Swinburne University of Technology Sarawak Campus Faculty of Engineering, Computing and Sciences
The Study of Rolling Element Bearing Faults using Vibration Analysis
Bachelor of Engineering
Abstract Rolling element bearings are abundant and crucial in many machines, they play an important role in rotating machines. However, bearing failure is one of the main reasons that cause the breakdown of rotating machines. In most cases, the cost of bearings themselves is not significant, but the presence of faults in bearings may result in serious catastrophic consequences which will lead to costly downtime. Therefore, it is important to detect and identify the bearing faults in advance to avoid any unnecessary downtime cost. This project addresses the study of diagnosing rolling element bearing faults using vibration analysis. In this project, different types of faults are created artificially onto the rolling element bearings and then put to the test with Fast Fourier Transform (FFT). ( FFT). Analyzation of the vibration spectrums given by the bearings is shown in this report.
Acknowledgement First of all, I would like to express my deepest gratitude to everyone who has been providing me support in completing this report. Special appreciation to Dr. Ha How Ung who has been patiently guiding, assisting and encouraging me throughout the time of writing this report. Other than that I would like to thank the lab assistance, Mr Thomas, who gave me the permission to use all the required materials and equipment to complete the report.
Declaration I hereby declare that this report entitled “The Study of Rolling Element Bearing Faults using Vibration Analysis” is the result of my own project work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously or concurrently submitted by any other degree at Swinburne University of Technology (Sarawak Campus).
Name: Philip Chin Kai Wen ID: 7434243 Date: 20 May 2017
Table of Contents List of Figures ............................................................ .................................................................................. ............................................ ........................... ..... vi List of Tables............................................... Tables..................................................................... ............................................ ......................................... ................... vii 1.
2
Introduction.......................................... ................................................................ ............................................ ........................................... ..................... 1 1.1
Background ......................................... ............................................................... ............................................ .................................... .............. 1
1.2
Problem Statement ......................................... ............................................................... ............................................ ......................... ... 2
1.3
Research Aim .......................................... ................................................................ ............................................ ................................ .......... 2
1.4
Research Objective ............................................. ................................................................... ........................................... ..................... 2
1.5
Hypothesis ........................................... ................................................................. ............................................ .................................... .............. 3
1.6
Research Significant ........................................... ................................................................. ........................................... ..................... 3
1.7
Research Question .......................................... ................................................................ ............................................ ......................... ... 3
1.8
Research Scope and Assumptions ............................................ ................................................................. ..................... 4
Literature Review ........................................... ................................................................. ............................................ ................................ .......... 5 2.2
Types of Bearing Faults ............................................ .................................................................. .................................... .............. 5
2.5.2
Ball Pass Frequency Outer Race (BPFO) ............................................ .............................................. 16
2.5.3
Fundamental Train Frequency (FTF) ........................................... ................................................... ........ 16
2.5.4
Ball Spin Frequency (BSF) ............................................ .................................................................. ........................ 16
2.7 3
Previous Research .......................................... ................................................................ ............................................ ........................ 17
Methodology ............................................ .................................................................. ............................................ ..................................... ............... 19 3.1
Methodology Description .......................................... ................................................................ .................................. ............ 19
3.2
Flow Chart ........................................... ................................................................. ............................................ .................................. ............ 21
3.3
Apparatus and Materials ............................................ .................................................................. .................................. ............ 22
3.3.1 Bruel & Kjaer Lan I/F 3560C 4CH 25kHZ Sound Vibration Acoustic FFT Analyzer ...................................................... ............................................................................ ............................................ .......................... .... 22 3.3.2
Bruel & Kjaer Accelerometer (Type 4508 B 001) ............................... ............................... 22
3.3.3
Bruel & Kjaer AO-0038-D-030 Cable................................................. Cable................................................... 23
3.3.4
Single motor test rig (Gunt TM170 Balancing Apparatus) .................. 23
3.3.5
NTN 127 Bearings ........................................... ................................................................. ..................................... ............... 24
3.4
Experimental Setup ............................................ .................................................................. ......................................... ................... 25
List of Figures Figure 1: Percent film vs lambda ratio (Λ) (S.J . Lacey, 2008) 2008) .................................... 9 Figure 2: Vibration Vibr ation caused by the wavy raceway racewa y (T. Momono et.al, 1999) .............. 10 Figure 3: Vibration Signal of a healthy bearing (S.J. (S.J . Lacey, 2008) .......................... 11 Figure 4: Vibration Signal of a Faulty Bearing (S.J. (S.J . Lacey, 2008) ........................... ........................... 11 11 Figure 5: The effect of bearing raceway racewa y defect on the positions of bearing ball (J. Liu et.al, 2012).................................... .......................................................... ............................................ ............................................ .................................. ............ 12 Figure 6: Amplitude modulation around the defective defecti ve area (S.J. Lacey, 2008) ........ 12 Figure 7: Bruel & Ksaer FFT Analyzer ...................................................... ..................................................................... ............... 22 Figure 8: Bruel & Kjaer Kja er Accelerometer ........................................... ................................................................. .......................... .... 22 Figure 9: Cable connector cable ............................................ .................................................................. ..................................... ............... 23 Figure 10: Single rotor test rig (www.gunt.de) ............................ .................................................. .............................. ........ 23
List of Tables Table 1: Dimension of 627 Bearing ......................................... ............................................................... .................................. ............ 24 Table 2: Characteristic Defect Frequency of 627 Bearing ......................................... ......................................... 27
1.
Introduction
1.1 Background
Rolling element bearings can be considered as the key elements in machinery, especially in the ones that exhibit rotational motion. However, the failures in them may damage the whole system to an unmanageable level. A typical rolling element bearing consists of an outer and inner raceway with a set of rolling elements or balls located in between, while a cage is installed to keep the balls in place. Rolling element bearings faults may occur in the raceways, the balls or even the cage, for example, scratches, cracks, on the surface of a raceway. Many bearings fail prematurely due to several factors that contribute in bearing malfunction. It is usually not easy to determine the exact cause but most likely they are due to the presence of foreign matter such as dirt in bearings, improper mounting, bearing misalignment, bearing corrosion or improper bearing lubrication. All these
how the bearing faults influence bearing dynamics, the measurement of vibration and the detection of bearing faults from the vibration characteristics.
1.2 Problem Statement
Rolling element bearings are among the most critical machine components that can be found in different industries. Throughout the years, bearings have been undergoing different kinds of improvement either in their design, materials and lubrication technology, as a result, bearings have proven to be long lasting and reliable when properly utilised. However, bearings do fail at some point of a time, and its failure is always associated with significant damage to machine parts and can be considered as one the main reasons that causes the breakdown of machines. To avoid this from happening, condition monitoring philosophy of bearings using vibration analysis method has been gaining wide acceptance throughout
industry. The problem in condition
2. To detect and diagnose rolling element bearings faults using vibration analysis method.
1.5 Hypothesis
1. Vibration amplitude will be higher with faulty bearings compared to healthy ones. 2. Types of bearing faults can be determined by the amplitude of vibration at a specific frequency.
1.6 Research Significant
The research is carried out to determine bearing faults using vibration analysis and to study how the faults in the bearing can affect the vibration spectrum of a bearing.
•
What machine or software?
•
Are the results obtained consistent?
4. What are the factors that might affect the outcome of the experiment? •
The speed of rotation?
•
How will different conditions of bearings affect the vibration characteristics?
1.8 Research Scope and Assumptions
In the research, literature review will be done to study more about the relationship between the bearing faults and its vibration spectrum. Vibration analysis will be done on several of NTN 627 bearings. Different faults will
2 Literature Review 2.2 Types of Bearing Faults 2.2.1
Wear - Abrasive Contamination
This mode of damage is created by the presence of foreign particles within the bearing. Some of the examples of these foreign particles are sand or fine metals resulted from grinding of gears and chipping of metals. These tiny unwanted particles regularly enter the bearings through defective def ective bearing seals and may build up as time goes by. The existence of these abrasive particles may cause the inner clearance of bearings to increase or in worst case scenario, create misalignments in bearings and reduce the bearings life. 2.2.2
Wear – Bruising and Pitting
Similar to abrasive contamination, this type of damage is also caused by the presence of hard foreign elements in the internal of the bearing. However, in this case, the foreign particles travel around the bearing with the lubrication flow and create dents
in the bearings to minimize the friction between the rolling elements and the contact surfaces during their operation. Therefore, it is crucial to determine the right amount of lubricants in the bearings, the viscosity, the type and the grade of the lubricants. There are four types of damages that can be c aused by inadequate lubrication:
-
Discolouration o
Caused by the insufficient lubricants in the bearings, which lead to excessive high temperature of bearings due to the presence of friction.
-
Scoring and Peeling o
Caused by inadequate amount of lubricant which can results in immediate alteration in temperature and operating conditions.
-
Excessive roller end heat o
Damages at the ends of the rollers with excessively high temperature because of improper lubricant
-
Total bearing lockup o
Change in the bearing’s initial geometry and all of the elements in the bearings due to localized high heat
Chipping or spalling in bearings may be caused by the weakening of bearing materials. Normally the failures of bearing races and rolling elements start as a small fracture and gradually become more severe until the particles of the metal eventually flake away. This may lead to the increase of roughness to the surface of the bearings races and introduce the presence of loosen metal met al particles within the bearings.
2.3 Condition Monitoring and Acoustic Emission Response As indicated by A.B. Kufman in 1975, there is innumerable number of techniques that have been created to screen the state of machines. Indeed, even with simply the utilization of sight and sound, we can decide the state of a machine effectively. Despite the fact that there are numerous systems that can be utilized to screen the state of a machine, vibration checking and investigation is the most all around acknowledged and broadly utilized strategy for the reason. This strategy is utilized to gather the vibration information and capture important frequencies that determine whether or not the machine is in good condition.
(Smith, 1982). In 1990, a study conducted by N. Tandon and B.C. Nakra showed that Acoustic Emission parameters for instance, peak amplitude and counts are capable of detecting defect in radially loaded rolling element bearing at low to medium speed. The peak amplitude and counts are also utilized to inspect the quality of bearings (V. Bansal et al, 1990).
2.4 Sources of vibration Complex vibration frequencies are generated as the components in a rolling element bearing, namely races, rolling elements and cage interact together. Despite the fact that bearings now are manufactured with strict quality control using profoundly précised machines under clean environment, the bearings will still possess imperfections and produce vibration as they operate. With today’s technology, even though we are able to reduce the amplitude of surface imperfections of a bearing to a small as nanometres range, vibrations can still exist in the frequency within the entire audible range which is 20 Hertz to 20 Kilo Hertz (S.J. Lacey, 2008). The intensity of
=
ball RMS roughness
=
raceway RMS roughness
Figure 1: Percent film vs lambda ratio (Λ) (S.J. (Λ) (S.J. Lacey, 2008)
Figure 1 above shows the relationship between percent film and the lambda ratio. We are able to see that lambda ratio increases with percent film. As the lambda ratio is
vibration in bearings. Gustafsson’s analysis in his study has been confirmed by numerous researchers.
Figure 2: Vibration caused by the wavy raceway (T. Momono et.al, 1999)
Although the waviness of bearing cannot be eliminated completely, the vibration caused by this case can only be minimized by reducing the waviness of the surfaces of bearing races. Regardless, extra attention is needed while mounting the bearing
Figure 3: Vibration Signal of a healthy bearing (S.J. Lacey, 2008)
Figure 4: Vibration Signal of a Faulty Bearing (S.J. Lacey, 2008)
From figures 3 and 4 above, we can see the comparison of vibration signal between a healthy and a faulty bearing. It was shown that the fault in the bearing has produced a
Figure 5: The effect of bearing raceway defect on the positions of bearing ball (J. Liu et.al, 2012)
become less stable and result in the increasing of sidebands of other fundamental bearing frequencies (S.J. Lacey 2008). Large impact forces will also be generated between the cage and the balls while accelerating and decelerating as the clearance of the cage gets bigger. 2.3.3.3 Rolling 2.3.3.3 Rolling Element Defect Defect Damages on the rolling elements of bearing can produce frequencies two times as quickly as ball spin frequency and also the fundamental train frequency. This is because the defect on the rolling element hits both inner and outer raceways of the bearing. However, this can be difficult to detect as the defects defect s in the rolling roll ing elements will not always strike both of the raceways as the rolling elements are able to spin in various directions.
2.5 Vibration Analysis on Bearings faults Vibration analysis is one state of the art method for monitoring rolling element bearings fault by utilizing vibration information such
waveform, phase and
oscillate and further destroy the components of the machine if the issue is not managed properly. In 1982, T. Igarashi et al stated that the presence of defects in rolling element bearings can cause the vibration level to increase in the high frequency range of spectrum. This is due to the natural frequencies of the bearing being excited by the impulsive force caused by the defects in the bearing. According to T. Igarashi et al, the frequency of faulty bearings usually falls in the low frequency region, which is less than 500Hz, while the resonance frequency of bearing lies around medium to high frequency range, somewhere around 10 kHz. The interaction between the local defect on a bearing element and its mating components creates an impulsive force that lasts for a very short duration. This impact results in vibration which can be analysed and examined for the presence of defect. In 1979, K. Nishio et al stated that there are two techniques to investigate the mechanism of bearing failure. The first technique is by running a brand new healthy bearing on a rotating rotati ng shaft of a working machine until it fails. The vibration signal is
bearing resonance indicators (HFNBRIs). HFNBRIs can detect frequencies ranging from 3 kHz to 50 kHz which are can be both sonic (<20 kHz) and ultrasonic (>20 kHz). Archambault, 2009 stated that shock or friction can produce these frequencies and HFNBRI method is an effective way in identifying these frequencies and show early indication of bearing faults. To determine the reasons of HFNBRIs’ reactions, discrete frequency indicators are used. Normally, Fast Fourier Transform (FFT) velocity spectrum is unable to detect bearing faults until they get more severe. In spite of that, an acceleration spectrum which is partitioned into two bands can effectively track the vibration from different sources. The first one is used to monitor frequencies produced by bearing faults, while the second one is to inspect the characteristic of the frequencies produced. By observing each of these bands, analysts are able to distinguish the severity of bearing faults the rate bearing wears. (Berry & Robinson, 2001) In 2011, Brian Graney and Ken Starry stated that conditions of bearings diagnosed by HFNBRI and discrete frequency frequenc y indicators can be established est ablished with FFT and time-
These frequencies will be generated while bearings operate, and they vary with the geometry of bearings. According to a journal by Baldor Dodge in 2007, there are four types of frequencies, each of them is related to a particular part of a rolling element bearing, namely: 2.5.1 Ball Pass Frequency Inner Race (BPFI)
The reoccurrences of rollers that go through a particular point in the inner race of a bearing. In other words, in one rotation rotat ion of inner race, how many times will a specific point in inner race passes through rollers.
, =
2
(1 +
)
2.5.2 Ball Pass Frequency Outer Race (BPFO)
The frequency of specific point in outer race that passes through rollers in one single revolution of inner race.
, =
2
(1 −
)
= ø =
2.7 Previous Research Vibration analysis is often regarded as one of the most reliable methods of identifying problems or flaws that occur within rolling element bearing. Different methods of vibration analysis have been developed over the years to further improve the reliability of the analysis. Plenty of researchers have hypothetically and theoretically conducted studies and experiments on the development of faults in bearings and the methods of locating the faults in bearings. In 1999, Dr Alexej. V. Barkov expressed that the faults detection techniques in rolling element bearing by making use of spectral analysis on high frequency vibration envelope started in the mid 1970’s. By that time, the algorithms for diagnosis and faults prediction of rolling element bearings were just recently created.
readings for brand new flawless bearings and the flawed bearings with inner and outer races faults, HHT technique was able to provide multiple resolutions in distinct frequency scales and take the variation of frequencies into consideration. Through this comparative analysis, V.K.Rai and A.R. Mohanty have demonstrated the existence of amplitude regulations and were able to get hold of the frequencies of defect accurately. Tuncay Karacay et al. in 2009 conducted an experiment by installing two brand new rolling element bearings onto a test rig and the bearings let to operate nonstop throughout their entire lifespan under consistent rotating velocity and load. The development of defects was measured regularly at 15 minutes interval and the parameters that were collected are the vibrations’ peak-to-peak amplitude and its root mean square (RMS). Meanwhile, the bearings’ crest factor and kurtosis number were also determined to predict the condition of the bearings. From the experiment, they have discovered that the first defect formed in the bearings is at the inner race caused by the slight defect found in bearing balls. As experiment went on, the defects on both inner race and balls developed, and finally followed by the outer race.
3 Methodology 3.1 Methodology Description
Bearings are abundant in many types of machines, especially the ones that exhibit rotational movements. Bearings reduce friction as component in a machine rotates, thus providing smoother and quiet spin. Indirectly, bearings also prevent heat generation caused by friction. However, bearings may be damaged at some point of the time. Several factors, such as misalignment, rust, excessive loading or the presence of foreign particles can cause bearings to be faulty. When bearings are damaged, rotation will be rough, thus creating vibration and unpleasing sound. This condition will certainly be very unfavourable for machineries as vibration can causes looseness in other parts of machineries and in a worst case scenario, the entire machinery may face a catastrophic failure. Bearings are usually located very deep inside a machinery, thus making it to be very inaccessible, especially when one has to take apart many different machine
specific characteristic defect frequencies. This was based on the journal by Baldor Dodge stated earlier in the literature review section, where it indicated that each component in the bearing will have their own specific frequencies. Ball spin frequency of inner race (BPFI) for the inner race, ball spin frequency of outer race (BPFO) for outer race, Ball Spin Frequency (BSF) and Fundamental Train Frequency (FTF) for the cage. At any location of the bearing where defect was present, amplitude spike would show up at their respective frequencies. Characteristic defect frequencies were obtained through a series of calculation according to the bearings’ dimension and the rotational speed.
3.2 Flow Chart
Selection of Bearings
Creation of Artificial Faults onto the Bearings • •
Healthy Cracked o Inner race o Outer race o Ball
Calculation of characteristic defect frequencies based on the specification of the chosen bearing o o o
Load the bearings onto the test rig
o
BSF BPFO BPFI FTF
3.3 Apparatus and Materials 3.3.1 Bruel & Kjaer Lan I/F 3560C 4CH 25kHZ Sound Vibration Acoustic FFT Analyzer
Bruel and Kjaer FFT analyser is a versatile, noise and vibration analysis system. It contains input and output channels for microphone and accelerometers and is capable of performing real-time measurement for signal and system analysis. The FFT analyser collects vibration signals through accelerometer and displays them in a form of readable graphs or spectrums. This apparatus is connected to a desktop computer and can only be accessed through its software, call ed “PULSE”.
3.3.3 Bruel & Kjaer AO-0038-D-030 Cable This cable acts as a connector that links the accelerometer and FFT analyser together.
This cable is designed to eliminate mechanically induced noise, thus giving a more accurate result.
Figure 9: Cable connector cable
3.3.4 Single motor test rig (Gunt TM170 Balancing Apparatus) The will be the platform where the bearing will be installed to. It is essentially a
balancing apparatus, however it can easily be converted to a simple s imple single si ngle rotor test
3.3.5 NTN 127 Bearings Few bearings of this type will be used in this research report. The dimension or
specifications of the bearings given are as follow: Inner/Bore Diameter
7mm
Outer Diameter
22mm
Bearing Pitch
22mm
Pitch Diameter
14.7mm
Number of Balls
7
Ball Diameter
3.969mm Table 1: Dimension of 627 Bearing
3.4 Experimental Setup 3.4.1 Bearing Preparation Different modes of defects were created artificially to the bearings to simulate different real bearing conditions:
i. ii.
Healthy Bearing (Figure 11) Inner race Crack (Figure 12)
Figure 12: Defect on bearing inner race
iii.
Outer Race Crack (Figure 13)
3.4.2 Experimental Platform Configuration There are two supports for the shaft on the tes t rig as shown in Figure 15. The shaft is held in place with two bearings. For the experiment, bearing on one end of the shaft was replaced with test bearings created earlier while another end was left unaltered. As the bearings are loaded to a test rig, they were set to rotate at a constant speed of 17HZ. At the same time, an accelerometer is used to pick up the vibration signals of the test bearings, in this case, it was situated right on top of the test bearing as shown in Figure 16 for better capturing of vibration signal. The signals are then sent to FFT analyzer, where vibration spectrums for each of the bearings are produced for analyzation.
bearings, namely the number of balls, pitch diameter of bearings, diamete r of bearing balls and the contact angle. Calculations were done to determine characteristic defect frequency for NTN 627 bearings. Based on the specifications and dimensions of the bearings shown in section 3.3.5, the defect frequencies are shown in Table 2 below. Theoretically, as the bearing was loaded onto the test rig, FFT analyzer will produce a vibration spectrum. Any faults within the bearing either at the outer ring, inner ring or the ball, will cause a rise of amplitude at their respective frequencies. NTN 627 Bearing
Speed of Shaft
17HZ
Ball Spin Frequency =
2
(1 −
Ball Pass Frequency of Outer Ring
29.2HZ 2
)
4 Results and Discussion 4.1 Healthy Bearing
Figure 17: Vibration Spectrum of Healthy Bearing
4.2 Bearing with Cracked Inner Race
Figure 18: Vibration Spectrum of Bearing with Cracked Inner Race
Figure 18 shows the vibration of bearing with cracked inner race. From the vibration spectrum, it can be observed that the vibration vibr ation is greater than healthy healt hy bearing. A peak can be observed at 17HZ as the bearing was rotat ing at 17HZ. The crack in inner race gave an amplitude rise of 0.03m/s 2 at ball pass frequency of inner race (BPFI)
4.3 Bearing with Cracked Outer Race
Figure 19: Vibration Spectrum of Bearing with Cracked Outer Race
Figure 19 shows the spectrum by bearing with damaged outer race. There was an amplitude of vibration at 17HZ as this was the speed that the bearing was spinning. Vibration can be seen at 43.3HZ with an amplitude of 0.045m/s 2 as shown in the figure above, which was essentially the ball pass frequency of outer race (BPFO),
4.4 Bearing with Damaged Ball
Figure 20: Vibration Spectrum of Bearing with Damaged Ball
Figure 20 shows the vibration of bearing with defected ball. Similarly, there was an amplitude rise at 17HZ because of the constant speed that the bearing was rotating. Vibrations could be seen clearly in Figure 20. Peak amplitude at 0.032m/s 2 can be observed at ball spin frequency (BSF), at 28.9HZ, along with its harmonic due to the defect at the ball.
5. Conclusion In this paper, the vibration characteristics of different types of bearings are being compared. FFT analyzer was used to generate the vibration spectrum for bearings with different conditions, namely healthy bearing, bearing with defected ball, bearing with cracked inner race and bearing with cracked outer race. From the results obtained, the vibration of healthy bearing was clearly lower than the defected ones. For bearings with defects, peak amplitude will show up at the characteristic defect frequencies, which is calculated according to the dimensions of bearing. FFT analysis has proven to be an effective way to diagnose rolling element bearing faults without having to disassemble it. It can be concluded that different types of bearing defects will affect the vibration characteristic in a certain way: •
Defected outer race - rise in amplitude at ball pass frequency of outer race (BPFO)
•
Defected inner race – rise in amplitude at ball pass frequency of inner race
6. Recommendations for Future Work From the results obtained, noise is present in every situation. Noise is random and very unpredictable. Although not significant, these random signals can spike to a higher amplitude in a way that it can even causes confusion while analysing the vibration graph. Noise cannot be totally eliminated, as the accelerometer is very sensitive, not only to bearing’s vibration, but also to the test rig and other sources that cause vibration. However, it can be reduced to some extend through the following recommendations: • •
Isolate the test rig from any other moving mechanisms Install dampening material under the feet of test rig to minimize vibration signal from the surrounding
There are some other recommendations that can be done to further study bearing faults using vibration analysis. These will benefit us in understanding deeper the relationship between bearing defects and its vibration characteristics. They are: •
•
Aside of localized defect, we can create defect around the circumference of inner and outer ring to mimic a severely severel y worn out bearing Instead of creating defect in a form of pit, we can create a hump to the races
References 1) Lacey, S.J 2008, An Overview Overview of Bearing Vibration Analysis Analysis , Maintenance & Asset Management Journal, vol. 23, Maintenanceonline, Surrey, pp.32-42. 2) Dong, W 2009, ‘Rolling element bearing fault detection using an improved combination of Hilbert and Wavelet transforms’ , Journal of Mechanical Mechanical Science Science and Technology, vol. 23, no. 2009, pp. 3292-3301. 3) Howard, I.M 1994, A Review of Rolling Rolling Element Element Bearing Bearing Vibration “Detection, “Detection, Diagnosis and and Prognosis” Prognosis” , Aeronautical and Maritime Research Laboratory Airframes and engines Division, Melbourne. 4) Nikalaou, N.G & Antoniadis, Antoniadis, I.A. 2002, Rolling element element fault fault diagnosis using wavelet packets, NDT&E International , Elsevier B.V, Vol. 35, pp. 197-205. 5) Alexej, B & Natalia, B 1999, Diagnostics Diagnostics of Gearing Gearing and Geared Geared Couplings Using Envelope Spectrum Methods, VibroAcoustical Systems and Technologies Inc., Saint-Petersburg, Russia. 6) Rai, V.K. & Mohanty, A.R. 2007, Bearing Faults Faults Diagnosis Diagnosis using FFT of Intrinsic mode functions functions in Hilbert-Huang Hilbert-Huang Transform, Transform, Mechanical Systems and Signal Processing, vol.21, pp. 2607-2615. 7) Tuncay, K & Nizami, A 2009 , Experimental Experimental Diagnostics Diagnostics of Ball Ball Bearings using 42, pp. 836 – 843. Statistical and Spectral Methods , Tribology International , vol. 42,
16) Tandon, N & Nakra, B 1990, Defect detection detection in rolling element element bearings bearings by Emis sion, vol. 9, pp. 25-88. acoustic emission method , J. Acoustic Emission, 17) Gustafsson, O & Tallaron, T 1962, Detection Detection of damage in in assembled assembled rolling Societ y of Lubricant Engineer, vol. 5, pp. 197-209. element bearing, American Society 18) Yoshioka, T & Fujiwara, T 1982, A new acoustic acoustic emission emission source locating system for the study of rolling contact fatigue , Wear, vol. 81, pp 183-186. 19) Yoshioka, T & Fujiwara, T 1984, Application Application of acoustic acoustic emission emission techique to detection of rolling element bearing failure , Acoustic emission monitoring and analysis in manufacturing, ASME, pp. 55-75. 20) Bansal, V Gupta, B Prakash, A & Eshwar, Y 1990 , Quality in inspection inspection of rolling element bearing using emission technique , J. Acoustic Emission, vol. 9,pp 142-146. 21) Boto, P & Fernlund, I 1972, Shock Pulse measurement of bearings , Wear, vol.19, pp.367-371 22) Igarashi, T & Hamada, H 1982, Studies on the vibration and Sound of defective J SME, vol.25, pp. 994-997. rolling Bearings , Bulletin of JSME, 23) Nishio, 23) Nishio, K Hoshiya, S & Miyachi, Miyachi, T 1979, An Investigation Investigation of the early detection detection of defects in ball bearings by the vibration monitoring , ASME Paper 79-DET-45 ASME, New York. 24) Williams, T, Ribadeneria, X & Billingtons, S 2001, Rolling Element Element bearing bearing diagnostics is tun-to-failure lifetime testing , Mechanical System and Signaling
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