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Vibration Analysis Case Study - Inner Race Bearing Damage
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Inner Race Bearing Damage - Examples of spectrum readings

What was the problem?
Machine Roll Bearing Issue

Equipment Used

  • Enpac 1200A Data Collector, 100mV/g Accelerometer and Probe
  • PL31b Data Collector, 100mV/g Accelerometer and Magnet
  • Emonitor Odyssey Deluxe Software

Readings Taken

  • All the readings that were taken on the bearing during this report period had a spectrum maximum frequency of 30Kcpm (500Hz). 800 lines of resolution were used for each spectrum and the readings were taken using peak signal detection.
  • The trend and spectrum readings that were taken from the roll front side bearing on the 14th October 2005 (Fig 1), showed signs of ball pass inner race (BPIR) damage, this reading was taken with our Enpac 1200a data collector.
  • Another further set of readings were taken on the 26th October 2005 (Fig 2), these readings were a lot higher than the initial readings that were taken. The PL31b data collector was used to take these readings and a magnet was used rather than the normal probe.
  • A different data collector was used for the 2nd set of readings as this data collector belonged to the customer.
  • A third set of readings was taken on the 1st November 2005 (Fig 3) these readings were taken using the Enpac 1200a data collector. The trend reading has now reduced to the same level as the first reading. Again, inner race defect frequencies are present in the spectrum.
  • On the 7th November 2005 another set of readings on the roll taken with the Enpac 1200a data collector after the bearing had been changed (Fig 4), it can now be seen that the inner race damage that was present in the spectrum has gone.

Fig. 1 (click on picture for larger view)
Vibration Trend and Spectrum Readings

Fig. 2 (click on picture for larger view)
Vibration Trend and Spectrum Readings

Fig. 3 (click on picture for larger view)
Vibration Trend and Spectrum Readings

Fig. 4 (click on picture for larger view)
Vibration Trend and Spectrum Readings

Conclusion
From the first reading that was taken with the Enpac 1200a data collector, it was evident that there was a problem with the bearing. Once we new that the problem was with the inner race of the bearing we decided to take extra readings. The customer was advised of our findings and made arrangements for the bearing to be removed on the earliest available shut. When the bearing was removed it was found to have a split on the inner race of the bearing.

Estimated Cost Savings
Calculations based on the following

  • Downtime is calculated at £3,000 per hour (approx.)
  • Cost of new fabric is £15,000 (approx)
  • New roll journal cost £5,000 (approx)
  • New bearing cost £500
  • It would take approximately 8-hours to change the roll and the fabric.


    • Total Savings £44,500

    Author: Philip Robinson


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