Observations on a slow speed bearing survey.

 

Outline

The brief was to do a follow-up survey on slow speed bearings (some only turning at 1RPM) on a metal conveyor belt, moving large rock fragments.

A total of 16 slow speed bearings were surveyed. Most of the readings were consistent with bearings in a good condition. Unfortunately, we did find 6 bearings of interest that showed deterioration from the previous survey.

Two different surveys were done 4 months apart

 

The Methodology of the Inspection.

A UE Systems, Ultraprobe 15 000 was used to take the ultra sound readings.

The sound recordings were then entered into the UE Systems DMS Software and the recordings analyzed in the UE Systems Spectralisyer 4.2.6 software.

There are four different ways to analyze bearings with ultrasound technology:

• Audible quality

Just by listening to the sound of a bearing, potential problems can be identified. To listen to the potential fault recordings, go to the UE Systems website (www.uesystems.com) where you can listen to sound file examples.  

• Comparative 

Comparative analyses were done between similar bearings, and between the earlier readings and current readings.

The individual results of the bearings of interest will be discussed in the main part of this observation document.

• Historical trending

We could do historical trending on the bearings on the conveyors as we had recordings taken four months earlier. We found deterioration of various levels in six of the 16 bearings we surveyed. I will show 4 in the document.   

• Analysis with software

All the recorded sound files were analyzed in the UE Systems Spectralisyer Software.   Several of the bearings showed increased harmonics on the Time Wave Form Graphs and further action was recommend. Examples of some of the bearings of interest will be discussed.

 

Example of a bearing in good condition

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Figure 1: Example of a bearing in a good condition

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In this example of a bearing in a good condition the harmonics in the graph are smooth and there are no outstanding increased peak harmonics visible.

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Example of a bearing in bad condition

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Figure 2: Example of a bearing in a bad condition

In this example of a bearing in a bad condition; there are numerous increased harmonics in a repetitive pattern.

 

 

Slow Speed Bearings

 

I get a lot of questions asking me about the use of Ultrasound on slow speed bearings. Can it work?

One of the big advantages of using Ultrasound on bearings, is that the speed of the bearing turning is not a limitation. We often do surveys on bearings moving at 1RPM. The slowest bearings we have done to date, was a slew bearing taking 45 minutes to turn 260 degrees. 

 

My experience is that as long as there is movement with friction or potential for friction Ultrasound should work. There are a few conditions you need to consider e.g.:

• You may have to change the frequency to find the best recording. I have had to go down to between 20 and 25 kHz to get usable recordings on ultra-slow speed bearings.

• You need to record at least one complete full revolution. So, for a bearing that turns at 1RPM the recording needs to be at least 1 minute long.

• When you do ultra-slow speed slew bearings that turn in both directions you need to do recordings of the movement in both directions. 

• Make sure there is the highest possibility for friction when you take the samples. For instance, we found there is a big difference in the potential for friction between loaded and empty conveyor belts.

• Always be on the lookout for competing ultrasound.

• These are only some of the most obvious conditions and is not an full list.

 

I would be interested to hear from other Ultrasound technicians to add their experience regarding these points as well as additional points we can add to the list.

 

Competing ultrasound

As we were working on a metal conveyor belt (potential metal on metal friction of the belt moving) carrying large rock fragments (potential friction caused by rock fragments on moving conveyor belt) competing ultrasound was always going to be a possibility. So, to understand the potential for competing ultrasound caused by the metal conveyor belt, we took sound samples from the metal cage close to the metal conveyer belt, in between the bearings as a control recording.

 

 

Figure 3 Control recording on metal cage.

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Figure 3 was of a control recording taken off the metal frame of the conveyor to see if the metal conveyor belt would give competing ultrasound that may interfere in the recording of the bearing. The recording showed there was no competing ultrasound with the potential to interfere with the recording of the bearings.    

 

Recordings of bearings

 

Example 1: Left Front Bearing of Conveyor 1; First recording August.

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Figure 4 Recording 1 of Example 1- August

This recording was taken in August and was consistent with the recording expected of a bearing in a good condition.

 

 

Example 1: Left Front Bearing of Conveyor 1; Second Recording December.

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Figure 5 Recording 2 of Example 1 - December

The Ultrasound recording taken in December of the bearing shows harmonics similar to the harmonics of a bearing in early stages of wear.  This is visible deterioration from the recording made in August (Figure 4)

 

Example 2: Left Front Bearing of Conveyor 2; First Recording August

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Figure 6 Recording 1 of Example 2 - August

This recording was taken in August and was consistent with the recording expected of a bearing of potential Interest. This bearing was highlighted as a bearing of interest. In the August survey there were two bearings (out of the 16 tested) highlighted as potential bearings of interest. This one had the was the most visible increased harmonics of the two.  

 

 

Example 2. Left Front Bearing of Conveyor 2; Second Recording December

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Figure 7: Recording 2 of Example 2 - December

This ultrasound harmonic is dramatic and is consistent with a bearing in an advance stage of wear.  It is interesting to note that the recording of August only showed isolated harmonics of interest but the current reading is a vastly more intense.

 

It is recommended that this bearing is given urgent attention. 

 

Example 3: Right Front Bearing of Conveyor 2; Fist recording August 

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Figure 8: Recording 1 of Example 3 – August

This recording was taken in August and was consistent with the recording expected of a bearing in a good condition.

 

 

Example 3: Right Front Bearing of Conveyor 2; Second Recording December

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Figure 9: Recording 2 of Example 3 - December

This ultrasound harmonic is another dramatic recording and is consistent with a bearing in an advance stage of stage of wear.  It is, however, interesting to note that the recording of August (Figure 8) showed no harmonics of interest whatsoever.  It is also interesting that both bearings Figure 7 and Figure 9 on the shame shaft showed such dramatic deterioration in such a relatively short time.

 

It is recommended that both of these bearings are given urgent and special attention. 

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Example 4 Left from Bearing of Conveyor 3: Second Recording – December

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Figure 10: Recording 2 of Example 3 - December

This bearing shows numerous harmonics of interest that is consistent with a bearing that needs further attention. It is also interesting to note that the extended harmonics is consistent with both short intense, and long large, areas friction that seems to repeat

 

Refer to Harmonics marked as “A” and “B” in Figure 10

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The Figure 11 shows a short 92.9 millisecond cut of harmonic A (the first extended harmonic) on the graph and Figure 12 shows the second 92.9 millisecond cut of harmonic B (the second thin extended harmonic) on the main slide, shows intense friction over a small area.

 

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Figure 11: Recording 2 of Example 3 – December

An analysis of a 92.9 millisecond of point A in main graph, covers the full 92.9 millisecond and show friction over an extended area 

 

 

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Figure 12: Recording 2 of Example 3 - December

Analysis of a 92.9 millisecond of point B in main graph, shows intense friction over only small area of the recording. 

 

As this is a general example of the recordings possible when using Ultrasound in slow moving bearings, I specifically did not add any detailed discussions on the potential causes of the faults in the bearings, nor did I give any specific recommendations as the next steps, as such recommendations will normally be specific to a bearing, based on the operation and operational requirements and would not be appropriate for a general example such as this.

 

 

 

This observation document is for training and development purposes only and was drafted by Andre Jooste ISO Level II, February 2021. E: a.jooste@iinet.net.au.

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