Diligent Vibration Analysis Catches Pulverizer
Exhauster Problem
The equipment discussed in this case
study is a pulverizer exhauster, 885 rpm rotational speed, overhung
wheel, spherical and cylindrical
roller
bearings.
Routine vibration readings taken on
the exhauster mandrel showed 1/2x rotational speed harmonics, see Figure
1. This type of vibration is characteristic
of a mechanical looseness. Even though the amplitude levels of the 1/2x
rpm vibration are relatively low (0.03 to 0.05 in/sec); the presence
of this type of vibration generally indicates a serious problem.
PeakVue vibration data was also acquired
on the exhauster mandrel. PeakVue is a demodulation technique for analyzing
metal-to-metal impacting found in antifriction bearing and gear set problems.
The PeakVue
data
showed very high levels of impacting at rotational speed. Figure
2 compares PeakVue data taken on the 333 Pulverizer Exhauster
(the unit in question) to data taken on 332
Pulverizer Exhauster.
The decision was made to take the 333
Pulverizer out of service and to replace the exhauster mandrel and wheel.
The mandrel that was going to be used
had been scheduled to go into the 332 Pulverizer Exhauster during
an upcoming outage. However, the vibration data indicated that the 333
Exhauster
problem
was a higher priority.
Figure
3 shows the routine vibration
data taken on the 333 Pulverizer Exhauster after the maintenance was performed.
Figure 4 shows the condition
of the exhauster spherical bearing – the cage had been cracked.
This case shows
the importance of watching very closely for the presence of any
amplitude 1/2x rpm harmonics. It also illustrates the capabilities of PeakVue
in
helping to diagnose the presence of faults.
Submitted by Joe Dominick,
Allegheny Energy Supply.
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