session iii bearings

8/11/2019 Session III Bearings

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BEARINGS

Session III

Copyright 2006 LTC


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DEFINITION

Bearings are a basic machine

component developed to reducefriction between moving parts, to

support moving loads, and

maintain alignment.

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TYPES OF BEARINGS

Bearing

ShaftHousing

Ball

Raceway

Housing rings

Anti-friction bearings

Plain (Journal) bearings

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JOURNAL BEARING TYPES

Solid

Split

Half

Multi-Part

Ref: Slater Schematic Approach

Tilt Pad Radial

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Kingsbury Type Bearing

with Tilted Pivoted Shoe Construction

Hydrodynamic lubrication between collar

and pivoted shoes

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PROPERTIES OF PLAIN BEARINGS

Plain bearings carry a high radial load because of the

greater surface area

They cannot handle thrust loads

Typical clearances for a plain bearing is 0.001-0.002

inches or mm per inch or mm of shaft diameter

Thrust loading is along the shaft

Radial loading

Bearing area is d x L for full bearing

and r x L for half bearing

Copyright 2006 LTC


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PLAIN BEARING CONSTRUCTION

MATERIALS

Plain bearings are constructed of a

multi-layer metals, consisting of a

backing layer and one or more

lining materials.

Backing material, usually steel,brass, or aluminum, provides

strength to bearing.

Lining material, a single layer babbit

of either soft tin alloy or lead alloy

or multiple layers of several metals,

provides for conformity,embedability.

Single layer lining is usually for light

duty applications and multi-layer

linings are for medium to heavy

duty applicationsCopyright 2006 LTC


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JOURNAL BEARING MATERIAL Bearing materials are selected based on the following

criteria Fatigue strength

Compressive strength

Embeddability

Conformability

Compatibility

Corrosion resistance

Bearing surfaces must be composed of materialsdifferent from and softer than the mating surface toprevent welding if metal to metal contact occurs

Types of material used are Tin- base babbitt ( 84% Sn, 8% Cu, 8% Sb) Lead base babbitt ( 75% Pb, 15% Sb, 1% Sn )

Copper lead

Lead bronze

Tin bronze

Aluminum alloyCopyright 2006 LTC


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BEARING MATERIALS

Softer than shaft material

Fatigue resistant - stress w/o cracking

Embedability - absorb particles Compatibility - resist galling

Conformability - malleability to shaft & bearing

Thermal conductivity - absorb & dissipate heat

Corrosion resistance - resist acids Load capacity - withstand hydrodynamic pressure

Copyright 2006 LTC


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BEARING MATERIALS

Bronze - 80% Cu, 10% Sn, 10% Pb

More tin for heavier loads

Babbitt Tin based: 84% Sn, 8% Cu, 8% Sb

Lead base: 75% Pb, 15% Sb, 1% Sn

Do not have high load carrying capacity

Fatigue failure, pounded out

Thinner layer bonded to strong backing

Copyright 2006 LTC


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PLAIN BEARINGS OIL VISCOSITY

Speed, RPM Continuous Application

ISO VGLight load 100 PSI5000-10,000

3500-5000

2000-3500

1000-2000

500-1000

300-500

100-300

50-100

50

5-10

10-15

15-22

22-32

32-46

68-100

100-150150-220

220-320

Medium Load 100-250PSI1000-2000

500-1000

300-500

100-30050-100

50

32-46

68-100

100-150

150-220220-320

320-460

Heavy Load 250 PSI100-300

50-100

< 50

320-460

460-1000

460-1000

Copyright 2006 LTC


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APPPLICATION OF LUBRICANT IN

PLAIN BEARINGS Lubricant is applied to plain bearings through holes

and distributed by means of grooves

Chamfered oil groove prevents oil from being

scraped off and allows greater oil flow for bettercooling and distribution in load zone

The grooves must be away from the load carryingsurface for better distribution

There are applications where an oil film is neededimmediately at startup of heavy rotating machines

Lift to the shaft is provided hydrostatically by feedingoil under the bearing at a pressure which will supportthe full load at startup

Copyright 2006 LTC


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GROOVING FOR OIL

Oil supplied through the oil hole

Oil distributed by the oil groove Location dependent on

Supply system

Direction of the load

Type of load (constant or variable) Do not place in load zone

Constant load - axial groove through oil hole

Variable load - circumferential groove

Collection grooves - circumferential drain Chamfer - rounding of edges Prevents oil from being scraped off

Allows for better cooling

Greater oil flow

Better distribution to load zone

Copyright 2006 LTC


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Normal lubricant

application away

From the load zone

LUBRICANT APPLICATION OF PLAIN

BEARINGS

Ref: WillsCopyright 2006 LTC


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CONTINOUS LUBRICATION WITH

DISC AND RING OILERS

Oil is thrown on top of bearing opening

Ring should be 1.5-2.0 size of shaft and oil level should be 1/8to 3/8 inch

above inside bottom of ringIf bearing speed is too fast oil will be thrown outwards and not reach

bearing

Disc lubrication can be used if shaft diameter(inches) x rpm < 8,000

Ring lubrication can be used if shaft diameter(inches) x rpm < 6,000

Copyright 2006 LTC


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PLAIN BEARING FAILURE MODES

High heat Improper grooving

Fatigue

Vibration

Shaft deflection

Contamination

Improper fit

Misalignment

Improper lubrication

Excessive load

Fretting damage to journal

bearing subject to vibration when

stationary.

Fatigue damage to journalbearing

Cleanliness of the oil supplyis essential for satisfactoryperformance and long life !!

Ref: Schematic ApproachCopyright 2006 LTC


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PRINCIPLES OF FRICTION

Sliding Friction Rolling Friction

Ref: NTN

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ANTI-FRICTION BEARINGS

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ADVANTAGES VS. PLAIN BEARING

Considerably Lower Starting Friction

High Speed Capabilities

Can Accommodate Thrust

Easily Repaired / Replaced

Can Carry High Loads (Roller Bearings)

Copyright 2006 LTC


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BEARING LOADS

Radial Load

Perpendicular to shaft.

Axial Load

Parallel to shaft center.

Ref: NTN

Copyright 2006 LTC


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LOAD ZONES AND CONTACT

POINTS

Load Zone:

The area of the bearing

supporting the load.(Approx. 1/3)

Contact Points:

Every point or surface

where loads are supportedby the bearing.

Ref: NTN

Copyright 2006 LTC


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BEARING COMPONENTS(DEEP GROOVE BALL BEARING)

Seal Rolling Elements Inner Ring

Outer ring Cage Seal

Ref: SKF

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ROLLING ELEMENT BEARING

CLASSIFICATIONS

Ball Cylindrical

Needle

TaperedSpherical

Ref: NTN

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Deep Groove

Ball Bearings Roller Bearings+Angular

Contact

Self-Aligning Cylindrical Taper Needle Spherical

Ref :SKF

Copyright 2006 LTC

ROLLER BEARING TYPES


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ROLLER BEARING TYPES

Ref: SKFCopyright 2006 LTC


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ROLLER BEARING ELEMENTS

Ref: SKF

Oil Hole

Oil Groove

Copyright 2006 LTC


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BASIC BEARING NUMBER

SYSTEM

6 2 03

Bearing

Series

Diameter

SeriesBore

Diameter

Ref: NTNCopyright 2006 LTC



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DIMENSIONS

Inner Diameter

Bore

Outer Diameter

Width

Radial ClearancePitch Diameter =

(d+D)

2

Copyright 2006 LTC

ROLLING ELEMENT BEARING TYPES


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Ref: Wills

Tapered bearings normally

preloaded during

installation to remove

internal clearances

between rollers and raceway

for greater stability

Copyright 2006 LTC

BALL BEARING TYPES


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BALL BEARING TYPES

Ref: WillsCopyright 2006 LTC



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Ref: NTNCopyright 2006 LTC

BEARING LIFE DESIGNATION


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Ball Bearings

Revolutio

ns

Total Number of Bearings

Failed

BEARING LIFE DESIGNATION

The amount of time any bearing

will perform in a specifiedoperation before failure.

L-10 Life or L-10 Rating

The number of revolutions that90% of a group of identicalbearings under identicalconditions will endure beforethe first sign of fatigue failure

occurs.L-50 rating is 5x > than L-10rating

90% of rolling element bearings fail

prematurelyCopyright 2006 LTC


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PROPERTIES OF ROLLING

ELEMENT BEARING TYPESBALL BEARING DOUBLE ROW

BALL BEARING

SPHERICAL ROLLER

BEARING

TAPERED ROLLER

BEARING

HIGH SPEEDS

LOW LOADING

LOW THRUST

PRODUCES HIGH

AXIAL MOVEMENT

GIVES LOW

FRICTION

LOW COST

It is important the correct bearing is used for the application

otherwise failure can occur

The choice of lubricant depends on the severity of the conditions

LOW SPEEDS

HIGH LOADING

HIGH THRUST

PRODUCES LOW

AXIAL MOVEMENT

GIVES HIGH

FRICTION

HIGH COST

Variations of the above bearings can be found with enhanced

properties

Copyright 2006 LTC


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VISCOSITY REQUIREMENTS FOR

ROLLING ELEMENT BEARINGS

Selection of an oils viscosity for a particular bearing

type can be calculated by knowing the bearings

speed, type, size, and operating temperature

It is important to determine the correct viscosity at

the operating temperature

The bearing speed factor (ndm) is used to calculate

the viscosity needed at the operating temperature

n= RPM

ndm= n (d+D) / 2

d = bearing bore in mm

D = bearing outside diameter in mmCopyright 2006 LTC

MINIMUM VISCOSITY REQUIREMENT


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MINIMUM VISCOSITY REQUIREMENT

FOR ROLLER BEARINGS BEARINGS

Minimum Viscosity @ Operating Temperature

Ball Bearing = 13.2 cSt (70 SUS)

Cylindrical Roller =13.2 cSt (70 SUS)

Spherical Roller = 20 cSt (100 SUS)

Spherical Roller Thrust = 33 cSt (150 SUS)

Copyright 2006 LTC


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MAXIMUM SPEED RATINGS (DN)

dN = inside dia.(mm) + outside dia(mm) X RPM2

Maximum Speed Ratings

OilLubricated Radial Ball Bearings = 500k

Oil Lubricated Cylindrical Roller Bearing = 500k Oil Lubricated Spherical Roller Bearings = 290k

Oil Lubricated Thrust Ball and Roller Bearings = 280k

Grease Lubricated Radial Ball Bearings = 340k

Grease Lubricated Cylindrical Roller Bearings = 300k

Grease Lubricated Spherical Roller Bearings = 145k

Grease Lubricated Thrust ball and Roller Bearings = 140k

Sealed for Life Ball Bearings = 108k

Copyright 2006 LTC


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K FACTOR CALCULATION

K factor calculations are used to show the relationship

between viscosity and bearing life

K = v1/v v = required viscosity of the oil

v1 = actual viscosity of oil

Example: If required viscosity at operating temperature

was 13 cSt but actual oil used had a

viscosity of 26 cSt the K factor would be

2.0

Normally the higher the K factor up to a certain point the

longer the bearing life

Copyright 2006 LTC

VISCOSITY REQUIREMENTS


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VISCOSITY REQUIREMENTS

Copyright 2006 LTC

CALCULATION OF VISCOSITY


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CALCULATIONOF VISCOSITY

REQUIREMENTS


VISCOSITY TEMPERATURE


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RELATIONSHIP




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RELATIONSHIP

Ref: SKF

Ref: Wills

Copyright 2006 LTC

BEARING LUBRICANT


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BEARING LUBRICANT

REQUIREMENTS

Bearing Type

Speed

Load

Low Medium

High

Temperature

Temperature Range

Metal/ material

Cooling requirements

Viscosity

Viscosity

Viscosity Anti-wear

Extreme Pressure

Oxidation / Thermal Stability

Viscosity Index / Pour Point

Non Aggressive Additives

Lubricant Type Grease vs. Oil

Consideration Oil Requirement

Copyright 2006 LTC

BEARING LUBRICANT


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BEARING LUBRICANT

REQUIREMENTS

Corrosion Protection

Water Resistance / Demulsibility

Pumpability

Method of Application Foam and Air Entrainment

Maintenance Intervals

Sealing

Lubricant Consolidation

Wear prevention

Corrosion Inhibitor Additives

Demulsifiers

Viscosity / Viscosity Index

Oil or Grease and Amount Balanced Anti-foam Additives

Oil Quality

Oil / Grease Seal Compatibility

Compromise

Oil Cleanliness and Filterability

Consideration Oil Requirement

Copyright 2006 LTC


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ROLLER BEARING FAILURE

ANALYSIS

Copyright 2006 LTC

MAJOR CAUSES OF BEARING


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MAJOR CAUSES OF BEARING

FAILURES

Defective bearing

Misalignment

Faulty mounting practices Incorrect shaft and housing fits

Inadequate lubrication

Ineffective sealing Vibration while bearing not rotating

Passage of electric current through bearing

Copyright 2006 LTC



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FAILURE MODES

Fatigue Subsurface

Surface Initiated

Wear Abrasive

Adhesive

Corrosion

Moisture

Fretting




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FAILURE MODES

Electrical Erosion Excessive Voltage

Current Leakage

Plastic Deformation Overload

Debris Indentation

Handling Indentation

Fracture Forced

Fatigue

Thermal CrackingRef: SKF

Copyright 2006 LTC

EXCESSIVE LOAD


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EXCESSIVE LOAD

Excessive loads cause premature fatigueRef: Baden

Copyright 2006 LTC

OVERHEATING


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OVERHEATING

Overheating can be caused insufficient cooling or lubrication

when loads and speeds are excessive Ref: BadenCopyright 2006 LTC

FALSE BRINELLING


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FALSE BRINELLING

Caused by externalvibration when

bearings are not

rotating.

Ref: Baden

Ref: BadenCopyright 2006 LTC

TRUE BRINELLING


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TRUE BRINELLING

Brinelling occurs when

loads exceed the

elastic limits of the ofthe ring material and

are characterized by

indentations in the

raceway.Any static overload on

sudden impact can

cause brinelling.

Ref: Baden

Copyright 2006 LTC

FATIGUE FAILURE


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FATIGUE FAILURE

This is usually called

spalling and is fracture ofthe running surface

resulting in removal of

small discrete particles

from the balls and rings.


CONTAMINATION


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CONTAMINATION

One of the leading

causes of bearingfailure which causes

raceway denting

resulting in vibration

Ref: Baden

Copyright 2006 LTC

LUBRICANT FAILURE


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LUBRICANT FAILURE

Noticeable from

discolored ball tracksand balls and excessive

wear will follow, causing

failure.

Ref: Baden

Copyright 2006 LTC

CORROSION


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CORROSION

Red/brown areas on

balls, raceways and

cages are symptomsof corrosion.


LOOSE FITS


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LOOSE FITS

Loose fits causerelative motion between

mating parts which can

cause fretting which is

generation of fine metal

particles which oxidize

to a brown or red color


TIGHT FIT


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TIGHT FIT

A heavy ball wear path in the

bottom of the raceway

indicates a tight fit

Heavy ball path

Ref: Baden

Copyright 2006 LTC

FLUTING


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Caused by vibration or

electric current as thecurrent seeks ground

which can be caused by

static short circuit, faulty

wiring, inadequate

insulation, or loose rotor

windings.

Fluting can be prevented

by insulating bearing or

putting brushes on shaft

to ground current.

FLUTING

Copyright 2006 LTC

FRETTING CORROSION


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FRETTING CORROSION

Fretting is a form

of wear resultingfrom small

amplitude

vibrations which

generate small

wear particles

from the rubbing

surfaces; with

ferrous metals the

wear particlesoxidize

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MISALIGNMENT


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Outer Ring Shaft Misalignment

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EFFECT OF VIBRATION ON

BEARING LIFE

Copyright 2006 LTC

BEARING LIFE BASICS


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BEARING LIFE BASICS

Vibration along with oil analysis is used on rolling element bearingsto detect impending failure

Direct correlation between vibration level changes and bearinglongevity

Seven major factors affecting impacting rolling element bearing life Shaft rpm

Design load rating of bearing

Type of rolling element Actual load applied

Lubricant ability

Contamination level

Operating temperature

Bearing life inversely proportional to speed changesdoubling

speed reduces life 50% Increasing load results in inversely exponential reduction in life

increasing load 25% decrease life by 50%

Reliabilit Ma azine Nov/Dec 1995Copyright 2006 LTC

VIBRATION FORCES


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VIBRATION FORCES

Vibration is a dynamic response to a dynamic force

Excessive vibration leads to excessive force which dramaticallyreduces bearing life

Sources of vibration Unbalance is a primary source of machine vibration and 50% more

destructive than other bearing sources

Shaft misalignment produces both radial and axial forces

Belt / drive tension Looseness

Rotor weight

Gear reaction

Process forces

Vibration has minor impact on bearing but the forces causing the

vibration affect bearing life Reducing vibration by 25% can increase ball bearing life by 137%

Reliability Magazine Nov/Dec 1995

Copyright 2006 LTC

BEARING FAILURE SUMMARY


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BEARING FAILURE SUMMARY

Poor maintenance

Poor design

Ineffective sealing Electrical arching across bearing

Wrong bearing for application

Overload or excessive speed

Insufficient lubrication

Incorrect lubrication Oil deterioration

Temperature variation

Contamination

Incorrect assembly/ installation

Misalignment

Incorrect clearances

Improper seating

Vibration

Fatigue

Copyright 2006 LTC

BEARING MOUNTING PROCEDURES


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BEARING MOUNTING PROCEDURES Use the highest quality bearing for the application

Handle bearings with care and keep sealed until time of theinstallation

Always follow the manufacturers recommendations when installing abearing

Work in a clean and dry environment

Never wash or wipe the bearings unless recommended by themanufacturer

Never use hard objects to pound a bearing into place

Utilize induction heaters, hydraulic presses, and hot oil baths formounting interference fit bearings

Never use an air blast to spin a bearing

Never hit or use force on the race flange

Never scratch or nick the bearing on any surface

Always use bearing pullers, heaters, arbor presses, and hydraulic oilinjection to remove bearings

Treat removed used bearings as new ones when they are to bereinstalled

Copyright 2006 LTC

TEMPERATURE MOUNTING


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TEMPERATURE MOUNTING

Good practice

Oven

Induction heater

Oil bath

session iii bearings

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