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VIBXPERT Balancing 11.2010
Chapter 2: Balancing
Increased vibrations on machines are undesirable phenomena. They
impair product quality, place additional strain on components and,
last but not least, reduce operational safety. The most frequent cause
for these increased vibrations is imbalance. The high centrifugal
forces that result lead to premature wear of machine components
such as bearings and seals, for example. Thus, the objective of
balancing rotors is to limit bearing forces and shaft deformations to
acceptable values.
VIBXPERT enables imbalance to be reliably detected and quickly
corrected. The balancing results are automatically compared with the
evaluation yardsticks of DIN ISO 1940 for the balancing condition of
rotating rigid bodies.
Imbalance
If a rotor is correctly balanced and this rotor is placed on balancing
rollers, any additional mass placed on the rotor will cause this mass
to immediately move downwards. This process is called 'roll off'.
Balancing: Introduction
If this rotor is now turned with the balancing RPM, a centrifugal force
is caused perpendicular to the rotational axis by the displacement of
the center of gravity.
A static imbalance has to be corrected using 1-plane balancing
because the planes of imbalance and center of gravity coincide.
Considered from the measurement plane, the imbalance is static at a
single location.
If two equally heavy masses are attached to a completely balanced
rotor so that they lie exactly opposite in two separately lying radial
planes, this is called a couple imbalance (or a dynamic imbalance).
The center of gravity of the rotor remains on the rotational axis. The
imbalances cause a centrifugal torque that gives rise to opposing
forces of the same size in the bearings. Such imbalances can only be
balanced using two-plane "dynamic" balancing - one-plane balancing
would not bring any improvement.
Couple (dynamic) imbalance
Rotational axis
Imbalance
Moment
inertia axis
Imbalance
