Download - A PRESENTATION BY WG CDR ARVIND KUMAR. BEARINGS, FAILURES CAUSES & REMEDIES

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.

Cage/Retainer

Inner ring / race

Rolling element

Outer ring / race

Side faces

Outer ring raceway

Shoulder

Inner ring raceway

Shoulder

7

ROLLING BEARING CONSTRUCTION

7

BEARING DIA

Outside Diameter

Bore

BEARING CONSTRUCTION-2

Seal Rolling Elements Inner RingOuter Ring Cage Seal

BEARING CONSTRUCTION-3Outer Ring

Cage

Inner Ring

Side faces W33 Lubrication Groove and

Hole

Rolling Element

Guide Ring

Inner Ring Raceway

VARIOUS ROLLING ELEMENTS

Spherical roller(asymmetrical)

Taper roller

Spherical roller(symmetrical)

Needle roller

Cylindrical roller

Ball

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

CARBON CHROMIUM STEEL CONTAINING APPROXIMATELY1 % CARBON AND 1,5 % CHROMIUM

CASE-HARDENING STEELS

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 80MoCrV42- 16 for temperature > 250°C (SKF)

• 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

BAR STOOL BEARINGS(Man’s wt. causes thrust load)

Thrust load

Bearings

RADIAL LOADS

Motors & Pulley Shaft Support Bearings

Radial loadMotor Tension

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 grooveB.B

Angular contactB.B

Self-aligning B.B

Ball Bearings

Radial load Axial load Speed Accommodates

carrying capacity carrying capacity capability misalignment

Radial Load

Axial Load(one direction)

Tapered Roller Bearing

Radial Load

Thrust Thrust

Double Tapered Roller Bearing

Radial Load

Thrust Thrust

Double Tapered Roller Bearing

360°

~150°

LOAD ZONE

Radialclearance / play

Axialclearance / play

BEARING CLEARANCES

•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

CLEARANCE DESIGNATIONS

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)

WARM

Reducedradial

clearance

Expansion

Compression

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

Excessive preload causes high stress and heat generation

Life

Preload Clearance

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



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


Corrosion

- Moisture,

- Fretting

- False Brinelling

Electrical Erosion

-Excess voltage

- Current leakage


• 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 ActionSmall indentations around the raceways and rolling elements. Dull, worn surfaces.

Lack of cleaning before and during mounting operation.

Ineffective seals.

Lubricant contaminated by worn particles from brass cage.

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.

WEAR-INADEQUATE LUBRICATION

Fig 20 Cylindrical roller with mirror-like 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-INADEQUATELUBRICATION


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


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


Small indentations distributed around the raceways of both rings and the rolling elements.

Ingress of foreign particles into the bearing.

Cleanliness to be observed during the mounting operation.

Uncontaminated lubricant.

Improved seals.

FRETTING CORROSION

FRETTING CORROSION


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


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


Dark brown or greyish black fluting (corrugation) 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.

Passage of electric current.

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


Uni-directional Radial Load


Uni-directional Axial Load


Uni-directional Radial Load + Creeping* Outer Ring


Uni-directional Radial Load + Tight Fit / Preloading


Oval Compression of Outer Ring


Outer Ring Misaligned


Inner Ring Misaligned


Combined Uni-directional Radial & Axial Loads

23-04-10 ©SKF Slide 80 [Code]

LUBRICATION MODES

Greased for lifesealed bearingsinitial grease selection important

Occasional relubrication / replenishingopen bearingsconsult SKF / General Catalogue

Continuous relubrication for highly demanding applications,

or for sealing purposesconsult SKF / General Catalogue

Lubrication modes:

SKF SKF

GREASE RUN-IN

AXIAL LOCATION

"Non-located" bearings that can move axially

CONDITIONS :

BEARINGS SHOULD BE STOCKED IN A SEPARATESTOCKING PLACE

* 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.”

BEARING STORAGE ROOM

STORAGE AND REPACKING

1. FIRST IN, FIRST OUT

2. DO NOT PILE UP TOO HIGH

3A. STOCK LARGE BEARINGS FLAT (O.D. > 420 mm)

3B. MEDIUM SIZE BEARINGS

3C. SMALL BEARINGS

* OLDEST BEARINGS ALWAYS IN FRONT AND ON THE TOP OF THE PILE

* IT DOES DAMAGE THE PACKING

* AT THE BOTTOM OF THE RACKS* STOCK FLAT (not vertical)

* STOCK UNOPENED (individually packed in box)* NUMBER READABLE (up front)

* NUMBER (designation) UP FRONT)

* IN DRAWERS OR BOXES (keep away from dust)* DESIGNATION ON DRAWER (box)

STORAGE IN RACKS


REMARK :

* 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

* LARGE SIZE BEARINGS ARE INDIVIDUALLY PACKED IN WOODEN

BOXES FOR PROTECTION.

3 GOOD REASONS TO KEEP BEARINGS IN THE ORIGINAL PACKING :

STOCKING RECOMMENDATIONS


* WHITE SPIRIT

* CLEAN AREA

* LET DRY

1. WASH

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 !!

RENEWING ANTI-RUST (AND PACKING)


Download - A PRESENTATION BY WG CDR ARVIND KUMAR. BEARINGS, FAILURES CAUSES & REMEDIES

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