Fluid film bearings 05 2006

c Pioneer Motor Bearing Company, 2006Introduction Pioneer Motor Bearing May 2006 VIBRATION INSTITUTE FLUID-FILM BEARINGS c Pioneer Motor Bearing Company, 2006 Outline n Pioneer Motor Bea

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(c) Pioneer Motor Bearing Company, 2006

Introduction

Pioneer Motor Bearing May 2006

VIBRATION INSTITUTE FLUID-FILM BEARINGS

Outline

n Pioneer Motor Bearing Company

n Thursday: Journal / Sleeve Bearings

n Fundamentals

n Operations impacts

n Installation / handling

n Friday: Thrust Bearings

n Extension of previous discussion

Pioneer Motor Bearing Co.

n Established in 1920; family-owned.

n Offers triad of engineering, new manufacture,

and repair services related to fluid-film bearings.

n Alliance partner with Michell Bearings

n Exclusive repair licensee of Siemens

(Westinghouse) and Alstom Power in North America for large-steam, babbitted products.

n Proprietary Fluid Pivot® tilting-pad journal

bearing.

n Customized training courses available.

North Carolina:

Engineering Manufacturing Service & Repair

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Pioneer Motor Bearing

Engineering

n Engineering & Technical Services

n Manufacturing to Customers’ Designs

n Manufacturing Pioneer’s Custom Designs

(Including Fluid Pivot® Journal Bearings)

n Repair, Modifications & Upgrades

Engineering Lyle A Branagan

Engineering Manager BSME, MS, Ph.D.

– 10 years with PG&E – Has substantial knowledge of rotor dynamics of turbomachinery – Extensive experience

in the field – An expertise in fluid film bearings and seals

Dr Lyle A Branagan

n Engineering Manager

n BSME / MSME – Machinery dynamics

n PhD – Fluid-film bearing analysis

n University of Virginia – ROMAC Lab

n Industrially-accepted design codes

n Pacific Gas & Electric – 10 years

n Specialist in bearings and rotordynamics

n Knolls Atomic Power Lab

n Pioneer Motor Bearing – 10 years

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Fred C Wiesinger

Office in Lansdale, PA 1-(215) 362-4074

Technical Services Manager

•Expertise in high speed gearboxes

•Expertise in thrust bearings

•Expertise in bearing repair services

Frederick (Fred) C Wiesinger

Technical Services Manager

n Drexel University

n BSME With Honors

n Philadelphia Gear – 7 Years

n Manager High Speed Gear Boxes

n Kingsbury, Inc – 14 Years

n Chief Engineer

n Manager, Repair & Service Division

n Vice President, Manufacturing

n Turbo Research, Inc – 3 ½ Years

Presentation Goals

•Understand operation of fluid-film bearings

•Relate vibration changes

to potential bearing changes

n Babbitted bearing damage

n Rotordynamics / journal bearings

n Predictive maintenance interface

n Installation and handling

n Questions and discussion

Focus on Thrust (Axial) Bearings

n Thrust bearing overview

n Babbitted bearing damage

n Rotordynamics / thrust bearings

n Predictive maintenance interface

n Installation and handling

n Questions and discussion

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Perspectives on Bearings

n Pioneer Motor Bearing Company

n Power Plant or Manufacturing Plant

n Maintenance

n Machine Designer

n Lubricant Vendor

n Vibration Specialist

Machine Design Perspective

n Allow rotating equipment to operate

n Separate rotating and stationary components

n Support the rotating load

n Adequate operational life

n Understand impact on oil analysis

Vibration Specialist Perspective

n Common point of measurement for vibration

n Potential interaction of sensors and sensor mounting

n Defines the measured quantity

n May define allowable vibration

n Bearing clearance

n Allowable bearing loads, esp dynamic

n Faults may affect vibration signature

n Excessive vibration may affect bearings

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(c) Pioneer Motor Bearing Company, 2006EndIntroduction

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Babbitted Bearing Overview

Pioneer Motor Bearing Company August 2006

PIONEER FLUID-FILM BEARING WORKSHOP

Fluid-Film Bearings APPLICATIONS:

n Radial turbine, generator, fan, pump, and motor bearings

n Turbine, generator, fan, pump, and motor thrust bearings

n Generator hydrogen and other high pressure seals

Opening Up the Machine

Bearing integral with shell

Bearing bolted to machine or mounted in end bell.

Opening Up the Bearing

End bell and housing top removed

Upper half and lower half showing ID

Load Orientations: radial/thrust

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Load Orientations: radial/thrust

n Horizontal machine

n Radial bearing

nGravity load

nRadial process / misalignment loads

n Thrust (axial) bearing

nAxial process loads

2 Transfer loads (static and dynamics)

from the rotating to the stationary structure

n Force transmission

3 Prevent undesirable vibrations

n Primary source of damping

4 Provide cooling

Separation

n Maintain close clearances

n Motors / Generators windings

n Fan seals and blades

n Turbine blades

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Hydrodynamic versus Hydrostatic

n Hydrodynamic – pressure

induced by relative motion.

n Hydrostatic – pressure

supplied by external source.

Hydrodynamic versus Hydrostatic

Ref: Intelligent Mechanics Lab, Pukyong University, website

Sleeve Bearing Geometry

Rotating Journal

Housing

Shell Babbitt

END VIEW CLEARANCEEXAGGERATED

ROTATINGJOURNALSHELL

SHELLBABBITT CLEARANCE

CONVERGINGCLEARANCE

DIVERGINGCLEARANCE

X

0 90 180 270 360 0

10 20 30

CON

G IN G

D

EG

Clearance space is filled

by a lubricant.

Clearance

n Assume 0.009” radial clearance

on a centered 12” diameter bearing

Human hair about 0.003” diameter

JOURNAL

BEARING

By comparison, the minimum operating clearance is only about 0.002”.

Clearance

n Assume 230 µm (0.009”) radial clearance on a centered 300 mm (12”) diameter bearing

Human hair about

75 µm (0.003”) diameter

JOURNAL

BEARING

By comparison, the minimum operating clearance is only about

50 µm (0.002”).

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Fluid-Film Bearing

Critical Geometry:

n Clearance space between the rotating

and stationary components

n CONVERGING SPACES develop pressure

n Circumferential grooves carry flow

n Axial grooves spread flow

n Tilting pads reduce cross-coupled forces

n Size on the order of 0.001” 0.050”

(40-2000 µm)

n Determine hydrodynamic (ω>0) or hydrostatic pressures (ω=0).

n Corrections for turbulence (G θ and G z ) and cross-film viscosity variations (µ(y)).

R h x h t

Sleeve Bearing Geometry

Converging

Film w/CCW

rotation

Pressures developed in the lubricant due to the converging wedge provide the bearing load capacity

Theoretical negative pressures in the diverging region are cancelled by air flow from the axial ends.

Reynolds Equation – 2-D Profile

PRESSURE

Sleeve Bearing Flows

Strong rotation with shaft; average velocity about ½ shaft surface velocity.

Lower, pressure driven axial velocity.

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“Cavitation” region, present in the upper half, generally occurs by air penetration, less frequently by oil vaporization

Area at minimum film limits the flow available.

Downstream increased volume

is only partially filled.

Cavitation - Experimental

Plexiglass bearing showing the formation

of cavitation in the region of increasing film thickness.

Ref Cole and Hughes, Proc.Inst.Mech.Engr., 170/17, 1956

Cavitation Demonstration

n Manual

n Take (2) small plates

n Spread thin layer of grease

n Press plates together with grease in between

n Open plates from one side

n Observe pattern of grease

n Demonstration rig

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Fluid-film Radial Bearing

radial position.

n Simple sleeve bearing

Bore Designs

Pressures in

an elliptical bearing at light loads.

Pressures in

an offset-half bearing.

Additional effect of a pressure dam – adds to the pressures from the cylindrical lower half.

Radial Bearing Components

ANTI-ROTATION PIN HOLE

LOWER HALF UPPER HALF (ROTATED)

BOLT HOLES

SPLITLINE

SLINGER RING GROOVE

Radial Bearing Components

LOWER HALF UPPER HALF (ROTATED)

DOWEL PINS OIL COLLECTION POCKETS

SIDEWELLS

BOLT HOLES

SLINGER RING GROOVE

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Joint Details

Oil-tight metal joint between the bearing halves.

metal-to-Top half secured by

by (4) joint bolts.

Alignment of top to bottom half by (2) dowel pins Pins captured in the lower half.

Dowel Pins

Damaged

Used to control alignment:

• Bearing shell halves

• Seal retainers to shell Unhardened allows deformation of the pin

Hardened dowels may damage shell under excess loading.

Care required to separate doweled pieces to avoid upset to the pieces or the dowel.

in the housing.

Bearings for Motors

Insulation required.

Potential damaging electrical ground current loops.

Ref: EPRI Manual.

Bearing Insulation

OD insulation on a motor bearing

Double insulated liner for exciter bearing.

Insulation to prevent electrical discharge across bearing surface.

Potential damaging current loops.

Bearing Support

Free-standing pedestal

Motor / generator end bell

Bearing housing on integral pedestal.

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Conforming Bearing to Shell

n Depends on the flexibility (stiffness)

of the bearing:

n Thin-shell bearings

n Liner type

n Insert type

n Medium wall bearings

n Thick wall bearings

Distribution-Precision Halves

Oil distribution features

Common in reciprocating and gear box service.

Circumferential groove sharply diminishes load capacity but allows for wider range of load angle.

Shell Wall Thickness

Thin wall (“liner” type):

shell conforms

to the housing geometry.

t < 0.03D

Thick wall: shell is supported by and aligned in the housing but retains its own shape.

t > 0.1D

Medium wall:

shell is supported by and aligned in the housing but

“somewhat”

conforms to the housing geometry.

Tilting Pad Radial Bearings

n Enhanced rotordynamic stability

n Enhanced control

of oil flows

n More components

n Higher cost

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Tilt-pad Radial Bearings

n Tilt-pad radial bearings

n Used to increase rotordynamic stability

nAvoid self-excited vibrations

n Segmented load bearing surface

n Mechanical pivot – load focused on a single contact point (Hertzian contact stress)

nLine pivot

nSpherical pivot (e.g ball in socket)

n Fluid Pivot®

nNo mechanical load concentration

n Flooded or directed lubrication

Mechanical Pivot

Shaft load distributed as oil pressure and concentrated in pad to the pivot (either a circular or elliptical contact region) Pressure will balance around the pivot.

Pivot can be hardened material (e.g

E52100 tool steel).

Tilt-pad Radial Bearings

C – pad clearance

M = 1 – C’/C

Tilting Pad Bearings

5-padLoad between padFlooded designMechanical pivotHydrostatic lift

Tilting Pad Bearings

Segmented film

Concentrated load

Single point, or line Contact support

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Specialty Journal Bearings

n Tilting pad bearings

n Uses continuing to expand

Conventional Pivot Types

CYLINDRICAL SPHERICAL BALL-IN-SOCKET

Quality of Pivot Contact

Contact varies with curvature, load, and temperature.

Ball-in-Socket Pivot Contact

Contact extent varies with curvature, load, and

temperature.

Operation requires sliding,

as well as rolling, motion

at the loaded contact.

Ref: KMC Bearing web site

Tilting action through deformation.

Smaller bearings benefit from the lack of a 2nd

tolerance for a detached pad.

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Stability Variation with Tilt Restraint

02004006008001000

n Tilt Freedom as a Function of:

Hertzian contact area or web thickness

ideal tilt pad

fixed pad

Shell, pads, stop pins

Fluid Pivot ® - Tilt Pad Bearing

Hydrostatic pivot, NOT a mechanical pivot.

Bearing includes shell, pads, stop pins

Fluid Pivot®

Flange-mounted, style JC

Gear box, style JC

Pedestal mounted, style JS

Fluid Pivot®

Pad supported on self-generated hydrostatic film on the OD of the pad.

Fluid Pivot® Exciter Assembly

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EndBearing Fundamentals I

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Babbitted Bearing Overview

Oil System Design Options

n Lubricant selection and maintenance

n Viscosity grade and viscosity index

n Hydrostatic lift systems

Oil Distribution Geometry

OIL INLET HOLE

Sprea

Groe

Oil Groove Geometry

Double loop groove & double figure eight groove recommended

for grease only.

Circular Straight

Half Eight

Double Figure Eight

Double Loop

Straight

&

Circular

Figure Eight

Single Loop

Grease grooving often passes thru the loaded region which reduces the bearing load capacity.

Do not use grooving associated with grease (long residence time) with oil lubrication (cooling flow).

Options Compared

Ref Constantinescu, Sliding Bearings, Allerton, 1985, p.474

Want to have efficiency and 100%

hydrodynamic fluid-film.

Best achieved with pressurized oil supply was effective axial distribution.

Main oil pump is shaft driven

AC & DC pumps

Sample Turbine Oil System

Schematic of Turbine- Generator Lubrication System

Each bearing has a separate pressurized supply (20 psig), orifice-metered, with a gravity (or slight vacuum) drain back to the reservoir

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Turbine Oil System Components

Slinger Rings

Slinger rings deliver oil from a reservoir below the bearing to the top of the rotating shaft, driven by friction between the rotating shaft and the ring.

Oil Grooving and Distribution

Axial distribution

Ref Elwelland Booser, Machine Design, 12/7/69, pp.111-115

Slinger Rings

Shaft

Slinger ring

Oil level (normal)

Bearing Babbitt

Ref: Mike King, Palisades Nuclear Station report

Slinger ring ID generally about twice the journal OD.

Oil level depth above slinger ring ID roughly 10% of ID.

Ring driven by shaft rotation.

n Oil depth is important

n Balance oil lift (submergence of the ID) with ring drag

Split Slinger Rings

Trapezoidal cross-section

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Slinger Ring Guides

Subject to wear or damage, particularly if misapplied.

Seek to maintain rings perpendicular

to shaft without introducing metal-to-metal friction Made

of bronze, steel, or aluminum.

Cast Slinger Ring Guide

Cast aluminum guide with oil scraper arrangement Single screw bolts guide upward into upper shell Guide

or screw should be staked to avoid looseness

or rotation

This guide showed rubbing wear on the upper part of the guide.

Slinger Ring Observation

“Bulls eye”

for viewing the rotation

of the slinger ring.

Ref: Mike King, Palisades Nuclear Station report

Level indicator should show change from static to operating oil level in reservoir.

Slinger Ring Observation

Hybrid System

n Combination of slinger ring and

pressurized system.

n Forced sump cooling

n Shaft driven main oil supply

Slinger Ring Demonstration

n Three slinger ring designs

n T-shape: common, inexpensive

n Trapezoidal:

heavier, speed

high-n Trapezoidal with grooves:

nBest oil flow

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