Vibration Analysis of Belt Drives in Rotating
Machinery
Lin Liu,
Suri
Ganeriwala
SpectraQuest Inc., 8201 Hermitage Road, Richmond, VA 23228
Published: July 2005
Abstract
Belt drives are commonly used in a variety of
power transmission applications. Improper installation and
maintenance of belt can have an enormous impact on the operation and
degradation of a machine. Vibration signatures are widely promoted
for studying belt drive malfunctions. This note presents the results
of an experiment performed on a two belt drive system. The effect of
belt tension, speed, sheave eccentricity, and misalignment
conditions were investigated. The results indicate that eccentric
sheave show amplitude modulation and produce high vibration. Sheave
eccentricity also excited belt natural frequencies easily.
Meanwhile, the effect of misalignment on the vibration signature is
not significant.
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Introduction
The equipments used in the experiment include:
One SpectraQuest Machinery Fault Simulator (MFS), two
A42 V belts, a laptop with VibraQuest data acquisition and
analysis software installed, a SpectraPad portable data
acquisition device, two PCB accelerometers, one Wilcoxon
tri-axial accelerometer.
First, baseline data is collected under different
rotor speeds and different belt tension forces. Then offset
misalignment is introduced into the driving belt sheave and data is
collected under the same speed and belt tension force as the
baseline. Finally, the driving belt sheave is replaced by an
intentionally made eccentric sheave and data is collected under the
same speed and belt tension force as the baseline. In the eccentric
sheave test, rotor speed is increased slowly to observe the
resonance of belts and the data under resonance condition are
collected.
The data acquisition frequency limit is 2000Hz
and 8 seconds data is collected for each case. The two rotor speeds
tested are 20Hz and 40Hz. It should be noted that these speeds are
read from the motor controller and because there are errors in the
controller, the actual speeds have some deviations from the
readings. The belt tension force can be adjusted by means of turning
a screw which will change the center distance of the two belt
sheaves. The two belt tension force cases, high and low, are
determined by hand feelings.
Some of the observations can be highlighted as:
The effect of sheave eccentricity on vibration
signature is significant. Although vibration magnitude is not
necessarily increased by a sheave eccentricity, sheave eccentricity
will create strong amplitude modulation. The natural frequencies of
belts can be excited by a sheave eccentricity easily. When the top
section of a belt is in resonance, the vibration level of the
machine is increased. However, an increase in machine vibration is
not significant when only the bottom section of a belt is in
resonance.
The effect of belt tension force on machine
vibration signature is significant. The vibration spectrum has the
tendency to move to the higher frequency as the the belt tension
force is increased. The reasons might be: 1) by increasing the belt
tension force, the whole machine structure is strengthened. 2) the
natural frequencies of the belt itself are increased by an increase
in belt tension force.
Fig 1: Experimental Setup
Fig 2: Misalignment data
with rotational nominal speed 20Hz
Fig 3:
Misalignment data
with rotational nominal speed 40Hz
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