MILITARY SEALIFT COMMAND Shaft Alignment
Transcript of MILITARY SEALIFT COMMAND Shaft Alignment
MILITARY SEALIFT COMMAND
Shaft Alignment
2UNCLASSIFIED 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
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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
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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 themathematics.
• 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 lifeof a machine
• Shaft alignment is always preferable tocoupling alignment
• Ensure contractors and shipyard workers areproviding a precision alignment
• For more information see the alignmenttextbook on the CMEO CD ROM
Summary