Page 337 - Machinery Component Maintenance

Balancing of Machinery Components 319

It is the purpose of this section to illustrate the possibilities of field
balancing on the basis of three typical balancing problems. The machines
chosen for these problems represent examples only and could at any time
be exchanged for machines with similar rotor systems. The solutions to
the problems indicated, therefore, apply equally to other machines and
types of rotor not specifically mentioned here. The following classifica-
tion will simplify the allocation of different types of machines to the three
problem solutions:

1st Problem Solution: Machines with narrow disc-shaped rotors such as
blowers, fans. grinding wheels, belt pullcys, flywhccls, couplings,
chucks, gear wheels, impellers, atomizer discs, etc.
2nd Problem Solution: Machines with long roll-shaped rotors such as
centrifuges, paper rolls, electric motors and generators, beater shafts.
machine tool spindles, grinding rolls, internal combustion engines, etc.
3rd Problem Solution: Machines having multiple bearing coupled rotors
such as standing machines, twisting machines. motor generator sets.
turbo generators. cardan shafts. etc.

Field balancing of very low speed rotating assemblies (cooling tower
fans, etc.) may require special techniques which are not covered here.
The reader should discuss special requirements with the machinery man-
ufact urer.

First Problem: Unbalance Vibration in Blowers
Build-up on blades, corrosion, wear, and thermal loading regularly
lead to unbalance in blowers. The presence of such unbalance shows it-
self externally in the form of mechanical vibration generated by the
blower rotor and transmitted via the bearings and the frame into the foun-
dations and finally into the environment. If the danger of this unbalance
vibration is not recognized. after a very short operating period costly
damage may be caused. This may frequently result in the destruction of
the bearings, cracks in the bearing housing and in the air channels, dam-
age to the foundation, and cracks in the building.

Solution: Field Balancing in One Plane

For economic reasons rebalancing of a blower should always be car-
ried out in the assembled state. This does away with the need to disassem-
ble the wholc plant, to makc available a balancing machine and to trans-
port the blower rotor to the balancing machine. Only the electronic
balancing instrument needs to be brought to where the blower is in-