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MILITARY SEALIFT COMMAND
Shaft Alignment
2UNCLASSIFIED//FOUO OPR: N7
• 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
3UNCLASSIFIED//FOUO OPR: N7
• 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
4UNCLASSIFIED//FOUO OPR: N7
Misalignment Results In …
VIBRATIONReduced Operating Life
OPERATING HOURS
OPERATING COST
And
5UNCLASSIFIED//FOUO OPR: N7
• Specification Errors
• Mechanical Errors
• Improper Methods
Causes of Misalignment
6UNCLASSIFIED//FOUO OPR: N74
HOT
COLD
Thermal Growth Improper Installation
Lack of TrainingLack of Training
Specification Errors
7UNCLASSIFIED//FOUO OPR: N7
FoundationFlexure
Shock
Corrosion
BentShaft
Loose Bolts / Soft Foot
Mechanical Problems
8UNCLASSIFIED//FOUO OPR: N7
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
10UNCLASSIFIED//FOUO OPR: N7
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
11UNCLASSIFIED//FOUO OPR: N7
Rim and Face Method
IndicatorRim
FaceIndicator
12UNCLASSIFIED//FOUO OPR: N7
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
13UNCLASSIFIED//FOUO OPR: N7
Types of Misalignment
Offset
Centerlinesmeet at
coupling center
Angularity
Parallel
AngularAngularity
Centerlines meet at coupling center
14UNCLASSIFIED//FOUO OPR: N7
Types of Misalignment
Skewed Misalignment (most common type)
Angular + Parallel
Centerlinesdo not meet
at coupling centerCenterlines do
not meet at coupling center
15UNCLASSIFIED//FOUO OPR: N7
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
16UNCLASSIFIED//FOUO OPR: N7
• 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
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