Welcome to the seminar: Basics of vibration technology Measurement & Analysis

Transcription

1 Welcome to the seminar: Basics of vibration technology Measurement & Analysis 1

2 Lecturer : Roland Kewitsch 2

3 Vibration analysis increases knowledge Provides necessary information for: Evaluation of machine condition Recognition of on-going machine damage symptoms Identification of the cause and the damaged components Prognosis of remaining service life 3

4 Machine damage in a power station Total destruction of a generator 4

5 Rolling-element bearing damage 5

6 Diagnosis methods Vibration measurement and analysis Displacement, expansion and process value measurement Temperature, speed and phase measurement Lubricant analysis (e.g. spectroscope, ferroscope, radionuclide) Optical examination (e.g. endoscope, microscope) Non-destructive testing (e.g. ultra-sound, X-rays) 6

7 Vibration Measurement in the past (& still today) 7

8 Diagnosis methods Diagnosis by vibration measurement Overall methods Machine assessment using Overall measurements = 8

9 Diagnosis methods Diagnosis by vibration measurement Overall methods Analytical methods Machine assessment using Overall measurements Fault identification using frequency analysis measurements Dynamic behaviour analysis With self-excitation methods With external excitation methods 9

10 Measuring machine condition in the past The first portable vibration measuring instrument from the Schenck company Demonstrated at an exhibition in Leipzig / Germany in 1925 Schenck was founded in

11 Modern machine diagnosis Measuring machine condition with a modern measuring Instrument (VT-60) 11

12 Measurement types for mechanical vibrations Vibration displacement s = deviation of measured point from rest position in µm or mil Vibration velocity v = velocity with which measured point moves about rest position in mm/s or ips Vibration acceleration a = acceleration with which measured point moves about rest position in m/s 2 or g 12

13 Characteristics of composite vibrations Narrow-band examination - Extraction into harmonic components (e.g. using a frequency analyser or tracking filters) Broad-band examination - Through a summing formation in a defined frequency range (e.g ,000 Hz) 13

14 Amplitude data for vibration measurement s s o = s peak = s m S average s rms = s eff t s peak-peak = s pp s u = s peak = s m 14

15 Composite vibrations X f t X + 2f t = X f + 2f t 15

16 Vibration in Time Domain vs. Frequency Domain x x t x x f t x x f t f

17 Influence of integration - Practice Vibration velocity spectrum Vibration acceleration spectrum Vibration displacement spectrum 17

18 Selecting the measurement type Vibration displacement: Machines with speeds under approx. 600 rpm (10 Hz) Structural vibrations or Relative motions (shaft vibrations) in journal bearing machines of any speed Vibration velocity: Vibrations in machines with speeds above 600 rpm (10 1,000 Hz) Vibration acceleration: Vibrations with frequencies of interest above 2,000 Hz 18

19 Vibration types in machines Rotor Relative shaft vibrations Absolute bearing vibrations Bearing casing Foundation 19

20 Measuring Absolute Bearing Vibration General rules: Measurement points should be exactly defined and clearly marked Measuring points should be flat, clean and free of grease Loose paint and rusted surfaces should be cleaned or avoided Sensor must sit securely and not wobble Sensor and cable should not move during measurement 20

21 Balancing and Acceleration sensors 21

22 Vibration velocity sensors 22

23 Measuring Relative Shaft Vibration A B 23

24 Eddy-current sensors Discrete type: Sensor with integral cable Calibrated extension cable Separate converter (oscillator) Note: Cable lengths may not be altered! 24

25 Eddy-current sensors Integrated type: Sensor with built-in oscillator and extension cable Advice: Cable can be extended up to 1,000m in length Use in temperatures above 110 C is not possible 25

26 Machine assessment using the Trend 26

27 Machine assessment acc. to Standards and Guidelines A number of important Standards and Guidelines for rotating masses have been replaced during the last years by: DIN ISO 10816, parts 1 to 6 (absolute bearing vibrations) and DIN ISO 7919, parts 1 to 5 (relative shaft vibrations) Reciprocating machines, including compressors, can be assessed according to DIN ISO (Reciprocating machines with > 100 kw) DIN ISO (Reciprocating internal combustion machines) 27

28 Assessment of an electric motor acc. to ISO

29 Assessment zones Assessment zones according to DIN ISO 10816: Zone A: Vibration in newly-installed machines Zone B: Machines may be operated for an unlimited time without restriction Zone C: Machines may be operated for a limited time Zone D: Vibrations are at a dangerous level and may cause damage to the machines 29

30 DIN ISO Part 3, Group 2 Medium-sized machines with nominal power from 15 kw to 300 kw; Electrical machines with shaft height 160 mm H >315 mm 30

31 Vibrations created in damaged bearings 31

32 Impulses from a damaged bearing 32

33 Damage frequencies in a rolling-element bearing ß D ß d n N Contact angle Rolling-element diameter No. of rolling elements Speed of shaft n N Outer race damage f o = ( 1 - d cos ß ) 2 60 D n N d Inner race damage f i = ( 1 + cos ß ) 2 60 D d [ ] ² D N Rolling-element damage f r = ( 1 - cos² ß ) d 60 D N Cage damage f c = ( 1 - d cos ß ) 2 60 D 33

34 Damage frequencies in a rolling-element bearing Ball-bearing SKF 6211 Dimensions D = 77.5 mm D = 14.3 mm n = 10 ß = 0 Damage frequencies F o = N/ = 205 Hz F i = N/ = 295 Hz F r = N/ = 260 Hz F c = N/ = 20 Hz N = 3,000 rpm 34

35 BCU signal process X t f X t f X BCU t t 35

36 Trend observation Example: Damage progress in a rolling-element bearing Destruction 36