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 |  موضوع: محاضرة بعنوان Machinery Fault Diagnosis - A basic guide to understanding vibration analysis for machinery diagnosis الأحد 22 سبتمبر 2024, 1:44 am | |
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محاضرة بعنوان
Machinery Fault Diagnosis - A basic guide to understanding vibration analysis for machinery diagnosis
و المحتوى كما يلي :
Preface
This is a basic guide to understand vibration analysis for machinery diagnosis. In practice, many variables must be taken into account.
PRUFTECHNIK Condition Monitoring and/or LUDECA are not responsible for any incorrect assumptions based on this information.
 2011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Machinery Fault Diagnosis
A basic guide to understanding vibration analysis for machinery diagnosis.
12011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
This is a basic guide to understand vibration analysis for machinery
diagnosis. In practice, many variables must be taken into account.
PRUFTECHNIK Condition Monitoring and/or LUDECA are not
responsible for any incorrect assumptions based on this information.
2011 by PRÜFTECHNIK AG. ISO 9001:2008 certified. No copying or reproduction of this information, in any form whatsoever,
may be undertaken without express written permission of PRÜFTECHNIK AG or LUDECA Inc.
Preface
22011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Unbalance
Unbalance is the condition when the geometric centerline of a rotation axis doesn’t
coincide with the mass centerline.
F
unbalance = m d ω2
m
ω
MP MP
1X
A pure unbalance will generate a signal at the rotation speed and predominantly in
the radial direction.
Radial
32011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Static Unbalance
S
U
m
Static unbalance is caused by an unbalance mass out of
the gravity centerline.
The static unbalance is seen when the machine is not in
operation, the rotor will turn so the unbalance mass is
at the lowest position.
The static unbalance produces a vibration signal at 1X,
radial predominant, and in phase signals at both ends
of the rotor.
42011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Pure Couple Unbalance
m
S
U
-m
b
U = -U
Pure couple unbalance is caused by two identical
unbalance masses located at 180° in the transverse area of
the shaft.
Pure couple unbalance may be statically balanced.
When rotating pure couple unbalance produces a
vibration signal at 1X, radial predominant and in
opposite phase signals in both ends of the shaft.
52011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Dynamic Unbalance
S m
-m
U
U
Dynamic unbalance is static and couple unbalance at the
same time.
In practice, dynamic unbalance is the most common
form of unbalance found.
When rotating the dynamic unbalance produces a
vibration signal at 1X, radial predominant and the phase
will depend on the mass distribution along the axis.
62011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Documentation of balancing
Frequency spectra before/after balancing
and balancing diagram.
.. after balancing
before ..
Balancing diagram
72011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Overhung Rotors
A special case of dynamic unbalance can be found in
overhung rotors.
The unbalance creates a bending moment on the shaft.
Dynamic unbalance in overhung rotors causes high 1X
levels in radial and axial direction due to bending of the
shaft. The axial bearing signals in phase may confirm
this unbalance.
1X
Radial
Axial
82011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Unbalance location
The relative levels of 1X vibration
are dependant upon the location of
the unbalance mass.
92011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Misalignment
Misalignment is the condition when the geometric centerline of two
coupled shafts are not co-linear along the rotation axis of both shafts
at operating condition.
1X 2X
MP MP
A 1X and 2X vibration signal predominant in the axial direction is generally the
indicator of a misalignment between two coupled shafts.
Axial
102011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Angular Misalignment
Angular misalignment is seen when the shaft centerlines
coincide at one point along the projected axis of both
shafts.
The spectrum shows high axial vibration at 1X plus
some 2X and 3X with 180° phase difference across the
coupling in the axial direction.
These signals may be also visible in the radial direction
at a lower amplitude and in phase.
1X 2X 3X
Axial
112011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Parallel Misalignment
Parallel misalignment is produced when the centerlines
are parallel but offset .
The spectrum shows high radial vibration at 2X and a
lower 1X with 180° phase difference across the
coupling in the radial direction.
These signals may be also visible in the axial direction
in a lower amplitude and 180° phase difference across
the coupling in the axial direction.
1X 2X 3X
Radial
122011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Misalignment Diagnosis Tips
In practice, alignment measurements will show a
combination of parallel and angular misalignment.
Diagnosis may show both a 2X and an increased 1X signal
in the axial and radial readings.
The misalignment symptoms vary depending on the
machine and the misalignment conditions.
The misalignment assumptions can be often distinguished
from unbalance by:
• Different speeds testing
• Uncoupled motor testing
Temperature effects caused by thermal growth should also
be taken into account when assuming misalignment is the
cause of increased vibration.
132011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Alignment Tolerance Table
The suggested alignment tolerances shown above are general values based upon experience and should not be exceeded.
They are to be used only if existing in-house standards or the manufacturer of the machine or coupling prescribe no other values.
142011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Shaft Bending
A shaft bending is produced either by an axial asymmetry
of the shaft or by external forces on the shaft producing
the deformation.
A bent shaft causes axial opposed forces on the bearings
identified in the vibration spectrum as 1X in the axial
vibration.
2X and radial readings can also be visible.
1X 2X
Axial
152011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Rotating Looseness
Rotating looseness is caused by an excessive clearance between the rotor and the bearing
Rotation
frequency 1X
and harmonics
Radial
Rotation frequency
1X Harmonics and
sub Harmonics.
Radial
Rolling element bearing:
Journal bearing:
162011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Structural Looseness
Structural looseness occurs when the machine is not correctly supported by, or well
fastened to its base.
MP
MP
1X
Radial
• Poor mounting
• Poor or cracked base
• Poor base support
• Warped base
MP
MP
Structural looseness may increase vibration
amplitudes in any measurement direction.
Increases in any vibration amplitudes may
indicate structural looseness.
Measurements should be made on the bolts,
feet and bases in order to see a change in the
amplitude and phase. A change in amplitude
and 180° phase difference will confirm this
problem.
172011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Resonance
Resonance is a condition caused when a forcing frequency coincides (or is close) to the
natural frequency of the machine’s structure. The result will be a high vibration.
1st form of natural
flexure
2nd form of natural flexure 3rd form of natural flexure
t
v
tx
t
v
tx t
v
tx
f f
1st nat, flexuref2nd nat, flexuref3rd nat, flexure
no harmonic relationship
t
Shaft 1st, 2nd and 3rd critical speeds cause a
resonance state when operation is near these
critical speeds.
182011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Resonance
• Resonance can be confused with other common problems in machinery.
• Resonance requires some additional testing to be diagnosed.
2
Strong increase in amplitude of the rotation
frequency fn at the point of resonance, step-up
dependent on the excitation (unbalanced condition)
and damping.
1 = 240° 2 = 60...80°
1.
O.
MP MP
1
1.
O.
Phase jump
by 180°
Resonance
Step-up
Grad
rev/min
1 2
rev/min
Amplitude at rotation frequency fn by residual
unbalance on rigid rotor.
192011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Resonance Diagnosing Tests
Run Up or Coast Down Test:
• Performed when the machine is
turned on or turned off.
• Series of spectra at different RPM.
• Vibration signals tracking may
reveal a resonance.
The use of tachometer is optional
and the data collector must support
this kind of tests.
202011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Resonance Diagnosing Tests
Bump Test:
Response – component vibration
t
F/a
5 ms
Double beat
s
1 2
3
t
1
2
3
Decaying function
Excitation – force pulse
Shock component, natural vibration, vertical
t
Frequency response, vertical
Natural frequency,
vertical
Frequency response, horizontal
Natural frequency,
horizontal
1st mod.
2nd mod.
212011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Journal Bearings
Journal bearings provides a very low friction surface to support and guide a rotor through a cylinder
that surrounds the shaft and is filled with a lubricant preventing metal to metal contact.
Clearance problems (rotating mechanical looseness).
Oil whirl
• Oil-film stability problems.
• May cause 0.3-0.5X component in the spectrum.
0,3-0,5X 1X
Radial
High vibration damping due to the oil film:
• High frequencies signals may not be transmitted.
• Displacement sensor and continuous monitoring
recommended
222011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Rolling Element Bearings
• Lifetime exceeded
• Bearing overload
• Incorrect assembly
• Manufacturing error
• Insufficient lubrication
Wear
Wear
1. Wear:
The vibration spectrum has a higher
noise level and bearing characteristic
frequencies can be identified.
Increased level of shock pulses.
232011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
3
2
1
4
Angle of contact
D Arc diameter
d Rolling element diameter
Z Number of rolling elements
n Shaft RPM
Rolling Element Bearings
Roller bearing geometry and damage frequencies: 1 - Outer race damage
2 - Inner race damage
3 - Rolling element damage
4 - Cage damage
Dimensions
d =77.50 mm
D =14.29 mm
Z = 10
= 0
Rollover frequencies
BPFO = n / 60 4.0781 = 203.77 Hz
BPFI = n / 60 5.9220 = 295.90 Hz
2.f
w = n / 60 5.2390 = 261,77 Hz
f
K = n / 60 0.4079 = 20.38 Hz
Example of rollover frequencies:
Ball bearing SKF 6211
RPM, n = 2998 rev/min
Dw
D
pw
2. Race Damage:
BPFO = ( 1- cos )
BPFI = ( 1+ cos )
BSF = ( 1- cos )
TFT = ( 1- cos )
Z n
2 60
Z n
2 60
n
2 60
D n
d 60
d D
2
d D
d D
d D
Ball pass frequency, outer race:
Ball pass frequency, inner race:
Ball spin frequency:
Fundamental train frequency:
242011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Rolling Element Bearings
Outer race damage frequency BPFO as well as
harmonics clearly visible
Outer race damage:
(Ball passing frequency, outer range BPFO)
Inner race damage frequency BPFI as well as
numerous sidebands at intervals of 1X.
Inner race damage:
(Ball passing frequency, inner range BPFI)
BPFO 2 BPFO 3 BPFO 4 BPFO
f
n
BPFI 2 BPFI 3 BPFI 4 BPFI
Sidebands at intervals of 1X
252011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Rolling Element Bearings
Rolling element damage:
(Ball spin frequency BSF)
FTF and 2nd, 3rd, 4th harmonics
2 BSF 4 BSF 6 BSF 8 BSF
Sidebands in intervals of FTF
Rolling elements rollover frequency BSF with
harmonics as well as sidebands in intervals of FTF
Cage rotation frequency FTF and harmonics
visible
Cage damage:
(Fundamental train frequency FTF)
262011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Rolling Element Bearings
Lubrication Problems:
Lubricant contamination
• Race damage
• Defective sealing
• Contaminated lubricant used
Major fluctuation in
level of shock pulses
and damage
frequencies
Insufficient lubrication
Subsequent
small temperature
increase
• Insufficient lubricant
• Underrating
Over-greasing
Large temperature
increase after
lubrication
• Maintenance error
• Defective grease
regulator
• Grease nipple blocked
272011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Rolling Element Bearings
Incorrect mounting.
Bearing rings out of round, deformed.
• Incorrect installation
• Wrong bearing storage
• Shaft manufacturing error
• Bearing housing overtorqued.
Dirt
Damage
frequencies
envelope
Shock pulse
Air gap
Bearing forces on floating bearing.
• Incorrect installation
• Wrong housing calculation
• Manufacturing error in bearing
housing Severe vibration
Bearing temperature
increases
Fixed
bearing
Floating
bearing
Cocked bearing.
• Incorrect installation
Axial 1X, 2X
and 3X.
282011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Blade and Vanes
MP
MP
f
BPF
Radial
29
Example characteristic frequency:
3 struts in the intake; x=3.
9 blades; Bn=9.
f
BP x = N Bn x
Characteristic frequency = N 27
Identify and trend fBP.
An increase in it and/or its harmonics may be a
symptom of a problem like blade-diffuser or volute
air gap differences.
A blade or vane generates a signal frequency called
blade pass frequency, fBP:
fBP = Bn N Bn = # of blades or vanes
N = rotor speed in rpm2011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Aerodynamics and Hydraulic Forces
There are two basic moving fluid
problems diagnosed with vibration
analysis:
• Turbulence
• Cavitation
MP MP
f
1X BPF 1X
Cavitation: Turbulence:
Random Random
302011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Belt Drive Faults
MP MP
MP MP
Belt transmission a common drive system in
industry consisting of:
• Driver Pulley
• Driven Pulley
• Belt
The dynamic relation is: Ø1 ω1 = Ø2 ω2
Ø1
Ø2
ω1
ω2
Belt frequency:
: belt length
l
fB 3,1416 1 1
l
312011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Belt Drive Faults
Pulley Misalignment:
The belt frequency fB and first two
(or even three) harmonics are
visible in the spectrum.
Radial
2 f
B generally dominates the spectrum
Belt Worn:
1X of diver or driven pulley visible and
predominant in the axial reading.
f
n
1X,2X,3XfB
Offset Angular Twisted
322011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Belt Drive Faults
Eccentric Pulleys:
The geometric center doesn’t coincide with the rotating
center of the pulley.
High 1X of the eccentric pulley visible in the spectrum,
predominant in the radial direction.
Easy to confuse with unbalance, but:
• Measurement phase in vertical an horizontal directions
may be 0° or 180°.
• The vibration may be higher in the direction of the belts.
Belt Resonance:
If the belt natural frequency coincides with either the
driver or driven 1X, this frequency may be visible in the
spectrum.
Belt
direction
332011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Gear Faults
Spur Gear:
Planet Gear:
Worm Gear:
gear wheel
gear wheel pair
gear train
Driving gear
Driven gear
Gear (wheel) Pinion
Gear
Worm gear
Bevel gear
Bevel gear
Sun gear
Carrier
Planet gear
Ring (cone)
Bevel Gear:
342011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Gear Faults
Starting point of
tooth meshing
Pitch point
Working flank
Non working flank
Right flank
Pitch line
Left flank End point of tooth
meshing
1
2
4 3
5
6
85
86
88 87
89
Top land
Tip edge
Pitch surface
Root mantel flank
Flank line
Flank profile
Tooth
Tooth
space
Root flank
Gear Meshing:
Gear meshing is the contact pattern of the pinion
and wheel teeth when transmitting power.
The red dotted line is the contact path where the
meshing teeth will be in contact during the
rotation.
Gear mesh frequency fZ can be calculated:
F
z = z fn
Where z is the number of teeth of the gear rotating
at f
n.
352011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Gear Faults
Incorrect tooth meshing
Wear
MP
MP
z2
z1
fn1
fn2
fz
MP MP
X
Detail of X:
fz
fz
2 f
z 3 fz
fz
2 f
z 3 fz 4 fz
362011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Gear Faults
Incorrect tooth shape
MP
MP
fz
Detail of X:
X
fz
fz
and
harmonics
Sidebands
Tooth break-out
MP MP
z1 z2
X fz
Detail of X:
fn1 fn2
372011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Gear Faults
Eccentricity, bent shafts
MP MP
X
Detail of X:
fz
fz
and
harmonic
sidebands
“Ghost frequencies" or machine frequencies
fz
f
M “Ghost frequency"
Cutting tool
Gearwheel being
manufactured
z
M
Worm drive part of the
gear cutting machine
382011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Electrical Motors
Electromagnetic forces vibrations:
Twice line frequency vibration: 2 fL
Bar meshing frequency: fbar = fn nbar
Synchronous frequency: fsyn = 2 fL / p
Slip Frequency: fslip = fsyn – fn
Pole pass frequency: fp=p fslip
f
L: line frequency
n
bar: number of rotor bars
p: number of poles
• Stator eccentricity
• Eccentric rotor
• Rotor problems
• Loose connections
392011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Electrical Motors
Stator Eccentricity:
Loose iron
Shorted stator laminations
Soft foot
MP MP
1X
2 f
L
2X
1X and 2X signals
f
L without sidebands
Radial predominant
High resolution should be used when
analyzing two poles machines.
Radial
402011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Electrical Motors
Eccentric Rotor:
Rotor offset
Misalignment
Poor base
MP MP
1X
2 f
L
2X
Radial
f
p
t [ms]
T
slippage
f
p, 1X, 2X and 2fL signals.
1X and 2fL with sidebands at fP.
Radial predominant.
High resolution needed.
Modulation of the vibration time signal with the slip
frequency fslip
T
slip 2-5 s
412011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Electrical Motors
Rotor Problems:
1X
Radial
f [Hz]
1. Rotor thermal bow:
Unbalanced rotor bar current
Unbalance rotor conditions
Observable after some operation time
2. Broken or cracked rotor bars:
1X
Radial
2X 3X 4X
1X and harmonics with sidebands at fP
High resolution spectrum needed
Possible beating signal
422011 PRÜFTECHNIK Condition Monitoring – Machinery Fault Diagnosis. Distributed in the US by LUDECA, Inc. • www.ludeca.com
Electrical Motors
1X
Radial
f [Hz]
3. Loose rotor bar:
f
bar and 2fbar with 2fL sidebands
2f
bar can be higher
1X and 2X can appear
f
n
Radial
2f
2f n L 2f
L excessive signal with sidebands at 1/3 fL
Electrical phase problem
Correction must be done immediately
2X f
bar 2fbar
Loose connections:
43
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رابط من موقع عالم الكتب لتنزيل محاضرة بعنوان Machinery Fault Diagnosis - A basic guide to understanding vibration analysis for machinery diagnosis
رابط مباشر لتنزيل محاضرة بعنوان Machinery Fault Diagnosis - A basic guide to understanding vibration analysis for machinery diagnosis 
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