MILITARY SEALIFT COMMAND

Shaft Alignment

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• Define “Soft Foot” condition • Define “Bar Sag” and discuss how to correct

using dial indicators• Define “Thermal Growth” as it relates to shaft

alignment

Alignment Objectives

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• Shaft alignment is…– positioning shafts so they rotate about the same centerline.

• Shaft mis-alignment occurs when...– ...end-coupled shafts do not rotate about the same centerline.

Shaft Alignment Goals

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Misalignment Results In …

VIBRATIONReduced Operating Life

OPERATING HOURS

OPERATING COST

And

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• Specification Errors

• Mechanical Errors

• Improper Methods

Causes of Misalignment

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HOT

COLD

Thermal Growth Improper Installation

Lack of TrainingLack of Training

Specification Errors

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FoundationFlexure

Shock

Corrosion

BentShaft

Loose Bolts / Soft Foot

Mechanical Problems

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Wrong Tools:

• Ruler

• Level

• Carpenters Square

• Feeler Gage

Coupling Alignment

Coupling faces can be perfectly aligned while shafts are misaligned

Improper Techniques

9UNCLASSIFIED//FOUO OPR: N7

Proper Techniques

• Reverse Indicator Method• Using Dial Indicators• Using Lasers

• Rim and Face Method• Using Dial Indictors

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Reverse Indicator Method

"A" DISTANCE BETWEEN INDICATORS"B" DISTANCE FROM COUPLING CENTER TO "MI""C" DISTANCE FROM "MI" TO FRONT FOOT"D" DISTANCE BETWEEN MOTOR SUPPORTS"MI" "MOTOR" INDICATOR (DRIVER)“PI" "PUMP" INDICATOR (DRIVEN)"MTBM" "MACHINE TO BE MOVED"

StationaryMachine

MTBM

CL

B

A

C D

MI

PI

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Rim and Face Method

IndicatorRim

FaceIndicator

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Dial Indicators or Lasers?

Sag

Sag

L R

no sag LR

Dial Indicators• Must ensure bar sag is taken

into consideration.

• This adds complexity to the mathematics.

• Kit cost is approx $2000

Lasers• Bar sag is not an issue

• This simplifies the mathematics.

• Kit cost ranges from $3.6K to $20K

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Types of Misalignment

Offset

Centerlinesmeet at

coupling center

Angularity

Parallel

AngularAngularity

Centerlines meet at coupling center

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Types of Misalignment

Skewed Misalignment (most common type)

Angular + Parallel

Centerlinesdo not meet

at coupling centerCenterlines do

not meet at coupling center

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Dowel Pins

TAPER=1/4" / FOOT

MATERIAL: 304 STAINLESS

Typical Dowel Pin

Machine Foot

Base Plate

Pin Removal

WashersNut

Installation

Base Plate

Machine Foot

Hold Down Bolt

Dowel Pin• Repositions machine after repair• Prevents horizontal drift

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• Misalignment will significantly shorten the life of a machine

• Shaft alignment is always preferable to coupling alignment

• Ensure contractors and shipyard workers are providing a precision alignment

• For more information see the alignment textbook on the CMEO CD ROM

Summary

Slide Number 1Alignment ObjectivesShaft Alignment Goals Misalignment Results In …Causes of MisalignmentSpecification ErrorsMechanical ProblemsImproper TechniquesProper TechniquesReverse Indicator MethodSlide Number 11Dial Indicators or Lasers?Types of MisalignmentTypes of MisalignmentDowel PinsSummary