introdution on bearings

7/30/2019 Introdution on Bearings

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An Introduction to Bearing

Technology


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The word BEARING derived from the word BEAR

which means TO SUPPORT

Which is what bearings do ...

SUPPORT and GUIDE

other machine elements

The ball bearings in thiselectric motor supportand guide the rotor

Why bearings?

Understanding bearings


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A short history of Bearings

2012-12-29 SKF Slide 3 [Code]SKF [Organisation]


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Bearing Evolution

700 B.C.

3500 B.C.

40 A.D.

1869

1995


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Sven Wingquistand his Self-Aligning Ball Bearing


meansSwedish Bearing Factory


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Bearing Innovations



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Basics Of Bearings



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Bearing functions


Reduce friction

Carry loads

Support shaft

Locate shaft vis--vis housing


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Rolling and Sliding friction


Plain bearings:sliding friction

Rolling bearings:rolling friction


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Two types?

ANTI-FRICTION bearings

so called because they have a lowercoefficient of friction (0.00015 - 0.004) ascompared to that of journal bearings (0.008to 0.020)

SLIDING or BUSH or JOURNAL bearings

ROLLING or ANTIFRICTION bearings

and

The lower coefficientof friction is achievedby the super-finishingof raceways



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Whats the difference?

The shaft which supports theload runs in a lubricated bush

Journal bearingLubricant

JOURNAL BEARINGS

The shaft which supports theload is mounted on rollingbearings whose rolling elementstransmit the load roll throughhardened rings

Hardenedinner ring

Rollingelement

Hardenedouter ring

ROLLING BEARINGS



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Roller Types

Spherical roller(asymmetrical)

Taper roller

Spherical roller(symmetrical)

Needle roller

Cylindrical roller

Ball


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Outer Ring

Inner Ring

Cage

Rolling Element

Component Parts of a Ball Bearing


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Component Parts of a Ball Bearing

Seal Rolling elements Inner ringOuter ring Cage Seal


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Rolling bearings are classified as Ball Bearings

and Roller Bearings depending on the shape oftheir rolling elements

Classification?

Ball Bearings

Deep Groove Ball Bearings

Angular Contact Ball Bearings

Self Aligning Ball Bearings

Thrust Bearings

Single Row Double Row

Angular Contact Thrust Bearings



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Classification?

Rolling bearings are classified as Ball Bearings

and Roller Bearingsdepending on the shape oftheir rolling elements

Roller Bearings

Cylindrical Roller Bearings

Spherical Roller Bearings

Taper Roller Bearings

Spherical Roller Thrust Bearings

Single Row

Cylindrical Roller Thrust Bearings

Double Row


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Exceptions to the rule ...

Cylindrical Roller Bearings without inner rings fordirect shaft running arrangements

Full complement Cylindrical and Needle RollerBearings without cages

Componentsin a RollingBearing

Cage

Rolling elements

Inner ring

Outer ring



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Additional Components in a Rolling Bearing (optional)


Integrated seals Metal Shields Rubber Seals

Snap rings

An indispensable component in bearings

AND

Any othercomponents?

LUBRICATION

GREASE OIL


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Deep grooveball bearing

Angularcontactball bearing

Self-aligningball bearing

Ball bearings

Cylindricalrollerbearing

Taperrollerbearing

Needlerollerbearing

Sphericalrollerbearing

Roller bearings

Ball Bearings

Roller Bearings


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Terminology Used

Bore surface

Bore

O.D. surface

O.D.


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Terminology Used

Inner ring raceway

Side faces

Inner ring land

Outer ring racewayOuter ring land


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Axial, Radial and Combined loads


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The Principle SKF Rolling Bearing Range

Ball bearings

Roller bearings


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Deepgroove

Ball bearings Roller bearings+Angularcontact Self-aligning Cylindrical Taper Needle Spherical

Ball and Roller Bearing Ranges


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Load Capabilities


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Relative Speed Limitations


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Ball Bearing Capabilities

Deep groove Angular contact Self-aligning

Radial load Axial load Speed Accommodates

carrying capacity carrying capacity capability misalignment


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Cylindrical Roller Bearing Capabilities

More and largerrollers

optimised

surface finish

Improved rollerend/flange contactgeometry

3 cage variants:steel, polyamide, brass

NU NJ NUP

N NJ+HJNU+HJ


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Taper Roller Bearing Capabilities

OptimisedSKF design optimised

surface finish increasesservice life

Improved rollerend/flange contactgreatly reduces friction

Optimum utilisation ofcross section


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Spherical Roller Bearing Capabilities

Symmetrical rollersprovide maximum lifeunder any conditions

Floating guide ringgives minimum frictionand helps ensurereliable operation

Window-type steel cages

strong and tolerant tohigh temperatures


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CARB Toroidal Roller Bearing Capabilities

Accommodates shaftmisalignment to maximiseservice life

Axial displacementcapability minimisesfriction

High radial carrying

capacity increasesreliability


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Materials Used for SKF Rolling Bearings

2012-12-29 SKFSlide 35 [Code]SKF [Organisation]


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Materials Used for SKF Rolling Bearings

Bearing rings and rolling elements

Through-hardening steels

Carbon chromium steel

containing approximately1 % carbon and1.5 % chromium

Case-hardening steels

Chromium-nickel alloyed steeland manganese-chromiumalloyed steel

containing approximately 0.15% carbon


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Heat Treatments

AdvantagesBainitic hardening

Tough structure

Automatic dimensionalstability

Compressive residualsurface stresses

Case hardening

Hard surface and soft coreresists through cracking

Highest compressive

residual surface stresses

Martensite hardening

Less costly

Fixture can be used toreduce distortion

DisadvantagesBainitic hardening

Somewhat more costlythan martensite

Lower hardness

Case hardening

Time consuming andcostly process

Martensite hardening

Highest risk of propagationof surface cracks


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Dimensional Stability

Change in diameter (m/100 mm)

Holding time at 200 C (392 F)

Hours

Martensite

Bainite


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Classification of Dimensional Stability

Stabilisationclass

Operatingtemperature

HardnessHRC

SN

S0

S1

S2

S3

S4

up to 120 C (248 F) 59 to 63

up to 150 C (302 F)

up to 200 C (392 F)

up to 250 C (482 F)

up to 300 C (572 F)

up to 350 C (662 F)

58 to 62

57 to 61

56 to 60

54 to 58

50 to 54


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Hardening Processes - Effects

Martensitehardening

Standard applicationsStandard bearings

Bainitehardening

Heavily loaded bearingsSpherical roller bearings

Casehardening

Extreme heavily loaded bearings (+ shock loads)Large size bearings

Specific applicationsBearings fitted with loose fit (rolling mills)

Surfacehardening

Specific applicationsHub units, slewing rings


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Cage



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Function of the cage

Prevent immediate contact betweenrolling elements to minimize frictionand heat generation

Guide the rolling elements

Provide space for lubricant

Retain the rolling elements whenbearings of separable design

are mounted or dismounted


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Cage Variants

Polyamidecage

Window-typesheet steel cage

Window-typesolid brass cage


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Cages

Two halves ofthe steel cage

Steel rivet

Steel cages used in deep groove ballbearings are made from sheet metalwhich is formed in different stages tosuit the ball which is held between them

The two halves of the steel cage are

riveted to hold them together

Polyamide cagesare moulded

Brass cages aremachined


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Polyamide Cages

+ Lightweight

+ High elasticity

+ Good sliding properties

+ Good marginallubrication properties

Operating temperature< +120 C


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2012-12-29 SKF Slide 46 [Code]

SKF [Organisation]

Window Type Sheet Steel Cages

+ Lightweight

+ High strength

+ High vibration andacceleration resistance

Sensitive topoor lubrication

+No operating

temperature limit


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2012-12-29 SKF Slide 47 [Code]

SKF [Organisation]

Window Type Solid Brass Cage

+ Very high strength

+Suitable for very highspeed in connectionwith circulating oil

Relatively (very)expensive

+ Very high vibration andacceleration resistance


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Commonly used system for bearing nomenclature


How arebearingsnumbered?

PREFIX

Defines acomponent or a

design

EXAMPLE

In cylindricalroller bearings

NU, NJ, NUP, N,NF, NCF, etc

Shaft and Housingwashers in case

of thrustbearings; GS, WS

etc

BEARING NUMBER

6 2 0 5

DeepGrooveBall

BearingWidth

Series O

Outerdiameterseries

x 5 =Bore

diameter

Exception

Borediameter< 20 and> 495 mm

SUFFIX

Defines radialradial clearance,

seal design, sealmaterial, specialgrease filling,special heattreatment,

special designs

Example

6205.2RSR.C3.L40


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Examples of Basic Codes of Bearings


How arebearingsnumbered?


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Understanding radial clearance...

A clearance is always maintainedbetween the rolling elements andthe raceways in a bearing ...

What is radial clearance andhow is it defined?

This clearance is termed as Radial Clearance and thevalue is specified in microns (1/1000 th of a mm)

and is defined as thedisplacement of the outer ringwith reference to the inner ringand balls in the radial direction


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How is radial clearanceclassified and designated?

C2, C0, C3 & C4

Depending on the relative radial displacement ofbearing rings, Radial Clearance of bearings is

classified into four categories ...

C2 < C0 < C3 < C4

Normal

Special requirement

C2

C3C

0

C4

C2

C3C

0

C4


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What is C2, C0, C3 and C4?Do all bearing manufacturers categorise

radial clearances similarly?

C2, C0, C3 and C4represent four radial

clearance categories

Each category representsa range of values ...

which is specified and

defined by internationalstandards which arefollowed by all bearingmanufacturers worldwide


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Are the values the same for all sizesand all types of bearings?

The radial clearance value and rangespecified in any particular radialclearance category depends on ...

bearing type (whether it isdeep groove ball bearing, acylindrical roller bearing, aspherical roller bearing, etc)

bearing bore (whethercylindrical or tapered) andbore diameter


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How do the different radialclearance categories compare?

C2

C0

C3

C4

(Normal)

This is how radial

clearance values in acategory compare anoverlapping range exists


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Radial clearance in deepgroove ball bearings ismeasured by displacing the

outer ring relative to theinner ring and balls usingspecial machines

Radial clearance of cylindrical andspherical roller bearings is measuredusing a feeler gauge whose feelers

are passed between the rollers andrings. The thickest feeler which canpass through easily is the value ofradial clearance

How is radial clearance measured?


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?Where can informationabout radial clearancespecifications be found?

In every reputed bearingmanufacturers cataloguesare tables which giveinformation regarding the

radial clearance of variousbearing types and sizes

Reputed bearing manufacturersmark the radial clearance on

the bearing, i.e 6204.C3,except when the bearing hasnormal or C0 radial clearance


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Why radialclearance?

To provide enough space

within the bearing to ...

.. allow the lubricant tofunction between the ballsand raceways and prevent

metal to metal contact

.. Compensate

for the influencesof tight inner and/ or outer ringfits

.. Compensate for the rise intemperature of the rotatinginner ring (normally 5 - 10oChotter than the outer ring)


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?

Why is it necessary to

compensate tight fits?

A tight fitted inner ringexpands on the shaft A tight fitted outer ringcontracts in the housing

Expansion ofinner ring

+Contraction of

outer ring

=Reduction of

radialclearance


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?

What is difference

between RadialClearance and Axial

Clearance

Displacement of one ringwith respect to anotherring, in radial direction isknown as Radial Clearance

Displacement of one ringwith respect to anotherring, in axial direction isknown as Axial Clearance

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