Page 78 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Rotating Machinery: Practical Solutions

weights. In this situation, a balancing ring may be installed to aid
in the balancing process. A balancing ring is simply a flat metal
ring that can be bolted to the rotating assembly, and has provi-
sions to add trial weights.
Note: the balancing ring must be in perfect balance to pre-
vent interference with the balancing process, unless it is to remain
in place permanently. If the exact correction weight is found,
material of equal weight may be removed 180 degrees opposite
the correction weight location. Drilling, grinding or cutting can be
used for this purpose.

Cautions
When balancing, assure the rotor operates at the same speed
throughout the balancing process. A change in speed, load tem-
perature and other operating conditions can alter the results. If a
change occurs start the balancing process over.
By following these steps and cautions, field balancing pre-
sents few problems. However, if repeated attempts to balance a
rotor fail in providing satisfactory results, and the analysis data
point to unbalance as the problem, there may be other problems
with the machine. Some of these problems that are frequently
encountered are:

1. LOOSE MATERIAL - Machines such as blowers and fans
may accumulate dirt or water in recesses, hollow blades and
hollow shafts. This debris may take a new position each time
the machine is stopped and restarted. Of course this will af-
fect the balancing procedure.

2. ROTOR LOOSE ON ITS SHAFT - This problem is encoun-
tered on rotors that are pressed onto their shaft. If the inter-
ference fit is incorrect, the rotor may rotate slightly on the
shaft during load changes due to the high torque during start
up.

3. OPERATING IN RESONANCE - If the supporting structure
or an element of the machine is resonant at or near the oper-