Vibration monitoring and analysis for rotating machine

Introduction to mechanical vibration

Outline

Introduction

Vibration monitoring and analysis

Vibration : Measurement

Data Acquisition

Types of transducer

Mounting method

FFT analysis

Example

Unbalance

Misalignment

Spur gear

Centrifugal pump

Introduction

Static equipment

Ex. Pressure vessel, Tank

Rotating equipment

Pump, Compressor, turbine

Vibration monitoring and analysis

Raw Data

Time domain

Analysis data

Frequency domain

FFT analyzer Sensor

Vibration : Measurement Amplitude Units

Displacement, D Micrometer peak to peak

Velocity, V mm/s - peak or rms

Acceleration, A mm/s2 - peak or rms

Types of transducer

Proximity Probe Seismic Velocity

Probe Acceleration Probe

Relative displacement Velocity Acceleration

0 1,500 Hz 8 1,500 Hz 1 20,000 Hz

Mounting method

Method Frequency limit (Hz)

Hand held 500 Magnet 2,000

Adhesive 2,500 4,000

Bees wax 5,000

Stud 6,000 10,000

FFT analysis

Fast fourier

transform (FFT)

Vibration monitoring and analysis

Raw Data

Time domain

Analysis data

Frequency domain

FFT analyzer Sensor

Example Unbalance

Misalignment

Spur gear

Centrifugal pump

Type of unbalance 1. Static unbalance 2. Couple unbalance 3. Dynamic unbalance

12

Static Unbalances

Corrected

balance weight in one plane at rotor centre of gravity (CG).

Couple Unbalances

180

Corrected

balancerequires correction in two planes at 180.

Dynamics Unbalances

static couple Static unbalance Couple

Special case of Dynamics Unbalances

Corrected

Overhung rotors often have both static and couple unbalance each of which may require correction.

Overhung Rotor Unbalance

Balancing cooling tower

Cooling Tower

1. (transducer) (Tachoprobe)

2. 1 - (Magnitude :mm/sec) - (phase angle)

3. (trial weight) Rotor

4. 2 - (Magnitude :mm/sec) - (phase angle)

5. Polar graph

(Trail weight) Wt = 30 x Wr / r

Wr Static weight : g r (radius of trial weight : mm)

(correct weight) Vc = Vo x Wt / Vt

Vo Unbalance : mm/sec Vt : mm/sec

Reference by : Machinery vibration & Balancing /Victor Wowk.

spectrum cooling #4 1X rpm Amplitude Unbalancing

Frequency : 355.3

Amplitude: 4.379

Phase : 84 degree

( )

Vector correct & angle phase on Polar graph

Data: 1.Rotor & Fan weight : 26 kg ,(4x32 kg)

2. Radius of trial : 220 mm.

Vector unbalance Vo: 4.379 mm/sec

Phase Vo: 84 degree.

Trial weight : 25 g (21 g)

Vector unbalance +weight V1: 7.4 mm/sec

Phase V1: 215 degree.

Vector from trial weight Vt: 10.8 mm/sec

Phase : 329 degree. (Vt-Vc)

Position of point to correct (Balancing)

Trial weight : 25 g (21 g)

Phase : 84 degree.

Correct weight ,Mc : 10.1 g

Correct phase : 31 degree.

Before..

After..

Amplitude: 1.684 mm/sec

4.375

()

Misalignment

Misalignment

Introductio

n

What is it ?

Misalignment is a condition

where the centerlines of

coupled shafts do not coincide.

EX.

Introductio

n Misalignment

Introductio

n

Bearing, Coupling, Seal and Shaft failure

Lost time to repair machine

Lost opportunity to run process

Lost Maintenance Cost

Misalignment

Type of

misalignmen

t Misalignment

Detection

method Misalignment

Introductio

n Misalignment

Misalignment Detection

method

Time- Frequency Domain

Fast fourier

transform (FFT)

Type of

misalignmen

t Misalignment

Type of

misalignmen

t Misalignment

Shear force

Bending moment

2X component will be higher than 1X.

Depend on the coupling type

Axial 1X and 2X levels will be low

Symptoms: 2X radial, smaller 1X

radial

Type of

misalignmen

t Misalignment

Bending moment

Also be fairly

strong radial

1X and 2X levels

Symptoms: High axial vibration: 1X

strong (but 2X and 3X can also be

strong)

Type of

misalignmen

t Misalignment

Can be 3X, 4X all the

way up to 8X peaks

The noise floor is

not raised(unlike

rotating looseness)

Frequency: 1X and 2X (and 3X and

4X) axial and radial

Spur Gear

Failure Mode : Backlash, Tooth wear and Broken teeth etc.

Normal

Backlash

Normal

Tooth wear

Normal

Tooth load

Normal

Broken Tooth

Normal

Broken Tooth

Normal

Vibration in centrifugal pump

Loosen components

Gap between blade vanes and case is too small

-the BPF will increase

Turbulence flow

-random amplitude

at low frequency

Cavitation

-random amplitude

at high frequency