Dynamic Behaviors of Rotor with
Fluid Film Journal and Rolling Element Bearings
Lin Liu,
Suri
Ganeriwala
SpectraQuest Inc., 8201 Hermitage Road, Richmond, VA 23228
Published: November, 2005
Abstract
Using a MFS-Lite Extended TM machine,
studied the behavior of a rotor shaft supported on fluid film
journal bearing as well as rolling element bearing from the
perspectives of rotor resonance frequencies and rotor orbit shapes.
The experiment results indicate the effect of bearing types on the
rotor natural frequencies can not be neglected. Moreover, the rotor
orbit displays totally different shape for journal fluid film
bearing and rolling element bearing.
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Introduction
SpectraQuest has designed a new
simulator which is called Machinery Fault Simulator-Lite Extended™.
It is an innovative tool specially designed to study the dynamic
behavior for rotor supported by oil lubricated journal bearings.
A SpectraQuest Lube Oil Pump is provided with MFS-Lite Extended
to
drive the lubrication fluid. Besides that, it is an invaluable tool
for studying signatures of common machinery faults without
compromising factory production or profits.
This new simulator is used in this work to
investigate the dynamic performance of rotor supported by fluid film
journal bearing as well as rolling element bearing. The experiment
is concentrated on the rotor system dynamic characteristics under
resonance conditions. There are four approaches that you can adopt
to excite a rotor natural mode on the Machinery Fault Simulator-Lite
Extended™.
1.
change the number of disks or loaders on a shaft
2.
change the positions of disks on a shaft
3.
change the position of bearing house on the rotor deck
During the resonance test, we are trying to
obtain a balance between the speed and vibration. If you introduce
too much unbalance, or the unbalance is located at the position with
the maximum vibration amplitude of a specific mode, the motor
controller might be cut-off because the load is too high. However,
in order to excite the resonance, you need certain amounts of
unbalance. Therefore, you need to have the unbalance large enough to
excite the mode but not cut-off the motor. The rule of thumb to
achieve some kind of balance on the unbalance is: for low speed
resonance, unbalance weight can be used. For high speed resonance,
(the third mode) unbalance weight is not needed. The unbalance of
the disks by themselves is enough to excite them.
By appropriate configuration of the rotor disks
on the shaft, we can excite the first three rotor natural
frequencies.
For proximity probes are installed on the two
bearing housings of the rotor shaft to collect the displacement data
of the shaft. Two proximity probes for each bearing housing, one in
the horizontal and one in the vertical directions respectively.
Fig 1: MFS
Lite-Extended
Figure 2: Orbit Graphs of Shaft
with Fluid Film Journal Bearings
Figure 3. Orbit Graphs of Shaft with Rolling
Element Bearings
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