What is unbalance?
Unbalance is that condition which exists when a rotor
causes a vibratory force at its bearings due to Unequal distribution of mass about its rotating centre line”.
(I.S.O. Definition) A more common phrase for this condition is mass centre displacement (MCD)
What is dynamic balancing?
Excessive vibration in rotating machinery can substantially reduce the life of shaft bearings.
Dynamic balancing is the procedure used to reduce this unbalance to a level that will not adversely effect the
bearing life. The unbalance is caused by an effective displacement of the mass centre line from the true axis
caused by some mass eccentricity in the rotating equipment.
Why should I balance my new fan?
When a new fan is installed it is very important to check that the fan balance
is still in tolerance with the factory standards. When a typical fan comes from the manufacturer they
are usually dynamically balanced at the factory. Using a spin balancing machine that has (2) correction plains.
They should typically add weight to the outside of both sides of the fan by welding on attached weight.
This is usually done with a balancing arbor. Then a permanent shaft is installed when the fan is being assembled
at the factory. Since no standard (2) shafts are identical in run-out or dimension, also the fan and bearings
can be off-set slightly from where it was previously balanced on the factory balancing arbor. This is why we
recommend having your fan trim balanced on site after completion of installation. This will ensure that the fan
is running the right balancing tolerance.
Why should old fans be rechecked for balancing?
It is very common for a fan to go out of balancing tolerance due to the following: