This document discusses the methodology of in situ balancing of rotating machinery. It describes different types of unbalance, causes of unbalance, symptoms of unbalance, and reasons a machine may exhibit a 1x vibration component other than unbalance. The methodology of in situ balancing is explained in multiple steps, including measuring initial vibration, adding a trial weight, measuring vibration with trial weight, removing weight and constructing a vector diagram to determine the correction weight and position. Methods for locking balancing weights are also summarized, as well as an alternative four run balancing method. Reasons why balancing may not resolve vibrations are provided.

1. METHODOLOGY OF
IN SITU BALANCING

2. TYPE OF UNBALANCE
STATIC
QUASI STATIC
COUPLE
DYNAMIC

3. CAUSES OF UNBALANCE
POROSITY IN CASTING
RUN OUT OF THE SHAFTS
LOSS OF MASS (BLADE OR EARLIER BALANCING
WEIGHTS)
LOOSE PARTS IN HOLLOW PLACES
CORROSION AND EROSION
CHANGES IN GEOMETRIC AXIS OF ROTOR

4. CAUSES OF UNBALANCE
MAINTENANCE ACTIVITIES LEADING TO CHANGE
IN MASS DISTRIBUTION SUCH AS CLEANING,
GRINDING, CHANGING FASTERNERS ETC.
REBLADING / REPAIR OF ROTORS

5. CAUSES OF UNBALANCE

6. CAUSES OF UNBALANCE

7. SYMPTOMS OF UNBALANCE
PRE DOMINANT RUNNING FREQUENCY
COMPONENT
STEADY PHASE ANGLE
PHASE DIFFERENCE OF APPROXIMATELY 90
DEGREES BETWEEN HORIZONTAL AND VERTICAL
READING OF SAME BEARING PEDESTAL
IN THE SAME MODE, THE VIBRATION SHOULD
INCREASE WITH INCREASE IN SPEED AND VICE
VERSA

8. REASONS OF 1X COMPONENT
OTHER THAN UNBALANCE
ECCENTRICITY
LOOSENESS
MISALIGNMENT
UNEVEN AIR GAP IN ELECTRICAL MACHINES
RESONANCE COINCIDENT WITH RUNNING SPEED
DISTORSION

9. IN SITU BALANCING
MEASURE THE INITIAL VIBRATION (1X) AND
PHASE ANGLE AT BALANCING SPEED.
STOP THE MACHINE.
ADD A TRIAL WEIGTH Tw.
MARK THE POSITION OF TRIAL WEIGHT.
RUN THE MACHINE TO BALANCING SPEED,
MEASURE THE VIBRATION AMPLITUDE (1X) AND
PHASE ANGLE.

10. IN SITU BALANCING

11. IN SITU BALANCING

12. IN SITU BALANCING
STOP THE MACHINE AND REMOVE THIS TRIAL
WEIGHT.
CONSTRUCT THE VECTOR DIAGRAM AS SHOWN
IN FIGURE.
MEASURE THE VALUE OF RESPONSE FROM
VECTOR DIAGRAM.
APPLY CORRECTION WEIGHT AT CORRECT
POSITION.

13. IN SITU BALANCING

14. IN SITU BALANCING

15. IN SITU BALANCING

16. IN SITU BALANCING
RUN THE MACHINE TO SAME SPEED.
IF THE VIBRATION ARE STILL NOT REDUCED TO
THE DESIRED LEVEL, FURTHER BALANCING RUN
CAN BE REPEATED TILL ACCEPTABLE LEVEL OF
VIBRATION IS ACHIEVED.

17. IN SITU BALANCING
CORRECT WEIGHT = Tw x (O/T)
CORRECT POSITION = ANGLE MEASURED
BETWEEN VECTOR O & T

18. LOCKING OF BALANCING WEIGHTS
DRAWING ISSUED BY MANUFACTURING UNITS
MUST BE REFFERED FOR KNOWING THE
INSTRUCTION FOR LOCKING OF THE WEIGHTS
VARIOUS METHODS OF LOCKING
 CAULKING OF THE CORNERS OF THE WEIGHT
 CAULKING OF GRUB SCREW
 LOCTITE OF RECOMMENDED GRADE TO BE
USED FOR BALANCING WEIGHT SCREW
LOCKING

19. LOCKING OF BALANCING WEIGHTS

20. FOUR RUN METHOD
NO PHASE MEASUREMENT REQUIRED
VIBROMETER CAN BE USED

21. FOUR RUN METHOD
T
R
A
B
C

22. WHY BALANCING MAY NOT WORK
UNBALANCE MAY NOT HAVE BEEN THE PROBLEM
STRONG UNIDIRECTIONAL FORCES
COMPOUNDING EFFECTS
AXIAL OFF SET
INSTABILITY IN MACHINE SHOWING CHANGE IN
AMPLITUDE AND PHASE ANGLE (BALANCING
DONE NOT IN STEADY STATE CONDITION)
HIGHLY RESONANT CONDITION

23. THANK YOU