Page 336 - Machinery Component Maintenance

318 Machinery Component Maintenance and Repair

a machine with the transducer held with varying degrees of firmness.
Transducers of this type have internal seismic mountings and should not
be used where the frequency of the vibration being measured is less than
three times the natural frequency of the transducer.
A transducer responds to all vibration to which it is subjected, within
the useful frequency range of the transducer and associated instruments.
The vibration detected on a machine may come through the floor from
adjacent machines, may be caused by reciprocating forces or torques in-
herent in normal operation of the machine, or may be due to unbalances
in different shafts or rotors in the machine. A simple vibration indicator
cannot discriminate between the various vibrations unless the magnitude
at one frequency is considerably greater than the magnitude at other fre-
quencies.
The approximate location of unbalance may be determined by measur-
ing the phase of the vibration; for instance, with a stroboscopic lamp that
flashes each time the output of an electrical transducer changes polarity
in a given direction. Phase also may be determined by use of a phase
meter or by use of a wattmeter. Vibration measurements in one end of a
machine are usually affected by unbalance vibration from the other end.
To determine more accurately the size and phase angle of a needed cor-
rection mass in a given (accessible) rotor plane, three runs are required.
One is the “as is” condition, the second with a test mass in one plane, the
third with a test mass in the other correction plane. All data are entered
into a card-programmable pocket calculator and, with a few calculation
steps, transformed into amount and phase angle of the necessary correc-
tion masses with two selected planes. To simplify the calculation process
even further, a “rom” for the TI 58 and 59 has recently become available
which is permanently programmed for single plane or two-plane field
balancing,

Field Balancing Examples

As we saw, two methods are available for the systcmatic balancing of
rotors:

Balancing on a balancing machine
Field balancing in the assembled state

Both methods have specific fields of application. The balancing ma-
chine is the correct answer from the technical and economic point of vicw
for balancing problems in production. Field balancing, on the other
hand, provides a practical method for the balancing of completely assem-
bled machines during test running, assembly and maintenance.