Page 97 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Field Balancing

Note in the above calculations, the least significant digits
th
were set as 1/10 . By calculating using least significant digits to
th
1/1000 , the answers are slightly altered. In this case, the solution
would be:

CWN = 8.2 ounces @ 214 degrees.
CWF = 5.2 ounces @ 282 degrees.

Assuming the machine in example (5.4) operated at 1,750
rpm and the trial weights were placed at a radius of 16 inches
from the center, the difference would cause an unbalanced force
2
of: F = 1.77 × (1750/1000) × .2 × 16 or 17.34 pounds of force.
Depending on the weight of the rotor and the type of machine,
this may be significant.

WHICH METHOD

As a general guide, rotors with a W/D ratio of .5 or less may
be balanced using the single plane method if they operate at less
than 1,000 rpm. Above 1,000 RMP the two plane method should
be used. Rotors with a W/D ratio above .5 that operate below 150
rpm may use the single plane method of balancing. Those above
150 rpm should use the two plane method.

▲
W ▲

▲

D

▼

Figure 5-22. W/D Ratio for Rotors