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PROBLEM TYPICAL
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SOURCE SPECTRUM REMARKS
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BELT DRIVE PROBLEMS BELT FRED - ] 142 x PULLEY
RPM It PITCH Dom.
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A. WORN, LOOSE ORz MISMATCHED
BELTSEcr
VERT. PERPENDICULAR
TO BELT TENSfON
HORIZ. PULLEv 4 n
,(
o VERT
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Ô
m û
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Û
3 Z
x 1
r p
1
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BELT LENGTH
TIMING BELT FRED - BELT FRED XPBELTTEETH
· . pum.EV RPM X /PULLEY TEETH
x E Witt frequencies are below the RPM of er the motor or the
driven
machine. When they are worn, loose or mismatched,
they normally cause 110 4 multiples 01
ben frequency, Olten 2X belt Ireq. is the dominant peek,
RADIAL IN UNE Amplitudes are normally unsteady, sometimes
pulsing with attiser driver or
WITH BELTS
driven RPM, On timing belt drives.. wear or pulley misalignment
to
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NSION
PUL.EY
·2 4t+o Oo BELT
TENSION
_ HORIZ.
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PITCH QIAM, X RPM,
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p / PARALLEL TEl
indiEated by high amplitudes at the Timing Belt Frequency. Chain
drives will indicate problems at Chain Pass Frequency which equals e'Sprbdke1 .
PITCH OMAM, X APM., Teeth X RPM.
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B. BELT/PULLEY
3)ff11~,
OFF PIGEON 'f~ANGLE
SET ~~ TOE
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MISALIGNMENTin
AXIAL
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IX DRIVER
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Misalignment of pulley produces high vibration et lx
RPM predominantly the axial direction. The ratio of amplitudes
of driver to driven RPM
OR DRIVEN depends on where the data is
taken, as well as on relative mass and trame
stillness. Often with pulley
misalignment, the highest axial vibration on the motor null be
at tan RPM, or vice verse- Can be connrmed by phase
measurements by selling
Phase Filter at RPM o1 pulley with
highest axis!
emptilude: then compare at this frequency
phase panicular on each rotor
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-~ I-
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in the aural direction.
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C. ECCENTRIC PULLEYS e 02[41
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RADIAL
IX RPM ECCENTRIC
Ji
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Eccentric pulleys cause high vibration al 1X RPM oEfhe
eccentric pulley
The amplitude is normally highest in line with the belts. end
should show upon both driver and driven bearings. It aS
sOmebme5 possible to balance
PULLEY eccentric pulleys by alaching washers to taper Lock
bolts. However, even
ds in int
eber!. ty mil still
induce vibration be andreversible
it a di by
fatiguepphase stresses in the bort. Pulley eccentricity can be
Confirmed by phase
analysis showing honzonta & vanical phase differences
of nearly 0e or
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180'.
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D. BELT RESONANCEtXRPM OX.
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RADIAL
ii BELT RESONANCE
1
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Belt Resonance Can cause high amplitudes It the belt natural
frequency should happen to approach, or coincide with, either the motor or
driven
RPM Bet1 natural frequency can be altered by changing eerier the
bent
belt length Or cross i Can be
detectedonll tensioning and
tension.releasing
leen releasing ben while measuring Ilia
response pulleys or bearings,
However, when bell natural frequencies
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operating. will lend 10 De Slightly
higher on the tignt side and lower on the
slack side.
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l
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EAT v ~BR~i7I ~N
TWO FREQUENCIES 100' OUT OF PHASE Iwo SMILE
Hs
uotloulSOF D IFFERENT
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P
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"~
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HARMONICcommonly TWO IN
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PHASE
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FREQUENCIES
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A Beat Frequency is the result of two cioseiy spaced
frequencies equenes going into and out of
syncttronizalion with one another. The wideband spectrum
normally will show One pear pulsating up and down.
Wien you 200m +nib this peas (lower spectrum below(, it actually shows
two closely spaced
peaks. Trie difference in these two peaks (F2.Fi)
is Me beat frequency
which appears rtsell in the widebend spectrum.
The beat frequency is not
seen in normal frequency range measurements since it is
inherently low frequen, usually ranging from only approximately 5 to 100
cy.
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FREOUENCY
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CPM.
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Fi AND Frl.
BEAT FREQUENCY GENERATED BY TWO FREQUENCIES ABOVE
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Fe=
\
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F2
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· F1
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t
=
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BEAT r
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\
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FREQUENCY
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-
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Maximum anWatiOn (F,( comes into Minimum vibration
up 180' out of
°
F
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wAf result when the lime waveform of one frequency phase with
the waveform of the other frequency (F2)_ occurs
when waveforms of these two frequencies tine
phase.
PULSATinG
}F-
I AMPLITL DES
WIDEBAND SPECTRUM
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MINIMUM VIBRATION
OCCURS WHEN
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2
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\
\
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_
L
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MAXIMUM VIBRATION
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\
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OCCURS
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F, r2
p. BEAT FREQUENCT
ZOOM SPECTRUM
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FREQUENCIES ARE 1130" OUT OF PHASE
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WHEN 2 FREQUENCIES ARE IN PHASE
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SOFT FOOT, SPRUNG FOOT AND FOOT-RELATED
RESONANCE
a`
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B.!!
Mn'Foot
·Relafed
'Soft Foor occurs when a machines f00; Or frame deflects
greatly when a hold-down boll is loosened to hand tightness, causing the fool
to Ise more than approximately .002..003 inch This does not
always Cause a great vibration increase. However, it can da so if the Soft loot
affects alignment or motor air gap concentricity
'Sprung Foor can cause
great trame distortion, resulting in increased wbration, force and
stress w the treme, bearing housing, etc. This can RADIAL
DcEur when a hold
·duwe bolt is forceably torqued down
on the sprung
1 X RPM (Typ,) foot in an attempt
to level the foot.
Resonance' ran cause dramatic
amplitude increases from
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_"
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when e bolt (or combinations Of
5X to 15X or more. as compared with thatatVi
i bons) is loosened to hand tightness. When
tight, this bolt can notably
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change the natural frequency of trie foot or machine trame
itself.
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Solt Foot, Sprung Foot or Fool.Related
Resonance most open affects vibration at 1X RPM, but can also do so at 2X RPM,
3X RPM, 2X line
frequency, blade pass frequency, etc.
(particularly Foot-Related
Resonance).
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