Vibration and Force Signatures of Bent Shaft
Lin Liu,
Suri
Ganeriwala
SpectraQuest Inc., 8201 Hermitage Road, Richmond, VA 23228
Published: June 2006
Abstract
In this work, bearing vibration and reaction
force signatures caused by bent shafts were studied experimentally.
The vibration and force spectrum signatures between baseline and
bent shafts (center bent and coupling end bent) under two shaft
speeds, 1000 and 5000 RPMs were compared. The bearing reaction force
associated with a center bent shaft under different shaft speeds
were calculated by subtracting the baseline reaction force from the
total reaction force. The experiment results indicate that for low
shaft speed (1000 RPM), the effect of bent shaft on bearing
vibration can be neglected. Under high speed (5000 RPM), a center
bent shaft will increase the bearing vibration. However, a center
bent shaft will increase bearing reaction force for both low and
high speeds. The effect of a coupling end shaft on bearing vibration
and reaction force is not conclusive. Finally, the bearing reaction
force is not affected by the shaft speed significantly.
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Introduction
The tests were carried out on a machinery fault
simulatorTM (MFS) manufactured by SpectraQuest, Inc. By
using such a simulator, one can design kinds of intentionally faults
and conduct various experiments on rotating machinery diagnostics.
Three steel 5/8" shafts were tested in the
experiments. One is a straight shaft which is taken as the baseline.
The other two shafts were bent intentionally. One is bent 8 mils in
the center and the other one was bent 8 mils in the end which is
connected with the motor.
Vibration as well as force signals were collected
during the experiments.
The experiments were divided into two stages. In
the first stage, the focus was to compare the vibration and force
spectrum signatures between baseline and bent shafts (center bent
and coupling end bent) under two shaft speeds, 1000 and 5000 RPMs.
In the second stage, the focus was to observe the
bearing reaction force associated with a center bent shaft under
different shaft speeds. The shaft speed was increased from 500 RPM
to 5000 RPM with 500 RPM increment and the bearing housing forces
were collected for each speed.
Fig 1: Bearing Housing with Force Transducers
Fig 2: Total Bearing Housing
Force of a Center Bent Shaft in Horizontal Direction
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