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Hello. This is a different avenue than my usual posts, this one is a link to a paper I have just written with the great knowledge and help from Dr K.

 

Briefly:

I was introduced to Dr Knezevic (Dr K) of the Micre Akademy though a great mentor in thermal imaging Austin Dunne of the Institute of Infrared Thermography.

Please click on this link to learn more about the great work of the Micre Akademy

Please click on this link to learn more about the Institute of Infrared Thermography

 

About this Paper:

MIRCE Science is a theory for predicting expected functionability performance for a functionable system type. Accuracy of the predictions is governed by the degree of the scientific understanding of the physical mechanisms, and human rules, that govern the motion of functionable system types though MIRCE Space. The main objective of this paper is to address vibration monitoring as one of the possible mechanisms that governs motion of a gearbox through functionability states, which are contained in MIRCE Space. In general, and to illustrate this process through a case study related to heavy gearbox used in Plastics Manufacturing industry, conducted by the author with vibration data collected on site by Ian Graham.

 

Click here for the paper Vibration Monitoring Mechanism Of Motion

 

Acknowledgement:

The author wishes to acknowledge the support received from Dr Knezevic, MIRCE Akademy, Exeter, UK, while preparing this paper. As the “father” of MIRCE Science, Dr Knezevic, has inspired me to view how every day Condition Based Monitoring can have a significant impact on functionability performance of the whole system.  Consequently, I can now understand how many companies are performing Condition Based Monitoring but are not linking this to the business performance of the whole organisation/company. MIRCE Science is the body of knowledge that bring together these two very different but related disciplines, for the ultimate benefit of the user.

This is one I recently finished and thought it would be a great one to share so people know what can be achieved.

 

Background:

We had three pump sets suffering from elevated vibration levels when operated in different combinations. Conventional vibration analysis was performed and this indicated a structural resonant condition.

The pump motors are mounted on a false floor:

and the pump barrels are below the floor:

The pump with the worst motion was on pump 3, the one far away from the edge of the drop. Also this pump has the least structural support under the floor. When ran in certain combinations pump 3 would be excited very badly.

 

The cost effective solution.

I designed a vibration dynamic absorber.

Dynamic Absorbers are often overlooked and not used, they can be seen as a band aid or a last option for some vibration problems. Whereas in some cases they can be the only cost efficient option, and they are very effective.

The Vibration Dynamic Absorber is a unique bespoke item, maintenance free, that is designed to absorb unwanted energy. It is tuned to have the same resonant frequency as the structure to set up an out of phase signal reducing the signal generated by the structure.

 

How did I design these?

For this one it was more of a ‘gut feel’. I looked at the motor and then drew out a design that wouldn’t look out of place when mounted, and that had some adjustment to it when fitted as theory doesn’t always pan out in real life. Then from this I worked backwards to get the correct material dimensions/configuration so it was resonant at the target frequency. I also made some weight configurations so I could cover my target range.

I will be going back in 6 months to see how it fairs. I did consider a round bar and weight but thought that with the rectangular bar you have more control on what way it will be resonant. As once you have performed phase analysis on the motor you then know what way it is moving and can mount the absorber accordingly.

Image of Pump 2 Vibration Dynamic Absorber:

Image of Pump 3 Vibration Dynamic Absorber:

Pump 2 Live Motion Video

 

Pump 3 Live Motion Video

 

Pump 3 Slow Motion Video

 

What am I covering?

On pump 3 I am covering the one problem frequency, 1 Order, but the two arms are of different lengths in terms of the length from the point of pivot (clamping) to the mass. Also the arms are of different dimensions with different mass at the end so they could be tuned to the same frequency.

I also did find that the sweet spot was not necessary the point of higher deflection of the absorber and that the three motors all reacted differently.

 

Final Review of actual vs theory:

I have had time to review the final theoretical tuning of the three pumps to actual results. They are all different and no one motor is the same, they all have their own personalities dynamically wise.

Pump 3 had the highest overall vibration, one dominant frequency at 1 Order on pump 3 and this was successfully reduced.

Pump 1 and pump 2 had two frequencies in the data. And both of the vibration dynamic absorbers were tuned to the lower frequency not the one order.

 

Table of final overall levels:

Before After % reduction
Pump 1 Motor NDE (Top) 4.314 2.854 33.84%
Motor DE (Coupling end) 2.092 1.617 22.71%
Pump 2 Motor NDE (Top) 9.95 6.959 30.06%
Motor DE (Coupling end) 4.05 3.012 25.63%
Pump 3 Motor NDE (Top) 27.02 7.59 71.91%
Motor DE (Coupling end) 10.73 5.113 52.35%

 

Pump 1:

Pump 1 actually showed the text book results. The theoretical calculations for the tuned damper was for the lower frequency not the running speed (1520 CPM yes they are on soft start VFD). It actually split the frequency – text book……….beauty!!

 

I have more questions and theories now, this is pretty exciting stuff. Hopefully I can keep this going on other pumps.

Hello all

This month’s blog is slightly different from the usual ones we post. This month is more of an opinion regarding data dogs. We are seeing more equipment suppliers selling VA equipment that they promote as “anyone can use” and you know need to know or have experience to use. That the software will diagnose for you. Or even, just collect the data upload to the cloud and we will tell you if you have any issues.

I feel there are places for this type of program but one thing I dislike is companies sending “data dogs” to collect the data. These are cheap labour sent to press a button and collect the vibration data as fast as they can. This type of VA often gives this service a bad name as they miss diagnose, miss defects or the person in the office performing the analysis just gives the ‘wall chart analysis’ of its either misalignment, imbalance, looseness or resonance.

So much can be gained by a competent engineer or technician attending the asset to collect the vibration data. Most of your analysis should be performed at the machine, not in the air conditioned office!

We also find that there are many facilities/companies that are on the start of their reliability journey that require a person on site to promote and ensure the job is done and followed though correctly.

 

An Example:

The images below back up this point. A great friend of mine, James Pearce, was performing a quarry motor VA survey and while at a motor he sensed an abnormal noise, he tracked it down to the GTU take up conveyor pulley. The GTU is not on the vibration program but when you have an experienced engineer or technician collecting the data walking the plant they also use their other senses to ensure plant reliability.

 

James reported this to site that had a controlled shut down of the quarry immediately to replace the pulley bearings. Site confirmed that they would have not inspected this pulley and it would have catastrophically failed causing a lot of additional hard work. This controlled shutdown cost 3 hours of production. But this saved replacing the pulley shaft as there was no damage to the shaft. If this was left to totally fail this would have cost 9-11 hours production downtime at 2,000 Tons per hour. There is also the possibility that the pulley could have failed in a way that caused damage to the conveyor belt incurring more down time and a lot more costs.

 

 

And here is the video!

 

You can see the bearing there – this should not be glowing red. This bearing had totally failed!

So remember that 5 years of experience is not the same as 1 years of experience 5 times and you can’t analyse what you don’t know or understand.

Vibration Dynamic Absorbers:

Who has given these a try?

Dynamic Absorbers are often overlooked and not used, they can be seen as a band aid or a last option for some vibration problems. Whereas in some cases they can be the only cost efficient option, and they are very effective.

The Vibration Dynamic Absorber is a unique bespoke item, maintenance free, that is designed to absorb unwanted energy.

It is tuned to have the same resonant frequency as the structure to set up an out of phase signal reducing the signal generated by the structure.

Knowing the forcing frequency of interest, the material dimensions and parameters including Density (S.I. Units), Young’s Modulus (S.I. Units) and Area Moment of Inertia (si) we can design a component that is tuned to the problem frequency.

Example of a Vibration Dynamic Absorber in action on a horizontally mounted motor.

Example of a Vibration Dynamic Absorber in action on a vertically mounted motor in slow motion.

Here are some ‘Pearls of Wisdom’ to consider when setting up a program and working with customers within your external or internal business:

  1. The most important part of any program is the person performing the data collection and analysis.
  2. The second most important part of any program is the training given to the person selected.
  3. 5 years of experience is not the same as 1 year of experience 5 times.
  4. The most important question you can ever ask is “why”.
  5. It is important to understand the values of the numbers you are using.
  6. Physics of the machine is really important.
  7. You can’t analyse what you don’t know or understand.
  8. A person may not be stupid, they may just not understand what you are saying.
  9. 1 times RPM is not always imbalance.
  10. There are no universal vibration severity limits.
  11. Absolute amplitude in the frequency domain is relatively useless. Don’t forget the time domain & phase.
  12. There are no ghost frequencies or unknown frequencies but only frequencies not enough analysed.
  13. Don’t ignore the potential benefits of chit chat in the crib/break room with the operators and maintenance teams. They know their machines!
  14. When all else fails, leave the air conditioning, and go examine the operating equipment. Go look, touch, feel, smell and listen to the machinery.
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