = (C / P)10/3

(B / n) a

L10 in hours

C = radial rating of the bearing in lbf or NP = radial load or dynamic equivalent radial load applied on the

bearing in lbf or N. The calculation of P depends on the

method (ISO) with combined axial and radialloading

B = factor dependent on the method ; B = 1.5 106

for the Timkenmethod (3000 hours at 500 rev/min) and 10

6/60 for the ISO method


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a = life adjustment factor ; a = 1, when environmental conditions are not considered ;n = rotational speed in rev/min.

This can be illustrated as follows :

Doubling load reduces life to one tenth. Reducing load by one half increases life by ten, Doubling speed reduces life by one half. Reducing speed by one half doubles life.

In fact, the different life calculation methods applied (ISO 281) differ by the selection of the

parameters used.

Bearing RatingsDepending on the life calculation method used, the bearing ratings have to be selected

accordingly. The C rrating, based on one million revolutions, is used for the ISO method.

However, a direct comparison between ratings of various manufacturers can be misleading due

to differences in rating philosophy, material, manufacturing and design. In order to make a truegeometrical comparison between the ratings of different bearing suppliers, only the ratingdefined following the ISO 281 equation should be used. However, by doing this, you do not take

into account the different steel qualities from one supplier to another.

ISO 281 Dynamic Radial Load Rating C r

This bearing rating equation is published by the International Organization for Standardization(ISO) and AFBMA. These ratings are not published by any bearing manufacturers. However,

they can be obtained by contacting our company.

The basic dynamic load rating is function of :

Cr= bm fc (i Lwe cos a) Z Dwe

Cr = radial rating

bm = material constant (ISO 281 latest issuespecifies a factor of 1.1)

fc = geometry dependent factor

i = number of bearing rows within theassembly

Lwe = effective roller contact length

a = bearing half-included outer race angle

Z = number of rollers per bearing rowDwe = mean roller diameter

The Basic Bearing Numbering System


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Usually, with all the bearings discussed so far, the last two digits of the base bearing numberindicate the diameter (size) of the bearings bore in millimeters. The first four (4) must be

memorized.

00 = 10mm

01 = 12mm 02 = 15mm

03 = 17mm

Bore Dimensions

When the last two digits of the base bearing number are 04 or larger, simply multiply the double

digit number by five (5) and you have the bore size in millimeters, i.e., 04 = 20mm, 10 = 50mm,and 24 = 120mm.ball bearings.

Angular Contact Ball Bearings

Self Aligning Ball Bearings

Ball & Roller Thrust Bearings


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Bearing Series

Ball Bearings 600 6000

6200 6300

6400 6700

6800 6900

Angular Contact Bearing Series

7000

7200

7300

Double Row Angular Contact Bearing Series 3200 3300

5200 5300

Double Row Self Aligning Bearing Series 1200 1300

2200 2300

Thrust Ball Bearing Series 51100

51200 51300

51400

Bearing Selection

After knowing all about bearing the main important things is proper selection of bearing for anymoving vehicles or machines. The selection of ball and bearings for a given installation depends

upon the following factors.

1. The load carrying capacity.


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2. The speed of the shaft in r.p.m.3. The type of service.4. The anticipated life of the bearing.5. The proportion of thrust to radial load.

Selection parameters based on the type of bearing can be listed as under:


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Generally Ball bearings are suitable for small machines run at high speeds while RollerBearings are suitable for machines to be placed under heavy loads.

Deep Groove Angular contact Ball bearings are suitable where comparatively heavythrust load is to be carried at high speeds.

Self-aligning Ball Bearings and spherical Roller bearings are suitable for such parts as are

apt to be subject to permanent bindings or wraps. Cylindrical Roller Bearings are suitable for those shafts which have been allowed to

move freely longitudinally within certain limits.

Tater Roller Bearings are suitable for arrangement dealing with heavy composite loads asin of automobile parts.

Thrust Ball Bearings are suitable for arrangements put under light axial loads.

BEARING QUALITY

Anti-Friction Bearings are Precision made. Rolling elements are hardened and inner-outer are

machined to an extremely high degree of accuracy races are machined to an extremely highdegree of accuracy and finish. this high degree of precision makes anti-friction Bearings to

absorb considerable forces to which they are subjected, and this very high degree of precession,makes every anti-friction Bearings very susceptible to damages through minor negligence.

There are four basic and essential factors on the which the quality of a slandered Bill & RollerBearing depends:-

1. Quality of steel: which is alloy of high carbon chrome etc. The steel of 52100 is preferredthan En31.

2. Dimensional accuracy and surface finish of raceways and rolling elements which ismeasured in microns and also keep the radial run out within the limits.

3. Careful testing a nd assembly of Bearings: inner races and outer races are selected as pertrack dimensions if the two races and balls are selected accordingly.

4. Proper heat treatment: there are two major methods preferred by Manufacturers.1. Electric heat treatment process, wherein, components are thoroughly hardened.2. Gas Carbonizing process, wherein Computers get the case Harding.

Heat treatment of the Steel Balls are carried out in two ways, known as oil quench and salt bath,depending upon the usage. All above factors play vital role in the making a Bearing Perfect.

Quality control of any standard Bearing beings with the testing of raw material. Form raw

material to a finished bearing, every bearing undergoes more than 150 checking's, tests andinspections on most sophisticated instruments by skilled personnel

General Information About Bearings

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