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RELATIONSHIPS BETWEEN OUT OF BALANCE AND

NUSALIGNMENT AND THEIR VIBRATION CHARACTERISTICS

Chua Chee Siang

TA 355 C559 2004

Bachelor of Engineering with Honours

(Mechanical

Engineering

_{and Manufacturing}

Systems)

2004

BORANG PENYERAHAN TESIS

Judul: Relationships Between Out of Balance and Misalignment and Their Vibration Characteristics SESI PENGAJIAN _{: 2003/2004}

Saya CHUA CHEE SIANG mengaku membenarkan tesis ini disimpan di Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dengan syarat-syarat kegunaan seperti berikut:

1. Hakmilik kertas projek adalah di bawah nama penulis melainkan penulisan sebagai projek bersama dan dibiayai oleh Universiti Malaysia Sarawak, hakmiliknya adalah kepunyaan Universiti Malaysia Sarawak. 2. Naskhah salinan di dalam bentuk kertas atau mikro hanya boleh dibuat dengan kebenaran bertulis daripada

Universiti Malaysia Sarawak atau penulis.

3. _{Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dibenarkan membuat salinan untuk} pengajian mereka.

4. _{Kertas projek hanya boleh diterbitkan dengan kebenaran penulis atau Universiti Malaysia Sarawak.} Bayaran royalti adalah mengikut kadar yang dipersetujui kelak.

5. _{* Saya meabeaarkaft/tidak membenarkan Perpustakaan membuat salinan kertas projek ini sebagai bahan} pertukaran di antara institusi pengajian tinggi.

6. ** Sila tandakan () di mana kotak yang berkenaan SULIT

v

(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972).

TERHAD (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan).

TIDAK TERHAD

Disahkan oleh

(TANDATANGAN PENULIS) Alamat tetap: 193A, Lorong 1,

Jalan Semaba, Batu Lima 93250 Kuching, Sarawak. Tarikh: 29/03/2. Catatan ' *t

Wf

Dr Ha How Ung

Tarikh:

i A-Plk zab`F

Potong yang tidak berkenaan.

Jika Kertas Projek ini SULIT atau TERHAD, sila Iampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyertakan sekali tempoh kertas projek. Ini perlu dikelaskan sebagai SULIT atau TERHAD.

APPROVAL SHEET

This thesis entitled

"Relationships Between Out of Balance and Misalignment

and Their Vibration Characteristics"

was prepared and presented by Chua Chee

Siang as a partial fulfillment of the requirement for the degree of Bachelor of Engineering

with Honours (Mechanical Engineering and Manufacturing System) was hereby read and

approved by:

Date:

1

' I" /t / (- cf Dr Ha How Ung ! " ,.

Supervisor

Faculty of Engineering

Universiti Malaysia Sarawak

-In("-314ý_n

Pusat Khidmat

Maklumat

Akadendt

UNIVERSITI MALAYSIA SARAWAK 94300 Kota Sr. maraban

P. KNIDMAT MAKLUMATAKADEMK U NIMAS

11111

1000125803

imiuiiuiri

RELATIONSHIPS BETWEEN OUT OF BALANCE AND

MISALIGNMENT AND THEIR VIBRATION CHARACTERISTICS

CHUA CHEE SIANG

This project is submitted in partial fulfillment of

the requirements for the degree of Bachelor of Engineering with Honours (Mechanical Engineering and Manufacturing System)

i 'i Lrr-,.. ; Faculty of Engineering

UNIVERSITI MALAYSIA SARAWAK

Dedicated to my beloved family

ACKNOWLEDGEMENTS

The researcher would like to take this opportunity to express his sincere acknowledgement

and appreciation to several individuals and parties that provided helps and guidance

throughout the duration of the project.

Sincere gratitude and appreciation to the project supervisors, Associate Professor Dr. Sinin

Hamdan and Dr. Ha How Ung, who had helped in experiment's hardware preparation and had

providing a lot of guidance and opinion in conducting the experiment and writing this report.

Also, to Mr. Stanley, who kindly gave a lot of cooperation in setting up the rotor kit test rig.

In addition, the researcher would like to specifically thanks to the all Lecturer, Laboratory

Assistants, and other technical staff of Faculty of Engineering for their assistance in carrying

out laboratory works and testing during projects duration. Last but not least, not forgetting

everyone who had involved directly or indirectly to make this project success, I would like to

thank them very much for their help.

ABSTRACT

Majority of the machinery in industries nowadays consists of rotating or moving

components. Any fault in this rotary component may lead to adverse vibration and thus the

smooth running of the system. However, each type of machinery fault exhibits a

characteristic vibration signature which is uniquely its own. The signal is the sum total of the

design, manufacture, application, and wear of each of its components. Unbalance normally

generates 1x rotating speed (RPM) dominant vibration in vibration spectrum, due to the cyclic

excitation force that encounter each time the machine makes a full revolution. On the other

hand, 2x RPM dominant vibration will normally presented in vibration spectrum for misalignment problem, where each of the two shaft causing a cyclic excitation forces. Phase relationship between inboard and outboard bearing across coupling, will be the easiest way to differentiate the above 2 mechanical defect, as misalignment normally will also generate high vibration at 1x RPM.

AB STRAK

Kebanyakan mesin yang digunakan di dalam industri hari ini mengandungi komponen

yang berpusing dan bergerak. Sebarang kerosakan di dalam komponen berpusing ini

mungkin menyebabkan getaran, seterusnya mengakibatkan sistem tidak dapat berfungsi

dengan lancar. Walaubagaimanapun, setiap jenis kerosakan pada komponen berpusing ini

mempunyai sifat getaran yang unit. Signal ini merupakan hasil daripada kesalahan

rekabentuk, proses pembuatan, cara penggunaan, dan hakisan yang dialami oleh komponen

tersebut. Ketidakseimbangan biasanya menyebabkan 1xRPM dalam spectrum getaran,

disebabakan daya yang dialami setiap kali mesin membuat satu putaran lengkap. Sebaliknya, 2xRPM getaran akan muncul di dalam spectrum getaran sekiranya ketidaktepatan garispusat

aci merupakan masalah yang terbesar. Hubungan fasa di antara dua bearing sokongan,

merupakan cara yand terbaik untuk membezakan di antara dua masalah tersebut,

memandangkan ketidaktepatan garispusat aci kadangkala juga akan mengakibatkan getaran

tinggi di 1xRPM.

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TABLE OF CONTENTS

Description

Confirmation Letter of Project Report Submission Approval Sheet Title Page Dedication Acknowledgements

Abstract

Abstrak

Table of Contents

List of Figures

List of Tables

List of Appendixes

CHAPTER 1

INTRODUCTION

1.1

Background Of Vibration Monitoring

1.2

_{Objective of Work}

1.3

_{Definition of Terms}

1.3.1

_{Definition of Vibration}

1.3.2

_{Definition of Unbalance}

1.3.3

_{Definition of Misalignment}

Page

1 11 III iv V V1-1R 1R-X R1 X11

1

4

4

4

4

5

V1

CHAPTER 2

LITERATURE REVIEW

2.1

_{Review of Fundamental Vibration Theory}

2.2

Vibration Spectrum

6

8

2.2.1

Time Domain Analysis

9

2.2.2

Frequency Domain Analysis

11

2.3

_{Selection of Measurement Parameter :}

Displacement, Velocity or Acceleration

2.4

_{Important of Phase in Vibration Monitoring}

2.5

_{Typical Spectra and Phase Behaviors for Unbalance}

and Misalignment

2.6

_{Severity of Machinery Vibration}

2.6.1

Velocity RMS

2.7

Vibration Transducers

2.8

_{Rigid and Flexible Rotors}

2.9

Rotor Mode Shapes

CHAPTER 3

METHODOLOGY

3.1

Introduction

3.2

Bently Nevada Rotor Kit

12

15

16

17

20

22

23

27

31

31

3.2.1

Rotor Kit Components

33

3.2.1.1

_{Rotor and Base Assembly}

33

3.2.1.2

_{Motor and Motor Speed Control}

₃₄

3.2.1.3

_{Proximity Probes and Proximitor}

Assembly

₃₄

3.2.1.4

Auxiliary Components

34

3.2.2

Setting Up The Rotor Kit

35

3.2.2.1

Rotation Direction

35

3.2.2.2

Probes

35

3.2.2.3

Aligning the Mass

36

3.2.3

_{Rotor Kit Setup for Unbalance and Misalignment}

37

3.2.3.1

Mass Unbalance

3.2.3.2

Misalignment

3.2.4

Safety Precaution.

3.3

ADRE for Windows

3.4

Data Collector 2526

3.5 Experimental Procedure

CHAPTER 4

RESULTS AND DISCUSSION

4.1

_{Experimental Data of Various Rotating Speed.}

37

38

38

39

40

40

42

4.1.1

Discussion

45

4.2

_{Experimental Data of Various Unbalance Weight.}

47

4.2.1

Discussion

52

4.3

_{Experimental Data of Unbalance Weight at Various Angle.}

54

4.3.1

Discussion

₅₆

4.4

_{Experimental Data of Misalignment Condition.}

57

4.4.1

Discussion

₆₃

CHAPTER 5

CONCLUSION AND RECOMMENDATION

5.1

Conclusion

5.2

Recommendation

65

67

BIBLIOGRAPHY

69

APPENDIXES

71

LIST OF FIGURES

Description

Page

Figure 2.1 : Fast Fourier Transform 9

Figure 2.2 : Velocity and Displacement Spectrum 12

Figure 2.3 Sensitivity of Parameter to Failure 13

Figure 2.4 : Sinusoidal Wave Form 21

Figure 2.5 : Combination of Vibration Sources 22

Figure 2.6 : Rigid and Flexible Rotor 25

Figure 2.7 Measurement of Displacement on a Center Mounted Disk 28

Figure 2.8 : Rotation of Rotor

(a) Below and (b) Above its Shaft Critical Speed.

30

Figure 3.1 : Bently Nevada Rotor Kit

Figure 3.2

_{Rotation Direction of Rotor Kit}

Figure 3.3 : Mounting of Proximity Probe

33

35

36

Figure 3.4 : Aligning the Mass of the Flywheel.

37

Figure 4.1 : Orbit Plot for Inboard Bearing@1500 RPM.

47

Figure 4.2 : Orbit Plot for Outboard Bearing@1500 RPM.

47

Figure 4.3 : Bode Plot for Inboard Bearing@1500 RPM.

48

Figure 4.4 : Bode Plot for Outboard Bearing@1500 RPM.

48

Figure 4.5 : Vibration Spectrum for Inboard Bearing@1500 RPM.

49

Figure 4.6 : Vibration Spectrum for Outboard Bearing@1500 RPM.

49

Figure 4.7 : Reference Orbit Plot for Inboard Bearing@1800 RPM.

58

Figure 4.8 : Reference Orbit Plot for Outboard Bearing@1800 RPM.

58

Figure 4.9 : Orbit Plot for Inboard Bearing@1800 RPM

when in misalignment condition. 59

Figure 4.10: Orbit Plot for Outboard Bearing@1800 RPM

when in misalignment condition.

59

Figure 4.11: Reference Inboard Bearing Spectrum@ 1800RPM

60

Figure 4.12: Reference Outboard Bearing Spectrum@ 1800RPM

60

Figure 4.13: Misaligned Inboard Bearing Spectrum@ 1800RPM

61

Figure 4.14: Misaligned Outboard Bearing Spectrum@ 1800RPM.

61

Figure 4.15: Inboard Bearing Vibration Spectrum@ 1800RPM

62

Figure 4.16: Outboard Bearing Vibration Spectrum@ 1800RPM

62

LIST OF TABLES

Description

Page

Table 2.1 : Vibration Severity Criteria

Table 4.1

Inboard Bearing Vibration Displacement Parameter

for Various Speed.

Table 4.2 : Outboard Bearing Vibration Displacement Parameter

for Various Speed.

Table 4.3

Vibration Velocity at Various Speed.

Table 4.4 : Inboard Bearing Vibration Displacement Parameter

for Various Unbalance Weight.

Table 4.5

Outboard Bearing Vibration Displacement Parameter

for Various Unbalance Weight.

Table 4.6 : Vibration Velocity for Various Unbalance Weight.

Table 4.7

Inboard Bearing Vibration Displacement Parameter

for Various Phase Angle.

Table 4.8 : Outboard Bearing Vibration Displacement Parameter

for Various Phase Angle.

Table 4.9 : Vibration Velocity for Various Phase Angle.

19

43

44

44

50

50

51

53

54

54

xi

LIST OF APPENDIXES

Description

Page

Appendix A

_{Bode Plot and Spectrum for Experiment 1.}

71

Appendix B : Bode Plot and Spectrum for Experiment 2.

73

Appendix C : Bode Plot and Spectrum for Experiment 3.

76

Appendix D

General Vibration Severity Chart.

79

Appendix E

Comparison of Vibration Displacement, velocity and

Acceleration Severity

81

Appendix F

Vibration Diagnostic Chart

82

Appendix G : Application of FFT in Time Response Calculations

87

Appendix H : Application of DFT and FFT algorithms

89

CHAPTER 1

INTRODUCTION

1.1

Background Of Vibration Monitoring

In today's fast changing marketplaces, many industrial plants are seeking

methods and techniques to optimize the operating efficiency of their existing plants, by extending equipment life, and reducing operation and maintenance expenses, in order to remain competitiveness.

Suitable maintenance practice is necessary to ensure the continued, safe and

profitable operation of industrial

machinery and plant, that higher plant availability

and reliability are achieved in the most cost effective manner [Shrieve

and Hill, 1998].

Generally, maintenance activities may be categorized as either reaction based, time based, or condition based. Reaction-based maintenance normally takes the form of continuous operation until a failure occurs. Then, a correction action will be taken to repair the damage and return the machinery train to operation as soon as possible. This type of maintenance practice is also called Breakdown Maintenance. Time-based

maintenance, is concerned with interrupting production on machinery at regular

intervals for maintenance. This is done to reduce the number of unplanned stop that

can arise from breakdown maintenance strategy. This type of maintenance practice is

also called Preventive Maintenance. Condition based maintenance, on the other hand

is based upon reasonable knowledge of the mechanical condition of machinery, which

evaluates equipment condition to determine maintenance needs.

In order for the condition-based maintenance to be success, a condition-

monitoring program is therefore needed. Condition monitoring of machinery can

provide actual condition for a machine without the needs of dismantle, shutting down

or even direct contact to the equipment. It also can identify machine train problems before they become serious. This indirectly provides the opportunity of organizing

avoidance strategies to minimize lost time and unexpected costs, thus greatly

improving manufacturing efficiency.

For any condition monitoring programs, vibration analysis is one of the

dominant techniques used. The simple reason is that all machines vibrate, even

machinery which is in good operating condition will vibrates at certain degree. Vibrations normally arise from the cyclic excitation forces, which are present within a machine. These forces are sometimes built into the design of the equipment, or can be due to real changes in the dynamic properties of the individual machine elements. These excitation forces may be transmitted to adjacent components or the adjoining machine structure, thus causing parts of the equipment remote from the source to vibrate accordingly to varying degrees [Mathew, 1985].

Since each type of mechanical defect has its own unique vibration characteristic, any change in vibration is a signal showing that the mechanical health

of a particular machine is changing. Keeping this in mind and applying a systematic

method of monitoring vibration on a piece of equipment at set intervals, any increase in vibration level recorded over time provides an early warning of impending trouble. Once this change in vibration level exceeds preset tolerances, corrective action should be initiated to prevent a costly breakdown failure [Larry Bowler].

For rotating machinery, the excitation forces that cause vibration are usually

generated through the rotating motion of the machine parts. Because these forces

change in direction or amplitude according to the rotational speed (RPM) of the

machine components, it follows that most vibration problem will have frequency that

are directly related to the rotational speed [Gardiner, 1998]. For this reason, unit of velocity (in/sec or mm/sec) was recognized as the most accurate means of monitoring the overall health of a piece of machinery. Because any change in the amplitude or the frequency of a generated vibration signal will produce a change in the measured velocity value.

Therefore, combination of trend and vibration spectrum can be used to analyze the failure mode associated with shafts, bearings, gears, couplings, motors and many other machine components.

1.2

_{Objective of Work}

The aim of this project is to study the relationship between two common

machinery faults, which is out of balance and misalignment. Experiment and studies

will be carry out to determine the effects of out of balance and misalignment on the vibration characteristics of rotating machinery.

1.3 _{Definition of Terms}

1.3.1 Definition of Vibration

Vibration is defined by Webster's New World Dictionary as "to swing back and forth; to oscillate". In the vibration industry, vibration means the pulsating motion of a machine or a machine part from its original place of rest. Vibration is the response of a system to some internal or external stimulus or force applied to the system. In vibration monitoring, 3 important parameters are normally being encounter, which are the Amplitude (Severity), Frequency (How many times per minute or seconds) and phase (How it is vibrating).

1.3.2 Definition of Unbalance

Unbalance is a common feature of all rotational elements. It is a side

effect caused by the imperfection of material (e. g. heterogeneity) and the

manufacturing process, as well as the effect of wear by use (e. g. erosion).

Generally, each unbalance of mass in rotary motion is the source of rotational

forces and moments of inertial forces which, being transferred through the bearings to the body of the machine, evoke vibrations in the whole system. There are several types of unbalance, which is static unbalance, moment unbalance, quasistatic unbalance and dynamic unbalance [Cempel, 1991].

1.3.3 Definition of Misalignment

The power unit of machinery and its working part (e. g. Steam turbine and pump) form in general separate components that is joined by a coupling at the shaft end. This joint is often not aligned and can distinguish a fault called

misalignment. There are three types of shaft misalignment, which is radial,

angular and oblique misalignment. This misalignment is normally the source

of double rotary frequency (2 X RPM) vibration. The amplitude of these

vibrations is directly proportional to the radial displacement and the angular

displacement, and varies with the obliquity parameter [Cempel, 19911.

CHAPTER 2

LITERATURE REVIEW

2.1

_{Review of Fundamental Vibration Theory}

From the "Handbook of Condition Monitoring" edited by Alan Davies, D. W Gardiner had made a review of the fundamental of vibration theory. Vibration means the motion of a machine, or machine part, back and forth from its position of rest. The motion of the weight from its position of rest, to the upper limit of travel, then to the lower limit of travel, and returns to its original position represent one cycle or period of motion.

Three important characteristics that are important to define a vibration are :

amplitude, frequency and phase. Amplitude describes how much a machine of system

vibrates. Vibration amplitude can be measured in 3 main engineering units:

a)

Displacement

Total distance travelled by the vibration part from one limit to another,

normally referred as the "Peak to Peak" displacement.

b)

Velocity

The speed required for a vibration part to move, for a certain distance. Vibration speed is constantly changing, since during a cycle of motion the highest velocity is selected for measurement.

c) Acceleration

The measurement of "rate of change of velocity", normally expressed in g's peak, where ig is the acceleration produced by the force of gravity at the surface of the earth.

Vibration frequency describes the number of complete cycles that occur in a

specified period of time. In other words, vibration frequency is the inverse of the

period of the vibration, where

Frequency = 1/Period

The vibration frequency is normally measured in Hz (Hertz) or CPM (Cycle per Minute).

Phase is another important parameter required to describes vibration

characteristic. Phase is defined as "The angle between the instantaneous position of a

vibrating part and a fixed reference position". In short, phase measurement can

provide information regarding the relative motion between two or more machinery parts [Gardiner, 19981.

2.2

Vibration Spectrum

From the Training Manual "Advanced Vibration Diagnostic and Reduction Techniques" published by Technical Associates of Charlotte Inc, James E. Berry had discussed about what is a vibration spectrum.

A vibration spectrum is a graph that plots the amplitude (mils, in/sec or g's) versus the vibration frequency (CPM or Hz). In other words, it is the presentation of

vibration data in frequency waveform. Normally, vibration event are recorded by

using an oscilloscope or a real time analyzer, where the signals are in the form of time domain.

Displaying and using the time domain is a very precise method which display

the actual machine motion and to analyze the various vibration parameters. However,

analyzing the time waveform itself can be very cumbersome and labor intensive when

frequency needs to be determined. To simplify this process, vibration instruments are normally able to develop what is known as Fast Fourier Transform (FFT).

An FFT is the computer (microprocessor) transformation from time domain

data (amplitude versus time) into frequency domain data (amplitude versus

frequency). This FFT calculation technique was developed by Baron Jean Baptiste

Fourier. The process of FFT is illustrated in figure 2.1.

Amplitude

()

`tom Direction to slew graph o see frequency domain of Time waveform (a).

Amplitude ý Amplitude (a) I 1 4 %111 n w a --n----Time Frequency

Figure 2.1 : Fast Fourier Transform

From the figure, a total time waveform is captured in the time domain first (a). This time domain waveform is then separated into its separate sine waveforms and displayed in three-

dimensional _coordinates of amplitude, time and frequency (b). From the combined

waveform, the frequency of each sine wave is determined and the sine waves are placed in the respective position along the frequency axis. A view looking along each individual waveform is shown allowing the analyst to see the frequency domain of amplitude versus frequency (c). Details mathematic equations of FFT are shown in Appendix G and H.

2.2.1 Time Domain Analysis

Despite the usefulness of frequency domain vibration data, time

domain data can sometime be applicable. An article from an Internet website

has a discussion about the time domain analysis. The analysis of time

waveform data is not a new technique. In the early days of vibration analysis,

time waveform data was viewed on oscilloscopes and frequency components

calculated by hand.