Thrust bearing fundamentals 05 2006

c 2006, Pioneer Motor Bearing CompanyFluid Film Thrust Bearings: Fundamentals, Damage Evaluation, & Repair Pioneer Motor Bearing May 2006 VIBRATION INSTITUTE MEETING CHARLOTTE, NC Outli

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Fluid Film Thrust Bearings:

Fundamentals, Damage

Evaluation, & Repair

Pioneer Motor Bearing

May 2006

VIBRATION INSTITUTE MEETING

CHARLOTTE, NC

Outline

History

n Without question

the most

significant

mechanical

invention in the

world was:

The Wheel

History

n However, almost immediately upon discovery of the wheel, the need for bearings was also discovered:

History

n Which has

led to one

of the most

elusive

searches in

human

history

History

n As one can observe from this wooden wheel dating to 2700

BC, axels where used to allow support by radial and thrust bearings:

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Load Orientations: radial/thrust

Slide 8

Thrust Bearing

n e.g Water or steam pressure

n Generally flat (<13 µm = 0.0005”)

n Generally circumferential segments

n Trade-off

nLarger loaded area gives more friction loss

Thrust Clearance

Human hair about

75 µm (0.003”) diameter

Typical operating clearance

about 25 µm (0.001”).

RUNNER

BEARING

Ref: ROTECH

Thrust Load

n Load capacity based on

n Nominally

n Reduced by grooving

*

* 25

Area = π −

Thrust Bearing Designs

Bearing

Flat Washers

n Simple but useful only with minimal speed and load conditions

n Grease lubricated

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“Bumper” Thrust

Babbitted axial surfaces to resist motion of shaft collars.

Babbitted surface may have radial pockets or grooving.

Flat Babbitted Thrust Face with Grooves

or locating bearing

lubricated

capacity

around 50 to 75 PSI

“Bumper” Thrust

Radial grooves enhance load capacity.

Taper-Land Thrust Bearing

one speed and load combination

formation is machined into the bearing surface

to operation

150 to 225 PSI

Taper is steeper

at the inner diameter than

at the outer diameter Taper is generally 0.003” 0.007” Land region is visible.

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Fluid-film Thrust Bearing

n Annulus controls axial position.

Tilting-pad

bearing

Tilting Pad Thrust Bearing

on applied load and speed

re: potential modifications

excess of 600 PSI

Tilting Pad Thrust Bearings

Equalizing linkages correct for housing skew.

Equalizing linkages do not correct for rotating collar skew.

Ref: Kingsbury literature

Non-Equalizing Support

Ref: Constantinescu, p 354

Non-Equalized Bearing Self Equalizing Tilting Pad

Thrust Bearings

given space

film

collar to housing misalignment

dynamic misalignment

excess of 600 PSI

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Equalizing Linkages

Ref: Constantinescu, p 354

Intent is to equally load each of the thrust pads in spite of variations in pad thickness or misalignment of the housing to the runner.

Anti-Rotation Pins

Provides:

Locates shell in housing

•Circumferential Prevent rotation of the cage

in the housing.

Combined Journal Thrust

Lobed journal bearing Tapered thrust bearing

Oil Distribution Geometry

OIL INLET HOLE

Radial groove

Axial groove

Bleeder

Bleeders

Sprea

Gro e

Sprea

Gro e

Thrust Bearing Flows

Ref Kingsbury EQH-1

R ota tio n

Tilting Pad Thrust Bearings

Ref: Kingsbury literature

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So, how much load can my

bearing take?

n This depends

on where you

are operating

within the

regime of the

bearing

performance

parameters

n No, I am not a

lawyer

What can be done to increase load capacity?

of the existing bearing

the operating parameters

basic bearing design

Deal with low speed wear

n Hydrostatic lift system to provide

hydrostatic oil films where hydrodynamic

oil films may not otherwise be present

where startup loads exceed 2.5-3.0 MPa

(363-435 psi)

n May be required for lower loads

Hydrostatic Lift Systems

1000 psi) at the location of the highest loading

through pressure, film thickness is controlled by flow

by a common high pressure header

Hydrostatic Lift System

into bearing cavity for operation at

low surface speeds and high loads

Hydrostatic Lift System

Hydrostatic lift in tilting pad thrust shoes.

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Main oil pump is shaft driven

AC & DC pumps

Sample Hydrostatic Lift Oil System

Schematic of Turbine-Generator Hydrostatic Lift System

Each radial bearing #3-8 has a separate pressurized hydrostatic-lift supply (1500 psig), separate supply pump with a gravity (or slight vacuum) drain back to the reservoir

OK smart guy, I’ve already got

a tilting pad thrust bearing, Now what?

features of the assembly

Effect of Pivot Offset

Effect of Chrome-Copper Alloy Backing Material

Thrust Bearing Monitoring

Thrust Temperature Monitoring

n Thermocouples

n RTD’s

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Tilt-Pad Thrust Profiles

Ref Kingsbury EQH-1

Temperature profiles

show influence of

pressure peak over the

pivot (dashed circle), as

well as radial and

circumferential flow.

Embedded Sensors

n Proper Location

Thrust Load Measurement

n Basic Bearing

Design

n Leveling Plates

n Strain

Gage

Load Cell

Thrust Position Measurement

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Thrust Position Measurement

Damage Investigation

n Visual examination

n Background information

n Photographic records

n Event reconstruction

n Laboratory analysis

n Visual

Examination

“Say, is all that babbitt supposed

to be on the bottom of the bearing housing like that?”

n Visual examination

n Background information

n Photographic records

n Event reconstruction

n Laboratory analysis

n Centered over pivot

n More toward trailing edge

n More toward leading edge

n Leveling plates

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Babbitt Surface Damage

Damage located primarily along the trailing edge is indicative of debris,

electrolysis, or other trauma that occurred while the bearing was

otherwise operating in a normal condition

Damage located primarily opposite the pivot is indicative the bearing operating in an overloaded condition

Damage located primarily along the leading edge is indicative of a lack

of lubrication, either during start up, or during operation

Support Structure Damage

ring, or other support structure is usually indicative of thrust collar

or may have come loose in service

Collar Damage

scratching of the thrust collar is

usually indicative of debris in the oil

system

Damage Mechanisms

covered earlier by Dr Branagan

may help

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Minor Overload

Babbitt Fatigue

Overheating

Gross Overheating

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Pivot Fretting

Leveling Plate Fretting

Babbitt Erosion

Bearing Inspection

Thrust Bearing Surface

the load must be clean and flat

single edged razor blade

bluing with a calibrated plate and

finally with the mating thrust collar

Thrust Bearing Subsurface

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Thrust Collar Inspection

TIR

Assembled Runout Check

indicator as rotor float will impact measurement

required to limit rotor float during inspection

sufficient travel to stay in contact with collar face

Indicator position

Typical Measurement record

0.0010 0.0020 0.0030 360

0.0000 -0.0010 -0.0010 315

-0.0010 -0.0010 -0.0020 270

-0.0020 0.0025 0.0005 225

-0.0010 0.0020 0.0010 180

0.0000 0.0030 0.0030 135

0.0010 0.0050 0.0060 90

0.0020 -0.0005 0.0015 45

0.0010 -0.0010 0.0000 0

A-B B A Rotation

Column of calculated A-B values gives twice the

this example, the collar is running out 002 TIR

Assembled End Play

space and stacked height of the

bearing assemblies

end play

to confirm measurement

Repairs

can be accomplished on site

attempted is directly proportional to the experience level of the

technicians available

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Babbitt Surface Repairs

can be removed by

lapping or scraping

be repaired by first

locally puddling

babbitt and followed

lapping or scraping

Babbitt Puddling

Hand Scraping

Power Scraping

Thrust Collar Repair

repaired by hand stoning

corrected by turning, lapping, or

grinding

conducted in place

Conclusions

surface is a SOFT, sacrificial layer.

better understand the likely cause

of the bearing damage and reduce re-occurrence.

bearing depending on the nature, severity, and probability of future damage.

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