Page 99 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Field Balancing

its balance using data from bearing 1. These steps are repeated as
often as required to achieve an acceptable balance of the rotor.

NOTES ON BALANCING

First and foremost, assure the machine is truly suffering from
unbalance prior to attempting corrections to balance. Observe the
machine for obvious causes of unbalance, such as broken or miss-
ing cooling vanes on electric motors, loose impellers, missing key
material, excessive key material, different length bolts, etc. On
fans, blowers and compressors, check for buildup of debris which
can cause unbalance and clean first. Scale and rust buildup can
also alter the balance of this type machine.
Many large cooling tower fans and fin-fan coolers have hol-
low blades. Usually, the tip of the blade has a small hole drilled to
its center to allow any trapped moisture to escape. Assure these
holes are open and free to flow any moisture from the blade. In-
ternal corrosion and scale can also be a source of unbalance.
On fans with adjustable blades, assure they are all of the
same length and are set to the same pitch. Another source on vi-
bration that may appear to be unbalance is aerodynamic force
generated as blades pass over support members.
Assure the major component of the vibration is occurring at
1 × rpm.