Why Bearings Fail CAUSE SKF DESIGN FAILURE

BEARING FAIL

1. Why Bearings Fail?

2. How do Bearings Fail?
Not always due to Natural Causes

3. How do Bearings Fail?
Not always due to Natural Causes
Only
of bearings fail
due to Fatigue,
which is the basis
of life calculation.
34
%

4. How do Bearings Fail?
Poor Lubrication
is the reason for
of premature
bearing failures
36
%

5. How do Bearings Fail?
Contamination
is the reason for
of premature
bearing failures
14
%

6. How do Bearings Fail?
Poor Installation
is the reason for
of premature
bearing failures
16
%

7. Design Life of Bearing
Depends on 4 Assumptions
 Good and clean Lubrication in adequate amount will
always be available to the bearing
 The bearing will be mounted without damage
 Dimensions of parts related to the bearings will
be correct
 There are no defects inherent in the bearing

8. How do Bearings Fail?
Fatigue of Bearing Material
 Spalling
 Produced by normal end to useful life
 Improper Lubrication
 Mechanical Damage
 Material Defect

9. Design Life of Bearing
Definition
 The life of a rolling bearing is defined as
the number of revolutions ( or operating
hours at a given constant speed) which
the bearing is capable of enduring before
the first sign of fatigue (Flaking ,spalling
or crack )occurs on one of its rings or
rolling elements

10. Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Failure mode Classification

11. How do Bearings Fail?
Failure mode Classification -
Spalling

12. Why Bearings Fail?
Symptoms of Failures

13. Unusual operating behaviour indicating
damage :Subjective damage recognition
In the vast majority of bearing applications it is
sufficient when machine operators watch out for
uneven running or unusual noise in the bearing
system
Bearing Failures & Their Causes

14. Bearing Failures & Their Causes
Unusual operating behaviour indicating damage :
Subjective damage recognition
Symptoms Sources of Trouble Examples
Uneven runningDamaged ring or
rolling elements
Motor vehicles:
* More and more wheel wobbling
* Increased tilting clearance
* Vibration of steering system
Contamination Fans:
* Growing vibration
Excessive bearing
clearance
Saw Mills :
* More knocks and blows on
connecting rods

15. Bearing Failures & Their Causes
Unusual operating behaviour indicating damage :
Subjective damage recognition
Symptoms Sources of Trouble Examples
Reduced
working
accuracy
Wear due to
* Contamination
or
* Insufficient Lubrication
Lathe:
* Gradual development of chatter
marks on work piece
Damaged rings or
rolling elements
Grinders:
* Weavy ground surface
Change in adjustment:
* Clearance or
* Preload
Cold Rolling Mills :
* Periodic surface defects on
rolled material e.g., stretcher
strains or ghost lines

16. Bearing Failures & Their Causes
Unusual operating behaviour indicating damage :
Subjective damage recognition
Symptoms Sources of Trouble Examples
Unusual
Running
Noise
Whinning or
Squealing noise
Insufficient operating clearanceElectric Motors
Gears
Rumbling or
Irregular noise
Excessive Clearance
Damaged contact areas
Contamination
Unsuitable Lubricant
Gradual change
in running noise
Change in operating clearance due
to temperature
Damaged running track due to
contamination or fatigue

17. Why Bearings Fail?
A. Overheated bearing
B. Noisy bearing
C. Vibration
D. Shaft is jammed
E. Bearing clearance has increased
F. Lubricant has metallic debris
G. Unsatisfactory equipment performance
Symptoms of Failures

18. Contributing factors of Symptoms of Bearing Failures
Sr.
No
Causes Symptoms
ABCDEFG
1Improper Lubrication X X X X X X X
2Contamination X X X X X X X
3Wrong Clearence / preload X X X X X X X
4Wrong Shaft dimension / tolerance X X X X X
5Wrong housing tolerance X X X X X X
6Wrong mounting of bearing / seal X X X X X X
7Unbalance / eccentricity / loose component X X X X
8Misalignment X X X X X
9Overspeed X X X X X
10Overload X X X X X
11Vibration / Heat from external source X X X X
12Seal Friction / Malfunction / damage X X X X X X
13Wrong selection of bearing /cage material / sealX X X X X X
14Improper maintenance of seal X X X X
15Passage of electric current X X X X
16Improper Gear Mesh X X
17Soft foot / loose foundation bolt X X
18Spurious / Reconditioned Bearing X X X X X X X

19. Why Bearings Fail?
Improper lubrication
Wrong type lubricant for operating condition
Low oil level. Lubricant being lost through seal
Excessive lubrication causing churning
Oil return hole too small
Oil return hole blocked. Pumping action of seal
causing leakage
Lubrication starvation because of incorrect
amount / relubrication interval
Contributing factors of Symptoms

20. Why Bearings Fail?
Seal friction / malfunction
Contact seals are dried out
Radial lip seal has excessive spring tension
Rotating seals / flingers are rubbing against
stationary parts
Contact seals are excessively worn causing
lubricant loss or permitting dirt to enter bearing
Labyrinth seal not greased
Contributing factors of Symptoms

21. Why Bearings Fail?
Wrong housing / shaft size / tolerance
Housing bore is out of round / undersized
Housing is warped / distorted
Bore surface uneven
Housing bore too large
Housing material too soft. Resulting pounding
enlarges bore allowing outer ring to spin.
Shaft diameter is out of round / oversized
Shaft shoulder diameter too large, rubbing
against seal / cage
Shaft is bending due to incorrect shoulder dia
Shaft is distorted
Shaft shoulder out-of-square
Contributing factors of Symptoms

22. Why Bearings Fail?
Wrong mounting / preload
Bearings are axially preloaded
Both bearings are located
Adapter sleeve is tightened excessively
Washer prong is rubbing against bearing
Incorrect mounting method
hammer blow
Impact of roller edge on raceway
Adapter sleeve is loose – shaft undersized
Contributing factors of Symptoms