The theory of bearing failure or fatigue life of bearing

1. BEARING
FAILURE:
CAUSES
AND CURES
BARDEN
PRECISION
BEARINGS

2. aBARDEN
PRECISION
BEARINGS
Identitgingandcorrectingcauses
of bearing faihue.
Precisionballbearings are designed
to have a long and useful Ii€e.Assuming
the application is correctto begin with,
maximizinglongevitymeans bearings must
be properlyinstalled,lubricatedand
maintained.Poor operating environments.
oarticularlv moist or contaminated areas.
ind improper handlingpractices invite
premature bearing failure.
-
When a bearing does fail,it is important
to determinethe exact causesoapprcipriate
adiusfmentscan be made.Examinationof
th6failure modeo h n revealsthe true
causeof failure.?his procedureis compli-
catedbythe factthat onefailuremode may
initiate another.For example,corrosionin
aballraceleavesrust-an abrasive-which
can causewear,resulting in loss of preload
or an increasein radial clearance.?he wear
debris can,in a grease-lubricated bearing,
impede lubrication.resulting in lubrication
failure and subsequentoverheating.
?his guidewill assistinproperly
identifyingand analyzing 12 primary causes
of bearing failure.Each characteristicis
describedin detailand is shownin diagram
form,accompaniedby a color photograph.
Flaws,in most cases,arereadilyapparent.
In somecases,theimperfectionsmay
be virtually invisible to the naked eye.
Specificremedies for each situationare
also suggested.
YourAuthorized Barden Representative
will be happyto provideyou with additional
assistanceupon request

3. EXCES VERHEA? FALSE
LOAD isrnlnrstinl BRINE1
i'remahL~.
u,u..I.
area in ball path.
rings, ball, Elliptic:
marks s
.... -.
~teach
;ition.
ball por
LLING
lentations
Nays.
Ball in<
in racer
Balls sh
wear b;
metal fron
~ntact
surf?
CONTAMINATION
Denting of hearin
CORROSION
Chemical attack
g
r1
Is. Di
racewavs and bal results in
[b
tri
lue/brown) ball reddishlt
icks and balls. discolors
MISAI
Racem
1of
rfaces.
racewa scoloratiol
ounting su

4. Excessive loadsusually cause
EXCESSIVE prematurefatigue. itfits,
and improper preloading
can also ring aboutearly$time
Eailure,(seeT i tFits,p.15and
True&ine, p. 7).'Ibistype of
~ l u o k s t h e h e s a r a a s ~
fatigue.&+
bavyballwear
paths,evidenceof overheating
andamorewide@ spalling
[fafigyearea)areu
& evident
withshortenedlife.
?he selutionisto reducethe
load crredegignusinge~
bearing
with grsatsr capacity.

5. OVERHEATING
Symptomsare discoloration
of the rings,balls,and cagesfrom
BluelBlack gold to blue.Temperaturesin excess
of 400°F can annealthe ring and
ball materials.The resulting loss
in hardness reduces the bearing
capacitycausingearlyfailure.In
extreme cases,balls and rings will
deform.'Ihe temperature rise can
also degrade or destroy lubricant
Common culprits are heavy
electricalheatloads,inadequate
heat ~aths.
and insufficient coolinx
orlubricationwhen loads and
speeds are excessive.Thermalor
overload controls,adequateheat
paths,and supplementalcooling
are effectivecures.
Lookfor bluelblack
andsilv~rlgold
dtscolomtion Balls

6. FALSE
BRINELLING
-
/
Falsebrinelling-elliptical
B& path wear marks in an a
x
i
a
ldirectionat
each ballposition with a bright
finishand sharp demarcation,often
surroundedby a ring of brown
dehris-indicates excessive external
vibration.A smallrelative motion
betweenballs and raceway occurs
in non-rotatingball bearings that
are subjectto externalvibration.
When the bearingisn't turning,
an
oilfilm cannotbe formedto prevent
~ r i n a ~
~ m k s
racewaywear.Wear debris oxidizes
and acceleratesthe wear process.
Correctby isolatingbearings
from externalvibration,and
usinggreases containingantiwear
addiGes such as molybdenum
disulfidewhen bearinesonlv
Gillate or reverserapidly &in
aduator motors.
FalsebrineUa k a

7. TRUE
BRINELLING
B dPath
/
Ball Spacad
Brinelling occurswhen loads
exceedthe elasticlimitof the ring
material. BrineU marks showas
indentationsinthe racewayswhich
increasebearingvibration (noise].
Severebrinellmarks can cause
prematurefatiguefailure.
Anystaticoverload or severe
impactcan cause brinelling.
Examplesinclude:usinghammers
to remove or installbearings,
dropping or strikingassembled
equipment,and a bearing
onto a shaftby applying force to
the outer ring.
Installbearings by applying
forceonlyto the ring beingpress-
fitted,i.e., do not push the outer ring
to forcethe inner ring onto a shaft.
Carefulhandline A

8. NORMAL
FrnGUE
FAILURE
SpalledArea
Moderately spalled
area indicates
Fatiguefailure-usually
referredto as spalling-is the
fractureof the runningsurfaces
and subsequentremovalof small.
discreteparticles of material.
Spallingcan occur onthe
inner r
i
n
g
,
outerring, or balls.This
type of failure is progressive and
onceinitiatedwill spread as a result
of furtheroperation.Itwill always
be accompaniedby a marked
increasein vibration,indicating
an abnormality.
The remedyis to replacethe
bearing or considerredesigning
to use abearinghaving a greater
calculatedfatiguelife.
reachedthe limits
of its useful Me.

9. REVERSE
LQADING
are
designedto acceptan -1 oad
in onedirectionbnly.Whenloaded
intheoppositedirection,the
ellipticalcontad areaontheouterring
is truncatedby fhel
o
wshoulderon
that sideofthe outerr
i
n
g
.Themsutt
is excessivestressand an increase
in temperature,followed by
increasedvibrationand earlvfailure.
Failurenuodeisvery s&ir
tothatof heavyin%hnce(tight)
£%.?he balls will showapoved
wear band dbytheballM n g
overtheautdgeclgeafthe~y.
Correctiveactionisto simply
installthebearing w d .
wntactbeadqs mustbe
withtheresultant~onthewide
face-wbich ismarked %stn-of
the outerringandthe oppositeface
oftheinnerring.

10. Conhmhxdionisoneof the
leadinncausesof b
e
- failure.
hmguhdentsor
materialembedded
B d s will be
a i d & dented,
dull,or scratched.
-
Contamhationsymptomsare
dentingof the bearingraeeweys
andballs resultinginhighvibration
andwear.
Contaminantsincludeairborne
dust,dirt or anyabrasivesub-
stancethat findsitsway into the
bearing.Principalsourcesare dirty
tools,contaminated work areas,
d i i hands and fomignmatter in
lubricantsor cleaningsolutions.
Clean work areas,tools,fixtures
and hands help reduce contam-
ination failures.Keep grinding
operationsawayfrombearing
assemblyareasandkeepbearings
intheir originalpackagingu
n
t
i
lyou
arereadytoinstallthem.Seals
are critical-damagedorinoperative
sealscannot ~roted
bearinns

11. Discolored (bluelbrown)ball
LUBRICANT t r a h and balls are swptoms
FAILURE o
f lubricantfailure.Eiceisivewear I
of balls,r
i
n
g
.and cageswillfollow,
resultinain overheatinnand
Ballswfllalsobe
bluehkk
subseqGentcatastrophLcfailure.
Ballbearings depend on the
continuouspresence-of avery
thin-millionths o
f aninch-film o
f
lubricantbetweenballsandraces,
andbetween the cage,bearingrings, I!
and balls. Failuresaretypically i
caused byrestrictedlubricantf
l
o
w
or excessivetemperaturesthat
degradethe lubricant's properties.
Barden engineerscanadvise
i
users onthemostsuitablelubricant
9
e and quantitytouse.Referto
lu ricantsectionof BardenC-10
d o gfor moreinformation.Also,
i
any stepstakento correctimproper
1
fit controlpreloadbetter,and cool
I
the shaftsand housingswillreduce
bearingtemperatures and improve
lubricantlife.

12. CORROSION
Ball path
I
or depositson
dngs.
Redlbrownareas on balls,race-
ways,cages,or bands of ball
bearingsare symptoms of corrosion.
This conditionresults fmmexposing
@
bearings to corrosivefluidsor a cor-
rosiveatmosphere.Theusual result
isincreasedvibrationfollowed by
wear,with subsequentincrease
in radial clearance or loss of preload.
In extreme cases.corrosioncan
initiate earlyfatiguefailures.
Correctby divertingcorrosive
fluidsawayfrombearingareas and
useintegrallysealedbearingswhen-
ever possible.If the environment
isparticularlyhostile,the use of
externalsealsin additionto integral
seals shouldbe considered.?he
use of stainless steelbearings is
alsohelpful.

13. MISALIGNMENT
Misalignmedtcan be detected
shaftthreadsthatarenot square
with shaftseats,andlockingnuts
with faces thatare not squareto
the thread axis.'Ihe maximum
allowablemisalignmentvaries
greatlywith differentapplications,
decreasing,for example,with speed.
Appropriate correctiveaction
includes:inspectingshah and
housings for runoutof shoulders
andbearing seats;use of single
point-turned orgroundthreads on
nonhaedened shah and
Wideballpathon
pail ononter
m
.
1
Abnormal
temperaturedses
end pre-
wear ofcage
resultsfrom
ml4igument

14. LOOSE Loosefitscancauserelative
motion between matingparts.I
f
FITS the relativemotion between mating
parts is slightbut continuous,
frettingoccurs.
Frettingisthe generationof
finemetalparticleswhich oxidize.
leavinga distinctivebrown color.
Thismaterialis abrasiveandwill
aggravatethe looseness.If the
loosenessis enoughto allowconsid-
erablemovementof the inneror
outerring,themounting surfaces
Outerring slippage (bores,outerdiameters,h
]
will
causedby improper wear and heat (seephoto),causing
hoo~ing
fits. noise andrunoutproblems.
ConsultBarden C-10catalog
orBardenEngineeringfor
fitrecommendations.

15. H e w path
wear indicates
t
i
& 5
t
TIGHT A heavyballwear pathin the
bottom of the raceway aroundthe
Frrs entire circumferenceof the inner
ring and outer ringindicatesa
tightfit.
Where interferencefitsexceed
the radii clearance at operating
temperature,theballswillbecome
excessivelyloaded.?his will result
in a rapidtemperature rise accom-
panied by high torque. Continued
operationcan lead to rapid wear
andfatigue.
Corrective actionincludesa
decreasein totalinterference-
bettermatching of bearings to shafls
and housings-taking into consid-
erationthe differences in materials
and operatingtemperatures.
Increasedradii1clearancewill
alsoincreasebearing life under
the aboveconditions.