Teori Dasar Analisa Vibrasi

TEORI DASAR ANALISA VIBRASI

DARYANTO

Predictive Maintenance - CRM

PT KRAKATAU STEEL

PROGRAM KERJASAMA HUMAN CAPITAL DEVELOPMENT CENTER (PT.KRAKATAU STEEL)

DENGAN JURUSAN TEKNIK MESIN UNIV.SULTAN AGENG TIRTAYASA

Tujuan training : Bisa Membaca Spectrum Getaran



PREDICTIVE MAINTENACE PROGRAM

1. Data Collection – Monitoring schedule :

monthly, weekly, daily

2. Detection & Analysis

• Trends

• Alarms

• Spectral Analysis

3. Problem Correction



TUJUAN PENGUKURAN GETARAN

1. Menentukan kondisi mekanis mesin.

2. Merencanakan jadwal pemeliharaan.

3. Memeriksa hasil repair/overhaul.

4. Menghentikan mesin untuk mencegah gangguan serius.

5. Lokalisasi gangguan.

6. Pengesahan aspek keselamatan.



Vibration is a "back and forth" movement of a structure. It

can also be referred to as a "cyclical" movement



What Is Vibration Caused By ?

Imperfections in the Machine:

What Are Some Common Machine Problems? That Generate Mechanical Vibration:

● Misalignment ● Unbalance

● Worn belts & pulleys ● Bearing Defects

● Hydraulic Forces ● Aerodynamic Forces

● Reaction Forces ● Reciprocating Forces

● Bent Shafts ● Rubbing

● Gear Problems ● Housing Distortion

● Certain Electrical Problems ● Frictional Forces

Design Assembly

Manufacture Operation

Installation Maintenance



What Are Some Common Machine Problems

That Amplify Mechanical Vibration

(But Don't Cause It):

• Resonance

• Looseness











F = 1/T

T = The period of the wave

F = The Frequency of the wave

where d = instantaneous displacement,

D = maximum, or peak, Displacement = angular frequency, = 2f

t = time

where v = instantaneous velocity

where a = instantaneous acceleration



Displacement, Velocity and Acceleration

English Units:

Displacement = mils

Velocity = in/sec

Acceleration = g's

Frequency = cycles/min

Metric Units:

Displacement = um

Velocity = mm/sec

Acceleration = g's

Frequency = cycles/min

Displacement = (19,231 x V) / F Displacement = (19,231 x V) / F

Velocity = 0.000052 x D x F Velocity = 0.000052 x D x F

Acceleration = 0.00027 x V x F Acceleration = 0.0000107 x V x F



Example #1:

A Bearing Vibrates 100 Mils Pk-Pk @ 30 cpm

Displacement @ 1x rpm = 100 mils Displacement @ 1x rpm = 2540 um

English Units:

Velocity = 0.000052 x D x F

V = 0.000052 x 100 mils x 30 cpm

Metric Units:


V = 0.000052 x 2540 um x 30 cpm

V = 0.16 ips V = 4 mm/sec

Acceleration = 0.00027 x V x F

A = 0.00027 x 0.16 x 30


A = 0.0000107 x 4 x 30

A = 0.0013 g's A = 0.0013 g's

Example #2:

A Bearing Vibrates 10 Mils Pk-Pk At 1000 cpm

Displacement @ 1x rpm = 10 mils Displacement @ 1x rpm = 250 um

English Units:


V = 0.000052 x 10 mils x 1000 cpm

Metric Units:


V = 0.000052 x 250 um x 1000 cpm

V = 0.52 ips V = 13 mm/sec


A = 0.00027 x 0.52 x 1000


A = 0.0000107 x 13 x 1000

A = 0.14 g's A = 0.14 g's



Example #3:

A Bearing Vibrates 3 Mils Pk-Pk At 9,000 cpm

Displacement @ 9,000 cpm = 3 mils Displacement @ 9,000 cpm = 75 um

English Units:


V = 0.000052 x 3 mils x 9,000 cpm

Metric Units:


V = 0.000052 x 75 um x 9,000 cpm

V = 1.404 ips V = 35.1 mm/sec


A = 0.00027 x 1.404 x 9,000


A = 0.0000107 x 35.1 x 9,000

A = 3.41 g's A = 3.41 g's

Example #4:

A High Speed Compressor Rotor Shaft

Vibrates 0.003 Mils Pk-Pk At 1,080,000 cpm

Displacement @ 1,080,000 cpm = 0.003 mils

(3 millionths of an inch)

Displacement @ 1,080,000 cpm = 0.077 um

(7.7 millionths of a centimeter)

English Units:


V = 0.000052 x 0.003 mils x 1,080,000 cpm

Metric Units:


V = 0.000052 x 0.077 um x 1,080,000 cpm

V = 0.17 ips V = 4.32 mm/sec


A = 0.00027 x 0.17 x 1,080,000


A = 0.0000107 x 4.33 x 1,080,000

A = 50 g's A = 50 g's



Vibration Amplitude Measurement

The following definitions apply to the measurement of mechanical vibration amplitude.

Root Mean Square Amplitude (RMS) is the square root of the average of the

squared values of the waveform. In the case of the sine wave, the RMS value is

0.707 times the peak value



Lines of Resolution: 200, 400, 800,1600, 3200, 6400, 12800

Spectrum Resolution = Max Frequency (Fmax)

# of Lines of Resolution Fmax = # Lines / Time Sample

Fmax [Hertz] = 800 / 0.1 seconds = 8000 Hz Fmax [CPM] = 8,000 Hz x 60 = 480,000 cpm



The Resulting FFT

The Raw Signal

The Actual Signals

Used To Generate



1x rpm w/ amplitude of 1.8 (pk-pk), '+'

peak on y-axis

2x rpm w/ amplitude of 0.45 (pk-pk)

3x rpm w/ amplitude of 0.05 (pk-pk), '-'

peak on y-axis



Beats

'



Linear Amplitude Scaling

Logarithmic Amplitude Scaling

The Decibel

The decibel (dB) is defined by the following expression:

where: LdB = The signal level in dB L1 = Vibration level in Acceleration, Velocity, or Displacement

Lref = Reference level, equivalent to 0 dB

The vibration velocity level in dB is abbreviated VdB, and is defined as:

or

Amplitude Scales



ISO 10816-3









The Velocity Probe

Velocity Transducer The Accelerometer

Piezo-Electric Accelerometer

The Proximity Probe

VIBRATION TRANSDUCERS



Konfigurasi daripada meteran tingkat getaran



SENSITIFITAS SENSOR VIBRASI

Recommended Frequency Ranges for Different Amplitude Units

Displacement Units: < 600 cpm (< 10 Hz)

Velocity Units: 300 - 120,000 cpm (5 - 2,000 Hz)

Acceleration Units: > 60,000 cpm (> 1,000 Hz)



PENGAMBILAN DATA VIBRASI



RUANG LINGKUP PENGUKURAN GETARAN

1. Kelompok penggerak mula (prime mover) –

mesin-mesin yang mampu mengolah daya sendiri.

Contohnya: Elektric Motor, Steamturbin, Gasturbin,

Hydraulic & Pneumatic Motor dll.

2. Kelompok sistem transmisi – peralatan untuk

memindahkan daya. Contohnya : Gearbox,

Coupling, V-Belts dll.

3. Kelompok mesin bukan penggerak mula –

peralatan produksi yang harus digerakkan oleh

penggerak mula. Contohnya : Compressor,

Centrifugal Pump, Hydraulic Pump, Fans,

Reciprocating Pump, Cooling Tower Fans, Rolling

Machines dll.





MACHINE DATA SHEET

1. Plant Name

2. Train Name

3. Machine Name

4. Machine Description

5. Machine Sketch

6. Position

7. Direction

8. Measurement Units

9. Point Identification

10.Coupling Type

11.RPM

12.Number of Gear Teeth

13.Bearings (Type, manufacture, Number of

balls/Series Number)





Horizontal machines Vertical machines



MENENTUKAN ARAH PENGUKURAN



ANALISA DATA VIBRASI



Following is an example of forcing frequency calculation for a gear-driven machine:

Let us assume that the motor/gear/fan components have the following element counts:

Machine Component

Elements of Component

Number of Elements

Motor Cooling Fan

Fan Blades

11

Motor Rotor

Rotor Bars

42

Drive Pinion

Gear Teeth

36

Driven Gear

Gear Teeth

100

Fan

Fan Blades

9



Let us assume that the motor is again running at 1780 RPM.

Divide the drive pinion tooth count by the driven gear tooth count:

or

Next, multiply this ratio by the motor shaft RPM to find the fan shaft RPM;

We would now say that the fundamental frequency of the motor is 1780 CPM and

the fundamental frequency of the fan is 640.8 CPM.

Motor Shaft Elements Forcing Frequency, CPM

Rotation

1

1,780

Motor Cooling Fan

11

19,580

Motor Rotor

42

74,760

Drive Pinion

36

64,080

Fan Shaft

Elements Forcing Frequency,CPM

Rotation

1

640.8

Driven Gear

100

64,080

Fan

9

5,767.2



Formulas for Calculating Belt Frequencies:

You can calculate belt RPM with the following:

3.14 x PS1 x PD1/BL = Belt RPM

- or -

3.14 x PS2 x PD2/BL = Belt RPM

Belt Length = 1.57 x (PD1 + PD2) + 2(SD)

PS = Pulley rpm (PS1 = Driver Pulley Speed, PS2 = Driven Pulley Speed)

PD = Pulley diameter (PD1 = Driver Pulley Dia., PD2 = Driven Pulley Dia)

SD = Distance between shaft centers

BL = Belt Length



Deep Groove Ball Bearing

(BPFO)

(BPFI)

(BSF)

(FTF)

BPFO : Ball Pass Frequency Outer

BPFI : Ball Pass Frequency Inner

BSF : Ball Spin Frequency

FTF : Foundation Train Frequency





Spectrum Interpretation

(Troubleshooting chart)

The following pages are designed to provide typical examples of the vibration

spectrums that will result from different problems a machine might experience. They

are probability based and field testing should always be performed regardless of how

"sure" you are of the diagnosis.

Remember:

EVERY diagnosis made from an FFT interpretation can be characterized as:

An ASSUMPTION based on an ESTIMATE



Typical Radial FFT Generated By Unbalance

Typical Axial FFT Generated By Unbalance

Typical FFT Generated By Angular Misalignment Definition: Shaft Centerlines Intersect But Are Not Parallel

Typical FFT Generated By Offset Misalignment Definition: Shaft Centerlines Are Parallel But Do Not Intersect

Troubleshooting chart



MISALIGNMENT









Typical FFT Generated By Cocked Bearing

Typical FFT Generated By Shaft Bent Through The Bearing

Typical Radial FFT Generated By Mechanical

(Structural) Looseness

Typical Radial FFT Generated By Bearing Looseness



Typical Axial FFT Generated By Housing Distortion

Typical Radial FFT Generated By Housing Distortion

Relatively High Amplitudes Will Be Generated.

FFT Typical Of Pulley Misalignment



Typical FFT Showing Belt/Pulley Wear Problems

Typical FFT Showing Pulley Eccentricity / Bent Shaft

Near Pulley

FFT Showing Sleeve Bearing Looseness

FFT Resulting From Oil Whirl



Typical Spectrum Showing High Vane Pass Frequency

Typical Spectrum Showing Cavitation

Typical FFT Showing Flow Turbulence

Typical Spectrum Showing Indications Of

Variation In Air Gap, Winding Shorts, Stator

Weakness



Typical Spectrum Showing Indications Of Eccentric Rotor

One Possible Spectrum Caused By A Problem With A

Short In One Of The Phases Or Feeder Cables Another Possible Spectrum Caused By A Problem

With A Short In One Of The Phases Or Feeder Cables

Spectrum Showing Pattern Of Peaks Separated By 2xLine

Frequency (Sidebands) In High Frequency Range (30-

90xRPM)



Loose in Winding Slots, Iron, End Turns And/Or Connections

"Normal" FFT Taken On DC Drive Figure 1 - Full-Wave Rectified Velocity Spectrum w/ Drive

Problems



Figure 2 - Half-Wave Rectified Velocity Spectrum w/

Drive Problems Figure 3 - Spectrum on DC Motor w/ Speed Fluctuations

Normal Gear Spectrum Typical FFT For Eccentric Gear Or Gear On Bent Shaft



ANALISA DATA VIBRASI

1. Trends Data

14/ 02/ 2009 14/ 03/ 2009 11/ 04/ 2009 09/ 05/ 2009 06/ 06/ 2009 04/ 07/ 2009 01/ 08/ 2009 29/ 08/ 2009 26/ 09/ 2009 24/ 10/ 2009 21/ 11/ 2009 19/ 12/ 2009date

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

32

34

36

38

40

42

44

v [mm/ s] Strip Dryer Fan No.1 - G1.420\ Fan/ blower Dryer # 1\ BH3\ 101 Ov erall v eloc ity >600



0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 24000f [cpm]

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

6,0

6,5

7,0

7,5

8,0

8,5

9,0

9,5

10,0

v rms [mm/ s] Strip Dryer Fan No.1 - G1.420\ Fan/ blower Dryer # 1\ BH3\ 103 Mac h. spec tr. >600 13/ 11/ 2009 8:42:18

M

06/ 10/ 2009

09/ 09/ 2009

25/ 08/ 2009

07/ 08/ 2009

10/ 07/ 2009

12/ 05/ 2009

15/ 04/ 2009

24/ 03/ 2009

24/ 02/ 2009

24/ 01/ 2009

2. Waterfall Trends Data



0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 24000f [cpm]

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

6,0

6,5

7,0

7,5

8,0

v rms [mm/ s] Strip Dryer Fan No.1 - G1.420\ Fan/ blower Dryer # 1\ BH3\ 103 Mac h. spec tr. >600 06/ 10/ 2009 9:02:35

2

3

D

M

3. Single Spectra



Housing Bearing Gearbox Aus

A

M

P

L

I

T

U

D

O

MESIN &

SPESIFIKASINYA

POSISI &

ARAH PENGUKURAN

LOKASI / AREA MESIN

PUTARAN

POROS

KESIMPULAN



PROGRAM PREDICTIVE MAINTENANCE

1. Data Collection

• Pemantauan getaran terjadwal

2. Analysis (diperlukan Software)

• Domain frekuensi (harus tahu anatomi mesin)

• Domain waktu

• Frek. eksitasi getaran, database bantalan, gearbox dll

3. Diagnosis

• Prakiraan sumber masalah

• Dibantu oleh Software

• Human Interface (Tergantung pengalaman)



TERIMA KASIH

Documents

Teori Dasar Analisa Vibrasi