F:8 Rotor balancing
Measuring unbalance
Unbalance causes excessive vibration. However,
excessive vibration can have any number of other
causes. Thus, before attempting to balance a rotor,
we must first check that there is in fact an unbalance
problem and make sure that other vibration causes,
such as loose parts and misalignment, are eliminated.
As the ‘heavy spot’ rotates in the radial plane, the
vibration values measured in the horizontal (H) and
vertical (V) directions should be higher than the
vibration measured in the axial direction (A).
Check all three directions. For balancing, measure in
direction H or V, whichever yields the highest value.
Unbalance causes vibration with a frequency of 1X,
which is the shaft frequency in Hz (rpm/60), also called
the first order.
Check that the vibration spectrum has a clearly
dominant line at 1X . This line is marked in the Leonova
balancing spectrum.
All balancing methods use a first run to establish the
vibration behaviour of the rotor.
The following run is made with a trial weight fastened
at a convenient spot along the rotor. Thus, we add a
known unbalance factor, which allows us to calculate
the position and weight of the unknown ‘heavy spot’
from the change in vibration behavour.
1X
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