Condition Monitoring

CONDITION MONITORING VIBRATION ANALYSIS AND IN-SITU BALANCING VIBRATION: It is the motion of mechanical parts back and fort from its position of rest/neutral position. Causes of Vibration: Forces generated within the machine causes vibration. Most common machinery problems that cause vibration include: Mis alignment of couplings, Bearings and gears. Unbalance of rotating components. Looseness. Deterioration of Rolling Element Bearings. Gear Wear. Rubbing. Aerodynamic/hydrodynamic problems in fans, blowers & pumps. Electrical problems (Unbalance magnetic forces) in motors. Resonance. Eccentricity of rotating components such as “V” Belts pulleys or gears. COMPARISON OF MAINTENANCE PHILOSOPHIES: In general there are 3 ways to maintain machinery. 1.

BREAK-DOWN MAINTENANCE.

2.

SCHEDULED OR PREVENTIVE MAINTENANCE.

3.

PREDICTIVE MAINTENANCE

BREAK-DOWN MAINTENANCE: Break down maintenance is essentially no maintenance at all. The machine is simply allowed to run until complete failure, inefficiency or product spoilage forces a shut-down. SCHEDULED OR PREVENTIVE MAINTENANCE: Compared to break down maintenance, a program of periodic disassembly inspection & replacement of worn parts has a good advantage of lessening the frequency of break-down repairs and also permits scheduled shut-down. Under this program each critical machine is shut-down after a specific period of operation and partially or completely dismantled for a thorough inspection an replacement of worn out parts-if any. PREDICTIVE MAINTENANCE: Predictive maintenance involves the trending and analysis of machinery performance parameters to detect and identify developing problems before failure and extensive damage.

Vibration can takes place in 3 directions i.e Horizontol,Vertical,Axial. Note: Generally in vertical direction vibration amplitude value is low, because weight of the machine is acting on it. If it occurs that vibration is high in vertical direction we can conclude that major problem is there in the rotating body. By keeping transducer in the 3 directions vibration is captured individually .

The purpose of vibration is to identify effects and evaluate machine condition. Amplitude of vibrating motion are described using the following units. Displacement,mils-peak to peak (1000 mils= 1 inch) Velocity, in/sec-peak

or rms )

IRS=peak or mm/sec

Acceleration ,g’s= peak or rms (3816.1 in/sec2=1g) Frequency=CPM

cycles/minute ,cycles/hz

Phase is expressed in(deg) in which one revolution of a shaft or one period of revolution. Speeds are expressed in revolutions/minute (RPM) VELOCITY(mm/sec): Velocity is the time rate of change of displacement. It is dependent on both displacement and frequency. VIBRATORY MOTION: The fundamental characteristics of vibration are Frequency, amplitude and phase. Frequency: Frequency is defined as no of cycles or events per unit time. Amplitude: Maximum value of vibration at a given location on the machine. Phase: Phase is the time relationship mentioned I degrees.

Vibration Standards: Machinery Classification in accordance with ISO 2372.

CLASS I : Individual parts of engines and machines, Integrally connected with the complete machine in its normal operating.(Production electrical motors of upto 15 KW.) CLASS II : Medium sized machines ,(typically electrical motors with 15 to 75 KW output) without special foundations ,rigidly mounted engines or machines(upto 300 KW ) on special foundations CLASS III : Large prime movers and other large machines with rotating masses mounted on rigid and heavy foundations which are relatively stiff in direction of vibration measurement. CLASS IV : Large prime movers and other large machines with rotating masses mounted on foundations which are relatively soft in direction of vibration measurement (e.g. ,turbo generator sets, especially those with light weight sub structures.)

For Example: Recommended values of vibration values of class1 & class2 machines are given in below table. Class-I machines

SL

GRADE

PEAK

NO

VALUE(mm/

01 02 03 04

sec) 1.0-1.58 1.58-2.5 2.5-6.4 6.4-25

A B C D

Class II Machines:

SL

GRADE

NO

Where

A: GOOD,

B: ROUGH,

PEAK VALUE(mm/

sec) 01 A 1.10-1.58 02 B 1.58-4.00 03 C 4.00-10.00 04 D 6.4-25 C: STILL ACCEPTABLE, D: UN ACCEPTABLE

STEPS FOR ANALYSIS `1.Prepare a rough sketch of the machine to be analyzed. 2. Fill up the table below.

Displacement, Velocity (mm Acceleration, (mu) H V A

H

/sec) V A H

(g) V A

01 02 03 04 05 06 3. Note down the rpm ,Kw, foundation load and operating parameters. 4. Note down the engineering parameters ,Bearing No, Coupling details etc. 5. Note down maintenance recently done on the machine. 6. Physically observe the machine. GENERAL GUIDE LINES (for Velocity) 1. If “ H” is higher –Most likely “Unbalance for simply supported rotors, for over hung rotors unbalance produces high axial vibrations also. 2. If “V” is high –most likely Looseness. 3. If “A” is high ,Most likely Misalignment, bearing defect, bent shaft etc. 4. If “H” & “A” is high, Good indicator of mis-alignment.

BASIC CHECKS 1. Compare “H” &”V” ………..”V” should not be more than 25% of “H”. 2. Vertical “V” should be same everywhere.

3. Axial should not be more than the 50% of highest radial(H/V). For correction, alignment tolerances: SL Machine RPM Tolerance(mm NO 01 02 03 04