Transcript Document

A PRESENTATION BY
WG CDR ARVIND KUMAR
BEARINGS, FAILURES
CAUSES & REMEDIES
 CONCEPT
 CONSTRUCTION
 BEARING MATERIALS
 TYPES OF LOADS & BEARINGS
 BEARING CLEARANCES
 WHY BEARING FAILS!
 FAILURES, CAUSES & REMEDIES :FEW EXAMPLES
 PATH PATTERN INTERPRETATION
 OTHER IMPORTANT POINTS
 TV-2 STATISTICS
 PRACTICAL DEMONSTRATION
CONCEPT OF ROLLING
BEARING
• Things roll better than they slide.
Hence the invention of WHEEL.
• Rolling friction is far lesser (>100
times less) than sliding friction.
• Microscopic contacts get peeled off
and not sheared off in rolling.
ROLLING BEARING CONSTRUCTION
Outer ring raceway
Cage/
Retainer
Shoulder
Inner ring / race
Inner ring raceway
Rolling element
Shoulder
Outer ring / race
Side faces
7
BEARING DIA
Outside
Diameter
Bore
7
BEARING CONSTRUCTION-2
Seal
Rolling Elements
Outer Ring
Inner Ring
Cage
Seal
BEARING CONSTRUCTION-3
Outer Ring
Cage
Inner Ring
Inner Ring Raceway
Guide Ring
Rolling
Element
Side faces
W33 Lubrication
Groove and
Hole
VARIOUS ROLLING ELEMENTS
Ball
Spherical roller
(symmetrical)
Cylindrical roller
Spherical roller
(asymmetrical)
Taper roller
Needle roller
POINT / LINE CONTACT
PROPERTIES : BEARING
MATERIALS
•
•
High wear resistance
High rolling fatigue strength
• Non-metallic inclusions like O, S etc. increase fatigue
cracking
•
•
•
•
•
•
•
High dimensional stability
Heat treatable to high hardness in depth
High corrosion resistance
High wettability with oil
Low coefficient of semi-dry friction
Good heat conductivity
Good antiseize properties
MATERIALS-SKF BEARINGS
BEARING RINGS AND ROLLING ELEMENTS
THROUGH-HARDENING STEELS
CASE-HARDENING STEELS
CARBON CHROMIUM STEEL
CONTAINING APPROXIMATELY
1 % CARBON AND
1,5 % CHROMIUM
CHROMIUM-NICKEL ALLOYED STEEL
AND MANGANESE-CHROMIUM
ALLOYED STEEL CONTAINING
APPROXIMATELY 0,15 % CARBON
SKF BEARING MATERIALS -2
•
~SAE 52100
•
C-Cr Bearing steel ( ISO 683 -17:1999)
•
Ceramics like Si3N4 for ultra high
speed applications
•
Stainless steels like X65Cr14
(ISO 683-17:1999)
BEARING MATERIALS -3
•
•
•
Highly alloyed steels like 80MoCrV42temperature > 250°C (SKF)
16
for
Case Hardening Steel for shock loads
DMRL analysis for Russian bearing (6-7000108B,
Central Drive B.B on Ist support assy of TV-2 engine of Mi-8
heptr)
 C~1.0%
 Cr~1.8%
 Si~0.23%
 Mn~0.33%
 steel nearly equivalent to AISI-52100
• Original Russian material is Sh Kh 15
SPECIAL FEATURES
•
Hard Surfaces


HRC 58-65 for C-Cr bearing steel (SKF)
DMRL analysis of Russian Bearing
- HV/5Kg : 930 (HRC : 68)
•
•
•
Perfectly round and incredibly smooth
Very high surface finish : CLA ~ 0.5 microns
Addition of Si to improve heat resistance
dimensional stability) at 150-200°C

Radial loads

Axial Loads

Combined loads
AXIAL / THRUST LOADS
Thrust load
Bearings
BAR STOOL BEARINGS
(Man’s wt. causes thrust load)
RADIAL LOADS
Motor
Tension
Radial load
Motors & Pulley Shaft Support Bearings
COMBINED LOADS
Car Wheel Bearing




CYLINDRICAL ROLLER BRG : Radial load
only (Heavy)
BALL BRG : Both axial & radial
TAPERED ROLLER BRG : Radial load &
Axial load in
one direction
also
Axial load is also called as Thrust load
RADIAL LOAD
Cylindrical Roller Bearing
Deep groove
B.B
Angular contact
B.B
Self-aligning B.B
Radial load
Axial load
Speed
Accommodates
carrying capacity
carrying capacity
capability
misalignment
Ball Bearings
Radial Load
Axial Load
(one direction)
Tapered Roller Bearing
Radial Load
Thrust
Thrust
Double Tapered Roller Bearing
LOAD ZONE
360°
~150°
BEARING CLEARANCES
Radial
clearance / play
Axial
clearance / play
CLEARANCE DESIGNATIONS
•C1 - less than C2 clearance
•C2 - less than normal clearance
•CN - normal clearance
•C3 - greater than normal clearance
•C4 - greater than C3 clearance
•C5 - greater than C4 clearance
•Russian System ?
Example:
A 6210 /C3 ball bearing has 18 - 36 µm
(microns) or 0.0007” - 0.0014” radial internal
clearance
AXIAL INTERNAL CLEARANCE
Example:
A 5210 / C3 ball bearing has
33 - 54 µm or 0.0013” – 0.0021”
axial internal clearance
 25-126114P ball bearing used
in TV-3 aeroengine 2nd Support
should have 140-220 µm axial
internal clearance
EFFECT OF TEMPERATURE
ON CLEARANCE
COLD (by 5-10°C)
Reduced
radial
clearance
Compression
Expansion
WARM
EFFECT OF FIT ON
CLEARANCE
• INTERFERENCE FIT between shaft and
bearing (inner race) reduces radial
clearance by approx 80% of the fit.
• Because the inner ring expands and the
outer ring contracts.
EFFECT OF LOOSE FIT
N = 3 000
10 hours/day
30 days = 18 000 min
Sliding motion
=0,013 x π x 3 000 x 18 000 = 2,2 x 106 mm
= 2,2 km (1.4 miles)
creep
LOAD DISTRIBUTION & CLEARANCE
Less Clearance
More Clearance
Pressure between rolling element and races can reach 4 lakhs PSI
EXCESSIVE CLEARANCE
•
•
•
•
•
•
Loading area reduces & stress increases
Bearing rigidity reduces
Alignment of rolling elements decreases
Vibration increases at high speeds
Noise increases
Running and locating accuracy reduces
PRELOAD
• Small amount of loading before running of brg

Causes negative clearance

Elastic deformation & compressive stress at
contact area

Bearing rigidity improves

Vibration at high speeds reduces

Noise reduces

Alignment of rolling elements improves
(Thrust brgs)

Running and locating accuracy improves
EFFECT OF CLEARANCE ON
BEARING LIFE
Life
Preload
Clearance
Excessive preload causes high stress and heat generation
BEARING LIFE
• Repeated compressive stresses (rolling fatigue)
cause flaking of material of raceways and rolling
elements and hence failure.
• Basic Rating Life L10 (90% reliability) of the
bearing is the total number of revolutions in
millions which 90% of the bearings out of the lot
reach before or at which the first signs of flaking
occur under identical operating conditions.
BEARING LIFE-2
• L10 = (C / P)n
C = Design Load {Basic dynamic rating
load (constant radial or axial load when brg is
rotating) in N that will give bearing life of 106
revs in accordance with ISO 281:1990}
P = Actual equivalent dynamic load in N
n = 3 for ball bearings
3.33 for roller bearings
BEARING LIFE-3
• If actual load is half of the rated load, life of a ball
bearing will increase by 8 times. (Min. Load*)
• If actual load increases by 25% above the rated
load, the life of a ball bearing gets nearly halved.
• Actual service life may be reduced even further
below the calculated value because of factors
like contamination, misalignment, improper
installation or lubrication etc.
• Effect of overload is more severe on roller brg.
LIFE ADJUSTMENT FACTOR




Higher the expected reliability, the
lesser is the bearing life.
L5 (95% reliability) = 0.62 L10
L3 (97% reliability) = 0.44 L10
L1 (99% reliability) = 0.21 L10
WHY BEARINGS FAIL!
• Study in Scandinavian countries
indicates :
 - ~1/3 brgs fail because of Poor
Lubrication
 - ~1/6 brgs fail because of
Contamination
 - ~1/3 brgs fail because of Fatigue
 - ~1/6 brgs fail because of Bad
Installation
WHY BEARINGS FAIL!-2
In India, there is likely to be greater percentage of
failures because of :

Contamination
Improper installation and lubrication
Lesser percentage of failures because of :-

Fatigue
FAILURE MODE CLASSIFICATION-1
• As per ISO 15243:2004, there are 15 main
failure modes classified as:
 Fatigue (Repeated compressive stresses)
-Subsurface
-Surface initiated (metal to metal contact)
 Wear
-Abrasive
-Adhesive
FAILURE MODE CLASSIFICATION-2
 Corrosion
- Moisture,
- Fretting
- False Brinelling
 Electrical Erosion
-Excess voltage
- Current leakage
FAILURE MODE CLASSIFICATION-3
• Plastic Deformation
- Overload
- Indentation from debris
- Indentation by handling
• Fracture
- Forced
- Fatigue
- Thermal Cracking
SYMPTOMS OF BEARING FAILURE
- Overheating
- Noise
- Vibration
- Obstruction of movement (RDT reduces)
- Shaft jammed
- Others ?
FAILURES,
CAUSES & REMEDIES
– FEW EXAMPLES
CORROSION
CORROSION
Appearance
Cause
Action
Grey black streaks
across the raceways,
mostly coinciding with
the rolling element
spacing. At a later
stage, pitting of
raceways and other
surfaces of the
bearing.
Presence of water,
corrosive substances
in the bearing over a
long period of time.
Improve sealing. Use
lubricant with better
rust-inhibiting
properties.
WEAR-ABRASIVE PARTICLES
Fig 19 Outer ring of a
spherical roller bearing
with raceways that have
been worn by abrasive
particles. It is easy to
feel where the dividing
lines goes between
worn and unworn
sections.
WEAR-ABRASIVE
PARTICLES
Appearance
Cause
Action
Small indentations
around the raceways
and rolling elements.
Dull, worn surfaces.
Lack of cleaning
before and during
mounting operation.
Do not unpack bearing
until just before it is to
be mounted. Keep
workshop clean and
use clean tools.
Check and possibly
improve sealing.
Always use fresh
clean lubricant. Wipe
the grease nipples.
Filter the oil.
Ineffective seals.
Lubricant
contaminated by worn
particles from brass
cage.
WEAR-INADEQUATE LUBRICATION
Fig 20 Cylindrical roller with mirrorlike surface on account of lubrication
starvation
Fig 21 Outer ring of a spherical roller
bearing that has not been adequately
lubricated. The raceways have a
mirror finish
WEAR-INADEQUATE
LUBRICATION
Appearance
Cause
Action
Worn, frequently
mirror-like surfaces.
At a later stage blue
to brown
discoloration
Lubricant has
gradually been used
up or has lost its
lubricating
properties.
Check that the
lubricant reaches the
bearing. More
frequent lubrication.
WEAR DUE TO VIBRATION
WEAR DUE TO VIBRATION
Appearance
Cause
Action
Depressions in the
raceways. These
depressions are
rectangular in roller
bearing and circular in
ball bearing. The
bottom of these
depressions may be
bright or dull and
oxidized.
The bearing has been
exposed to vibration
while it was
stationary.
Secure the bearing
during transport.
Provide a vibration
damping base.
Where possible use
ball bearing instead of
roller bearing. Employ
oil bath lubrication,
where possible.
INDENTATIONS FOREIGN PARTICLES
Fig 31 Indentations
caused by dust in one
of the raceways of a
roller bearing-50 x
Magnification
INDENTATIONS FOREIGN PARTICLES
Appearance
Cause
Small indentations
Ingress of foreign
distributed around the particles into the
raceways of both rings bearing.
and the rolling
elements.
Action
Cleanliness to be
observed during the
mounting operation.
Uncontaminated
lubricant.
Improved seals.
FRETTING CORROSION
FRETTING CORROSION
Appearance
Cause
Action
Areas of rust on the
outside surface of the
outer ring or in the bore
of the inner ring.
Raceway path pattern
heavily marked at
corresponding positions.
Fit too loose.
Shaft or housing seating
with error of form.
Proper fit and housing.
SMEARING
SMEARING
Appearance
Cause
Action
Scored and discolored
roller ends and flange
faces
Sliding under heavy
axial loading and with
inadequate lubrication.
More suitable
lubricants.
ELECTRIC CURRENT EROSION
ELECTRIC CURRENT EROSION
Appearance
Cause
Dark brown or greyish
Passage of electric
black fluting (corrugation) current.
or crater in raceways and
rollers. Balls have dark
discoloration only.
Sometime zigzag burns in
ball bearing raceways.
Localised burns in
raceways and on rolling
elements.
Action
Re-route the current to
bypass the bearing.
Use insulated bearings.
When welding, arrange
earthing to prevent
current passing through
the bearing.
• Working surfaces become dull after operation.
• ‘Path Pattern’ (dull surface) varies in
appearance according to the rotational and
loading conditions.
• By experience, we can learn to distinguish
abnormal paths from normal paths and hence
get clues to brg failure reasons.
PATH PATTERN INTPT-2
Uni-directional Radial Load
PATH PATTERN INTPT-3
Uni-directional Radial Load
PATH PATTERN INTPT-4
Uni-directional Axial Load
PATH PATTERN INTPT-5
Uni-directional Radial Load + Creeping* Outer Ring
PATH PATTERN INTPT-6
Uni-directional Radial Load + Tight Fit / Preloading
PATH PATTERN INTPT-7
Oval Compression of Outer Ring
PATH PATTERN INTPT-8
Outer Ring Misaligned
PATH PATTERN INTPT-9
Inner Ring Misaligned
PATH PATTERN INTPT-10
Combined Uni-directional Radial & Axial Loads
LUBRICATION MODES
2015-07-07 ©SKF Slide 80 [Code]
GREASE RUN-IN
AXIAL LOCATION
"Non-located" bearings
that can move axially
STORAGE AND REPACKING
BEARING STORAGE ROOM
BEARINGS SHOULD BE STOCKED IN A SEPARATE
STOCKING PLACE
CONDITIONS :
* CLEAN (no dust)
* DRY (Max 60 % humidity)
* DRAUGHTS TO BE AVOIDED (no windows opened)
• AWAY FROM VIBRATION
• TEMPERATURE AROUND 20 DEGREES C.
* NO TEMPERATURE FLUCTUATIONS (avoid condensation)
“AIR CONDITIONED” IN HOT & HUMID CLIMATES
“Never touch aviation bearing with hand.”
STORAGE AND REPACKING
STORAGE IN RACKS
1. FIRST IN, FIRST OUT
* OLDEST BEARINGS ALWAYS IN FRONT AND ON THE TOP OF THE PILE
2. DO NOT PILE UP TOO HIGH
* IT DOES DAMAGE THE PACKING
3A. STOCK LARGE BEARINGS FLAT (O.D. > 420 mm)
*
*
*
*
AT THE BOTTOM OF THE RACKS
STOCK FLAT (not vertical)
STOCK UNOPENED (individually packed in box)
NUMBER READABLE (up front)
3B. MEDIUM SIZE BEARINGS
* NUMBER (designation) UP FRONT)
3C. SMALL BEARINGS
* IN DRAWERS OR BOXES (keep away from dust)
* DESIGNATION ON DRAWER (box)
STORAGE AND REPACKING
STOCKING RECOMMENDATIONS
3 GOOD REASONS TO KEEP BEARINGS IN THE ORIGINAL PACKING :
* BEARINGS ARE CLEAN AND ARE PROTECTED WITH A RUST
INHIBITIVE OIL.
* BEARINGS ARE WRAPPED IN A SPECIAL PAPER OR PLASTIC
SHEETING FOR PROTECTION.
* BEARINGS ARE PACKED IN CARDBOARD BOXES FOR PROTECTION
REMARK :
* LARGE SIZE BEARINGS ARE INDIVIDUALLY PACKED IN WOODEN
BOXES FOR PROTECTION.
STORAGE AND REPACKING
RENEWING ANTI-RUST (AND PACKING)
1. WASH
* WHITE SPIRIT
* CLEAN AREA
* LET DRY
2. INHIBITING OIL PROTECTION
*
*
*
*
40 % QUAKER 5815 BASE AND 60 % WHITE SPIRIT
DIP AND ROTATE
DRY 7 HOURS
CLEAN AREA
3. PACK
* WRAP IN POLYETHYLENE COATED "VPI" PAPER
* PACK IN (CARTON) BOXES
4. IDENTITY
* INDICATE FULL BEARING NUMBER
* INDICATE BRAND !!