For New Technology Technology Network
®
NTN corporation
3017/E
CAT.NO.
Care and Maintenance of Bearings
Explanation of the Photos. These are microscopic photographs of peeling damage generated on the surface of a ball/roller ball/roller bearing. Peeling can occur when the surface roughness is high, or when the lubrication performance is poor. Peeling has a flat-colored appearance, and when observed under a microscope, shows minute flaking and cracks. The top photo shows an example of minute flaking interconnected with cracks. The photo in the middle shows an example of partial separation of the surface, occurring after a number of areas areas where minute flaking occurred have been connected. This is often seen when grease lubrication is used. The bottom photo shows an example in which a directionality is seen in the minute flaking. The example also shows cracks due to slippage.
Care and Maintenance of Bearings (Revised) We thank you for your interest in NTN bearings. This booklet is intended as a guide to bearing maintenance, with the main consideration being on-site bearing maintenance. Bearings may fail earlier than than the expected rolling fatigue life. Early failure is mostly attributable to inadequate handling or maintenance. We will be pleased if this guide book assists the user in preventing preventing early bearing failure or in troubleshooting the causes of bearing failure.
Care and Maintenance of Bearings Contents 1.
Introd Introduct uction ion ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... .. 5
2.
Inspec Inspectio tion n of Bearin Bearings gs ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... .. 5
3.
Inspec Inspectio tion n When When Machin Machine e is Run Runnin ning g ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... .. 5
3.1
Bearing Bearing Tempera emperatur ture e ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .... 5
3.2
Operati Operating ng Sounds Sounds of Bearing Bearing ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ....... ... 5
3.3
Vibratio Vibration n of Bearing..... Bearing......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... 7
3.4
Lubrica Lubricant nt Select Selection ion ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... .. 7
3.5
Relubri Relubricat cation ion ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .... 7
4.
Check Che ck of Bearing Bearings s afte afterr Oper Operatio ation n ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ....... ... 9
5.
Bearing Bearing Fail Failures ures and Solut Solution ions s ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... 9
5.1
Flakin Flaking g ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ....... ... 10
5.2
Peeling Peeling ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ....... ... 12
5.3
Spallin Spalling g ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... .. 13
5.4
Smeari Smearing ng ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ....... ... 15
5.5
Wear ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... .. 15
5.6
Speckle Speckles s and Discol Discolorat oration ion ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .... 16
5.7
Indent Indentati ations ons ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ....... ... 17
5.8
Chippin Chipping g ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .... 18
5.9
Cracki Cracking ng ........ ............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .... 19
5.10
Rust and Corrosion Corrosion .................... .............................. .................... .................... ..................... ..................... .................... .................... ................... ......... 20
5.11 5.11
Seizing .................... .............................. .................... ..................... ..................... .................... .................... .................... ..................... ..................... ................. ....... 21
5.12
Fretting Fretting and Fretting Fretting Corrosion Corrosion ..................... ............................... .................... .................... .................... ..................... ..................... ............ 22
5.13
Electrical Electrical Pitting Pitting .................... .............................. ..................... ..................... .................... .................... ..................... ..................... .................... ............. ... 23
5.14
Rolling Rolling Path Skewing Skewing .................... .............................. ..................... ..................... .................... .................... ..................... ..................... ............... ..... 24
5.15
Damage Damage to Retainers Retainers .................... .............................. ..................... ..................... .................... .................... ..................... ..................... ............... ..... 25
5.16
Creeping Creeping ..................... ............................... .................... ..................... ..................... .................... .................... ..................... ..................... .................... ............. ... 26
1. Introduction The rolling-contact bearing is an element of machinery with a very important role, and it dominates the performance of the machine. If one of the bearings breaks or seizes, not only the machine but also the assembly line may stop. If one of the axle bearings of an automobile or a railway car breaks down, a serious accident could occur.
3. Inspection When Machine is Running 3.1 Bearing Temperature Bearing temperature generally rises with start-up and stabilizes at a temperature slightly lower than at start-up (normally 10 to 40(C higher
To avoid trouble, every bearing manufacturer should make efforts to
than room temperature) in a certain time. time. The time before before stabilizing
assure the highest quality for each bearing, and should emphasize that
depends on the size, type, speed, and lubrication system of the bear-
the user carefully handle and maintain all bearings.
ing and the heat dissipation condition around the the bearing. It ranges
Every bearing becomes unserviceable in the course of time even if it
from about 20 minutes to as long as several hours. If bearing tempera-
is installed correctly and operated properly. prope rly. The raceway surfaces and
ture does not stabilize but continues to rise, r ise, the causes shown in Table
the rolling contact surfaces of the rolling elements are repeatedly sub-
3.1 are conceivable. Operation should be stopped and an appropriate
jected to compressive loads, and the surfaces eventually flake.
corrective action should be taken.
The life of a rolling-contact bearing is defined as the total number of
High bearing temperature is not desirable in view of maintaining an
revolutions (or the number of operation hours at a given constant speed)
adequate service life and preventing lubricant deterioration. A desir-
before flaking occurs.
able bearing temperature is generally below 100°C.
The bearing may also become unserviceable because of seizing, breakage, wear, false brinelling, corrosion, etc. These problems are caused by improper selection or handling of the
Table Table 3.1 Major causes of high bearing temperature temperature
bearing. The problems are avoidable avoidable by correct selection, proper han-
(1) Extremely Extremely insufficient insufficient or excess excessive ive lubricant
dling and maintenance, and are distinguished from the fatigue life of
(2) Poor instal installat lation ion of of the bea bearing rings s
the bearing.
(3) Extremely Extremely small small bearing bearing clearance clearance or extremely extremely heavy heavy load
However, However, breakdowns due to improper application, bearing bea ring design, and maintenance are more frequent than flaking due to rolling fatigue
(4) Extremely Extremely high high friction friction between between lip and seal seal groove groove
in the field.
(5) (5) Impr Improp oper er lubri lubrica cant nt type type (6) Creep Creep bet betwee ween n the fitt fitting ing surf surface aces s
2. Inspection of Bearings Inspection of a machine’s bearings during operation is important to prevent unnecessary unnecessary bearing bear ing failure. The following following methods are gen-
3.2 Operating Sound of Bearing
erally adopted to inspect the bearing.
The following Table 3.2 lists typical abnormal bearing sounds and
(1) Che Check ck of bearing bearings s in operati operation on
their causes. Please note that the decription of some some of these sounds
Included are the check of bearing temperature, noise, and
is rather subjective and thus could vary considerably from person to
vibration, and the examination of the properties of lubricant to
person.
determine when lubricant should be replenished or exchanged. (2) Inspection Inspection of of bearings bearings after after operati operation on Any change of the bearing is carefully examined after operation and during periodic inspections so as to take measures to prevent recurrence. It is important for proper bearing maintenance to determine inspection requirements and intervals, according to the importance of the system or machine, and adhere to the established schedule.
Table 3.2 Typical Abnormal Bearing Sounds and Their Causes Sound
Features
Causes
Hiss
Small Bearings
Raceway, ball or roller surfaces are rough.
Buzz to Roar
Loudness and pitch change with speed.
Resonation Poor fit (Poor shaft shape) Bearing rings deformed. Vibration of raceways, raceways, balls, or rollers (For large bearings, if this sound is minor, then this is considered normal). Brinelling
Crunch
Felt when the bearing is rotated by hand.
Scoring of raceway surface (regular). Scoring of balls or rollers (irregular). Dust/Contamination Deformed bearing ring (partial interference clearance).
Hum
Disappears when power supply is switched off.
Chatter
Noticeable at low speeds. Continuous at high speeds.
Clang/Clatter
Metallic, loud bumping sound. Thin hin sect ection ion larg large e bear bearin ing g (TT (TTB) at low low speed peeds. s.
Bearing ring deformed. Grat Gratin ing g of of key.
Screech/Howl
Occurs mainly on cylindrical roller bearings. Sound changes with speed. Loud metallic sound that disappears temporarily when grease is added.
Large radial clearance. Poor lubrication/grease consistancy.
Squeak
Metal-to metal spalling sound. High pitch
Spalling of roller and rib of roller bearing. Small clearance Poor lubrication
Squeal
Generated irregularly due to grating.
Slip on fitting surfaces. Grating on mounting seat, of key, etc.
Faint tinkle
Irregular (not changing with speed). Primarily on small bearings.
Rustle
Sound quality remains the same even if speed changes (Dirt). Sound quality changes with speed (Scoring).
Dirt Raceway, ball, or roller surfaces are rough.
Rustle
Generated intermittently at regular intervals.
Chafing at the labyrinth. Contact of cage and seal.
Rustle patter
Regular and continuous at high speed.
Gener ated by retainer. Normal if sound is clear. Grease is inadequate if sound is generated at low temperatures (Use soft grease). Wear of cage pockets. Insufficient lubricant. Low bearing load.
Growl
Continuous at high speeds.
Quiet Fi Fizzing/Popping
Generated irirregularly o on ns sm mall be bearings.
Large Sound Pressure
Large Sound Pressure
Electromagnetic sound of motor. Bumping in cage pockets (insufficient lubr icant)( Eliminated by clearance reduction or pre-loading. Rollers bumping into each other on full-roller bearing.
Dust in bearing.
Scor ing on raceway, balls, or rollers. Bursting s so ound of of bu bubbles in gr grease. Rough raceway, roller, or ball surfaces. Raceway, rollers, or balls are deformed by wear. Large clearance due to wear.
3.3 Vibration of Bearing
(2) Oil lubrication
Damage to the bearing can be detected early by measuring the vi-
Oil lubrication is generally suitable for high speed or high tempera-
bration of the machine. The degree of damage is inferred from quanti-
ture operations. It is also suitable for carrying heat away from the bear-
tative analysis of the amplitude and frequency of the vibration. How-
ing.
ever, values measured differ depending on the measuring point and the operating condition of the bearing. It is desirable to accumu-late accumu-late measurement data and establish evaluation criteria criter ia for each machine.
Oil viscosities required for the operating temperatures of bearings are given in Table 3.4. Carefully study the viscosity, viscosity index, oxidation resistance, corrosion resistance, foaming resistance, etc. to select an oil. Table 3.5 gives a guide for selecting viscosity. Fig. 3.1 shows the variation of viscosity with temperature for several
3.4 Lubricant Selection
lubrication oils. Use Table 3.5 to select an oil with an adequate adequa te viscos-
The purpose of lubrication the bearing is to cover the rolling contact
ity for the operating temperature of the bearing.
surfaces and sliding contact surfaces with a thin oil film to avoid direct metal-to-metal contact. Effective Effective lubrication of the rolling-element bear-
Table Table 3.4 Viscosities Required for Operating Temperature
ing has the following effects.
of Bearings
(1) Reduces friction friction and abrasion
Kinematic viscosity mm2/s
(2) Transports heat generated by friction (3) Prolongation of service life
Bear ing Type
(4) Prevents rust (corrosion) (5) Keeps foreign objects (or contamination) away from rolling elements and raceways For these purposes, a lubricant should be selected by referring to
Bal Ball, cyli cylind ndri rica call rol roller ler and needl eedle e roll rolle er bea bearing rings s
13
Self-aligning rro oller be bearings, ta tapered rro oller bearings and thrust needle roller bearings
20
Self-aligning thrust roller bearings
30
the following criteria:
(1) Grease lubrication Grease is generally used for lubricating rolling-element bearings bea rings because it is easy to handle and simplifies the sealing system. Carefully examine the type and properties of the base oil, thickener and additives of the grease, and select a grease appropriate for the operating condition of the bearing. The general relation between consistency of grease and the application of the bearing is given in Table 3.3. The types and properties of greases are given in the bearing section of the NTN general catalog.
3.5 Relubriation In grease lubrication, the lubricating characteristic of grease deteriorates with operating hours, thus requiring relubrication of the bearing at appropriate intervals. Relubrication intervals of grease depend on the type, dimensions, and speed of the bearing, and the type of grease. A line diagram serving as a rough guide of grease relubrication interi ntervals, is given in the bearing section of the NTN general catalog. For oil lubrication, oil changing intervals depend on the operating condition of the machine and the type of lubrication system (a rough guide to oil changing intervals and for oil analysis intervals is given in
Table 3.3 Consistenc y of Grease
Tables 3.6 and 3.7).
NLGL consistency No.
JIS(ASTM) consistency after 60 workings
0
355-385
Centralized lubrication
1
310-340
Centralized lubrication
2
265-295
General, prelubricated
Application
bearing 3
220-250
General, high temperature
4
175-205
Special applications
3000 2000 1000
1: 2: 3: 4: 5: 6:
500 300 200
s /100 2
ISO ISO ISO ISO ISO ISO
VG VG VG VG VG VG
320 150 68 46 32 22
7: ISO VG 15
m50 m30 y 20 t i 15 s o 10 c s 8 i V 6
1 2 3 4 5
5
6
4
7
3 -30
-20
-10
0
10
20
30
40
50
60
70
80
90 10 100 110 120 130 140 15 150 16 160
Temperature C °
Fig. 3.1 Lubrication oil viscosity-temperature viscosity-temperature line diagram
Table Table 3.5 Selection Guide For Lubrication Oil Viscosity Bearing operating
ISO viscosity grade of oil (VG)
temperature
dn value
°C
x10
-30~0
Heavy or impact
4
Normal load
Applicable bearing types
load
Up to allowable speed
22
32
46
All types
~ 1.5
46
68
100
All types
1.5~8
32
46
68
All types
8~15
22
32
32
Except for thrust ball bearings
0~60
15~50
10
22
32
Single row radial ball bearings Cylindrical roller bearings
~1.5
150
220
All types
1.5~8
100
150
All types
8~15
68
15~50
32
60~100
100
150
Except for thrust ball bearings
68
Single row radial ball bearings Cylindrical roller bearings
100~150
Up to allowable speed
0~60
Up to allowable speed
60~100
Up to allowable speed
320 46
All types 68
150
Self-aligning roller bearings
Remarks 1. The table above is applicable to oil bath lubrication and recirculation lubrication. 2. Consult NTN if your operating condition is not shown in the table.
Table Table 3.6 Lubrication Oil Properties and Serviceable Serviceable Limits Serviceable limit Property Viscosity Deterioration mm2/s
Circulating oil Less than 10%
Gear oil 25% max., 10 to 15% is preferable
Remarks Caused by oxidation or mixing with different type of oil.
Water content in volume %
0.2 max.
0.2 max.
May be reusable after water removal
Insoluable matter Normal
0.2 max.
1.0 max.
Additive carbon particles
in weight
Pentane % Benzene %
Sedimentation value ml/10ml
Dust 0.9 max.
0.5 max.
0.1 max.
Contaminants such as water and dust, or worn metal particles.
Total acid value KOHmg/g
2 to 3 times that of new oil
Adopt higher value according to additives
Ash %
—
0.2 max.
Iron content in ash %
—
0.1 max.
Table Table 3.7 Frequency of Lubricating Oil Analysis Analysis
The bearing is generally usable up to the end of the rolling fatigue life
Lubrication
Inspection interval
system
Normal operating Severe operating conditions
conditions
Disk lubrication method
One year
6 months
Oil bath or splash
6 months
3 months
9 months
1 to 3 months
lubrication Circulating lubrication
if handled properly. If it fails earlier, it may be due to some fault in the selection, handling, lubrication, and/or mounting of the bearing. It is sometimes difficult to determine the real cause of bearing failure because many interrelated factors factors are possible. It is, however, however, possible to prevent the recurrence of similar problems probl ems by considering possible causes according to the situation and condition of the machine on which the bearings failed. Also, installation location, operating condi-
Severe operating conditions means: (1) Severe water condensation or ingress (2) Excessive ingress of dust, gas, etc. etc. (3) Operating temperature exceeding 120°C
tions, and surrounding structure of the bearings should be taken into consideration. Bearing failures are classified and illustrated in photos in this section. Use the section as a guide for troubleshooting. Figures 5.1 to 5.7 show the names of bearing parts referred to in i n the descriptions of the failure cases.
Bearings after operation and those removed during periodic inspection should be carefully checked visually for systems on each component to evaluate shether the bearings’ operating conditions are satisfactory. If any abnormality is detected, find the cause and apply a remedy by checking the abnormality against the failure cases given in Section 5. “Bearing Failures and Solutions.”
5.1 Flaking Condition
Cause
Solution
Raceway surf urface ace is flak laked
Rollin ling fatigue. Flaking may be caused early
(1) Find ind the cause of the heavy loa load.
Surfa Surface ce afte afterr flak flaking ing is very very rough rough..
by over over-lo -load ad,, exce excess ssiv ive e loa load d due due to impr improp oper er
(2) Exam Examin ine e oper operat atin ing g con condi diti tion ons s and and adop adoptt
han handling, ng, poor shaft or hous ousing ing accura uracy,
bear earings with large rger capa apacity ity as
installation er error, in ingress of of fo foreign ob objects,
necessary. ry.
rusting, etc.
(3) Increase viscosity of oil and improve lubrication system to form an adequate lubricating oil film. (4) Eliminate Eliminate installation installation errors. errors.
Photo A-1 • Deep g groov roove e ball bearing. bearing. • Inner ring, ring, outer outer ring, and balls balls are flaked. flaked. • The cause cause is excess excessive ive load. load.
Photo A-2 • Outer Outer ring of angular angular contact contact ball bearing bearing • Flaking of raceway surface surface spacing equal to distances distances between balls. • The cause cause is improper improper handli handling. ng.
Photo A-3 • Inner ring ring raceway raceway of a deep groove groove ball bearing bearing
Photo A-4 • Outer ring raceway raceway of an angular contact contact ball bearing bearing
Photo A-5 • Inner ring ring of deep groove groove ball bearing bearing • Flaking on one one side of the raceway surface • The cause cause is an excessiv excessive e axial load. load.
Photo A-6 * Inner ring ring of spherical spherical roller bearing. bearing. * Flaking only on one side of the raceway raceway surface. * The cause cause is an excessive excessive axial axial load.
Photo A-7 • Tapered apered roller roller bearing • Flaking on 1/4 circumference circumference of inner inner ring raceway with with outer ring and rollers discolored light brown. • The cause cause is excessive excessive pre-load. pre-load.
Photo A-8 • Outer ring of double row angular angular contact ball bearing. • Flaking on 1/4 circumference circumference of outer ring raceway raceway. • The cause cause is poor installat installation. ion.
Photo A-9 • Thrust Thrust ball ball bearin bearing g • Flaking on inner inner ring raceway raceway (bearing ring fastened to shaft) and balls.
Photo A-10 • Outer ring raceway raceway of double double row tapered tapered roller bearing (RCT bearing) • Flaking originated from electric pitting on the the raceway
5.2 Peeling Condition
Cause
Solution
Peel Peelin ing g is a clus luster ter of very very small mall
Lik Likely ely to occu occurr in roll roller er bear bearin ings gs.. Tends ends to
(1) (1) Cont Contro roll of surf surfac ace e roug roughn hnes ess s and and dust dust
spalls (size about 10µm).
occur if surface of oppisite part is rough or
(2) Selection of appropriate lubricant
Peeling can also include very small
lubrication characteristics are poor.
(3) Proper break-in
crac crack ks w whi hic ch dev devel elop op into into spal spalls ls..
Peel Peelin ing g may may dev develop elop into into flak laking. ing.
Photo B-1 • Rollers Rollers of spherical spherical roller bearing bearing • Peeling Peeling on rolling contact contact surface surfaces s • The cause cause is poor lubricat lubrication. ion.
Photo B-2 • Tapered apered roller bearing bearing • Development of peelling to flaking flaking on inner ring and rollers • The cause cause is poor poor lubrication lubrication..
5.3 Spalling Condition
Cause
Solution
Score accompanying seizing.
Poor mounting and removing practice. Oil Oil
(1) (1) Improve ovement in mounti nting and and removi oving
Mounting score in axial direction.
film discontinuation on the contact surface
Scor Scores es on roll roller er end end fac face e and and guid guide e
due due to to exc exces essi sive ve radi radial al load load,, for forei eign gn obje object ct
(2) (2) Impr Improv ovem emen entt in in ope opera rati tion on cond condit itio ions ns
ribrib-c cyclo ycloid idal al scor scores es.. Scra Scratc tche hes s in in
trap trappi ping ng,, or exce exces ssive sive prepre-lo load ad.. Slip Slippa page ge or
(3) (3) Corr Correc ecttion ion of of prepre-lo load ad
spinning di direction on on ra raceway
poor lu lubrication of of ro rolling el elements.
(4) Selection of of ad adequate lu lubricant an and
surface and rolling contact surfaces.
procedures.
lubrication system (5) Improveme Improvement nt of sealing efficiency efficiency
Photo C-1 • Inner ring of cylindrical cylindrical roller roller bearing • Spalli Spalling ng on on rib • The cause cause is excessive excessive load. load.
Photo C-2 • Inner Inner ring of cylindrical cylindrical roller roller bearing • Spallling on raceway raceway surface surface and cone back face rib • The cause cause is poor lubricat lubrication. ion.
Photo C-3 • Rollers Rollers of tapered tapered roller roller bearing bearing • Cycloidal spallling spallling on the end faces (Scuffing) (Scuffing) • The cause cause is poor lubricati lubrication. on.
Photo C-4 • Roller Roller of cyllindrical cyllindrical roller roller bearing bearing • Score in axial direction direction on rolling contact contact surface caused caused during mounting.
5.4 Smearing Condition
Cause
Solution
Surf Surfac ace e is roug roughe hene ned d and and tiny iny
Roll Rollin ing g elem elemen entts slip lip in roll rollin ing g motio otion n and and
(1) (1) Sele Select ct opti optimu mum m lubr lubric ican antt and and lubr lubric icat atio ion n
particles adhere.
characteristics of lubricant are too poor to
system capable of forming sound oil film.
prevent slippage.
(2) Use a lubricant including extreme pressure additive. (3) Take precauti precautions ons such as as a small radial radial clearance and pre-load to prevent slippage.
Photo D-1 • Inner ring ring of cylindrical cylindrical roller roller bearing bearing • Smearing Smearing on racew raceway ay suface suface • The cause is slippage of rollers due to to foreign objects objects trapped within.
Photo D-2 • Roller of same bearing as that of the inner ring ring shown in Photo D-1 • Smearing Smearing on rolling rolling contact contact surface surface • The cause is slippage of rollers due due to foreign objects trapped within.
Photo D-3 • Rollers of spherical thrust roller bearings bearings • Smearing at middle of rolling contact contact surfaces • The cause is slippage of rollers due to to foreign objects objects
Photo D-4 • Inner ring of double row tapered roller bearing (RCT bearing) • Smearing Smearing on raceway raceway surface surface
5.4 Stepped wear Condition
Cause
Solution
Surface is worn and dimensions are
Ingress of solid foreign objects.
(1) Selection of optimum lubricant and
reduced compared with other
Dirt and other foreign objects in lubricant.
portions. Su Surface mostly roughened
Poor lubrication.
(2) Improvement in sealing efficiency
and scored.
Skewing of rollers.
(3) Filtration of lubricating oil
lubrication system
(4) Eliminat Elimination ion of misalign misalignmen mentt
Photo E-1 • Outer ring ring of cylindrical cylindrical roller roller bearing bearing • Stepped Stepped wear on raceway raceway surface surface • The cause cause is poor lubricati lubrication. on.
Photo E-2 • Inner ring of cylindrical roller bearing (inner ring of which is shown in Photo E-1) • Stepped wear on full circumference of raceway raceway • The cause cause is poor poor lubricatio lubrication. n.
Photo E-3 • Outer ring of double row angular angular contact ball bearing (hub (hub unit bearing) • Wear on one side side of the racew raceway ay
Photo E-4 • Retainer Retainer of cylindrical cylindrical roller roller bearing bearing • Wear of pockets of machined machined high tensile brass brass casting retainer (G1)
5.6 Speckles and Discoloration Discolorat ion Condition Speckles
Cause
Solution
Ingress of foreign objects
Speckles
Raceway surface is matted and
Poor lubrication
(1) Improvement in sealing efficiency
speckled.
Temper color by overheating (2)
Filtration of oil
Depos eposit itio ion n of of det deter erio iora rate ted d oil oil on surf surfac ace e
(3) (3) Impr Improv ovem emen entt in in lub lubri rica cati tion on syst system em
Spec Speckl kles es are are clu clus sters ters of tiny tiny dent dents. s. Discoloration
Discoloration
The surface color has changed.
(1) Oil deposition is removable by wiping with an organic solvent (oxalic acid). (2) If roughne roughness ss is not remo removab vable le by polishing with sandpaper, it is rust or corrosion. If completely removable, removable, it is temper color due to overheating.
Photo F-1 • Inner ring of double row tapered roller bearing (RCT bearing) • Raceway Raceway surface surface is speckl speckled ed • The cause cause is electri electric c pitting. pitting.
Photo F-2 Ball of deep groove ball bearing • Speckl Speckled ed all all over over • The cause cause is foreign objects objects and poor lubrication. lubrication.
Photo F-3 • Outer ring ring of spherical spherical roller roller bearing bearing • Partial oil deposition on raceway raceway surface surface
Photo F-4 • Spherical Spherical roller bearing bearing • Discoloration of inner and outer ring raceway raceway surfaces • The cause cause is deterioration deterioration of lubrican lubricant. t.
5.7 Indentations Condition Hollows in raceway surface
Cause
Solution
Ingress of solid foreign objects
(1) Keeping out foreign objects
produced by solid foreign
Trapping of flaked particles
(2) Check involved bearing and other
objects trapped or impacts
Impacts due to careless handling
(False brinelling)
bearings for flaking if dents are produced by metal particles. (3) Filtra Filtration tion of oil oil (4) Improvement Improvement in handling handling and mounting mounting practices
Photo G-1 • Inner ring (cut off piece) of self-aligning roller roller bearing • Dent Dents s on one side side of the raceway raceway • The cause is trapping of of solid foreign foreign objects.
Photo G-2 • Rollers Rollers of spherical spherical roller roller bearing bearing • Dents on on rolling contac contactt surfaces surfaces • The cause is trapping of solid foreign objects. objects.
Photo G-3 • Rollers Rollers of tapered tapered roller roller bearings bearings • Dents all over over rolling contact surfaces. (Temper (Temper color at two ends.)
Photo G-4 • Inner ring ring of tapered tapered roller roller bearing bearing • Dents on raceway raceway surfac surface e • The cause cause is trapping trapping of foreign objects. objects.
5.8 Chipping Condition
Cause
Solution
Part artial ial chipp ipping of inner ring ing, out outer
Trapping ing of lar large solid foreign objec jects
ring, or rolling elements.
Impact or excessive load Poor handling
(1) Trouble shoot ooting ing an and im improveme ements of of impacts and excessive load (2) Improvement in handling (3) Imp Improv roveme ement nt in sealing sealing charact characteris eristic tics s
Photo H-1 • Cylindric Cylindrical al roller roller bearing bearing • Chipping of guide ribs of inner and outer outer rings • The cause cause is excessive impact load. load.
Photo H-2 • Inner ring ring of spherical spherical roller bearing bearing • Rib chippe chipped d • The cause cause is excessive impact load. load.
Photo H-3 • Inner Inner ring of tapered tapered roller roller bearing bearing • Chipping Chipping of cone back back face face rib • The cause cause is impact impact due to poor poor mounting. mounting.
Photo H-4 • Inner ring ring of double row tapered tapered roller bearing bearing • Chipping Chipping of side side face face • The cause cause is impact due to improper improper handling. handling.
5.9 Cracking Condition
Cause
Splits, and cracks in bearing rings
Excessive load
and rolling elements.
Excessive impacts
Solution (1) Examination and improvement of cause of very large load
Over Overhe heat atin ing g by cree creepi ping ng and and rapi rapid d cool coolin ing g
(2) (2) Prev Preven enti tion on of cree creep p
Ver y loose fit
(3) Correction of fit
Large flaking
Photo I-1 • Inner ring ring of spherical spherical roller bearing bearing • Split of raceway raceway surface surface in the axial direction • The cause is excessive excessive interference interference fit.
Photo I-3 • Outer ring of four-row cylindrical roller roller bearing • Split of raceway raceway surface surface in the circumferential circumferential direction, originated from large flaking.
Photo I-2 • Fracture Fracture of inner inner ring shown shown in Photo I-1 • Originating point is ibserved at the middle middle of the left raceway surface.
Photo I-4 • Outer ring of angular contact ball bearing • Split of raceway raceway surface surface in the circumferential direction • The cause is slipping of balls due to poor lubrication. lubrication.
5.10 Rust and and Corrosion Condition
Cause
Solution
Rust Rustin ing g or corr corros osio ion n of bear bearin ing g ring ring
Ingr Ingres ess s of wate waterr or corr corros osiv ive e mate materi rial al (suc (such h
(1) (1) Impr Improv ovem emen entt in seal sealin ing g eff effect ect
and rollling element surfaces
as acid)
(2) Pe P eriodic inspection of lubricating oil
Some Someti time mes s rus ruste ted d at at spa spaci cing ng equa equall
Cond Conden ensa sati tion on of mois moistu ture re cont contai aine ned d in in the the air air.
(3) (3) Care Carefu full han handl dlin ing g of of bea beari ring ng
to the the dis dista tanc nces es betw betwee een n the the rol rolli ling ng
Poor Poor pack packag agin ing g and and stor storin ing g con condi diti tion ons, s, and and
(4) (4) Meas Measur ures es for for pre preve vent ntin ing g rus rusti ting ng when when
elements
handling with bare hands.
not operating for a long period of time.
Photo J-1 • Inner Inner ring of tapered tapered roller roller bearing bearing • Rusting on raceway surface surface spacing equivalent to the distance between rollers. rollers. The cause is water in lubricant.
Photo J-2 • Outer Outer ring of tapered tapered roller roller bearing bearing • Rusting on raceway surface surface spacing equivalent to the distances between between rollers. The cause is water in lubricant. Some points are corroded.
Photo J-3 • Roller Roller of spherical spherical roller roller bearing bearing • Rust as well as corrosion corrosion on rolling contact surface surface • Ingres Ingress s of wate waterr
Photo J-4 • Inner ring (split type) type) of self-aligning roller roller bearing • Rust and corrosion of the raceway raceway surface surface • The cause cause is ingress ingress of water water..
5.11 Seizing Condition
Cause
Solution
Bear Bearin ing g gen gener erat ates es heat heat and and is is sei seize zed d
Diss Dissip ipat atio ion n of of hea heatt gen gener erat ated ed by bear bearin ing g is is
(1) (1) Impr Improv ove e dis dissi sipa pati tion on of heat heat from from bear bearin ing g
up by heat disabling spinning.
not enough. Poor lubrication or lubricant
(2) Selection of suitable lubricant and
Disc iscolorat ration ion, so softening, an and we weldi lding
improper. Clear earance ex excessively small.
determination of of op optimum lu lubric ricant
of raceway surface, rolling contact
Excessive load (or pre-load).
feeding rate.
surfaces, and rib surface.
Roller skewing and installation error.
(3) Prevention of misalignment (4) Improvement Improvement in clearanc clearance e and pre-load pre-load (5) Improvement Improvement in operati operating ng conditio conditions ns
Photo K-1 • Inner ring ring of double row tapered tapered roller bearing bearing • Seizing-up discolors discolors and softens inner ring producing stepped wear at spacing equal to distances between the rollers. • The cause cause is poor poor lubricati lubrication. on.
Photo K-2 • Rollers Rollers of double row tapered tapered roller roller bearing bearing • Rollers of same bearing as that of the inner ring shown shown in Photo K-1. Discoloration, spalling, spalling, and adhesion due to seizing up on rolling contact surfaces and end faces of rollers.
Photo K-3 • Outer ring ring of spherical spherical roller bearing bearing • Stepped wear due to seizing seizing up of raceway surface. surface. • The cause cause is poor lubricati lubrication. on.
Photo K-4 • Inner ring ring of tapered tapered roller roller bearing bearing • Large end of the raceway surface and cone back face rib surface are seized up.
5.12 Fretting and Fretting Corrosion Condition
Cause
Solution
Frett rettin ing g surf surfac aces es wear wear prod produc ucin ing g red red
If a vibr vibrat atin ing g load load work works s on cont contac actting ing
(1) (1) Inne Innerr ring ring and and oute outerr ring ring shou should ld be
rust colored particles that form
elements resulting in small amplitude
packaged separately for transportation. If
hollows.
oscillation, lubricant is driven out from contact,
not separable, bearings should be
On the raceway surface, dents called
and par ts are wor n remarkably.
preloaded.
fals false e brin brinel elli ling ng are are form formed ed at spac spacin ing g
Osci Oscill llat atio ion n angl angle e of the the bear bearin ing g is smal small. l.
equal to distances corresponding to
Poor lubrication (no lubrication)
the rolling elements.
Fluctuating load
(3) Change lubricant
Vibration during tr ansportation
(4) Fix shaft and housing
Vibr Vibrat atio ion, n, shaf shaftt def defle lect ctio ion, n, inst instal alla lati tion on erro errorr,
(5) (5) Impr Improv ove e fit fit
(2) (2) Use Use oil oil or high high cons consis iste tenc ncy y grea grease se when when bearings are used for oscillation motion.
loose fit.
Photo L-1 • Inner ring ring of cylindrical cylindrical roller roller bearing. bearing. • Corrugated fretting along along full circumference circumference of raceway raceway.. • The cause cause is vibrati vibration. on.
Photo L-2 • Inner Inner ring of deep groove groove ball bearing bearing.. • Fretting along full circumference circumference of raceway raceway.. • The cause cause is is vibratio vibration. n.
Photo L-3 • Outer ring ring of cylindrica cylindricall roller bearing bearing • Fretting Fretting rust on outside outside diameter surface surface
Photo L-4 • Outer Outer ring of tapered tapered roller roller bearing bearing • Fretting rust on the outside diameter surface surface
5.13 Electrical Pitting Condition
Cause
Solution
Surf Surfac ace e is is spe speck ckled led visu visuall ally y and and the the
Elec Electr tric ic curr current ent pass passes es thro through ugh bear bearin ing, g, and and
Avoid void flow flow of elect electric ric curr current ent by avert avertin ing g
spec speckl kles es are are clu clust ster ers s of tiny iny pits pits
spar sparks ks are are gen gener erat ated ed to fuse fuse the the rac racew eway ay
curre urrent nt with ith a slip lip rin ring g or or ins insul ulat atio ion n bear bearin ing. g.
when hen vie view wed thro throug ugh h a mic micro rosc scop ope. e.
surf surfac ace. e.
Further development leads to a corrugated surface.
Photo M-1 • Inner ring ring of cylindrical cylindrical roller roller bearing bearing • Raceway surface surface is corrugated corrugated by electric pitting pitting
Photo M-2 • Rollers Rollers of tapered tapered roller roller bearings bearings • Electric pitting pitting at middle of rolling contact contact surfaces surfaces
Photo M-3 • Magnified (x400) pitting of roller shown in Photo M-2 • Nital etchant develops a white layer on the cross cross section
Explanation of magnified photo M-3
5.14 Rolling Path Skewing Condition
Cause
Solution
Roll Rollin ing g elem elemen entt cont contac actt path path on
Defo Deform rmat atio ion n or tilt tilt of bear bearin ing g ring ring due due to poor poor
raceway surface strays or skews.
accuracy of shaft or housing
(1) (1) Impr Improv ovem emen entt in mach machin inin ing g accu accura racy cy of shaft and housing
Poor rigidity of shaft or housing
(2) Improvement in rigidity of shaft and
Deflection of of s sh haft du due to to ex excessive c cllearance
housing (3) Employment Employment of adequate adequate clearance clearance
Photo N-1 • Spherical Spherical roller roller bearing bearing • Contacts on inner ring, outer ring, and rollers are not not even. • The cause cause is is poor mounti mounting. ng.
Photo N-3 • Rollers of tapered roller bearing of which which outer ring is shown in Photo N-2. • Contact marks marks on rolling rolling contact surfaces are not even.
Photo N-2 • Outer Outer ring of tapered tapered roller roller bearings bearings • Cont Contact act path on raceway raceway surface surface strays. strays. • The cause cause is poor mounti mounting. ng.
5.15 Damage to Retainers Retainers Condition
Cause
Solution
Breaking of retainer
Excessive moment load
(1) Im I mprovement in load conditions
• Wear ear of of poc pock kets ets or or gui guide de
High High speed peed spinn pinnin ing g or or lar large ge fluc flucttuat uation ion of spee speed d
(2) (2) Impro mprove veme ment nt in lubr lubric icat atio ion n sy system stem and and
• Loosening or breaking of rivet
Poor lubrication
lubricant
Tr apping of foreign objects
(3) Selection of optimum retainer
Heavy vibration
(4) IIm mprovement in handling
Poor mounting (cocked bearing)
(5) Study in rigidity of shaft and housing
Excessive heat (plastic retainer in particular)
Photo O-1 • Reta Retainer iner of angular angular contact contact ball bearing bearing • Breakage of machined high tension brass retainer L1 • The cause cause is poor lubricati lubrication. on.
Photo O-2 • Retainer Retainer of spherical spherical roller roller bearing bearing • Breakage of partitions partitions between between pockets of pressed steel retainer
Photo O-3 • Reta Retainer iner of tapered tapered roller bearing bearing • Breakage of pockets of pressed steel retainer
Photo O-4 • Reta Retainer iner of cylindrical cylindrical roller roller bearing • Breakage of partitions between between pockets of machined high tension brass casting retainer L1.
5.16 Creeping Condition
Cause
Solution
Fitting surf urface aces are glazed or
Fitting of inner ring is loose on inner ring drive
(1) Improv rovement in fit
matt matted ed,, and and some someti time mes s spa spall lled ed as
bear bearin ing, g, and and tha thatt of of the the oute outerr rin ring g is is loo loose se on
(2) (2) Impr Improv ovem emen entt in in mac machi hini ning ng accu accura racy cy of
well.
outer ring drive bearing. If the housing is
shaft and housing
made of a light alloy such as aluminum, fit may become loose due to the difference of thermal expansion.
Photo P-1 • Inner Inner ring of deep deep groove groove ball bearing bearing • Bore wall glaze glazed d by creep creep
Photo P-2 • Inner ring ring of tapered tapered roller roller bearing bearing • Spalling due to to creep at the middle of bore wall
Photo P-3 • Inner Inner ring of thrust thrust ball ball bearing bearing • Spalling and friction friction cracking cracking due to creep on bore wall.
Photo P-4 • Inner ring ring of tapered tapered roller roller bearing bearing • Spalling and friction friction cracking cracking on width surface due to creep Crack develeped into a split reaching bore wall.
For New Technology Network
®
Care and Maintenance of Bearings
Sales Operations
Production
NTN BEARING CORPORATION OF AMERICA Head Office/1600 East Bishop Court
AMERICAN NTN BEARING MANUFACTURING C ORPORATION
Mount Prospect, Illinois 60056 Phone: (800) 468-6528, (847) 298-7500 Fax: (847) 699-9744
Elgin, Illinois General Product: Radial Ball Bearings, Taper Roller Bearings, Hub and Car tridge Wheel Bearing Units
EASTERN REGION SALES 650 Pennsylvania Avenue
Exton, Pennsylvania 19341 Phone: (800) 394-4686, (610) 458-1100 Fax: (610) 458-1063
SOUTHEASTERN REGION SALES 5475 Peachtree Industrial Boulevard Norcross, Georgia 30 30071 Phone: (800) 241-0568, (770)448-4710 Fax: (770) (770 ) 448-6969
AMERICAN NTN BEARING MANUFACTURING C ORPORATION Schiller Par k, Illinois General Product: Radial Ball Bearings
NTN•BOWER CORPORATION Macomb, Illinois General Product: Cylindrical Roller Bear ings, Large Size Taper Roller Bearings
NTN-BOWER CORPORATION GREAT LAKES REGION SALES 1600 East Bishop Court Mount Prospect, Illinois 60056 Phone: (800) 252-8123, 252-8123, (847) 699-4060 Fax: (847) 294-1364
CENTRAL REGION SALES 111 West Washington Street, Suite 310 East Peoria, Illinois 61611 Phone: (800) 545-0434, (309) 699-8600 Fax: (309) 699-8670
WESTERN REGION SALES 2200 Century Circle Irving, Texas 75062 Phone: (800) 441-0825, 441-0825, (214) (214) 721-1808 Fax: (214) 438-4101
Hamilton, Alabama General Product: Taper Roller Bearings
NTN DRIVESHAFT, INC. Columbus, Indiana Genera Generall Produc Product: t: CV CVJ J and Forg Forging ing Facility for Bearing Rings
NTN BEARING CORPORATION OF CANADA, LTD. Ontario, Canada General Product: Radial Ball Bearings
PLANTS (OVERSEAS): Japan (Kuwana, Iwata, Takarazuka, Okayama, Nagano), Germany, Taiwan
AUTOMOTIVE OEM SALES 28333 Telegraph Road, Suite 220 Southfield, Michigan 48034-6286 Phone: (800) 929-3892, (810) 262-1450 Fax: (810) 354-2074
CAT. NO. 3017/E 03/96 Printed in U.S.A.
