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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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2012-12-29 SKF Slide 5 [Code]SKF [Organisation]
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2012-12-29 SKF Slide 6 [Code]SKF [Organisation]
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Sven Wingquistand his Self-Aligning Ball Bearing
2012-12-29 SKF Slide 7 [Code]SKF [Organisation]
meansSwedish Bearing Factory
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Bearing Innovations
2012-12-29 SKF Slide 8 [Code]SKF [Organisation]
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Basics Of Bearings
2012-12-29 SKF Slide 9 [Code]SKF [Organisation]
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Bearing functions
2012-12-29 SKF Slide 10 [Code]SKF [Organisation]
Reduce friction
Carry loads
Support shaft
Locate shaft vis--vis housing
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Rolling and Sliding friction
2012-12-29 SKF Slide 11 [Code]SKF [Organisation]
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
Understanding bearings
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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
Understanding bearings
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2012-12-29 SKF Slide 14 [Code]SKF [Organisation]
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2012-12-29 SKF Slide 15 [Code]SKF [Organisation]
Roller Types
Spherical roller(asymmetrical)
Taper roller
Spherical roller(symmetrical)
Needle roller
Cylindrical roller
Ball
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2012-12-29 SKF Slide 16 [Code]SKF [Organisation]
Outer Ring
Inner Ring
Cage
Rolling Element
Component Parts of a Ball Bearing
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2012-12-29 SKF Slide 17 [Code]SKF [Organisation]
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
Understanding bearings
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Understanding bearings
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
Understanding bearings
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Additional Components in a Rolling Bearing (optional)
Understanding bearings
Integrated seals Metal Shields Rubber Seals
Snap rings
An indispensable component in bearings
AND
Any othercomponents?
LUBRICATION
GREASE OIL
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2012-12-29 SKF Slide 22 [Code]SKF [Organisation]
Deep grooveball bearing
Angularcontactball bearing
Self-aligningball bearing
Ball bearings
Cylindricalrollerbearing
Taperrollerbearing
Needlerollerbearing
Sphericalrollerbearing
Roller bearings
Ball Bearings
Roller Bearings
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2012-12-29 SKF Slide 23 [Code]SKF [Organisation]
Terminology Used
Bore surface
Bore
O.D. surface
O.D.
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2012-12-29 SKF Slide 24 [Code]SKF [Organisation]
Terminology Used
Inner ring raceway
Side faces
Inner ring land
Outer ring racewayOuter ring land
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2012-12-29 SKF Slide 25 [Code]SKF [Organisation]
Axial, Radial and Combined loads
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2012-12-29 SKF Slide 26 [Code]SKF [Organisation]
The Principle SKF Rolling Bearing Range
Ball bearings
Roller bearings
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2012-12-29 SKF Slide 27 [Code]SKF [Organisation]
Deepgroove
Ball bearings Roller bearings+Angularcontact Self-aligning Cylindrical Taper Needle Spherical
Ball and Roller Bearing Ranges
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2012-12-29 SKF Slide 28 [Code]SKF [Organisation]
Load Capabilities
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2012-12-29 SKF Slide 29 [Code]SKF [Organisation]
Relative Speed Limitations
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2012-12-29 SKF Slide 30 [Code]SKF [Organisation]
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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2012-12-29 SKF Slide 31 [Code]SKF [Organisation]
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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2012-12-29 SKF Slide 32 [Code]SKF [Organisation]
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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2012-12-29 SKF Slide 33 [Code]SKF [Organisation]
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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2012-12-29 SKF Slide 34 [Code]SKF [Organisation]
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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2012-12-29 SKFSlide 36 [Code]SKF [Organisation]
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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2012-12-29 SKFSlide 37 [Code]SKF [Organisation]
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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2012-12-29 SKF Slide 38 [Code]SKF [Organisation]
Dimensional Stability
Change in diameter (m/100 mm)
Holding time at 200 C (392 F)
Hours
Martensite
Bainite
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2012-12-29 SKF Slide 39 [Code]SKF [Organisation]
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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2012-12-29 SKF Slide 40 [Code]SKF [Organisation]
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
2012-12-29 SKF Slide 41 [Code]SKF [Organisation]
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2012-12-29 SKF Slide 42 [Code]SKF [Organisation]
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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2012-12-29 SKF Slide 43 [Code]SKF [Organisation]
Cage Variants
Polyamidecage
Window-typesheet steel cage
Window-typesolid brass cage
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Understanding bearings
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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2012-12-29 SKF Slide 45 [Code]SKF [Organisation]
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
Understanding bearings
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
Understanding 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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Understanding radial clearance...
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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Understanding radial clearance...
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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Understanding radial clearance...
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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Understanding radial clearance...
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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Understanding radial clearance...
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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Understanding radial clearance...
?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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Understanding radial clearance...
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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Understanding radial clearance...
?
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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Understanding radial clearance...
?
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