Page 283 - Machinery Component Maintenance

Balancing of Machinery Components 265

Classification of Centrifugal Balancing Machines
Centrifugal balancing machines may be categorized by the type of un-
balance a machine is capable of indicating (static or dynamic), the atti-
tude of the journal axis of the worlcpiece (vertical or horizontal), or the
type of rotor-bearing-support system employed (soft- or hard-bearing) .
In each category, one or more classes of machines are commercially
built. The four classes are described in Table 6-1.

Class I: Trial-and-error Balancing Machines. Machines in this class are of
the soft-bearing type. They do not indicate unbalance directly in weight
units (such as ounces or grams in the actual correction planes) but indi-
cate only displacement and/or velocity of vibration at the bearings. The
instrumentation does not indicate the amount of weight which must be
added or removed in each of the correction planes. Balancing with this
type of machine involves a lengthy trial-and-error procedure for each ro-
tor, even if it is one of an identical series. The unbalance indication can-
not be calibrated for specified correction planes because these machines
do not have the feature of plane separation. Field balancing equipment
usually falls into this class.
A programmable calculator with field balancing programs, either con-
tained on magnetic strips or on a special plug-in ROM, will greatly re-
duce the trial-and-error procedure; however, calibration masses and
three runs are still required to obtain magnitude and phase angle of un-

Table 6-1
Principle I Unbalance I Attitude of I
Classification of Balancing Machines

emnloved indicated shaft axis Twe of machine
%rtical Pendulum
Gravity Static Horizontal Knife-edges Not classifiec
(nonrotating) (single-plane) Roller sets
1 *rtical I Soft-bearing
Hard-bearing I Not classifiec
Centrifugal Static Horizontal Not comme&ally
(rotating) (single-plane) available
Dynamic
(two-plane); Vertical Soft-bearing
also suitable Hard-bearing
Centrifugal for static Horizontal Soft-bearing
(rotating) (single-plane) Hard-bearing