Teori Dasar Analisa Vibrasi

PROGRAM KERJASAMA HUMAN CAPITAL DEVELOPMENT CENTER (PT.KRAKATAU STEEL) DENGAN JURUSAN TEKNIK MESIN UNIV.SULTAN AGENG TIRTAYASA

TEORI DASAR ANALISA VIBRASI

DARYANTO

Predictive Maintenance - CRM PT KRAKATAU STEEL


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: Design

Assembly

Manufacture

Operation

Installation

Maintenance

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


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:

Metric Units:

Displacement = mils Velocity = in/sec Acceleration = g's Frequency = cycles/min

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: Velocity = 0.000052 x D x F 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

Acceleration = 0.0000107 x V x F 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: Velocity = 0.000052 x D x F V = 0.000052 x 10 mils x 1000 cpm

Metric Units: Velocity = 0.000052 x D x F V = 0.000052 x 250 um x 1000 cpm

V = 0.52 ips

V = 13 mm/sec

Acceleration = 0.00027 x V x F A = 0.00027 x 0.52 x 1000

Acceleration = 0.0000107 x V x F 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: Velocity = 0.000052 x D x F V = 0.000052 x 3 mils x 9,000 cpm

Metric Units: Velocity = 0.000052 x D x F V = 0.000052 x 75 um x 9,000 cpm

V = 1.404 ips

V = 35.1 mm/sec

Acceleration = 0.00027 x V x F A = 0.00027 x 1.404 x 9,000

Acceleration = 0.0000107 x V x F 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: Velocity = 0.000052 x D x F V = 0.000052 x 0.003 mils x 1,080,000 cpm

Metric Units: Velocity = 0.000052 x D x F V = 0.000052 x 0.077 um x 1,080,000 cpm

V = 0.17 ips

V = 4.32 mm/sec

Acceleration = 0.00027 x V x F A = 0.00027 x 0.17 x 1,080,000

Acceleration = 0.0000107 x V x F 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


Spectrum Resolution =

Max Frequency (Fmax) # of Lines of Resolution

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

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


The Raw Signal

The Actual Signals Used To Generate

The Resulting FFT


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

'


Amplitude Scales Linear Amplitude Scaling

Logarithmic Amplitude Scaling

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

The Decibel

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


ISO 10816-3





VIBRATION TRANSDUCERS The Proximity Probe

The Velocity Probe

Velocity Transducer

The Accelerometer

Piezo-Electric Accelerometer


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: 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

Machine Component


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. Elements

Forcing Frequency,CPM

Rotation

1

640.8

19,580

Driven Gear

100

64,080

42

74,760

Fan

9

5,767.2

36

64,080

Motor Shaft

Elements

Forcing Frequency, CPM

Fan Shaft

Rotation

1

1,780

Motor Cooling Fan

11

Motor Rotor Drive Pinion


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) (BSF) (BPFI) (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


Troubleshooting chart

Typical Radial FFT Generated By Unbalance

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

Typical Axial FFT Generated By Unbalance

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


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

Spectrum Showing Pattern Of Peaks Separated By 2xLine Frequency (Sidebands) In High Frequency Range (3090xRPM)

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


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

Figure 1 - Full-Wave Rectified Velocity Spectrum w/ Drive

"Normal" FFT Taken On DC Drive

Problems


Figure 2 - Half-Wave Rectified Velocity Spectrum w/

Figure 3 - Spectrum on DC Motor w/ Speed Fluctuations

Drive Problems

Normal Gear Spectrum

Typical FFT For Eccentric Gear Or Gear On Bent Shaft


ANALISA DATA VIBRASI 1. Trends Data v [mm/ s]

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

44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 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/ 2009 date


2. Waterfall Trends Data v rms [mm/ s]

10,0 9,5 9,0 8,5 8,0 7,5 7,0 6,5 6,0 5,5 5,0 4,5 4,0 3,5 3,0 2,5 2,0 1,5 1,0 0,5 0,0

St rip D ryer Fan N o. 1 - G1. 420\ Fan/ blow er D ryer # 1\ BH 3\ 103 Mac h. spec t r. >600 13/ 11/ 2009 8: 42: 18

06/ 10/ 2009 09/ 09/ 2009 25/ 08/ 2009 07/ 08/ 2009 10/ 07/ 2009 12/ 05/ 2009 15/ 04/ 2009 24/ 03/ 2009 M

24/ 02/ 2009 24/ 01/ 2009

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

24000

f [cpm]


3. Single Spectra v rms [mm/ s] 8,0

Strip D ryer Fan N o.1 - G1.420\ Fan/ blow er D ryer # 1\ BH 3\ 103 Mac h. spec tr. >600 06/ 10/ 2009 9:02:35

7,5

M

7,0 6,5 6,0 5,5 5,0 4,5 4,0 3,5 3,0 3 2,5 2,0 1,5 1,0 2 0,5

D

0,0 0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

24000 f [cpm]

Housing Bearing Gearbox Aus


KESIMPULAN LOKASI / AREA MESIN MESIN & SPESIFIKASINYA

POSISI & ARAH PENGUKURAN

A M P L I T U D O

PUTARAN POROS


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

Teori Dasar Analisa Vibrasi

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