Equipment Vibration

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AMCA International Technical Seminar 2009

• Equipment Vibration
• Presented by
• Bill Howarth, Illinois Blower Inc.

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• The Air Movement and Control Association
  International (AMCA), has met the standards and
  requirements of the Registered Continuing
  Education Providers Program. Credit earned on
  completion of this program will be reported to
  the RCEPP. A certificate of completion will be
  issued to each participant. As such, it does not
  include content that may be deemed or construed
  to be an approval or endorsement by NCEES or
  RCEPP.

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• Learning Objectives

• Describe the distinction between balance and
  vibration
• Know the levels of balance quality
• Know the levels of installed vibration
• Understand the importance of an adequate
  foundation
• Recognize symptoms and causes of problems
• Know how to avoid vibration problems

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Equipment Vibration

• Presented by
• Bill Howarth
• Hartzell Fan, Inc.

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ANSI / AMCA 204-96

• Balance Quality and Vibration Levels for Fans
• Balance
• Vibration

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BALANCE

• Balance
• Synonymous with Unbalance. A physical property
  results in centrifugal force being applied to the
  fan impeller.
• Measured as the product of unbalance mass and
  distance from axis of rotation (oz-in).

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UNBALANCE

• EXAMPLE
• ROTOR WEIGHT 300 LBS
• RADIAL SEPARATION OF CENTER OF MASS FROM AXIS OF
  ROTATION0.0052 INCHES
• UNBALANCE 300 LBS 16 OZ/LB 0.0052 IN.25
  OZ-IN.

Center of Mass
Shaft
Axis of Rotation
Fan Impeller
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UNBALANCE
A. Particulate builds up uniformly on the rotor.
Sticky-wet particulate in gas stream
Scrubber
B. A piece of particulate flies off.
Fan
C. Center of mass shifts so that it no longer
coincides with the axis of rotation.
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UNBALANCE
Dead spot 250?F at top of housing
250?F
Top of shaft 188?F
Bottom of shaft 187?F
120?F
Fan wheel weight 8500 lbs. Differential
Expansion (188? - 187?) (6.5E-6in/in-?F)
(200 in) 0.0013 in Shaft Bows Upward!
120?F at bottom of housing
? Displacement from axis of rotation
0.36 Then Unbalance (8500)(16)(?) 49,000
oz-in
200.0013
?
200.0000
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UNBALANCE
Dust accumulation inside hollow airfoil blade.
Rotation
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UNBALANCE
Buildup of dust on the backside of backward
curves blades.
Rotation
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UNBALANCE
Hub
Shaft
Setscrews initially hold hub tightly in position
on the shaft. Setscrew tips are corroded or worn
by fretting over time. This allows the hub and
entire fan wheel to be displaced relative to the
axis of rotation causing unbalance.
Interference fit eliminates the possibility of
the hub being displaced relative to the shaft in
most systems.
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EFFECT OF TEMPERATURE CHANGE
Fan impeller initially operating at 70?
F. Process gas temperature increases rapidly.
Weld
Integral hub and shaft for very rapid temperature
change applications.
Fan impeller and hub heat up more quickly than
the shaft.

• Example
• Shaft dia. 3.9375 in.
• Hub average temp 215 F
• Shaft average temp 80 F
• Then hub growth relative to shaft
• (3.9375) (80) (6.5E-6) 0.002 in.
• Fan impeller weight 250 lbs..
• (250 lbs. x 16 oz/lb. x 0.002 inches)
• Resulting unbalance 8.0 oz-inches

• Conclusion
• Initial interference fit should be in excess of
  0.002 inches to allow for thermal expansion plus
  an allowance for hub expansion due to centrifugal
  force.

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ANSI / AMCA 204, TABLE 4-1
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ANSI / AMCA 204, TABLE 5-1
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ANSI / AMCA 204, APPENDIX C.2
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VIBRATION

• Vibration
• The alternating mechanical motion of an elastic
  system, components of which are amplitude,
  frequency and phase.
• In general practice vibration values are reported
  as
• Displacement - mils
• Velocity - inches/second
• Acceleration - peak gs

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VIBRATION VELOCITY
1780 RPM
Uper 12.72 oz-in
Maximum Vibration (in free space) 2.5 mm/sec (or
0.10 in.sec)
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VIBRATION

• Note that the bearing housing is considerably
  lower than the expected vibration of the rotor in
  free space.

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SLEEVE BEARING
Proximity Probe measures shaft surface movement
relative to the bearing housing.
Shaft (rotating)
Bearing Liner (static)
Bearing Housing
Oil Film supports shaft
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EFFECT OF STRUCTURE
Mass
Fan Mass
Cyclic Forces
Structural Steel
acts as a spring
Circus Flagpole
cyc/min
Fn 1200
Fan operating
Acrobat
speed 1180
RPM
Flagpole acts as
a spring
cyc/min
Fn 30
Foundation
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SOLID FOUNDATION
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STRUCTURAL STEEL MOUNTING
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FLEXIBLE MOUNT
Expansion Joint
Expansion Joint
Discharge Duct
Inlet Duct
Rigid Sub-Base (Often concrete filled)
Spring Isolation with static deflection of 1.0
inches Fn 187.7/1.5 187.7 cyc/min
Structural Steel Platform
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ANSI / AMCA 204, TABLE 6-3
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VIBRATION UNITS
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TRANSDUCER MOUNTING

• SWSI Centrifugal Fans

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TRANSDUCER MOUNTING

• DWDI Centrifugal Fans

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TRANSDUCER MOUNTING
Vertical
Axial
Horizontal
Vertical

• Axial Fans

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VIBRATION SPECTRUM
0.20
Filter Out
Filter In
0.15
Velocity (In./sec.)
0.10
0.05
0.00
0
500
1000
1500
2000
2500
Speed (RPM)
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ANSI / AMCA 204, TABLE 6-4
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• Questions?

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