Page 58 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Rotating Machinery: Practical Solutions

CORRECTING STATIC UNBALANCE

Static Unbalance Weight

Unacceptable

Correction Weight

Figure 4-4. Creating a Couple Unbalance

Although the correction weight is equal to the unbalance and
is placed 180 degrees away, it is not in the same plane. The piece
is statically balanced, but when rotated the two weights act in
different planes causing couple unbalance.
Couple unbalance is illustrated in Figure 4-5. Note that even
though the shaft is statically balanced, the element would tend to
wobble about its center when the shaft is rotated. Both ends of the
shaft would vibrate with the same amplitude, but be 180 degrees
out of phase.

COUPLE UNBALANCE

FORCE

FORCE

Figure 4-5. Forces in Couple Unbalance