Page 295 - Machinery Component Maintenance

Balancing of Machinery Components 277

be satisfactorily corrected at low speed by applying correction masses in
two or three planes. Should the ratio exceed 0.2, the rotor will generally
have to be balanced at or near its service speed.

Direction of Rotation

The direction of rotation in which the rotor runs while being balanced
is usually unimportant with the exception of bladed rotors. On these (or
others that create windage) it is recommended to run in the direction that
creates the least turbulence and thus, uses the least drive power. Certain
fans need close shrouding to reduce drive power requirements to an ac-
ceptable level. Tbrbine rotors with loose blades should be run backward
(opposite to operational direction) to approximate the blade position in
service, while compressor rotors should run forward (the same as under
service conditions).

End-Drive Adapters

Design Considerations
End-drive adapters used on horizontal balancing machines to drive
workpieces need to be carefully balanced so as not to introduce a balance
error into the workpiece.
Considerations should be given to the following details when designing
an end-drive adapter:

1. Make the adapters as light in weight as possible, consistent with ca-
pability to transmit the required driving torque. This will reduce
balance errors due to fit tolerances which allow the adapter to lo-
cate eccentrically, i.e., offset from the shaft axis of the workpiece.
2. Maintain close tolerances on fit dimensions between end-drive
adapter and workpiece, and between adapter and balancing machine
drive. Loose fits cause shifting of the adapter and consequent
changes in adapter balance. Multiply the weight of the adapter in
grams by one half of the maximum radial runout possible due to a
loose fit to obtain the maximum balance error in gram-inches that
may result.
3. Design adapters so that they may be indexed 180" relative to the
workpiece. This will allow checking and correcting the end-drive
adapter balance on the balancing machine.
4. Harden and grind adapters to be used in production runs to reduce
wear and consequent increase in fit clearances.