This document discusses common vibration issues in rotating machinery: 1) Unbalance causes 1x RPM vibration and can be identified by horizontal and vertical amplitudes being nearly the same. Misalignment produces 1x, 2x, or 3x RPM vibrations depending on the type and can be identified by directional radial vibration and phase shifts across couplings. 2) Mechanical looseness is caused by loose machine components or supports. Looseness of rotating parts causes multiple harmonics while loose supports produce 1x and 2x RPM vibrations. Looseness is identified by directional vibration and phase differences across loose interfaces. 3) The document provides details on identifying unbalance, the three types of misalignment, and looseness

1. Vibration Analysis of
Common Problems

2. IIPM 2
Vibration Analysis
Unbalance
 Amplitude proportional to the amount
of unbalance
 Vibration high normally in radial
direction (may be also in axial direction
incase of overhung and flexible rotors ).
 1* RPM vibration is greater than 80%
(normally) of the overall reading.

3. IIPM 3
Vibration Analysis
Unbalance
 Horizontal and vertical 1* RPM
amplitude should be nearly same,
although it also depends on system
rigidity on the particular direction.
 Other frequency peaks may be less
than 5% of the 1*RPM amplitude
 Phase shift of 90 deg. When sensor
moves from horizontal to vertical.

4. IIPM 4
UNBALANCE
 Operating conditions such as load, flow
condition and temperature effect
unbalance
 Balance under normal operating conditions
 Changes in track and pitch angle of fan
blades can result in “Aerodynamic
Unbalance”

5. IIPM 5
Typical Spectrum For
Unbalance

6. IIPM 6
MISALIGNMENT
 BIGGEST PROBLEM INITIALLY
 Operating temperature can affect
alignment
 Machines aligned cold can go out when
warm
 Bases or foundations can settle
 Grouting can shrink or deteriorate
 Increases energy demands

7. IIPM 7
MISALIGNMENT
 Forces shared by driver and driven (not
localized)
 Level of misalignment severity is
determined by the machines ability to
withstand the misalignment
 If coupling is stronger than bearing the
bearing can fail with little damage to the
coupling

8. IIPM 8
Three Types of Misalignment
 Combination (most common)
 Angular
 Parallel or Offset

9. IIPM 9
General Characteristics Of
Misalignment
 Radial vibration is highly directional
 1X, 2x, and 3x running speed
depending on type and extent of
misalignment
 Angular 1x rpm axial
 Parallel 2x rpm radial (H & V)
 Combination1,2,3x rpm radial and axial

10. IIPM 10
Typical Spectrum for
Misalignment

11. IIPM 11
Vibration Analysis
Misalignment
Angular Misalignment
 High axial vibration
( Greater than 50% of the radial vibration)
 1* , 2*, 3* RPM normally high.
 180 deg. Out of phase across the coupling

12. IIPM 12
Angular Misalignment
 Produces predominant 1x rpm component
 Marked by 180 degree phase shift across the
coupling in the axial direction

13. IIPM 13
Vibration Analysis
Misalignment
Off-Set Misalignment
 High Axial vibration. Also shows high radial
vibrations.
 1*, 2*, 3* RPM high. 2* often larger than 1*
 In case of severe misalignment, much high
harmonics (4* - 8*) or even a whole series of
high frequency harmonics will be generated.
 180 deg. Out of phase across coupling

14. IIPM 14
Parallel Or Offset Misalignment
 Produces a predominant 2x rpm peak in the
spectrum
 Marked by 180 degree phase shift across the
coupling in the radial direction.

15. IIPM 15
Typical Spectrum for
Misalignment

16. IIPM 16
Axial Phase Showing
Misalignment

17. IIPM 17
Other Types Of Misalignment

18. IIPM 18
Vibration Analysis
Mechanical Looseness
Caused by structured looseness / weakness of
machine feet, base plate or foundation; also
by deteriorated grouting, loose base bolts
and distortion of the frame or base.
 Radial vibration high
 2* RPM & 1* RPM dominant
 180 deg. Phase differences between
mating surfaces which have looseness
between them.

19. IIPM 19
Looseness
 Looseness produces
2X RPM Freq.

20. IIPM 20
Vibration Analysis
Mechanical Looseness
Caused by looseness in bearing housing bolts
and cracks in the frame structure.
 Radial vibration high
 2* RPM normally dominant. 0.5*, 1* and 3*
RPM may also be present
 Substantial Phase difference between mating
surfaces which have looseness between them

21. IIPM 21
LOOSENESS
 Not an exciting force
 Allows exciting frequencies already
present to exhibit much higher
amplitudes
 Loss or reduction in normal stiffness
 Caused by:
 loose mounting bolts
 deterioration of grouting
 cracked welds

22. IIPM 22
Two Types Of Looseness
 Looseness of Rotating Components
 Loose Rotors
 Bearings Loose on the Shaft or in Housing
 Excessive Sleeve Bearing Clearances
 Looseness of Support System
 Loose Mounting Bolts
 Grouting Deterioration
 Cracks
 Poor Support
 Frame Distortion

23. IIPM 23
Looseness Of Rotating System
 Rattling condition cause impacts due to
excessive clearance in a rolling element
or sleeve bearing
 Impacts cause multiple running speed
harmonics to appear in the spectra
 Identified by:
 multiple harmonics
 unstable phase
 highly directional radial vibration

24. IIPM 24
Typical Spectrum for
Looseness of Rotating System

25. IIPM 25
Looseness Of Support System
 FFT readings show 1x rpm, 2x rpm, and 3x
rpm components
 Structural looseness / weakness will cause
high 1xrpm peak in FFT
 Identified by
 Highly directional radial vibration
 Bouncing
 Taking comparative phase readings across
interfaces and look for amplitude variation
 Typically loose in vertical direction

26. IIPM 26
Looseness Of Support System

27. IIPM 27
Notes