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PROBLEM TYPICAL PHASE
SOURCE SPECTRUM RELATIONSHIP REMARKS
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MECHANICAL LOOSENESS
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RADIALBASE Mechanical Looseness is indicated
by aimer Type A, B or C vexation
PLATE e e spectra.
lx len_yA ion, e Type A
its Caused by Structural loosenesstweakness of
machine Witt,
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·
TYPE A ~ 4EAt]4nE FOOT
·
baseplate Or IOundatipn. BISri by pelerpreled grpr!ng,~oose
hUd
·dOwn
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ei. .... bons et the ease, and distortion o1
fie trame or base Ire., Ste toot) Phase
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ii sir 6701.
x RADIALstructure
X C'.l
X~yc TYPE B \
ir1 t7 , -
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analysis may reveal approv 90
· to 180* phase deerence
between vertical measurements on bort, machine foot, basedale or base
utselt.
Type B rs generally
caused by loose prllowbiock bolts, cracks in trame or
in bearing pedestal_
Typa C is normally generated by improper le between component
parts which win cause many harmonics due to nonlinear response
of loose pans 10 dynarniC iOrces mom rotor Causes a truncation of time waveform
and a raised nose floor in the spectrum. Type Cis often caused by a bearing
liner
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loose in es cap. a bearing loose and turning on es Shah,
excessive clearance in either a sleeve or rotting element
bearing, a loose impeller on
TYPE C eiellem a shat;, etc Type C
Prince aoften unstable and may vary widely morn one
X ', /L. rnea5urement to nest.
part..-ula
·ly d race shpts position on shalt horn one
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NOTE RAMSED NOISE FLOOR
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isa h
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Xycxx
X x< startup to ned Mechanical Looseness rs orten highly
directional and may
tear nr0 mho If
· cause very Cillement read rigs
when comparing levels at 30' incrernenls in
Lr~
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INDICATING LOOSENESS
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n ~ fir,' radial direction all the way around
one bearing housing. Alao, note that
f
1 1 looseness will ohen cause subharrnomc multiples
at exactly 1/2 Or 1/35
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Min
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RPM (.5X, I.55, 2.5X, etc )
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ROTOR RUB
FLATTENED
WAVEFORM
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TRUNCATEDX
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Rotor Rub produces similar spectra to Mechanical
Looseness when rag parts Contact stanonary o0mpnnents Rue may
be arther partial or
throughout the entire shah revoluton.
Usually -venerates a series of
RADIAL X frequencies, ohen eroding one or more
resonances Grien excites integer
traction Subharmonl s of running speed (1/2,
1/3, 1/4, 1/5,...1/n),
x ?c
X depending On location rubon of
rotor natural frequencies Rotcan excite
X~ is X many high ereouenc.es (similar to wide-band noise when
chalk ea drug
u1 o ',tong blackboard). h cari be very
serious and of short duration if caused
X Ni1i\i
ry by shah conteceng bearing babbitt A luit annular rub
throughout an entire
shah revo(Wron can induce 'reverse
precession
· with the rotor whirling at
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critical speed In a direction opposite shah
rotation (inherently
unstable
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which can lead to catastrophic lalure)
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JOURNAL BEARINGSSX
A. WEAR!CLEARANCE PROBLEMS
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1X y( N
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RADIAL Latter stages of ve rnnie bearing wear
are normally ev dented by presence
of wnole series 01 running speed harmonies (up
to 10 or 20)- Wroed
4X 5X lownai
bearvrgs ohlen van allow large venicai amplitudes compared to
6X 7X nordontal. but. may show
only one pronounced peek a! IX RPM-
Journal
bearings ver" excessive clearance may
allow a minor unbalance and/or
a misalignment Io cause high vioration which
be H
would much lower
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NOTE
MUSED NOL,E F1005 iNOICATeeG CLEARAwcEROOSE NESS
!searing clearances were Set to spec.
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B. OIL WHIRL INSTABILITY
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·
[_(ix RADIAL
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/ I 40
·.48 X RPM)Considered
cm Whorl Instability occurs at .40
·
.48X RPI/ and is often quite severe.
excessive when emptitube exceeds 40% Of bearing
clearances. Oit Whirl rs an c.1 lam excited
vioration where deviations in
normal operating conditions (attitude angle
and eccentricity ratio) cause oit
4` wedge to 'push' Shatt arOund within ari
beng. Destabilizing force in
l ° direction or rotation reSu's in a
whit (or forwards precession) Ge W flit is
unstable since it increases
cenrnlugal farces 'Mach increase whrd forces Can
Cause oit to no longer support shah and can become unstable
when
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venirl frequency coincides wrai a rotor
natural Irequency. Changes in oil
viscosity, lube pressure and 6aternel pretoadS
tan affect oit whirl.
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C. OIL WHIP
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oaf eaS4 weALAect
· Oil Whip
°LYnar ro.cT'ravie may occur if machine
operated at Or above 2X rotor critical
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Ir`onlev
uenCy. When rotor up to twice critical speed,
whirl win be very
âet
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INSTABILITY
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~~~~ ° dose
I rotor critical and cause a:passive vibration tISa1 al Alm
may
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-. wuwwayar seray
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lose mat.x no longer Cie capable of
supporting Ma speed will actually lock ortto
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- eoioasmec.
· r'el 2x, wear rotor
critira! and this peak rail not pass through it aven i1 maceine is
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brought to high higher and speeds Produces a laterai forward
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~
·q~
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precessional subharrnonic vibration at rotor critical frequency.
Inherently
CRITICAL SPEED
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' FAEoucNcy unlade which can lead to catastrophic
(allure.
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ROLLING ELEMENT BEARINGS
(4 Failure Stages)
1,.. - Natural Frequencies of Installed Bearin Components
and Support Structure
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TOREA
x_
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DOMINANT
FAILURE
ZONE a
B ARINO OEFrlcr $EeRrNC
MEC REGION INATURAI
STAGE I
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SCENARIO
ZONE C
COMPON, FRED REGION
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4 ROLLING ELEMENT BEARING FAILURE
STAGES
STAGE 7: Eames: rndicaboes of
bearing problems appear in ultrasonic kequencres ranging from
shout 250,000
· 350,000 Hz; later, as wear increases,
usually drops to approximately 20,000. 60.000 Hz (1,200,000
·
ZONE- D 3,600,000 CPU).
These are mequenoes evaluated by Spike Energy (gSE).
SPxf HFD(g) and Snook Pulse (d$) For example, spike
energy may Ant
fNENGT appear at about 25 gSE in Stage
+ actuel value depending on
INlo1 measurement location and
macnine speed). Acquiringhigh Ire ency
n g R
LL enveloped spectra confirms weather or net beaming is in
Failure Stage 1.
V STAGE 2: Slight bearing defects
begin to 'ring' bearing component
natural Irecluen:ies ff,1 which credominantly occur
in 30K
· 120K CPM
range Such natural bequences may also be
resonances of bearing
11-11-
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BEARraiG DEFECT FREQUENCIES
sail
· N /I u, CDsa a RPM
l P
aero. Ne f 141, WS el. RNA
2 1 Pe /
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l 'o;
STAGE 2
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n.
rZ:
ica
m (~~
a
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support structures- S'deband frequencies appear above And
below
naturel hequeriCy peak at end of Stage 2 Overall Spike energy
grows (Ion example, from 25 to 50 gSE)-
= SiOEAANO
FRED STAGE 3: Roaring detect freq.
encies and harmonics appear. Wnen wear
ÎI progresses, more defect Irequeney
narmOruCS appear end number of
sidebands grow. boue around these and bearing Component
natural
II-11-
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ear
· PQ I.. 12 (COS
012 1. aqui
~e l bat J
FTF
· I re Pa COS
aI' aoU
1 1
Where.-
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STAGE 3 OLL Cr
$ m
fl
m N
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.~ le
P
1
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frequencies, Overall spike energy Continuel to increase (for
example,
tram .5 ho over I gSE). Wear rs now usually visible and
may addend
throughout periphery of Dearing, particularly wean many
wen Iprmed
sidebands accompany bearing deleCt Irequency harrnoni
High
frequency demodulated end enveloped spectre het n
cofirm g
Replace bearings now!
(inWpendent of bearing defect frequency
arepbtudea In vibration spectre).
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BPFI a Inner Race frequency
ReFO. Our Reea Hequeruy
55F . Ball SpinFreeu$ncy
FTC .Fund. Train (Cepa) Treq
N.
· N.fabN N llMa Or Roars
P.
· Beanrig P4Ui 0.am
·le. (n or
mm} e
· Cmsacl Angle (degrees)
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x
x n at
n
1.
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B, - BaNlloar Domeier fin or
mm(SICNIfr('AYrLY
STAGE
4
RAN i ell{
FRED.
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~~~
HIGH
IBRATIOH
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JI
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(F
Of /MM STAGE 4: Towards the end,
amplitude Of IX RPM
4
etta Pk is even O arrn .
h
usrs grows, and normally causes growth
of many running Speed harmonics.
ArfM21, Discrete bearing [mica: and
component natural Irequencies actuallybegin
ri"Ci ew2 to 'disappear and are replaced by random, broadband
high frequency
noise tOOr' . In addition, amplitudes of born
high frequency noise 1100)
AT END and Spike energy
may in l= decrease; but j'AS: prior to ftilure,
spike
energy and HFD will usually grow Ici excessive amplitudes
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