Page 76 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Rotating Machinery: Practical Solutions

2. Stop the rotor and attach a trial weight to the rotor at a diam-
eter where the correction weight can be added or removed.
Record the amount and location of the trial weight.

3. Operate the rotor at balancing speed and again record the
vibration amplitude and the phase angle of the reference
mark. These data are the O + T run.

4. Using polar graph paper, construct both the O and the O + T
vectors. Connect the head of the O vector to the head of the
O + T vector and label the new vector T. Note: assure the T
vector points from the O vector to the O + T vector.

5. Measure and record the length of the T vector. This is the
vibration amplitude caused by the trial weight. Determine
the amount of correction weight required by:

Correction Weight = Trial Weight × O/T

6. Use a protractor to measure the angle between the O and the
T vectors, and record its value. The correction weight will
need to be placed this angle away from the trial weight loca-
tion, in a direction opposite to the direction the reference
mark shifted.

7. Be sure to remove the trial weight after securing the correc-
tion weight in place. Run the rotor again and record the
amplitude of vibration and the reference mark location.

If additional balancing is required, this run will become the
original data. Follow the steps 1 through 7 above until satisfactory
results are achieved.

TRIAL WEIGHTS AND FORCE

Care should be exercised in the selection of the proper trial
weight size. If it is too small, no change in phase or amplitude
may be noted, and one trial run will have been wasted. If the trial
weight is too large, it could cause damage to the machine, espe-