Lin Liu & Suri Ganeriwala
Vibration and Force Signatures of Bent Shaft
SpectraQuest Inc., 8227 Hermitage Road, Richmond, VA 23228
Published: May, 01 2006
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.
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