CAT.NO.B3001E

Ball & Roller Bearings: Failures, Causes and Countermeasures
1. Time of fracture occurrence and causes ______________ 1
2. Abnormal operations, their causes andcountermeasures ___________________________________ 2
1. Types of failure _____________________________________ 3
2. Types of failure and parts in which they occur _________ 3
3. Failures and causes ________________________________ 4

1. Bearing Fracture

2. Bearing Failure

3. Failures, Causes and Countermeasures___ 9______
10
6 Rust and Corrosion
7 Pear skin, Discoloration __ 11
8 Smearing _______________ 12

1 Flaking, Pitting ___________ 5

5 Scratches and Scuffing

2 Wear and Fretting ________ 6
3 Cracks and Chips ________ 7
4 Brinelling and Nicks ______ 8

9 Creep __________________ 13__________ 14
11 Seizure _________________ 15
12 Failure of Cage __________ 16
10 Electric pitting– Rolling bearing: Description of each part –Outer ring

Ball
Inner ring bore surface
Inner ring
Inner ring raceway surface（Raceway groove）
Cage（Pressed cage）

Outer ring（Cup）

Outer ring front face

（Tapered) Roller

Large rib

Cage
（Pressed cage）

Guide rib face

Inner ring（Cone）
Small rib

Inner ring
raceway surface

Roller small end face

Rolling surface

Inner ring front face

Rivet

Inner ring back face

Roller large end face

Outer ring O.D. surface
Outer ring back face
Side surface（a）Deep groove ball bearing

Outer ring（c）Tapered roller bearing

Outer ring

（Cylindrical）Roller
Inner ring

Center rib
Inner ring raceway surface

Inner ring
Inner ring
raceway surface

Rib
Guide rib face
Guide rib face
Cage
（Machined cage with rivet）
Rivet

Rolling surface
Roller end face（b）Cylindrical roller bearing（Spherical）Roller
Cage（Machined cage）

Roller filling slot
Small rib
Rolling surface
Roller large end face（d）Spherical roller bearingIntroduction
Even when bearings are being used under ideal

When bearing failure is found, even if it is insignificant, it

conditions, failures of bearings are caused by deteriorationof the material due to rolling fatigue. Generally, the service
life of bearings is expressed either as a period of time or as
the total number of rotations before the occurrence offailures in the inner ring, outer ring or rolling element

is important to investigate the phenomenon to determine
the causes. At this time, not only the bearing but also theshaft, housing, and lubricant used with the bearing should
be comprehensively investigated, together with thebearing.

because of rolling fatigue, due to repeated stress.

To judge the causes of failure, sufficient knowledge andRolling bearings sometimes fracture earlier than
expected. The following causes should be considered;q Inappropriate use of bearings
w Faulty installation or improper processing
e Improper lubricant, lubrication method or sealing

experience in bearings and lubricants and a goodunderstanding of the characteristics of the equipment arenecessary. In addition, consideration of the installation
conditions and operational process of the bearing isrequired.

device〔Reference〕 Rated service life of rolling bearingr Inappropriate speed and operating temperaturet Contamination by foreign matter during installation

（ ）
10 C
L＝
60 （ P ）L＝y Abnormally heavy load

Cr
P
6

h

p

p

r

n

L : Rated service life, 106 rotations
Lh : Rated service life, h
Cr : Basic dynamic load rating, N
P : Dynamic equivalent load rating, N
n : Rotational speed, min-1
p : 3 ……Ball bearing,
10/3 …Roller bearing

1. Bearing Fracture
1. Time of fracture occurrence and causes
For failure analysis, it is important to accurately
determine the time a fracture occurs, because the possible
causes of failure can be limited in according to the time offracture occurrence.

For reference, time of fracture occurrence and relatedcauses are categorized and listed in Table 1–1.

Table 1–1 Time of Breakage Occurrence and CausesTime offracture occurrence

Inappropriate Faulty design of shaft, Improper lubricant, Defect inuse ofhousing or otherlubrication method bearings
Causesbearings
installation aspects or or sealing device
improper processing(1) Fracture occurring immediately
after bearings were mounted orwithin a short time after mounting

○

○

○

(2) Fracture occurring immediately
after overhaul○(3) Fracture occurring immediately
after lubricant was supplied○(4) Fracture occurring immediately
after repair or removal of shaft,housing or other parts○(5) Fracture occurring during
normal operation1○

Mis-mounting Defect in sealing device,of bearings
contamination of water, dust
or other foreign matters, orshortage of lubricant
○

○

○

○

○

○

○

2. Abnormal operations, their causes and countermeasures
Causes and countermeasures of abnormal operations are
categorized and listed in Table 1–2.
Table 1–2 Abnormal Operations, their Causes and Countermeasures

Abnormal operation

Noise at uniform
intervals
Noise at nonuniform High-pitchedintervals
metallic noise

Excessively loud noise or foreign noise

Increase in temperature

Excessively high vibration

Excessively large
rotational torqueCausesCountermeasures (supplementary countermeasures)

1. Excessively tight bearing
internal clearance
2. Creep on bearing ring

Replace with a new bearing.（Correct bearing internal
clearance and interference.）
Replace with a new bearing.（Correct interference.）

3. Excessively heavy load
4. Improper centering inmounting

Remounting（Correct load by adjusting housing.）
Remounting（Correct centering, or widen mounting clearance.）

5. Defect in bearing

Replace with a new bearing.（Take proper countermeasures,
after inspecting the causes.）
Correct lubricant volume.

6. Improper volume of lubricant
7. Improper lubricant
8. Improper lubrication method

Change to proper lubricant.
Correct lubrication method by remounting or replacement withnew parts.

9. Oil seal
– Excessive interference– Shortage of lubricant– Improper oil seal
10. Abnormal contact withlabyrinth seal or other parts

Correct interference by installing new seal or changing seal
type.
Supply lubricant.
Correct oil seal type or sealing method.
Remounting or modify parts.

1. Flaws including scratches,brinelling, etc.
2. Electric pitting

Repair bearings or replace with new ones.（Care should betaken in handlingbearings.）
Repair bearings or replace with new ones.（Prevent electricity
from passing through bearings by modifying their design.）

3. Cracking of inner or outerring（s）
4. Flaking of raceway surface
5. Receway surface roughened
by foreign matter（s）

Replace with a new bearing.

1. Excessively narrow internal
clearance
2. Shortage of lubricant
3. Sliding of rolling element

Replace with a new bearing or widen internal clearance.

1. Contamination by foreign
matter（s）
2. Contact with another rollingpart

Change to proper lubricant.

3. Flaw or flaking on rolling
element
4. Wear of cage

Replace with a new bearing.

1. Contamination by foreign
matter（s）
2. Excessively wide clearance
3. Flaw on raceway surface orrolling contact surface

Change to proper lubricant.

1. Improper mounting

Remounting（Widen internal clearance. Care should be takenwith centering.）
Remounting（Reduce interference of oil seal.）
Decrease lubricant volume.（Care should be taken not to supply
an excessive amount of lubricant.）

Replace with a new bearing.
Repair bearings or replace with new ones.

Supply lubricant.
Change to proper lubricant or decrease operational clearance.

Remounting or modify parts.

Replace with a new bearing.

Remounting bearing or replace with a new one.
Replace with a new bearing.

2. Improper sealing device
3. Improper lubricant

22. Bearing Failure
1. Types of failure
Defects in the appearance of bearings are referred to as
bearing failures. Table 2–1 describes bearing failures, firstassigning a general term to each type of failure, thenadding more detailed classifications.

Table 2–1 Bearing Failure

Bearing failures
FailuresMain cause (reference)

Failure details

Rolling fatigue

Flaking, Pitting

Wear

Wear, Fretting

Unavoidable

Fracture

Cracks, Chips

Flaw

Brinelling, Nicks, Scratches, Scuffing

Rust

Rust, Corrosion

SeizureSeizure, Discoloration, Smearing

Improper lubrication

Creep

Creep

Improper fitting

Electric pitting

Electric pitting

Passage of electricity

Improper handling

2. Types of failure and parts in which they occur
Table 2–2 describes bearing failures, parts where theyoccur, and standards for judging the failures.
Table 2–2 Bearing Failures, Parts in which they Occur, and Standards for Judging Failures

Bearing ring, Rolling element

Bearing ring

· Roller guide surface· Cage guide surface· Roller end face

· Fitting surface

Bearing failure · Raceway surface· Rolling surface

Flaking, Pitting
Wear
Fretting
Cracks
Chips
Brinelling
Nicks
Scratches
Scuffing
Rust
CorrosionPear skin
Discoloration
Smearing
CreepElectric pitting
SeizureFailure of cage

· Others

Cage· Pocket surface· Guide surface· Rivet

×

−

−

−

−

−

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○

○

○

○

×

○

−

−

○

−

−

×

×

×

×

×

×

×

×

○

×

×

×

○

○

○

○

−

−

○

○

○

○

○

○

○

○

○

○

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−

−

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−

−

−

−

−

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−

−

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−

−

−

−

−

−

−

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−

−

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−

−

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−

×

×

×

×

×

−

−

−

−

−

○

×

Notes） × : In principle, not reusable.
○ : Reusable in accordance with seriousnes of failure, by repairing or meeting required conditions.
− : No failure of this part.

3

3. Failures and causes
Table 2–3 describes failures and causes. For further
detail, refer to Section "3 . Failures, Causes andCountermeasures" .
Table 2–3 Failures and Causes

FailureCause

Circumference on one side

Sketches of failures

Excessive axial load
（Fig. 1）OthersRust, Corrosion

Wear

Creep

Cracks, Chips

Scratches, Scuffing

Flaking

Symmetrical flaking on each side

Inclined mounting, or shaft or housing not in the
shape of a circle（Fig. 2）

Flaking on one side or flaking in the formof an oblique line on raceway surface ofbearing ring on fixed side
（Fig. 3）Distortion of shaft, insufficient centering,
bearings not installed on shaft at the correct
angle

Partial flaking on thrust bearing

Eccentric mounting

Flaking found on part only

Contamination by foreign matter（ s）, flaws,
initial stage of flaking

Scuffing on roller end face and guide rib
face（Fig. 4）

Excessive axial load, improper lubrication

Scraches on raceway surface

Grease of too high viscosity, excessive
acceleration in starting

Scratches on raceway surface oh thrustbearing

Sliding of rolling element caused by centrifugal
force during rotation

Cracks or chips of rolling element

Improper bearing material, excessive impact too
wide internal clearance of cylindrical roller
bearing（Fig. 5）
Cracks or chips of inner ring or outer ring
（Fig. 5）
Cracks, chips of rib

Fig.1 Flaking along circumference on one side.
(Deep Groove Ball Bearing)Fig.2 Symmetrical flaking on each side.
(Tapered Roller Bearing)Fig.3 Flaking in the form of an oblique line.
(Deep Groove Ball Bearing)

Advanced stage of flaking, improper bearing
material, interference too large, housing of
inaccurate design
Impact in mounting, axial impact, load too heavy（Fig. 5）
Cracks, chips of cage

Improper lubricant or lubrication method, highspeed operation, vibration impact too strong,advanced stage of wear

Creep on inner/outer rings

Insufficient interference

Wear on inner/outer rings

Sliding abrasion, bearing of insufficient
hardness, contamination by foreign matter（s）,
shortage of lubricant, improper lubrication

Wear caused by creep

Creep

Wear on cage

Contamination by foreign matter（s）, improper
lubrication, inclined bearing

Rust on inner ring bore surface or outerring O.D. surface

Fretting, water, humidity

Rust covering whole bearing surface,corrosion

Defective washing oil or lubricant, water,
humidity

False brinelling

Progressing stage of flaws caused by load fromvibration when machine is not running.

Fig.4 Scuffing on roller end face and guide rib
face. (Cylindrical Roller Bearing)Fig.5 Cracks and/or chips on inner ring or roller.
(Spherical Roller Bearing)Fig.6 False brinelling on inner ring.
(Deep Groove Ball Bearing)（Fig. 6）
Fluting on raceway surface or roller rollingsurface（Fig. 7）

Passage of electricity

Discoloration

Heat generation, chemical action

FlutingFig.7 Type of Electric pitting.

4

Pitting

3. Failures, Causes and Countermeasures
1

Flaking, Pitting
Phenomena, causes and countermeasures■

Examples of failures

Flaking is a phenomena in which the bearing surface turns■ Flaking on inner ring of Deep Groove Ball Bearing

scaly and peels off due to contact load repeatedly received on
the raceway and rolling surface during rotation.

service life is near.
●(A-6977)

Phenomena

Occurrence of flaking indicates that the end of a bearing's

Pitting is a phenomena in which small holes 0.1 mm in depth
are generated on the raceway surface by rolling fatigue.
■ Flaking on inner ring of Cylindrical Roller Bearing※Flaking and pitting are often found at an early stage. In thiscase, countermeasures should be taken, after examining the(A-7024)

causes.

Flaking and pitting occur early in a bearing's service life
under the following conditions:1）During operation, bearing internal clearance becomesnarrower than specified.

■ Flaking on outer ring of Double-Row Cylindrical Roller Bearing

2）Bearing ring is mounted at an inclination by mistake.

Causes3）Flaw is created during mounting, or brinelling, nicks, rust,etc. occur on the raceway surface or rolling surface.
(A-6466, 6473)

4）Inaccurate shape of shaft or housing（imperfect circle,
depressions on surface.）■ Flaking on inner ring of Tapered Roller Bearing

Flaking(A-6644, 6645)

a）Use a bearing with heavier rated load.

Countermeasuresb）Check if abnormal load is being generated.
c）Improve lubrication method to ensure better formation of
lubricant film, by increasing the viscosity.
d）When a failure is discovered at an early stage, thecountermeasures described above should be taken, afterinvestigating the causes.
●■ Flaking on inner ring of Spherical Roller Bearing

Pittinga）Increase viscosity of lubricant to ensure better formationof lubricant film.
（Care should be taken because foreign matters appear
similar to holes caused by brinelling or corrosion.）

5(A-6476)■

3. Failures, Causes and Countermeasures
2

Wear and Fretting
Phenomena, causes and countermeasures■

Examples of failures

Wear is caused mainly by sliding abrasion on parts including■ Wear on roller and face of Cylindrical Roller Bearing

the roller end face and rib, cage pocket surface, cage, and theguide surface of the bearing ring.
Wear due to contamination by foreign matter and corrosion occurs
Fretting is a phenomena which occurs when slight sliding isrepeatedly caused on the contact surface.

(A-4718)

Phenomena

not only to the sliding surface but also to the rolling surface.
●On the fitting surface, fretting corrosion occurs, generating arust like powder.
▲■ Wear on outer ring raceway surface

If bearings receive a vibration load when they stop orof Double-Row Cylindrical Roller Bearing

operate, slight sliding occurs in the section between therolling element and bearing ring due to elastic distortion.
False brinelling, a flaw similar to brinelling, is generated bythis condition.
Wear(A-6714)■1）Improper lubricant or shortage of lubricant.
2）Contamination by foreign matter（s）.
●● Fretting on inner ring bore surface of Tapered Roller Bearing

Fretting
1）Vibration load.

(A-6649)

Causes2）Slight vibration on fitting surface caused by load.

● Fretting on outer ring O.D. surface of Deep Groove Ball Bearing

Vertical fretting at symmetric positions 180º apart.

■

Wear

(A-6735)a）Review and improvement of lubricant and lubrication
method.
c）Improvement of sealing.
●▲ False brinelling on inner ring raceway surface

Frettinga）Investigation and countermeasures for the source ofvibration.

of Deep Groove Ball Bearingb）Investigation and increase of interference.
c）Enhancement of shaft rigidity.

(A-7278)

Countermeasuresb）Filtering of oil.

6

3

Cracks and Chips
Phenomena, causes and countermeasures

Examples of failures■ Crack and chip in a Spherical Roller Bearing■

Cracks include slight cracks, splitting and fracture.

●

Chips are a type of failure occurring at a certain part of a

(A-6395)

Phenomena

bearing ring rib or corner of a roller.

■ Crack on outer ring of Four-Point Contact Ball Bearing

Crack starting from key groove on O.D. surface.

Cracks

(A-6625)■

1）Heavy load.
2）Excessively heavy internal load caused by improper
installation.

■ Crack in outer ring of Double-Row Cylindrical Roller Bearing

Causes3）Excessive interference at fitting, or shaft and housing of
improper shape.
4）Instantaneous heat generation of bearing caused bysudden sliding at rolling surface, sliding surface or fitting
surface.
(A-6626)5）Abnormal heat is generated due to shortage of lubricant.
●Chips1）Abnormally heavy axial load or impact load.
2）Partial impact of hammer or other tool used when bearing
is mounting or dismounting.

■● Chip in outer ring rib of Cylindrical Roller Bearing

Cracks(A-6555)a）Investigation followed by countermeasures for excessively
heavy load.
c）Improvement of interference（decrease of interference.）●

Chipsa）Improvement of mounting and dismounting procedures.

● Chip in outer ring rib of Cylindrical Roller Bearingb）Improvement of handling method.
c）Investigation followed by countermeasures for excessively
heavy load.

(A-6658)

Countermeasuresb）Removal of thermal impact.

7

3. Failures, Causes and Countermeasures
4

Brinelling and Nicks
Phenomena, causes and countermeasures■

Examples of failures

Brinelling is depressions created on the part of the raceway
surface which comes into contact with the rolling element,■ Brinelling on outer ring raceway surfaceof Deep Groove Ball Bearing

and is due to plastic deformation.
Brinelling is also small depressions on the rolling surface●

Nicks are a flaw caused by the direct impact received when(A-6474)

Phenomenacaused by contamination by solid foreign matters.

bearings are hit by a hammer or other solid tool.

■ Brinelling on inner ring raceway surfaceof Tapered Roller Bearing

Brinelling
1）Extremely heavy load（static load, impact load）applied
to bearing.
2）Solid foreign matter caught in bearing parts.

Causes●

Nicks1）Faulty bearing mounting or dismounting.
2）Mis-handling of bearings.

■

Brinellinga）Investigation followed by countermeasures for excessively
heavy load or impact.

Countermeasuresb）Enhancement of sealing capability.
c）Careful washing of shaft and housing to remove foreign
matter.
d）Filtering of oil.
e）Investigation of flaking in target bearing together withother bearings.
●

Nicksa）Improvement of bearing mounting and dismounting.
b）Improvement of bearing handling.

8(A-6617)■

5

Scratches and Scuffing
Phenomena, causes and countermeasures■

Examples of failures

A scratch is a relatively shallow flaw caused by sliding■ Scratch on roller rolling surface of Cylindrical Roller Bearing

contact.
●

Scuffing is a flaw caused by high contact pressure and heaton the rolling surface.
1）Flaw in the axial direction（flaw occurring in mounting）
In the mounting of bearings whose outer rings and innerrings are separable, a flaw in the axial direction issometimes caused by contact with the edge of rollers or
raceway surfaces.
These are referred to as flaws in the axial direction.

(A-6451, 6453)

Phenomena

In general, more serious scratches are regarded as scuffing.

■ Scratch on roller rolling surface of Cylindrical Roller Bearing

Scratch occurring in circumference direction.

2）Scuffing on roller end face and rib face
Cycloidal flaws can occur on the roller end or rib face ofthe bearing ring, which guides rollers.
Flaws such as scratches, which occur on these parts arecalled scuffing.
(A-6452)（1）Flaw generated during mounting.
1）Careless handling in mounting or dismounting.
（2）Scuffing on roller end face and rib face.

■ Scratch on outer ring raceway surface of Double-Row

Cylindrical Roller Bearing

1）Improper lubrication at contact face.

Roller which slides when running.

Causes2）Excessive preload.
3）Intrusion of foreign matter.
4）Abnormal axial load.
（3）Scratches and scuffing on raceway surface and rolling(A-6470)

surface.
1）Improper rotation of rolling element.
2）Improper lubrication.
3）Intrusion of foreign matter.

● Scuffing on inner ring bore surface of Tapered Roller Bearing（1）Flaw generated during mounting.

(A-6736)（2）Scuffing on roller end face and rib face.
a）Review and improvement of lubricant and lubrication
method.

● Scuffing on inner ring rib face and roller and faceof Cylindrical Roller Bearing with ribb）Inspection and countermeasures for abnormal load.
c）Enhancement of sealing capability.
（3）Scratches and scuffing on raceway surface and rollingsurface.
a）Review and improvement of lubricant and lubrication
method.
b）Enhancement of sealing capability.
c）Sufficient cleaning of shaft and housing.

9(A-6669)

Countermeasuresa）Improvement in operations involved in mounting anddismounting.
（Implementation of accurate center adjustment.）

3. Failures, Causes and Countermeasures
6

Rust and Corrosion
Phenomena, causes and countermeasures■

Examples of failures

Rust is a film of oxide, hydroxide, or carbonate produced on

Bearinga metallic surface by chemical action.
●■ Rust on outer ring raceway surface of Double-Row Angular Ball

Rust on raceway surface of one row.

Corrosion is the phenomena of oxidation or dissolution（electric chemical action including combination or cell
restructuring）with acid or alkali.
(A-6494)

Phenomena

occurring on the surface and is produced by chemical action■ Rust on outer ring raceway surfaceof Double-Row Cylindrical Roller Bearing

Rust

Causes1）When equipment is stopped and its temperature
decreases to the dew point, humidity in the housing turns
into drops of water. The water drops often contaminate
the lubricant. As a result, rust is generated on the bearing
surface.

(A-6472)■

Rust on roller pitch.

■ Rust on roller rolling surface of Cylindrical Roller Bearing

Rust at one position the rollers.

2）When bearings are stored in a humid place for a long time,rust is generated on the raceway surface at intervals equal
to the rolling elements spacing.
●Corrosion2）Corrosion occurs when water gets inside bearings.

(A-6479)

1）Corrosion occurs when a sulfur or chlorine compoundcontained in lubricant additives decomposes under hightemperature.
■ Rust on inner and outer rings and on rollerof Tapered Roller Bearing

■

Rust

●

Rust on roller pitch of one row.

Corrosiona）Enhancement of sealing capability.
(A-7130)c）Provision for adequate rust prevention during storage ofbearings.

■ Rust on outer ring raceway surface of Tapered Roller Bearing(A-7051)

Countermeasuresb）Periodic inspection of lubricant.

107Pear skin, Discoloration
Phenomena, causes and countermeasures■

Examples of failures

Pear skin is a condition of the rolling surface where small
depressions are created entirely as a result of many foreign■ Pear skin on inner ring raceway surfaceof Double-Row Cylindrical Roller Bearing

matters being caught between parts.
A rolling surface suffering from pear skin appears dim and isby heat.
●(A-6556)

Phenomenarough in texture. In the worst case, the surface is discolored

Discoloration is a phenomena in which the bearing surface isdiscolored by staining or heat generated during operation.
■ Pear skin on inner ring raceway surfaceof Deep Groove Ball Bearing(A-6960)Pear skin
Since pear skin is mainly caused by contamination by foreign
matter or lack of lubricant, these two points should be● Discoloration on ball surface of Deep Groove Ball Bearing●

Discoloration

Countermeasures2）A brown discoloration of the rolling or sliding surface iscaused by adhesion of acidic powders generated byabrasion during operation.
In general, these powders adhere uniformly to the bearing
circumference.
■

Pear skina）Careful washing of shaft and housing.
b）Enhancement of sealing capability.
c）Filtering of oil.
d）Review of lubricant and lubrication method.

●

Discoloration
Discoloration can be classified as follows: staining, electric
pitting, rust, corrosion, and temper color. Stains can be removed
by wiping with an organic solvent（aceton）. When observed by
microscope, electric pitting is small depressions caused byelectric discharge. If unevenness remains on the surface after
wiping with sand paper, the phenomena are judged to be rustand corrosion. If unevenness is completely removed, thephenomena is judged to be temper color caused by heat.
a）Improvement of heat dissipation from bearings.
b）Improvement of lubrication.
c）Review followed by countermeasures for bearing operating
conditions.

11(A-6639)1）Discoloration（staining）is caused by deterioration of the
lubricant or adhesion of colored substances to the bearing
surface.
Some of these substances can be removed by scrubbing or
wiping with a solvent.

● Discoloration on raceway surface, roller rolling surfaceof Cylindrical Roller Bearing(A-6725)

Causesinspected most carefully.

● Discoloration on inner ring and roller of Tapered Roller Bearing

Staining(A-6982)■

3. Failures, Causes and Countermeasures
8

Smearing
Phenomena, causes and countermeasures■

Examples of failures

Smearing is a phenomena where minute seizure is concentrated■ Smearing on inner ring raceway surfaceof Deep Groove Ball Bearing

on the rolling surface.
In smearing, the surface is partially melted by heat of hightemperature generated by friction; and on some parts, the(A-6640)

Phenomena

surface damaged becomes significantly rough.

■ Smearing on inner ring raceway surface of Angular Ball Bearing

2）In ball bearings, smearing is caused by sliding or spinningof balls; and, in roller bearings, smearing tends to occur
when the roller enters into on from the load zone.

(A-6642)

Causes1）Smearing occurs if the oil film disappears as rolling
elements stop rotating due to inappropriate use or
improper lubrication, and then start to slide on the
raceway surface.

(A-6641)■ Smearing on ball surface■ Smearing on outer ring raceway surfaceof Cylindrical Roller Bearinga）Review followed by countermeasures to improve theformation of oil film.
(A-7435)c）Adoption of countermeasures to prevent sliding.
（by diminishing mounting clearance.）■ Smearing on roller rolling surface of Cylindrical Roller Bearing(A-6480)

Countermeasuresb）Provision for extreme-pressure lubricant.

12

9

Creep
Phenomena, causes and countermeasures■

Examples of failures

Creep is the displacement during operation of a bearing ring,■ Creep of Deep Groove Ball Bearing inner ring

(A-6726)

Phenomena

relative to the shaft or housing.

(A-6957)■ Creep of Deep Groove Ball Bearing outer ring

Creep occurs when interference is too small in relation to theheat or load generated during operation.

(A-6647)

Causes■ Creep of Double-Row Cylindrical Roller Bearing inner ring

■ Creep of Tapered Roller Bearing inner ring

Review of interference between inner ring and shaft andCountermeasures(A-6616)

between outer ring and housing.（Increase of interference.）13

3. Failures, Causes and Countermeasures
10

Electric pitting
Phenomena, causes and countermeasures■

Examples of failures

Electric pitting is a phenomena in which the bearing surface
is partially melted by sparks generated when electric current■ Electric pitting on Deep Groove Ball Bearing

Fluting on inner ring raceway surface.

enters the bearing and passes through an extremely thin oilfilm at the rolling contact point.
which the rolling contact surface propagates. Depressions
like craters can be observed when pitting is magnified,(A-6652)

Phenomena

Electric pitting can be classified into pitting or ridge marks,

indicating that the surface has been melted by sparks.
・Significant electric pitting causes flaking.
In addition, since the hardness of the rolling contact surface■ Electric pitting on Cylindrical Roller Bearing

deteriorates, the surface tends to be easily worn.
・If a fluting surface is found by manual inspection, or pitting isobserved by normal visual inspection, the bearing cannot be
re-used.
(A-6653)

Bearing surface is partially melted by electric current passing
through the bearing.

(A-5180)

Causes■ Electric pitting on Cylindrical Roller Bearing inner ring

■ Fluting on Cylindrical Roller Bearing inner ringa）Improvement of grounding or improvement of grounding
maintenance.
(A-6651)

Countermeasuresb）Provision of insulation for bearings or for the section nearbearings.

(A-6409, 6650)■ Fluting on Spherical Roller Rolling surface

14

11

SeizurePhenomena, causes and countermeasures■

Examples of failures

Although scuffing and smearing can be categorized as
seizure, scuffing is generally regarded as a more serious type■ Seizure of Cylindrical Roller Bearing

Rollers are removed because pocket surface of cage has become worn.

of failure. The seizure described in this section is the kind inwhich bearing parts are melted and adhere to one anotheras a result, the bearing can no longer rotate.
・Once seizure occurs, the bearing cannot be used again(A-6457)

Phenomena

due to abnormal heat or the rolling surface becoming rough;because the hardness has deteriorated and smooth rotation is
impossible on the rough surface.
■ Seizure of Cylindrical Roller Bearing with rib(A-6464)

Seizure results from abnormal heat generated by improper
lubrication, excessive preload, or improper contact of rolling
elements with the raceway surface, which cannot becompensated for by the cooling method or lubrication
employed in the bearings.

■ Seizure of Tapered Roller Bearing(A-6679)

CausesHeat is generated on roller end face and inner ring rib face.

Causes should be investigated; and appropriate counter-

Countermeasures

measures corresponding to the results should be taken.

153. Failures, Causes and Countermeasures
Failure of Cage
Examples of failures

1）Cracks and Chips
If a seriously cracked bearing is used under heavy
operating conditions, it will fail.

Phenomena2）Flaw and Distortion
・Since cages are made from soft material, they tend to bedamaged or become distorted by external forces or fromcontact with other parts.
・Since cages with a serious flaw also have distortion, theiraccuracy may decrease.
And the motion of the rolling element is consequently
affected; therefore, especially the size and location of theflaw should be checked with care.

● Crack of Deep Groove Ball Bearing cage

(A-6455)

Phenomena, causes and countermeasures● Crack of Tapered Roller Bearing cage3）Rust and Corrosion
If rust or corrosion is found on cages, it can be assumed
that it is also occurring on the bearing ring and rolling
element.
4）WearAs described in Section 2 , cages under the following
conditions can no longer be used because proper rotationof the rolling element is hindered: cages whose pocket
surface has been worn down in the shape of the rolling
elements; cages which cannot maintain the rolling
elements, and cages whose guide surface for the bearing
ring has been eccentrically or severely worn.

(A-6670)

12● Distortion of Cylindrical Roller Bearing cage16

● Looseness of Cylindrical Roller Bearing cage rivet(A-6481)1）Cracks and Chipsa）Careless handling.
b）Abnormal load, Vibration impact.
2）Flaw, Distortiona）Careless handling.
3）Rust, Corrosiona）Improvement of sealing capability.
Periodic inspection of lubricant.
b）Provision of adequate rust prevention during storage ofbearings4）Weara）Improper lubricant or shortage of lubricant ...
Investigation followed by countermeasuresinvolving lubricant and lubrication method.
b）Contamination by foreign matter ... Improvement ofsealing capability.
5）Looseness and Cut-Off of Riveta）Improper bearing mounting ... Reduction of bearing
inclination.
b）Severe load or vibration ... Consultation with Koyo.

● Rust on Tapered Roller bearing cage

(A-7131)

Causes and countermeasures(A-7026)5）Looseness and Improper Riveting
Looseness of the rivet is caused by an error in bearing
mounting, moment load, variable load, vibration, etc.
If a bearing is operated with improper riveting, the bearing
cannot be returned to service because the rivets may
break.

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