7/25/2019 FD Fan Vibration Diagnostics
1/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
170
Condition Monitoring of FD-FAN Using Vibration AnalysisN. Dileep1, K. Anusha2, C. Satyaprathik3, B. Kartheek4, K. Ravikumar5(ASST.PROFFESOR)
1, 2, 3, 4B.Tech Graduate, Mechanical, V. R. Siddhartha Engineering College,Vijayawada, Krishna (Dt), Andhrapradesh, India.
Abstract--Machines of some kind are used in nearly every
aspect of our daily lives; from the vacuum cleaner and
washing machine we use at home, to the industrial machinery
used to manufacture nearly every product we use in our daily
life. When a machine fails or break down, the consequences
can range from annoyance to the financial disaster or
personal injury and possible loose of life. For this reason early
detection, identification and correction of machinery
problems is paramount to anyone involved in the maintenance
of industrial machinery to insure continued, safe and
productive operation. In order to run the machines efficientlyand to know the onset of impending defects condition and
monitoring of machines is important. There are several
indicating phenomenon like Vibration, noise, heat, debris in
oil, sound beyond human abilities etc., which emanate from
these inefficiently running machines. Monitoring of these
indicators provide early warnings of impending failures.
This paper is primarily focused on the implementation of
vibration based maintenance on critical rotating machines
namely FORCED DRAFT FAN (FD FAN 6B) at DR.NTTPS
which is one of the boilers auxiliary. FD fans for boilers force
ambient air into the boiler, typically through a preheater to
increase overall boiler efficiency. The required vibration
readings were taken. The levels of vibration of the fan driving
end (hub1) are beyond the safe limits of desired velocity and
displacement limit values. These further may cause to failure
of the fan. This paper also explains about the Spike energy
readings which were calculated and explained. After reading
are taken it was noticed that fan driving end bearing was
failed due to long life time of bearing, which is one of the
cause for the increase of vibrations. This problem was
rectified by replacing the new bearing and again vibration
readings are noted found to be in safe limits of velocity.
Keywords-- MDE, MNDE, FDE (HUB 1), FNDE (HUB 2),
Spectrums, Spike energy, Displacement, Velocity, Condition
Monitoring
I. INTRODUCTION TO MONITORING
Monitoring is the systematic collection and analysis andinformation as a project progresses. It is aimed at
improving the efficiency and effectiveness of a project or
organization. It is based on targets set and activities
planned during the planning faces of work. It helps to keep
the work on track and can let management know when
things are going wrong. If done properly, it is an invaluable
tool for good maintenance, and it provides a useful base for
evaluation.
It enables you to determine whether the resources you
have available are sufficient and are being well used,
whether the capacity you have is sufficient and appropriate
and whether you are doing what you planned to do.
1.1 Maintenance strategies are classified by three
developmental stages:
1. Break down maintenance
2. Preventive maintenance
3. Predictive maintenance
1.1.1 Break Down Maintenance:
This provides the replacement of defective part or
machine after the machine becomes incapable of further
operation. Break down maintenance is the easiest method
to follow and it avoids the initial costs and training
personnel and other related upfront costs.
1.1.2 Draw backs of break down maintenance are:
1.
Failures are untimely
2. Since machine is allowed to run till to failure repair
is more expensive. Sometimes total replacement is
required
3.
Failures may be catastrophic. Hence loss will bemore.
4.
Production loss will be more, as it requires more time
to restore normalcy.
5.
It reduces the life span of the equipment
1.2.1 Preventive maintenance:
In preventive maintenance, maintenance is scheduled on
calendar or hours to run and is performed irrespective of
machine condition.
1.2.2 Advantages:
1.
Down time of machine is reduced by 50-80%
2.
Lower expenses of over pay may same as much as
30%
3.
Increases the equipment life expectancy.
4.
Reduces the maintenance cost by reducing the capital
spending by 10-20%, labour cost by 10%,
material cost by 30%
5. Improve the employees safety
6. Preventive maintenance results in a catastrophic
failure and down time is required to complete all
scheduled maintenance costs
7.
Damage to machine is less
7/25/2019 FD Fan Vibration Diagnostics
2/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
171
1.2.2 Disadvantages:
1.
Periodically dismantling of each and every criticalmachine is expensive and time consuming.
2.
It may lead to unnecessary inspections even on
healthy machine also which may further lead to more
complications.
3.
It is difficult to predict time interval between
inspections which ultimately may lead to break down
maintenance.
4. Preventive maintenance alone cannot eliminate break
down. The causes of equipment failure change with
the passage of time. Fig 1 shows the failure rate
curve which is also called as bath tub curve. Failure
rate is taken on ordinate and time is taken on abscissa
when the equipment is new there is high failure ratedue to design and manufacturing errors. Failure rate
increases once again since the equipment approaches
the end of its failure.
FIG 1: BATH TUB CURVE
1.3.1 Predictive Maintenance:
Trending and analyzing machinery parameters we can
detect the developing problems in early stages. Hence
repair works can be carried out before failure of a machine.
1.3.2 Advantages:
1. Shut down can be done at convenient times
2. Work schedule can be prepared for mobilizing men ,
tools and replacement parts before shut down
reducing machinery down time
3. Identifying problem, costly trial and error procedures
to solve a problem can be avoided.4.
Machine in good running condition can run
continuously as long as problem develops
1.3.3 Disadvantages:
1. Require skilled labour
2. It is costly affair.
For all machines common characteristic is vibrations
and hence vibrations become a powerful tool inimplementing predictive maintenance program
The vibration predictive maintenance program has
four steps:
i. Detection
ii. Analysis
iii. Correction
iv. Conformation
i. Detection:
First select all available critical machines in the plant.
Prepare a schedule for all these machines for data
collection identify bearing locations of the machine train
motor non drive end, MND, FNDE, FDE, PNDE, PDE,etcidentify the directions where vibration data is
collected like H, V, A etc. define which vibration
parameters are to be collected via displacement, velocity,
acceleration etc. after doing all these start collecting
vibrating data and related data and record them. Collect the
data for every fortnight or monthly or so by trending and
interpreting the data, identify source of vibration.
ii.
Analysis:
After identifying the source of vibrations analyze to pin
point the root cause for vibrations. This can be achieved by
eliminating process. Follow confirmative procedures in
support of analysis.
iii.
Correction:
Open and inspect he machine at a convenient time and
make necessary corrections
iv.
Confirmation:
After corrections put the machine in service and again
collect vibration data and look for elimination of source.
II.
CONDITION MONITORING
Condition monitoring is the process of monitoring a
parameter of condition in machinery, such that a significant
change is indicative of a developing failure. The most
efficient way of doing predictive maintenance is bycondition monitoring technique. Predictive maintenance by
condition monitoring technique will boost up the
availability of the equipment; will increase the efficiency
and industrial safety.
The various steps involved in condition monitoring
program are:
1. Plant survey feasibility report.
2. Machine selection strategic and economic importance.
7/25/2019 FD Fan Vibration Diagnostics
3/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
172
3. Select optimum monitoring techniques there is a large
number of parameters that can be collected and analyzed inorder to determine machine condition. No single parameter
has given consistent results.
4. Establish a predictive maintenance programmed-
inspection schedule, data handling, administration and
training.
5. Set acceptable condition, data and lists based on machine
severity charts, manufacturers specializations and
experience.
6. Machine base line measurements are taken after many
corrective actions.
7-10. Routine monitoring programmed the object of this
is to detect significant deterioration in machine condition
through trend analyzed of the measured data.11. Condition analysisis in the death analysis of machine
condition often involving the joint application of number of
techniques. The object of this is to confirm the existing
fault, location and the corrective action required.
12. Fault correction having diagnosed the fault it is
required to schedule the corrective action. The details of
the identified faults should feedback to the diagnosis and
improve the diagnostics capabilities of the program.
CONDITION MONITORING TECHNIQUES:
Vibration monitoring
Debris analysis lubes oil analysis
Corrosion monitoring
ThermographyVisual monitoring
Contaminant monitoring
Performance and behavior monitoring
This paper is mainly focused on vibration monitoring
which is the most commonly used method for rotating
machines
2.1. Vibration Monitoring:
Vibration monitoring is well established method for
determining the physical movement of the machine or
structure. Vibration is the best indicator of overall
mechanical condition and the earliest indicator of the
developing defects. There are other indicators liketemperature, pressure and flow and oil analysis. If only one
indicator is to be used to monitor machine health then
vibration is usually the best choice.
All rotating and reciprocating machines vibrate either to
a smaller or to a greater extent. Machines vibrate because
of defects or in accuracies in the system. When the
inaccuracies are more it results in increased vibration.
Each kind of defect produces vibration, characterized in
a unique way. Therefore, recording vibration level of amachine indicates the condition of the machine.
2.1.1 Advantages of condition monitoring over planned
maintenance:
Improved system reliability
Decreased maintenance cost
Decreased number of maintenance operations causes
decreasing of human error influence
2.1.2 Disadvantages:
High installation costs, for minor equipment items
more than value of equipment
Unpredictable maintenance periods are causing
costs to be divide un equally Increased number of parts(CBM installation ) that
need maintenance and checking
III. VIBRATION ANALYSIS
Vibration analysis is a non-destructive technique
which helps early detection of machine problems by
measuring vibration.
Vibration analysis has been proven to be the most
successful predictive tool when used on rotating
equipment, both in increasing equipment availability and
reliability. In order to maximize the finite life
associated with rolling element bearings and optimize
equipment production life, excessive wear caused bymisalignment, unbalance, and resonance must be
minimized. The presence of trained vibration specialists
with equipment to conduct analysis will form the basis of a
strong vibration program.
3.1
Causes for vibrations:
1.
Change in direction with time, such as a force
generated by a rotating unbalance.
2. Change in amplitude with time, such as unbalanced
magnetic forces generated in an induction motor due
to unequal air gap between the motor armature and
stator.
3.
Result in friction between rotating and stationarymachine components is much.
4.
Cause impacts, such as gear tooth contact or the
impacts generated by the rolling elements of a bearing
passing over a flaw in the bearing raceways.
5.
Cause randomly generated forces such as flow
turbulence in the fluid handling Devices such as fans,
blowers and pumps; or combustion turbulence in gas
turbines or boilers.
7/25/2019 FD Fan Vibration Diagnostics
4/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
173
3.2 Machine vibration:
A vibrating object moves to and fro, back and forthmotion. We experience many
An example in our daily life like vehicles driven on
rough terrain vibrates.
There are various ways we can tell that something is
vibrating. We can touch a vibrating object and feel the
vibration. We may also see the back and forth
movement of a vibrating objects.
Fig 2: Machine Vibrations
3.3 Sources of vibration:
1.Misalignment of couplings, bearings and gears.
2.Unbalance of rotating components.
3.Looseness
4.
Deterioration of rolling element bearings
5.
Gear wear
6.
Eccentricity of rotating components such as "v "belt
pulleys or gears.
3.4. Detection by Vibration Analysis:
1 Unbalance(Static, Couple, Quasi-Static),
2
Misalignment(Angular, Parallel, Combination)
3
Eccentric Rotor, Bent Shaft
4
Mechanical Looseness, Structural Weakness, Soft
Foot
5
Resonance, Beat Vibration
6
Mechanical Rubbing
7 Problems Of Belt Driven Machines
8 Journal Bearing Defects
9 Antifriction Bearing Defects (Inner race, Outer race,
Cage, Rolling Elements)
10Problems of Hydrodynamic & Aerodynamic
Machines (Blade or Vane, Flow turbulence,Cavitations)
11
Gear Problems (Tooth wear, Tooth load, Gear
eccentricity, Backlash, Gear misalignment, Cracked
or Broken Tooth)
12 Electrical Problems of AC & DC Motor (Variable
Air Gap, Rotor bar Defect, Problems of SCRs)
3.5 Methods to detect causes of vibration:
There are literally hundreds of specific mechanical and
operational problems that can result in excessive machinery
vibration. However, since each type of problem generates
vibration in a unique way, a thorough study of the resultant
vibration characteristics can go a long way in reducing the
number of possibilities hopefully to a single cause. A
simple, logical and systematic approach that has been
proven successfully in pinpointing the vast majority of the
most common day-to-day machinery problems.
Interpreting the Data:
Obtain horizontal, vertical and axial spectrums at eachbearing of the machine train in order to take the readings.
Once horizontal, vertical and axial FFTs have been
obtained for each bearing of the machine train, the obvious
next question is: "What is this data telling me?" Essentially,
amplitude-versus-frequency spectrums serve two very
important purposes in vibration analysis:
1.Identify the machine component (motor, pump, gear
box, etc.) of the machine train that has the problem And
2.
Reduce the number of possible problems from several
hundred to only a limited few.
Identifying the Problem Component Based On Frequency:
Figure3 shows a fan operating at 2200 RPM, belt drivenby an 1800 RPM motor. The rotating speed of the belts is
500 RPM. Assume that a vibration analysis was performed
on this machine and the only significant vibration detected
had a frequency of 2200 CPM or 1 x RPM of the fan. Since
the vibration frequency is exactly related to fan speed, this
clearly indicates that the fan is the component with the
problem. This simple fact eliminates the drive motor, belts
and possible background sources as possible causes.
Most problems generate vibration with frequencies that
are exactly related to the rotating speed of trip in trouble.
These frequencies may be exactly 1 x RPM or multiples
(harmonics) of 1 x RPM such as 2x, 3x, 4x, etc. In addition,
some problem's may cause vibration frequencies that are
exact sub harmonics of 1 x RPM such as 1/2x, 1/3x or 1/4 x
RPM. In any event, the FFT analysis data can identify the
machine component with the problem based on the direct
relationship between the measured vibration frequency and
the rotating speed of the various machine elements.
7/25/2019 FD Fan Vibration Diagnostics
5/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
174
Fig 3: Components generate different vibration frequencies
Identifying the Problem Component Based On Amplitude:
Identifying the fan as the source of vibration based on
vibration frequency was quite easy in the above example
because of the notable differences in the rotating speeds of
the various machine components. The obvious question, of
course is: What about direct-coupled machines that isoperating at exactly the same speed?" In this case, the
component with the problem is normally identified as the
one with the highest amplitude. For example, consider a
motor direct coupled to a pump. Examining the analysis
data, it is noted that the highest vibration amplitude on
the motor is 1.0 in/sec compared to 0.12 in/sec on the
pump. In this case, the motor is clearly the problem
component since its vibration amplitude is nearly 8
times higher than that measured on the pump.
In general, the machine component that has the
problem is usually the one with the highest amplitude
of vibration. The forces that cause vibration tend to
dissipate in strength at increased distances from thesource.
However, there are exceptions to this rule such as the
example given earlier where a vertical pump was vibratingexcessively due to a resonance problem with the discharge
piping. In this case, the exciting force was actually
generated by the motor/pump but was being amplified by
the resonant condition of the piping.
Another exception to this rule involves misalignment of
direct coupled machines. Sir Isaac Newton's third law of
physics slates that "whenever one body exerts a force on
another, the second always exerts on the first a force which
is equal in magnitude but oppositely directed." In other
words, "for every action, there is an equal but opposite
reaction." In the case of coupling misalignment, the
vibratory force (action) is generated at the coupling
between the driver a driven components. As a result, the"reaction" forces on the driver and driven unit; will be
essentially equal, resulting in reasonably comparable
vibration amplitudes. The only reason one component may
have a slightly higher or lower amplitude than the other is
because of differences in the mass and stiffness
characteristics of the two components.
The following chart lists the most common vibration
frequencies is they relate to machine rotating speed (RPM),
along with the common causes for each frequency. To
illustrate how to use the chart, assume that the belt-driven
fan pictured in Figure3 has excessive vibration at 2200
CPM which is 1 x RPM of the fan. Of course, this clearly
indicates that the fan is the component with the problem
and not the drive motor or belts. In addition, since the
vibration frequency is 1 x RPM of the fan, the possible
causes listed on the chart are:
7/25/2019 FD Fan Vibration Diagnostics
6/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
175
TABLE 1
Vibration Frequencies andthe Likely Causes
Comparing Horizontal and Vertical Readings:
When comparing the horizontal and vertical data, it is
important to take note of how and where the machine is
mounted and also, how the bearings are mounted to the
machine. Basically, the vibration analyst needs to develop a
"feel" for the relative stiffness between the horizontal and
vertical directions in order to see whether the comparative
horizontal and vertical readings indicate a normal or
abnormal situation. Machines mounted on a solid or rigidbase may be evaluated differently than machines mounted
on elevated structures or resilient vibration isolators such as
rubber pads or springs.
Comparing Radial (Horizontal & Vertical) Data to Axial
Data:
The second important comparison that needs to be made
to tri-axial analysis data is how the radial (horizontal and
vertical) readings compare to the axial readings.
Relatively high amplitudes of axial vibration are
normally the result of
1.
Misalignment of couplings
2.Misalignment of bearings
3.Misalignment of pulleys or sheaves on belt drives
4.Bent shafts
Unbalance of "overhung" rotors.
IV.
SPIKE ENERGY
When flaws or defects appear in a bearing, the resulting
vibration will appear as a series of short duration spikes or
pulses such .The duration or "period" of each pulse
generated by an impact depends on the physical size of the
flaw; the smaller the flaw, the shorter the pulse period will
be. As the size of the defect increases, the period of the
pulse becomes longer.
Frequency
in Terms Of RPM Most Likely causes Other possible causes & Remarks
lx RPM Unbalance
I) Eccentric journals, gears or pulleys
2) Misalignment or bent shaft if high axial
vibration
2 x RPM Mechanical looseness
1) Misalignment if high axial vibration
2) Reciprocating force
3 x RPM Misalignment
Usually a combination of misalignment and
excessive
Axial clearance (looseness).
Less than
lx RPM
Oil Whirl(Less than1/2 x RPM)
I) Bad drive belts
2) Background vibration
3) Sub-harmonic resonance4) "Seat" Vibration
Synchronous (A.0 line frequency) Electrical Problems
Common electrical problems include broken
rotor bars,
eccentric rotor, and unbalanced phases in poly-
phase
Systems, unequal air gap.
2xSynch.Frequency Torque Pulses Rare as a problem unless resonance is excited
Many Times RPM
(Harmonically
Related Freq.)
Bad Gears, Aerodynamic Forces,
Hydraulic forces, Mechanical Looseness,
Reciprocating Forces
Gear teeth times RPM of bad gear
Number of fan blade t imes RPM
Number of i mpeller vane ti mes RPM
May occur at 2, 3, 4 and sometimes higher
harmonics
High Frequency
(Not Harmonically
Related)
Bad
Anti-Friction bearing
1) Capitation, recirculation and flow turbulence
causes
random high frequency vibration
2)Improper lubrication of journal bearings
3)rubbing
7/25/2019 FD Fan Vibration Diagnostics
7/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
176
A short-term (40 millisecond sec) time waveform that
was taken on a ball bearing with a small nick purposefullyground on the bearing inner race way. It can be seen that
the pulse period lasts only a few microseconds (1
microsecond = 1 millionth of a second). Of course, if the
period of a vibration signals is-known, the frequency of the
vibration can be found by simply taking the inverse of the
period. For example, if it takes 1/3600 minute to complete
one cycle of a vibration, then the vibration frequency is
3600 cycles per minute (CPM) or the inverse of the period.
In the case of the pulses generated by the bearing
defects, since the pulse periods are so short, the period
inverses (frequencies) are typically very high. To illustrate,
a MICRO-FLAW is generally defined as a defect that is so
small that it is essentially invisible to the naked eye. Thepulses generated by a micro-flaw are typically less than 10
micro-seconds (i.e. 10 millionths of a second). By taking
the inverse of a 10 micro-second pulse, the fundamental
frequency becomes 100,000 Hz (TOOK Hz) or 6,000,000
CPM. As bearing deterioration progresses, the flaw gets
larger. The next stage is a MACRO-FLAW or one that is
detectable with the naked eye. Since the macro-flaw is
larger, the duration or period of the pulse generated is
longer and, thus, the fundamental pulse frequency is lower.
Typically, a macro-flaw will generate a pulse with a period
exceeding 20 microseconds, resulting in a fundamental
pulse frequency of 50K Hz (3,000,000 CPM) or less. Of
course, as the bearing defects continue to increase in size,
the resultant pulse periods become even longer resulting in
a decrease in fundamental pulse frequency.
Experimentation has revealed that by the time the
fundamental pulse frequency has reduced to approximately
5k Hz (300,000 CPM), bearing deterioration has generally
reached severe levels.
With the above facts in mind, the following outlines the
basic features of the SPIKE ENERGY (abbreviated gSE).
Since the frequencies of bearing vibration are very
high, utilize a vibration acceleration signal from an
accelerometer transducer.
Incorporate a "band-pass" frequency filter that will
electronically filter out frequencies above 50K Hz
(3,000,000-GPM) -and below 5K Hz (300,000 CPM).By eliminating frequencies above 50K HI, micro-
flaws, defects that are undetectable with the naked eye,
will not affect the measurement. In other words, when
the SPIKE ENERGY (gSE) measurements reveal a
significant increase, a visual inspection of the bearing
should provide confirmation with a visible flaw.
Since the spike-pulse signals generated by bearing
defects have very low RMS values, incorporate a truepeak-to-peak detecting circuit instead of an RMS
detecting circuit.
V. DATA PAC 1500
Instrument:Data Pac 1500
Company:ENTEK IRD
Feature: portable data collector / analyzer in a small
lightweight package.
Data PAC 1500 is part of Entek's complete range of
monitoring products and services to all industry segments
worldwide. The data PAC 1500 is a fully featured portable
data collector.
Figure 4: DATA PAC 1500
Supported Measurements:
Acceleration
Velocity
Displacement
G Spike Energy (GSE)
Temperature
Thrust or axial position
DC voltage
VI.
BEARING FREQUENCIES
The bearing frequencies can be calculated based on 4typical components of bearings.
1.
BALL PASS FERQUENCY OUTER RACE
(BPFO)
2.
BALL PASS FREQUENCY INNER RACE(BPFI)
3.
BALL SPINNING FREQUENCY(BSF)
4.
FUNDEMENTAL TRAIN FREQUENCY (FTF)
7/25/2019 FD Fan Vibration Diagnostics
8/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
177
6.1 FORMULAS FOR BEARING FREQUENCIES:
BPFO:(nb/2 - 1.2) rpm
BPFI:(nb/2 + 1.2) rpm
BSF:1/2(nb/2 -1.2/nb) rpm
FTF:(1/21.2/nb) rpm
Where nb= no. of balls
Fig5 Rolling bearing element components.
Understanding Bearing Vibration
Example 1:
If you have the defect multipliers at your disposal, the
process of calculating the defect frequency is as follows:
1. Look up the bearing number that is exhibiting the
suspect vibration frequency on a table like the one below:
BEARING
ID
NO.OF
ROLLING
ELEMENTS
FTF BSF BPFO BPFI
9436 19 0.434 3.648 8.247 10.753
9437 19 0.434 3.648 8.247 10.753
9442 22 0.443 4.191 9.740 12.260
2. Multiply this number by the shaft speed mated with
this bearing and you have the defect frequency that would
be generated by a defect on the element in question. See
Figure 7.4 9.740 x 351 rpm shaft speed = 3419 cpm
Outer race bearing defect
If the frequency and harmonics (multiples) of it arepresent on the vibration spectra, you most probably have an
outer race bearing defect. It could be a spall on the
raceway, electrical fluting, false brinelling acquired during
bearing storage or equipment transport, etc.
Be advised that there will be occasions when the
calculated defect frequencies dont exactly match the
bearing defect frequencies that appear in the vibration
spectra. Typically this is due to higher than normal thrust
loads which cause the bearing to run at a different contact
angle. These abnormal thrust loads can be caused by
sources such as mis-alignment.
Also, not all bearing manufacturers use the same number
of rolling elements in a particular bearing size.The most common bearing problem is the outer race defect
in the load zone; inner race faults are the next most
common. It is very rare to see a fault at the bearings ball
spin frequency or BsF.
Action step:The presence of any of these four fundamental
fault frequencies should result in the repair technician
replacing the bearing and ensuring the housing fits and
shaft journals are within tolerance. Finally, its worth
discussing the presence of mechanical looseness, which
manifests itself as harmonics of 1x running speed, on a new
or re- built bearing housing or journal. This indication of
looseness could be coming from poor base mounting or one
of the following:1. Loose housing-to-outer race fits
2. Loose journal-to-inner race fits
3. Excessive internal bearing clearance
Sleeve Bearing Defects:
Sleeve bearings do not make use of rolling elements;
rather, the shaft rides on a layer of lubricating oil inside the
bearing bore. The lubricant is either sealed inside the
bearing, gravity fed to the bearing or pumped in (pressure
fed). Sleeve bearings which have excessive wear/ clearance
exhibit a vibration spectrum similar to the one in Figure
7.5. Notice the series of running speed harmonics (up to 10
or 20). Wiped sleeve bearings often show much higher
vertical amplitudes than horizontal. A higher axial reading
on one end than the other provides further indication, with
the higher vibration level on the end with the damaged
bearing.
7/25/2019 FD Fan Vibration Diagnostics
9/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
178
Figure6: Bad bearing fits between housing &outer race.
Looseness from wear nd clearence problem
Clearance Problems In contrast, mechanical looseness
caused by loose mounting bolts or cracks in the framestructure or bearing pedestal typically look like the
spectrum in Figure 7
Fig7: Loose mounting (Structural Looseness)
Excessive looseness can also cause sub harmonic
multiples at exactly 1/2 or 1/3 x rpm (.5x, 1.5x, 2.5x, etc.).
During bearing failure the harmonics are matched with
taking higher resolution of the spectrum, if it is found to
match with the spectrum it is said to be failure of bearing.
If the bearing failure occurs there will be little change in
the velocity values, no changes may occur in displacement
values but the spike energy value will be increasing.
During normal cases the spike energy value should be less
than one (gSE 60000 spike energy
values come into criteria.
VII. SPECIFICATION OF FD FAN
FD-MOTOR:
SPEED: 993 RPM
VOLTS: 3300V
CURRENT: 229amps
TYPE: induction motor.
FREQUENCY: 50HZ
PHASE: 3PHASE.
FD-FAN:
TYPE: axial reaction
MEDIUM HANDLED: fresh air
SPPED:1480 rpm
NO.OF BLADES:23
BEARING NO:NU226E
HUB DIA:1100mm
OUTERDIA:1800mm
Displacement readings taken on 17 oct 2012.
Table 2
vibration data sheet of FD fan 6B before rectification
S.No Position
Velocity
(mm/s)
Displacement
(m)
H V A H V A
1 MNDE 8.71 0.751 1.75 108 363 14.8
2 MDE 9.93 1.35 1.66 111 8.34 14.6
3 HUB1 8.83 1.8 5.14 108 20.5 14.5
4 HUB2 9.24 1.76 5.41 114 20.8 16.2
Where,
MNDE: motor non drive end
MDE: motor drive end.
Hub1: fan drive end
Hub 2: fan non drive end
H: horizontal
V: vertical
A: axial
Limits as per ISO 10816 part2 (mm/sec peak)
Good : 0 to 6.0 mm/sec
Satisfactory: 6.0to 12.3mm/sec
Alarm : 12.3 to 16.0 mm/sec
Not Permitted : >16.0mm/sec
VIII.
THE FOLLOWING ARE THE SPECTRUMS TAKEN TO
OBSERVE THE CAUSE OF VIBRATIONS
8.1 Spectrums
Velocity spectrum MNDE horizontal direction
7/25/2019 FD Fan Vibration Diagnostics
10/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
179
Velocity spectrum MNDE vertical direction
Velocity spectrum MNDE axial direction
Velocity spectrum MDE horizontal direction
Velocity spectrum MDE vertical direction
Velocity spectrum MDE axial direction
Velocity spectrum FDE (HUB 1) horizontal direction
Velocity spectrum FDE (HUB 1) vertical direction
Velocity spectrum FDE (HUB 1) axial direction
Velocity spectrum FNDE (HUB 2) horizontal direction
Velocity spectrum FNDE (HUB 2) vertical direction
7/25/2019 FD Fan Vibration Diagnostics
11/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
180
Velocity spectrum FNDE (HUB 2) axial direction
8.2 Observations from the spectrums
1) Overall vibrations of all the bearings are in in
satisfactory zone as per ISO 10816.
2) Horizontal direction vibration at MNDE, MDE.HUB1,and HUB2 are high side.
3) 1X Frequency is dominant in spectrums in all positions
4) Observed Blade pass frequency and 1XBlade pass
frequency and its side harmonics are present
in HUB1 and HUB2 in axial direction
5) High vibrations in Horizontal direction at MNDE, MDE,
HUB1 and HUB2 due to any flow obstruction in fan blades
or may be unbalance in fan rotor
Remarks:-
1) Check for partial close/open position of dampers in connectedduct.
2) check for impeller
Suggestion:
1) Check for bearing vibration and temperatures regularly untilcorrection.
IX. TABLE
Table3
Spike energy readings before rectification:
S.NO Date Position Direction Reading
1
17/10/12
MNDE HORIZONTAL 5.21
2 MDE HORIZONTAL 0.0339
3 HUB-1 HORIZANTAL 0.067
4 HUB-2 HORIZANTAL 0.033RPM: 1487
Normal value: 16.0mm/sec
7/25/2019 FD Fan Vibration Diagnostics
12/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
181
11.3 spectrums after rectification:
Velocity spectrum of MNDE in horizontal direction
Velocity spectrum of MNDE in vertical direction
Velocity spectrum of MNDE in axial direction
Velocity spectrum of MDE in horizontal direction
Velocity spectrum of MDE in vertical direction
Velocity spectrum of MDE in axial direction
Velocity spectrum of MNDE in vertical direction
Velocity spectrum of FDE in horizontal direction
Velocity spectrum of FDE in vertical direction
7/25/2019 FD Fan Vibration Diagnostics
13/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
182
Velocity spectrum of FDE in axial direction
Velocity spectrum of FNDE in horizontal direction
Velocity spectrum of FNDE in vertical direction
Velocity spectrum of FNDE (HUB 2) in axial direction
11.4 Spike energy readings:
RPM: 1487
Table 5
spike energy readings after rectification.(19/10/12)
S.NO Position Direction Reading
1 MNDE HORIZONTAL 0.032
2 MDE HORIZONTAL 0.066
3 HUB-1 HORIZANTAL 0.0061
4 HUB-2 HORIZANTAL 0.011
Normal value:
7/25/2019 FD Fan Vibration Diagnostics
14/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
183
XII.
RESULTS
The results that were obtained after rectification of FD fan are as follows:
12.1 Velocity displacement data
Data before Rectification:
S.
No
Date Position Velocity (mm/sec) Displacement(m)
17/10/2012
H V A H V A
1 MNDE 8.71 0.751 1.75 108 3.63 14.8
2 MDE 8.93 1.35 1.66 111 8.34 14.6
3 FDE(HUB1) 8.83 1.8 5.14 108 20.5 14.5
4 FNDE(HUB2) 9.24 1.76 5.41 114 20.8 16.2
Data After Rectification
S.
No
Date Position Velocity (mm/sec) Displacement(m)
19/10/2012
H V A H V A
1 MNDE 1.1 0.404 0.421 11.5 1.8 2.29
2 MDE 1.18 0.445 0.411 12.5 1.36 2.29
3 FDE(HUB1) 1.36 0.205 0.552 17.1 2.16 2.35
4 FNDE(HUB2) 1.37 0.228 1.19 17.6 2.67 2.94
Limits as per ISO 10816 part2 (mm/sec peak)
Good : 0 to 6.0 mm/sec
Satisfactory : 6.0to 12.3mm/sec
Alarm : 12.3 to 16.0 mm/sec
Not Permitted : >16.0mm/sec
By observing the above tabular forms higher values of velocity and displacement are obtained indicating a flaw in the
machine, which were rectified based on several considerations which were further discussed.
12. 2 Spike energy data
Spike energy data collected before rectification:
S.NO
Date Position Direction Reading
1
17/10/12
MNDE HORIZONTAL 5.21
2 MDE HORIZONTAL 0.0339
3 HUB-1 HORIZANTAL 0.067
4 HUB-2 HORIZANTL 0.033
Spike energy data collected after rectification:
S.NO Date Position Direction Reading
119/10/12
MNDE HORIZONTAL 0.032
2 MDE HORIZONTAL 0.066
3 HUB-1 HORIZANTAL 0.0061
4 HUB-2 HORIZANTAL 0.011
RPM 1487.
SAFE LIMITS OF spike energy (gSE):
3600 rpm: 1.4 gSE
1900 rpm: 0.70 gSE
1200 rpm: 0.50 gSE
900 rpm: 0.35 gSE
600 rpm: 0.25 gSE
The spike energy data is taken into criteria because of
frequency obtaining >600000 rpm. The equipment used in
V.T.P.S is set only to horizontal direction, where the
readings are obtained.
From the above data flaw is found out at MNDE, and
still the spectrum criteria is taken into considerations in
order to find out the existing defects.
7/25/2019 FD Fan Vibration Diagnostics
15/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
184
12.3 Spectrum data
In Vertical Direction at MNDE
Before Rectification
After Rectification
In vertical direction at MDE:
Before Rectification
After Rectification
Even after the replacement of the failed bearing with
new bearing there are still some irregular harmonicsobserved in axial direction at MDE, FDE (HUB 1) and
FNDE (HUB 2). The irregular harmonics in axial
directions are shown in the following spectrums.
In axial direction at MDE:
Before Rectification
After Rectification
In axial direction at FDE (HUB-1):
Before Rectification
After Rectification
7/25/2019 FD Fan Vibration Diagnostics
16/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
185
In axial direction at FNDE (HUB-2)
Before Rectification
After Rectification
Harmonics Observed In Axial Direction Indicates
Bending Of Shaft
XIII. CONCLUSION
From the above observed graphs the irregular harmonics
are observed in the axial direction, which indicates that thebending of the shaft caused due to bearing failure. After
replacement of bearing, the previously occurred irregular
harmonics were vanished in horizontal and vertical
direction.
The replacement of bearing requires a temporary pause
of FD-FAN (about a day). But the replacement of the shaftrequires the overall shut down of the unit. So instant
replacement of shaft is not possible as of bearing. So due
this factor the fan is allowed to run with irregular
harmonics in axial direction which doesnt affect majorly
for a period of time, and can be rectified during overall
maintenance.
REFERENCES
[1 ]
ISSN:0975-5462 International Journal of Engineering Science and
Technology
[2 ]
http://electromotores.com/PDF/InfoT%C3%A9cnica/EASA/Understanding%20Bearing%20Vibration%20Frequencies.pdf
[3 ]
http://www.bsahome.org/Archive/html/escreports/VibrationAnalysis
.pdf[4 ]
R.bandal,state of art in monitoring and rotating
machinesISMA2002, International conference on noise & vibrationengineering.
[5 ]
R.k Biswas , December 2006 vibration based condition monitoringon rotating machines
[6 ]
A.v Barkov, N.A.Barkov & Yu.Azovtsev, in 1997, vibration basedcondition monitoring on rotating machines.
[7 ]
DR.NTTPS vibration analysis material
[8 ]
http://www.vibrotek.com/ref.htm
[9 ]
Mechanical vibrations-G.K.Groover
[10 ]
Tanver(ref8), P.J.School of engineering, Durham university, gave
areview on CMBS on rotating electrical machines
[11 ]
Jones.N.B Yu-HuaLI (ref 1). Department of engineering, universityof Leicester, Leisister, UK had presented a paper on reciprocating
compressor condition monitoring.
[12 ]
http://en.wikipedia.org/wiki/Condition_monitoring
[13 ]http://en.wikipedia.org/wiki/Rolling-element_bearing
7/25/2019 FD Fan Vibration Diagnostics
17/17
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal,Volume 3, Issue 1, January 2013)
186
AUTHORBIOGRAPHY:
N. DILEEP is pursuing 4/4 B.Tech inDepartment of Mechanical Engineering atV.R.Siddhartha Engineering College,
vijayawada , India. Participated in varioustechnical paper presentations and secured 2nd
prize for Green Buildings paper
presentation.
K. ANUSHA is pursuing 4/4 B.Tech inDepartment of Mechanical Engineering atV.R.Siddhartha Engineering College,
vijayawada , India. Participated in various
technical paper presentations and secured 1stprize for OTEC paper presentation.
C.SATYA PRATHIK is pursuing 4/4 B.Tech
in Department of Mechanical Engineering atV.R.Siddhartha Engineering College,vijayawada , India.
B.KARTHEEK is pursuing 4/4 B.Tech inDepartment of Mechanical Engineering atV.R.Siddhartha Engineering College,vijayawada, India.
Sri K. RAVI KUMAR received B.Tech fromV.R. Siddhartha Engineering College,Kanuru, Vijayawada. He has received
M.Tech from JNTU-A, ANANTPUR,India.He is currently working as an Asst. Professorin the Dept of MECHANICAL, V.R.
Siddhartha Engineering College, Kanuru, Vijayawada, India. Hehas 5 years of teaching experience.