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Vibration InstitutePiedmont ChapterSymposium 2011

Presented by Tom McDermott

SKF Sr. Application Engineer

Friday May 13, 2011

SKF is a registered trademark of SKF USA Inc.

2010 SKF USA Inc.

The contents of this publication are the copyright of the publisher and may not be reproduced (even extracts) unless prior written permission is granted. Every care has been taken toensure the accuracy of the information contained in this publication but no liability can be accepted for any loss or damage whether direct, indirect or consequential arising out of useof the information contained herein.

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Vibration Institute SKF Group Slide 2

Discussion topics

Bearing basics

Bearing life expectancy

Bearing failure statistics Pre-operational damage

mode causes

Operational damage

mode causes Identifying loading patterns

ISO Standard 15243

Bearing damage analysis Securing evidence

Conducting analysis

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SKF bearing basics

Purpose and functions of a bearing

Bearing components and materials

Types of bearing loads Rolling elements ball vs. roller

Contact angle

Precision class Radial and axial clearance

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Purpose of a bearing and friction

To provide low friction rotation ofmachine parts.

To support and locate rotatingequipment.

Resistance to motion which occurs when oneobject slides or rubs against another object.

If not controlled, friction will result in:

Heat generation Increased wear Increased noise Loss of power

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Roles of a bearing

Reduce friction

Transmit loads

Support the shaft Locate the shaft

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Bearing components

Outer ring

Cage / retainer

Inner ring

Rolling elements(balls)

Outer ringraceway

Bore surface

Inner ringraceway

OD surface

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Functions of the cage

Minimize friction and heatgeneration.

Prevent contact between adjacentrolling elements.

Guide the rolling elements.

Provide a surface for the lubricantto adhere to.

Retain the rolling elements when

bearings of a separable design aremounted or dismounted.

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Types of bearing loads

Radial load

Axial load

Combined

load

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Point and line contact

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Types of ball bearings

Self-aligningAngular contactDeep groove

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Contact angle

The lower the contact angle, the higher the radial load capacity

The higher the contact angle, the higher the thrust load capacity

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Bearings and contact angles

As contact angleincreases, radial load

capacity decreases; andaxial load (i.e. thrust)capacity increases.

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Precision classes

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Note: Radial clearances are notthe same as precision classes

Radial clearance

Axialclearance

Bearing internal clearances

C1 < C2 < CN < C3 < C4 < C5

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How does temperature affect internal clearance?

Reduced

radialclearance

Expansion

Compression

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Bearing life expectancy

Based upon five assumptions :

1. The bearing is defect free.

2. The correct bearing type and size is selected for theapplication.

3. Dimensions of the bearing mating parts are correct.

4. The bearing will be mounted without damage.

5. Good lubrication in the correct quantity will always be

available to the bearing.

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Circle of bearing life

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Why bearings fail

Four predominantcauses of premature

bearing failure 90% of bearings outlive

their machinery

9.5% of bearings will be

removed for preventativereasons

0.5% of bearings fail intheir application (and this

is generally preventable)

16% Poor Installation

36% Poor Lubrication

14% Contamination

34% Fatigue

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Pre-operational damage mode causes

Damage during transportation, handling and storage.

Incorrect shaft and housing fits.

Defective bearing seats on shafts and in housings.

Faulty mounting practices.

Static misalignment. Passage of electric current through the bearing.

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Operational damage mode causes

Static vibration

Operational misalignment

Ineffective sealing

Ineffective or inadequate lubrication

Passage of electric current through the bearing Excessive loading

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Identifying loading patterns: inner ring rotation

LoadZone

LoadZone

Load

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Identifying loading patterns: outer ring rotation

LoadZone

LoadZone

Load

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Load zone when thrust loads are excessive

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Thrust load + radial load = combined loads

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Internal preload & out of round housing

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Out of round housing visible in outer ring

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Affects of misalignment in a bearing

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Classifications: ISO system

The ISO classification system is divided in six main areasand then further divided into sub-areas.

Going through the table, 15 categories in total can beobserved in which the damage can be classified.

These categories will be covered, one by one, indicatingthe features. A number of typical examples are shown.

There are some other reasons for bearing damage, suchas design problems, etc. These are not classified in theISO standard.

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Bearing damage classifications: ISO 15243

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Fatigue: subsurface fatigue

1. Fatigue1.1. Subsurface fatigue

1.2. Surface initiated fatigue

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Fatigue: surface initiated fatigue

Surface distress

Reduced lubricationregime

Sliding motion

Burnishing, glazing

Asperity micro-cracks Asperity micro-spalls



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Hair strand

(cross section)

50 microns

Dirt particle

1 micron

oil film =

0.2 micron

10 microns

F i f i i i f i

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F i f i i i d f i

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F ti f i iti t d f ti

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H d E b ittl t

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Hydrogen Embrittlement

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Wear: abrasive wear

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Wear: abrasive wear

2. Wear2.1. Abrasive wear

2.2. Adhesive wear

Wear: abrasive wear

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Wear: abrasive wear

Wear: adhesive wear

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Wear: adhesive wear

Low loads

Accelerations

Smearing / skidding / galling Material transfer / friction heat

Tempering / re-hardening

With stress concentrations andcracking or flaking


2.2. Adhesive wear

Wear: adhesive wear

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Wear: adhesive wear


2.2. Adhesive wear

Wear: adhesive wear

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Wear: adhesive wear

Corrosion: moisture corrosion

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3. Corrosion3.2.1. Frettingcorrosion

3.1. Moisture corrosion

3.2. Frictional corrosion

3.2.2. False brinelling

Oxidation / rust

Chemical reaction

Corrosion pits / flaking

Etching(water/oil mixture)


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Corrosion: frictional corrosion: fretting

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g





Micro-movementbetween matingsurfaces

Oxidation of asperities Powdery rust / loss of

material

Occurs in fit interfacestransmitting loads

Corrosion: frictional corrosion: fretting

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g





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Corrosion: frictional corrosion: false brinelling

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Rolling element / raceway Micro movements / elastic

deformations

Vibrations Corrosion / wear / shiny /

red depressions

Stationary: rolling element pitch

Rotating: parallel flutes


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Electrical erosion: excessive voltage

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High current / sparking

Localized heating in very short Interval / melting / welding

Craters up to 100 m

4. Electricalerosion

4.1. Excessive voltage

4.2. Current leakage

Electrical erosion: excessive voltage

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Electrical erosion: current leakage

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Low current intensity

Shallow craters closely positioned

Development of flutes on raceways & rollers, parallel torolling axis

Dark gray discoloration





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Plastic deformation: overload

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5. Plasticdeformation

5.1. Overload

5.2. Indentation from debris

5.3. Indentation by handling

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Plastic deformation: indentation from debris

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5.1. Overload



Plastic deformation: indentation from debris

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Plastic deformation: indentation from handling

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5.1. Overload



Indentation from handling: localized overloading

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Fracture: forced fracture

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Stress concentration >

tensile strength Impact / overstressing

6. Fracture

6.1. Forced fracture

6.2. Fatigue fracture

6.3. Thermal cracking


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6. Fracture





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Fracture: fatigue fracture

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Rings and cages - Crack initiation / propagation

Exceeding fatigue strength under bending

Finally forced fracture

6. Fracture




Fracture: fatigue fracture

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Fracture: thermal cracking

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High sliding and / orinsufficient lubrication

High friction heat

Cracks at right angleto sliding direction

6. Fracture




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Classifications: securing evidence

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Collect operating data, monitoring data

Collect lubricant samples

Check bearing environment

Assess bearing in mounted condition

Mark mounting position

Remove, mark and bag bearing and parts

Check bearing seats

Lubricant condition (color, presence of water, viscosity,consistency, distribution in the bearing, etc.)

Classifications: conducting the analysis

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Examine bearing and parts

Record visual observations

Record pictures of bearing and pertinent parts

Use the failure modes to eliminate improbable causes anddetermine the original cause of the failure

Use external resources such as SKF Bearing Inspector at

@ptitudeXchange.com or SKF Bearing Installation andMaintenance Guide #140-710

Contact external resources for assistance, if needed

Initiate corrective action, if desired. Consider SKF analysis services ($)

Available training courses

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WE201: Bearing Maintenance and Technology

WE202: Bearing in Rotating Machinery Applications

WE203: Lubrication in RollingElement Bearings

WE204: Root Cause Bearing

Damage Analysis

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Thank you!

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30 des 2014

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