Bearings-131 Part 1

8/10/2019 Bearings-131 Part 1

1/74

S.Mekid 1

Equivalent load

1

Except for pure thrust bearings and cylindrical roller

bearings, all other bearings are usually operated with

somecombinationof radialFrand thrust loadF

a.

Since catalog ratings are based only on radial loading (oronly on thrust loading),an equivalent radial loadF

emust

be calculated.

Remember equivalent stress


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S.Mekid 2

Equivalent load

2

efD FaF

The equivalent radial loadFe(for radial bearings) is calculated

using the following AFBMA equation:

airie FYVFXF

The design Load is thus:

FD Design Load

af Application Factor (service factor) obtained from table 11.5

Fe Radial Equivalent loadFr Radial load

Fa Axial (thrust) load

V Rotation factor (V = 1 for rotating inner ring, V= 1.2 for outer ring )

Xi & Yi respectively radial and thrust load factors obtained from table 11.1


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Equivalent load

3

Variation of Equivalent Load

with thrust (axial) Fa( Figure

11.6 see Table 11.1).


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Bearing Selection

4


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Bearing Selection

5

Only to ball, straight roller and spherical roller bearings


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Sample Problem on Bearing Selection

6

Select a ball Bearing for an industrial machine intended for

continuous one-shift 8-h/day operation at 1800 rpm.

The radial and thrust loads are 1.7 and 1.2 kN

respectively.

The machine operates with light to moderate impact

The desired reliability is 95%.Given

1. Ball bearing (a = 3)

2. Machine working 8-hr continuous (table 11.4)

3. nD

= 1800 rpm

4. Fr= 1.7 kN

5. Fa= 1.2 kN

6. Light to moderate impact

7. R = 0.95

Required:

Select ball bearing (C10?)


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S.Mekid 7 7

6.0)95.01(439.402.0

)1(439.402.0

483.1/1

483.1/1

DR

RK

a

R

DDKxFC

/1

10

483.1/1)1(439.402.0 DR RK

324010

60180030000

60

60/

610

RR

DDD

nL

nLLLx

Table 11.4 take highest to be conservativeBall bearing

5115.1

tablefroma

FaF

f

efD

Now the problem is finding the equivalent load Fe

Sample Problem on Bearing Selection


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S.Mekid 8

PROCEDURE:

Compute Equivalent Load?

SELECTION?

?7.17.11111 MaxkNVFXF re

2.17.1156.0 2222 YFYVFXF are1stIteration:1. Assume a value mid-range from Table 11.1: Y2=1.71or 1.63

Another method is to start from table 11.2 directly selecting candidate bearing

2. Compute Fe2:

3. Compute C10:

4. Select candidate bearing from Table 11.2 (02-series)

a. Try deep groove first (cheaper, easier to mount) C=83.2 kN and C0

=53 kN

b. If angular contact is considered: C=80.6 kN and C0=55 kN

kNFkNF ee 7.104.32.17.1156.0 12 71.1

kNK

xFC

a

R

DD 05.80

6.0

32405.104.3

3/1/1

10

Y2=?


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S.Mekid 9 9

21.00218.055

2.1

Re)(71.199.1

22.00226.053

2.1

0

2

0

eC

F

peatAssumedYtheneVF

F

eC

F

a

r

a

aFor Deep-Groove Bearing

For Angular Contact Bearing

2ndIteration:2. Compute Fe2:

3. Compute C10:


a. Try deep groove first (cheaper, easier to mount) C= 95.6 kN and C0= 62 kN

b. If angular contact is considered: C=90.4 kN and C0=63kN

kNFkNF ee 7.134.32.17.1156.0 12 99.1

kNK

xFC

a

R

DD 9.87

6.0

32405.134.3

3/1/1

10


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S.Mekid 10 10

For Deep-Groove Bearing

For Angular Contact Bearing

3rdIteration:2. Compute Fe2:

3. Compute C10:


a. Try deep groove first (cheaper, easier to mount) C= 95.6 kN and C0= 62 kN

b. If angular contact is considered: C= 90.4 kN and C0= 63kN

kNFkNF ee 7.142.32.115.27.1156.0 12

kNK

xFC

a

R

DD 90

6.0

32405.142.3

3/1/1

10

21.0019.063

2.1

Re)(99.115.2

21.0019.0

62

2.1

0

2

0

eC

F

peatoldYtheneVF

F

e

C

F

a

r

a

a


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S.Mekid 11 11

Since the 3rdbearing is the same as the 2ndwe stop and summarize:

02 series deep-groove ball bearing with load rating of 95.6 kN

and dimensions: d = 90 mm, D = 160 mm and W = 30 mm is the

suitable bearing for the application.

02 series angular contact ball bearing with load rating of 90.4

kN and dimensions: d = 90 mm, D = 160 mm and W = 30 mmmay also be selected for the application.

Note that in solving this problem no constraints concerning the

size of shaft and housing were considered. In reality, shaft and

housing dimensions are considered in the selection of bearings.

Tables 11.2 and 11.3 do not allow the freedom for such selection

but real catalogs do as shown in following SKF catalog tables.


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S.Mekid 12 12

Bearing SelectionTable 11-2


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Bearing SelectionTable 11-3- Straight (Cylindrical) Roller Bearings


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Bearing Selection

14


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S.Mekid 15 15

Bearing Selection

Principal Dimensions Basic load ratings Allowable

load limit

Speed ratings Abutment and fillet

Dimensions

Designation

db da bw

dynamic

C

static

C0 wall

grease oil

Db,min Da,max ra,max

mm

in

mm

in

mm

in

N

lbf

rpm mm

in

mm

in

mm

in

2.5

0.0984

8

0.3150

2.8

0.1102

319

71.7

106

23.8

4

0.899

67000 80000 3.7

0.146

6.8

0.268

0.1

0.004

60/2.5

5

0.1969

11

0.4331

3

0.1181

637

143

255

57.3

11

2.47

53000 63000 6.2

0.244

9.8

0.386

0.1

0.004

618/5

190.7480

60.2362

1720387

620139

265.85

36000 43000 70.276

170.669

0.30.012

635

7

0.2756

14

0.5512

3.5

0.1378

956

215

400

89.9

17

3.82

45000 53000 8.2

0.323

12.8

0.504

0.1

0.004

618/7

10

0.3937

19

0.7480

5

0.1969

1380

310

585

132

25

5.62

36000 43000 12

0.472

17

0.669

0.3

0.012

61800

26

1.0236

8

0.3150

4620

1040

1960

441

83

18.7

30000 36000 12

0.472

24

0.945

0.3

0.012

6000

35

1.3780

11

0.4331

8060

1810

3400

764

143

32.1

20000 26000 14

0.551

31

1.220

0.6

0.024

6300

15

0.5906

24

0.9449

5

0.1969

1560

351

800

180

34

7.64

28000 34000 17

0.669

22

0.866

0.3

0.012

61802

28

1.1024

7

0.2756

4030

906

2040

459

85

19.1

24000 30000 17

0.669

26

1.024

0.3

0.012

61902

32

1.2598

8

0.3150

5590

1260

2850

641

120

27.0

22000 28000 17

0.669

30

1.181

0.3

0.012

16002

32

1.2598

9

0.3543

5590

1260

2850

641

120

27.0

22000 28000 17

0.669

30

1.181

0.3

0.012

6002

35

1.3780

11

0.4331

7800

1750

3750

843

160

36.0

19000 24000 19

0.748

31

1.220

0.6

0.024

6202

42

1.6535

13

0.5118

11400

2560

5400

1210

228

51.3

17000 20000 20

0.787

37

1.457

1

0.039

6302

See Tables 11.2 for BB

11.3 for SRB

1998 McGraw-Hill

Single Row, Deep Groove Ball Bearings[From SKF Catalog (1991)]

with full outer

ring shoulders

with recessed outer

ring shoulders

ra

dadb

bw

Da Db


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S.Mekid 162010/2011 Chapter 11-Notes 16

1998 McGraw-Hill

Single Row Deep Groove Ball Bearings20-30 mm

Principal Dimensions Basic load ratings Allowableload limit

Spe ed ratings Abutm ent and filletDimensions

db da bw

dynamicC

staticC0 wall

grease oilDb,min Da,max ra,max

mmin

mmin

mmin

Nlbf

rpm mmin

mmin

mmin

200.7874

321.2598

70.2756

2700607

1500337

6314.2

19000 24000 220.866

301.181

0.30.012

371.4567

90.3543

63701430

3650821

15635.1

18000 22000 220.866

351.378

0.30.012

421.6535

80.3150

68901550

4050910

17338.9

17000 20000 220.866

401.575

0.30.012

421.6535

120.4724

93602100

50001120

21247.7

17000 20000 240.945

381.496

0.60.024

47

1.8504

14

0.5512

12700

2860

6550

1470

280

62.9

15000 18000 25

0.984

42

1.654

1

0.03952

2.047215

0.5906159003570

78001750

33575.3

13000 16000 26.51.043

45.51.791

10.039

722.8346

190.7480

307006900

150003370

640144

10000 13000 26.51.043

65.52.579

10.039

250.9843

371.4567

70.2756

4360980

2600585

12528.1

17000 20000 271.063

351.378

0.30.012

471.8504

120.4724

112002520

65501470

27561.8

15000 18000 291.142

431.693

0.60.024

622.4409

170.6693

225005060

116002610

490110

11000 14000 31.51.240

55.52.185

10.039

803.1496

210.8268

358008050

193004340

815183

9000 11000 331.299

722.835

1.50.059

301.1811 421.6535 70.2756 44901010 2900652 14632.8 15000 18000 321.260 401.575 0.30.01255

2.165413

0.5118133002990

83001870

35579.8

12000 15000 351.378

501.969

10.039

722.8346

190.7480

281006320

160003600

670151

9000 11000 36.51.437

65.52.579

10.039

903.5433

230.9055

436009800

236005310

1000225

8500 10000 381.496

823.228

1.50.059

Bearing Selection


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S.Mekid 18

Tapered Roller Bearings

2008/2009 Ch 11. Notes 18

Cup Can be easily removedfrom cone and

roller assembly because of this and

because even a pure radial load willinduce a thrust load because of the

taper TRB have to be mounted in

pairs:

Back to Back (Direct mounting)

Front to Front (Indirect mounting)

Timken Co.Data shows that the induced

thrust force can be estimated from Eq.

11-15:

Nomenclature

K

FF ra o

47.0)180(

K =ratio of rated radial to rated thrust

load approximated 1.5 for radialTRB

and 0.75 for steep angle bearings

Span


19/74

S.Mekid 19

Selection of Tapered Roller Bearings

The load rating for Timken Co. tapered roller bearings is

calculated as follows:a

RRRvT

DDf

nLKff

nLPaCC

/1

1090

60

60

For Timken Co. Catalogs:

LR

= 3000 Hours and nR

= 500 rpm (3000500 x60

= 90.10 6revolutions)

FD= a

fP

P is calculated as follows

3/25.1/1 )1(48.4))/1(ln(48.4 DDR RRK


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S.Mekid 20



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S.Mekid 21 21

X

O


X

O


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S.Mekid 22

Indirect mounting

Direct mounting

Indirect mounting

provides greater rigidity

when pair of bearings is

closely spaced: front

wheel of a car, drums,

sheaves,..

Direct mounting

provides greater rigidity

when pair of bearings is

not closely spaced:transmission, speed

reducers, rollers,..

X

O


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23

fV= Viscosity factor obtained from figure 11.17.


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fT=Temperature factor

estimated from figure(11-16):



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Solved Example


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S.Mekid 28 28

Direct

mount

Shaft + right

to Left


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S.Mekid 29 29


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S.Mekid 30 30


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S.Mekid 31

Mountingand Enclosure of Bearings

31

Alternative Mounting

dsdH

Positioning Floating

Takes thrust

No thrust and allows for

shaft expansion when hot

Retaining nuts on inner ringNo retaining devices on inner ring

Outer races completely retained

Shoulders in shaft and housing: See tables 11.2

and 11.3 for dimensions


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Use of 2 or more bearingsin one end of shaft for

additional rigidityor increased load capacity.



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S.Mekid 33 33

Two-bearing mounting with use

of washers against cone



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S.Mekid 34 34

Duplex Mountingof angular contact bearings: Bearings manufacturedfor this purpose have their rings ground with an offset so that they are

tightly clamped together and apreloadis automatically established

(as you have seen on the animation).

a) Face to face mounting (DF)for heavy Fr

and Fa

from either direction

b) Back to back mounting (DB)=a)+ aligning stiffness

c) Tandem arrangement (DT)for thrust which is always in the same

direction. Preload required.



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http://www.toydirectory.com/monthly/new_product.asp?id=25163


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http://www.toydirectory.com/monthly/new_product.asp?id=23961http://www.toydirectory.com/monthly/new_product.asp?id=25163


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S.Mekid 38

Needs preloadingSee p. 600.



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Low speeds Moderate to high speedsHigh to very

high speeds

spring

rubber



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S.Mekid 40

Lubrication

40

Elastohydrodynamic lubrication:Remember the movie showing athin film (mm) of oil between rolling elements subjected to

extreme pressures is transformed from a liquid lubricant (oil) into

a solid for a nano fraction of a second.

(from presentation by Saeed S. Aramco)


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Liquids (oils)

Semi-Liquids (greases)

Solids (Graphite)

41

Types of Lubricant

See Page 597 of text book for conditions


42/74

S.Mekid 42 42

Mineral

AdditivesBase Oil

Synthetic

NaphthenicParraffinic

Lubricating Oil



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S.Mekid 43 43

Grease

BaseOil Thickener Additives

70 90

%

3 30

%1 10

%

o Simple Metal Soapso Complex Metal Soap

o Non-Soap



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Common Oil Physical and Chemical Properties

Color Appearance

Flash point

Pour point

TAN

TBN

Density

Oxidation stability Viscosity

Viscosity Index

44


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Common Oil Physical and ChemicalProperties

Appearance Flash Point

Pour Point

TAN TBN

Density

Specific Gravity Viscosity

Viscosity Index

2008/2009 Ch 11. Notes 45


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S.Mekid 46

FAILURE OF BEARINGS

Failure causes1. - Manufacture and assembly

Mounting with improper tools,

Loose/tight fits, Misalignment, ...2. - Design and Operating conditions

Bad selection, Overload, Fatigue, ...

3. - LubricationUnsuitable/ excess/ lack, Contamination


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S.Mekid 47

FAILURE OF BEARINGS

Failure modes

Fracture/Separation

Spalling, Cracks, Smearing, Seizing,

DeformationIndentations, Brinnelling, Fluting,

Wear

Abrasive, Burning, Scuffing, ...

Corrosion

Etching, Fretting, Rust Staining


48/74

S.Mekid 48Ch 11. Notes 48

Table 10

Failure Causes of Rolling and Plain Bearings [5]

Failure Cause Occurrence, %

Rolling Plain

Bearings Bearings

Vendor problems 30.1 23.4

Workmanship 14.4 10.7

Errors in design/applications 13.8 9.1 Wrong material of construction 1.9 3.6

User-induced problems 65.9 69.6

Operational errors, maintenance

deficiencies, failure of monitoring 37.4 39.1

equipment

Wear 28.5 30.5

External problems 4.0 7.0

Contaminated lubricants; intermittent

failure of oil supply system 4.0 7.0


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FATIGUE FAILURE

49

VIDEOS 1 & 3

Simulation of progression of


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Simulation of progression offatigue failure

50

Hamrock , J acobson and SchmidMcGraw-Hil l 1998

Fatigue Wear

.

Text Reference: Figure 8.2 2, page 346

FATIGUE (E d f f l lif ) S lli


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S.Mekid 51 51

FATIGUE (End of useful life) Spalling

Progression of fatigue failure.

Spot

Flaking Failure-Noise


52/74

S.Mekid 52

FATIGUE- Spalling

52

P i


53/74

S.Mekid 53

Prevention

53

Fatigue failure cannot be prevented, but it can be

delayed by taking three steps:

1. Make sure that the replacement bearing is designed

to take the desired load.

2. Protect the bearing from damage and keep it clean

during the installation.

3. Lubricate adequately.

Mi li t


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S.Mekid 54

Misalignment

54

Certain types of bearings cantolerate only limited amounts

of misalignment.

In deep groove ball bearings

misalignmentwill produce

load zones not parallelto ballgroove which can be detected

easily.

MISALIGNMENT


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S.Mekid 55 55

MISALIGNMENT

Advanced spalling

caused by edge loading.

In cylindrical and tapered roller bearings

edge-load caused by misalignment causespremature spalling.

Fatigue caused by edge loading.

P ti


56/74

S.Mekid 56

Prevention

56

1. Make sure that the component is correctly aligned

during installation

2. Inspect shaft for any bowing

3. If new or modified design, the distance between bearings

should be determined by deformation analysis.

4. Make sure that bearing seat is smooth

5. After bearings are in place the shaft should be aligned

with the machine6. Whenever possible use correct self-aligning bearings

Lubrication related failures


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S.Mekid 57

Lubrication-related failures

57

1. Inadequate lubricationis the cause of a large

number of bearing premature failures.

2. Inadequate lubrication will cause surface damage

such as roughening, frostingleading to spalling.

3. Inadequate lubrication will cause discolorationof the surface

Spalling and discolration caused by


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S.Mekid 58

p g yinadequate lubrication

58

Progressive stages of spalling Dislocationcaused by

inadequate lubrication

Inadequate lubrication


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S.Mekid 59

Inadequate lubrication

59

Discolorationcaused by inadequate lubrication

Contamination & Improper


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S.Mekid 60

p pLubrication

60

The bearing failureappears to have beencaused by eitherabrasive wear from theintroduction of fineforeign particles and /or

over-lubrication

The failed rollers weresubjected to contactfatigue followed by heatchecking

Optimize frequency oflubrication and amountof clean grease

Contamination & Corrosion


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S.Mekid 61

Contamination & Corrosion

Corrosion results from the

chemical attack on bearingmaterials.

Symptoms include

red/brown areas on rollingelements, raceways, orcages.

Corrosion usually resultsin increased vibrationfollowed by wear, withsubsequent increase inradial clearance

61

Prevention


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S.Mekid 62

Prevention

62

1. Make sure that the correct Manufacturer specified type o

lubricant is used.

2. Sufficient elastohydrodynamic film prevents surface distress

(glazing, pitting).

3. Good boundary lubrication guards against smearing and sliding

surface wear.

4. Clean lubricants prevent significant wear of rolling surfaces.

5. Sufficient lubricant flow keeps bearings from overheating.

6. Change the oil or grease in the bearing according

Manufacturers schedule.

Mounting Related Failures


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S.Mekid 63


63

Fatigue from chipin bore Fragment denting

Improper mounting practices can cause:

1. Smearing or fragment denting2. Fatigue spalling (dirt)

3. Impact damage



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S.Mekid 64

gSmearing

64

Smearing caused by excessive

force in mountinga cylindrical

roller bearing.

(X 8) Enlargement ofsmearing.



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S.Mekid 65

gParasitic Thrust

65

Spalling from parasitic thrust (self-alignment bearing)

Damage due to improper fits


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S.Mekid 66


66

The degree of tightness or looseness is

Governed by both the levels of load and speed.

In general the rotating ring is mountedwith interference fitand the non-rotating

ring with slip-fit.



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S.Mekid 67

(Scoring)

67

Scoringof inner ring caused by creep, relative

movement between ring and shaft.



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S.Mekid 68

Damage due to improper fits(Wear)

68

Wear due to creep. Brilliant polish due to lubrication

penetration between ring and shaft seating. Face of ring

is also damaged by shaft shoulder.



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S.Mekid 69

Excessive Interference Fit

69

Axial crackscaused by excessive

interference fit.



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S.Mekid 70

Fretting Corrosion

70

Wear due Fretting corrosion

caused by unnecessary loose

housing fit.

Advanced Wear due to

Fretting corrosion.



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S.Mekid 71


71

Crack caused by faulty

housing fit.

Fretting caused by yield.

Electric Fluting


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S.Mekid 72

Electric Fluting

Findings:

The bearing hadundergone anincipient stage of

electrical pitting(fluting)

Recommendations:

Insulate thebearings properly

72

Other causes of failure


73/74

S.Mekid 73

Other causes of failure

73

Electric current arcing

Ineffective sealingVibration

References


74/74

References

1. J. E. Shigley and C. R. Mischke, Mechanical EngineeringDesign,McGraw-Hill, 2004 (7thEd.)

2. J. E. Shigley and C. R. Mischke, Mechanical EngineeringDesign,McGraw-Hill, 2000 (6thed.).

3. J. E. Shigley and C. R. Mischke, Standard Handbook ofMachine Design,McGraw-Hill, 1986.

4. B. J. Hamrock, B. Jacobson and S. R. Schmid,Fundamentalsof Machine Elements, McGraw-Hill,1999.

5. R. C. Juvinall and K. M. Marshek Fundamentals of Machine

Component Design,John Wiley & Sons, 2000 (3rd ed.). 6. H. P. Bloch and F. K. Geitner, Machinery Failure Analysis

and Troubleshooting, Vol.2, 2nd Ed., Gulf PublishingCo., USA, 1994.

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Bearings-131 Part 1

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