Tag Archives: vibration analysis

Home / vibration analysis
14 Posts

A profitable plant is reliable, safe and a cost-effectively maintained plant.

Introduction:

I often am lucky enough to use different vibration technologies and this post is a great example of how a vibration analysis program can protect the business using the SPM HD Enveloping technique. This post is with thanks to assistance from Dean Whiteside.

Background:

As part of a routine vibration data collection program a change in condition was noted at the fan motor vibration levels. Vibration monitoring frequencies were increased to daily as the defect deteriorated. This enabled planning and a controlled change out of the motor.

Air Fan

Vibration Analysis:

On inspection of the vibration data, bearing outer raceway (BPFO) damage was diagnosed at the drive end motor bearing. This was clearly evident in the SPM HD Enveloping.

Acceleration Data:

Figure 1 shows the Acceleration RMS trend from the motor drive end (DE) bearing location. This shows the steep increase in the impacting levels with an exponential increase in the final days of monitoring.

Fig1:

Acceleration RMS Trend

SPM HD Enveloping Data:

Figure 2 shows the SPM HD Envelope spectrum from the motor drive end bearing. This technique shows a clear impact at 3.09 Orders that matches the defect frequency for the bearing fitted. There are many harmonics indicating a very impactive signal.

Fig 2:

SPM HD Enveloping

Summary of vibration:

There is a clear distinct defect in bearing outer raceway, at these levels this would confirm a spalling to the raceway.

Corrective Actions:

Due to the risk of failure, a new motor was sourced and placed on-site encase of instant catastrophic failure. The risks was discussed with production and was deemed too high to the process and a plan was put in place for a controlled stop. But prior to this date there was an unexpected line stop, and as the motor was all prepared on site, the motor was changed during this downtime.

Vibration data after controlled change-out:

Figure 3 are the SPM HD Enveloping spectra from before and after motor change out. The top plot showed the clear bearing damage and now with the replacement motor there are no bearing defect signals present.

Fig 3:

Original Motor
New Motor

Figure 4 is the Acceleration trend from the motor drive end bearing location. This trend shows the increasing and then the lowest record level with the new motor installed.

Fig 4:

Acceleration RMS Trend

Bearing Inspection: After sectioning and cleaning

On visual inspection, it was found as expected, a large visible defect in the loadzone of the bearing outer raceway. Motor Drive End Bearing FAG 6316-C3

Image 1 is the drive end bearing sectioned.

Image 1:

Drive End Bearing

Image 2 is the defect located in the loadzone of the outer raceway.

Notice the flat bottom of the spalled area and the “neat” cracks around it. These are cracks that have come to the surface and in time, more material will break away.

Image 2:

Microscopic Image Outer Raceway

Image 3 is the defect located in the loadzone of the outer raceway.

Particle over roll as the bearing comes out of the load zone.

Image 3:

Microscopic Image Outer Raceway

Failure Mode:

ISO 15243:2004: 5.1.2 Subsurface initiated fatigue. Primary causes of Subsurface initiated fatigue are repeated stress changes and material structural changes. This leads to microcracks under the surface, crack propagation and then spalling.

This bearing was close to catastrophic failure

The bearing is damaged as soon as spalling occurs. Spalling gradually increases and gives rise to noise and vibration levels in the machine. This machine was stopped and repaired before the bearing collapsed. The period from initial spalling to failure depends on the type of machine and its operating conditions.

What is sub surface fatigue? In a rotating bearing, cyclic stress changes occur beneath the contact surfaces of the raceways and rolling elements. Consider the rotating inner ring of a radial bearing with a radial load acting on it. As the ring rotates, one particular point on the raceway enters the load zone and continues through an area to reach a maximum load (stress) before it exits the load zone.

During each revolution, as that one point on the raceway enters and exits the load zone, compressive and shear stresses occur. Depending on the load, temperature and the number of stress cycles over a period of time, there is a build-up of residual stresses that cause the material to change from a randomly oriented grain structure to fracture planes.

In these planes, so-called subsurface microcracks develop beneath the surface at the weakest location, around the zone of maximum shear stress, typically at a depth of 0,1 to 0,5 mm. The depth depends on the load, material, cleanliness, temperature and the microstructure of the steel. The crack finally propagates to the surface and spalling occurs.

Summary:

This is another example of how vibration technology and knowing system health and risk of failure enables data driven decisions to benefit the business. The motor was replaced when the line was down due to an unplanned shutdown, with no additional downtime occurred.

If this motor had failed without any planning this would have lost product and reduced profit. In addition these actions have protected the customers, supply chain and brand our reputation.

A profitable plant is reliable, safe and a cost-effectively maintained plant

This blog is to remind everyone that ‘this is the way we have allays done it’ doesn’t wash and also how important using the correct lubrication and lubricant cleanliness is!

Introduction:

This share has two questions;

  1. What the highest Acceleration levels you have recorded on a fan rotating at around 1498 RPM?
  2. Which bearing do you put as the fixed bearing on a fan shaft?

I appreciate the Accelerometer was only technically good for 50g’s but we had a reading of 116.28g’s Peak to Peak. Can you beat that?

Background:

We were requested to inspect a fan due to repeat failures of the fan bearings.

This fan process cold air, it is direct driven at 1498RPM and has two 22222 straight bore double row spherical roller bearings.

The fan NDE (Non-drive end / fan end) bearing was set as the fixed located bearing. The DE bearing at the coupling was set as the float bearing.

This fan had been in operation for 17 days.

Data was collected with a 100mV/g Accelerometer with a flat rare earth magnet.

Analysis:

The vibration data indicated that the motor to fan shaft alignment was good and there were no issues with the Velocity imbalance levels.

There was however extremely high Acceleration levels indicating excessive damage to the outer raceway together with an indication of poor lubricant condition.

Vibration Acceleration Data:

Figure 1 is the Acceleration Time Waveform from the Fan NDE (Fan end bearing). This shows the very high impacting levels with a -52.59g’s peak to +63.69g’s peak.

Fig 1: Acceleration Time Waveform

Figure 2 is the Autocorrelation of the Acceleration Time Waveform. This shows that all this activity is being generated mostly from the bearing outer raceway.


Fig 2: Autocorrelation of PeakVue Data

Figure 3 is the Acceleration Spectrum. This again shows that all this activity is being generated from the bearing outer raceway.

Fig 3: Acceleration Spectrum

Vibration PeakVue Data:

Figure 4 is the PeakVue Acceleration Time waveform. This shows very high general impacting up to 34.9g’s Peak.

Fig 4: PeakVue Time Waveform

Figure 5 is the Autocorrelation of the PeakVue Time Waveform. This shows that all this activity is being generated from the bearing outer raceway.


Fig 5: Autocorrelation of the PeakVue Time Waveform

Figure 6 is the PeakVue Spectrum. This shows that all this activity is being generated from the bearing outer raceway.

Fig 6: PeakVue Spectrum

Vibration Velocity Data:

Figure 7 is the Velocity Spectrum. This confirms that this is a late stage defect and that this energy is from the bearing outer raceway.

Fig 7: Velocity Spectrum

Inspection:

On visual inspection it was found as expected the grease looked oxidised in a poor state and there was a high area of damage to the bearing outer raceway – noticeably on one side of the rollers. Damage to this side of the raceway would have been caused by axial thrust from the fan shaft and motor.

Image 8: This is on removal of the bearing caps. This shows the oxidised poor condition lubricant.

Image 8

Images 9 to 12: These are further images of the grease condition.

Image 9: Grease extracted from the bearing housing
Image 10: Microscope image
Image 11 : Microscope image
Image 12 : Microscope image

Image 13: This shows the two tracks for the rolling elements on the outer raceway, and that it was highly loaded to one side.

Image 13

Images 14 and 15: These are close-ups of the defected area.

Image 14: Microscope image
Image 15 : Microscope image

Summary and Questions:

Researching the lubricant used we know this is not suitable for this application and that it will displace/separate and then oxidise.

But the question is what caused the high thrusting to the one side of the raceway, is it related to what is the fixed and free bearing? Is it true to say that due to the NDE (fan end) being the fixed bearing that expansion from the motor/ fan shaft would load up one side of the raceway?

A profitable plant is reliable, safe and a cost-effectively maintained plant

Background:

During an asset assessment survey of a Pump Set we detected an anomaly in the vibration data.

This is a ‘Brook Crompton Parkinson’ motor D112 Frame, 2865 RPM, 50Hz 3 Phase, 415V 4.9A with and integral ‘APE-Lee Howl Limited’ pump end.

Image 1 is of the pump set, this is a circulation pump for a water system.

Image 1:

Pump Set

Analysis:

Using experience, the human sense and the vibration data the conclusion was that there is a flow related issue.

 

Vibration Data:

Figure 1 is the Autocorrelation of the pump end PeakVue data in a circular plot.

Fig 1:

Figure 1.

This data shows the abnormal ‘wobble’ operation of the pump and that for each revolution there are three restrictions in the motion.

 

Inspection:

On visual inspection of the pump system it was found that the pump supply valve was closed. This was opened and water was then allowed thought the pump.

 

Follow up Vibration:

Figure 2 is the same PeakVue data as before but now with the pump system in its correct operational state.

Figure 2.

This data now shows the smooth circular motion of the pump.

 

Summary:

This case study brings a few things to mind

  1. The most important part of any program is the person performing the data collection and analysis
  2. When all else fails, leave the air conditioning, and go examine the operating equipment. Go look, touch, feel, smell and listen to the machinery

 

A profitable plant is reliable, safe and a cost-effectively maintained plant

I have been privileged and blessed to have experienced varied fields of Vibration Analysis, Condition Monitoring and Reliability, and had the opportunity to study under some of the great mentors and trainers in these discipline. I feel it is always good to share knowledge and learnings to help others who want to progress and to promote our discipline.

Often people discuss what makes a good vibration analyst? – electrical or mechanical background – degree or apprenticeship level, certification or experience……….. Then when we find an issue we always get asked “How long will it last?”, and our answer to this question, I feel, greatly depends on our experience and training.

In the discussions I have had with many other people, we have all spoken ‘Pearls of Wisdom’. The 14 statements below I feel are very important in the way we operate in our discipline.

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 and mentoring 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 unbalance.

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 analysed enough.

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.

Please share and if you have anymore ‘Pearls of Wisdom’ let everyone know.

Slow speed bearing defect detected though vibration analysis
(Case Study of a ≈ 20RPM Bearing Defect)

What is Condition Monitoring?

In general, Condition Monitoring techniques use instrumentation to take regular or continuous measurements of condition parameters, in order to determine the physical state of an item or system without disturbing its normal operation.

Condition Monitoring is basically applicable to components whose condition deteriorates with time. The objective of the Condition Monitoring technique is therefore to provide information with respect to the actual condition of the system and any change in that condition.

This information is required to schedule conditional maintenance tasks, on an as needed basis instead of relying on predetermined times. The selection of the Condition Monitoring technique(s) usually depend on the behaviour of the failures, type of equipment used and finally on economic and safety consequences.  

This case study shows that when you collect the correct data parameters, vibration analysis can be invaluable in early detected of slow rotating bearings to enable a controlled change out prior to disruption to production.

Benefits of Reliability

The main benefits of applying an effective condition based maintenance programme are that repairs can be scheduled during non-peak times, machine productivity and service life are enhanced, and repair costs due to a loss of production time are eliminated. Safety is improved – Maintenance costs managed – Reliability reduces Maintenance costs

Case History Background

We were asked if we could offer a solution to detect when a rolling element bearing was failing prior to catastrophic failure. The clients concerns was not the cost of the bearing but the cost of the disruption to the production schedule if the bearing failed during a production run. The client was unsure what would detect the bearing issues as the bearing only rotates at around 20 RPM and it is in a harsh environment.

Application:

This is a slurry pot in a dusty foundry environment, the slurry pot is approximately 1.5meters in diameter and 2 meters in height. The bearing installed is an INA U250433 four point contact bearing. The outer raceway is stationary and the slurry pot is connected to the inner raceway that rotates.

The image above is the four-point contact ball bearing, these are radial single row angular contact ball bearings with raceways that are designed to support axial loads in both directions.

Trial:

We set up various sampling rates, various number of sample and utilised different filters. Data was collected using a magnetically mounted 100mV/g accelerometer. Velocity, Acceleration and PeakVue data was stored for analysis in the frequency and time domain.

Trial Summary:

The vibration data that clearly indicated a defect was the PeakVue Time Waveform.

Trial data – Defective bearing PeakVue TWF
Trial data – Good bearing PeakVue TWF

The PeakVue time waveforms above are from the initial trial, and this compares the suspect failed bearing and a bearing that is expected to be good.

Trial data – Plot of an inner raceway defect

The above PeakVue spectrum is from the suspect bearing on the trial data. This data shows a mound of activity at 24.50 orders, and this activity is sidebanded by 1 orders. The theoretical overrolloing defect frequency for the rotating inner race way is 24.47. This indicates that we have an inner raceway defect.

We selected the slurry pot with the damaged bearing and requested the bearing to be change out and removed for inspection.

Comparisons of the original and new bearing

The above PeakVue time waveform comparisons show the before (in red) and the after with the new bearing fitted (in blue). This data confirms the new bearing has been fitted correctly and has no early defects. This also confirms that the bearing indeed had a defect.

Bearing Inspection:

On inspection the bearing cage elements had fatigued and failed, there is also a lot of spalling to the inner and outer raceway most probably due to subsurface and surface initiated fatigue.

ISO 15243: 5.4.2 Subsurface initiated fatigue

This shows that this bearing had reached its end of life, the cyclic stress changes occurring beneath the contact surfaces had initiated subsurface micro cracks this would have been in part of the bearing at the maximum shear stress. We are at the point where the crack has propagated to the surface and spalling has started to occur.

ISO 15243: 5.1.3 Surface Initiated Fatigue

Surface initiated fatigue basically comes from damage to the rolling contact surface asperities. This is generally caused by inadequate lubrication.

Damage to Retainers

Causes of damage to retainers can be due to Poor lubrication, Excessive heat (plastic retainer in particular) and Excessive moment load.

Bearing Images:

Image 1: Bearing as received collected from site prior to Sectioning
Image 2: Bearing as received collected from site prior to Sectioning

Once the bearing was split the outer races were moved to allow the rolling elements and cage pockets to be inspected as a whole. On inspection there are many areas of bearing cage failure.

Image 3: Bearing cage pocket failure
Image 4: Bearing cage pocket failure
Image 5: Cracked cage pocket
Image 6: Cage pockets in various stages of failure
Image 7: Inner raceway

Inner raceway, on the load side, has various stages of spalling all the way around with one area of heavy spalling.

Image 8: Inner raceway ‘Cracking and spalling’
Image 9: Inner raceway Spalling
Image 10: Inner raceway overrolling
Image 11: Outer raceway

The outer raceway has less of spalling but again there is one area of higher spalling.

Image 12: Outer raceway Spalling
Image 13: Outer raceway Splaing
Image 14: Outer raceway Cracking and spalling
Image 15: Rolling element damage

The rolling elements display damage from over-roll of the spalled inner and outer raceways

Summary:

The inspection confirmed that by utilising the correct data collection parameters a slow speed bearing defect can be detected in this working environment. We were successful in determining a failed bearing prior to catastrophic failure

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant

What’s the highest Acceleration levels on Gears you have recorded?

Apologies for the lack of posts over the month, it’s been a very busy time with the family.

This post is a short one just inquiring what levels of Acceleration impacting you have seen in the field from a gear set. This is one I came across a couple of months ago.

 

Summary:

  • Vibration data was collected with FMax of 10 KHz and Sample rate of 32,768.
  • The shaft rotates at 2990 RPM.
  • The gears are small and both have 65 teeth, their function is to transfer drive to an oil pump in a gearbox.
  • We recorded a Peak to Peak of 51.67 G’s compared to another identical asset running at 9.176 G’s.
  • Two weeks later the gears had a functional failure and stopped doing what they’re were designed to do.

 

 

Vibration Data:

This is the 1.3 Second Acceleration Time waveform comparing the suspect unit and an identical unit.

 

 

Images of Gears after Functional Failure:

Images of the gears on inspection.

 

 

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant

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.

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.

Ultrasound trending and Vibration Analysis working together.

This is a good example of how condition monitoring technologies work well as integrated technologies.

Through routine in house overall ultrasonic dB trending a change in condition was noted from one of the motor bearings and this was an increasing trend. I was called to verify the asset condition through vibration analysis.

 

Executive Summary:

  • Removal of the motor on condition of the bearing enabled a control change-out and a more cost efficient repair rather than running to failure.
  • The cause of the elevated Ultrasonic levels and the vibration defect frequencies was false Brinelling to the drive end bearing.
  • In addition there appears to be grease compatibility problems result from either mixing incompatible greases, or from ingress of other contaminate, Dry powers absorb the oil causing the grease to thicken.

 

Failure Mode:

From inspection the primary failure mode as per ISO 15243:2004 is 5.3.3.3 False Brinelling, there is also a secondary failure mode as per ISO 15243:2004 of 5.2.2 Abrasive Wear due to inadequate lubrication.

False Brinelling occurs in the contact area due to micromovements and/or resilience of the elastic contact under cyclic vibrations. Depending on the intensity of the vibrations, lubrication conditions and load, a combination of corrosion and wear can occur, forming shallow depressions in the raceway. In the case of a stationary bearing, the depressions appear at rolling element pitch.

In many cases, it is possible to discern rust at the bottom of the depressions. This is caused by oxidation of the detached particles, which have a large area in relation to their volume, as a result of their exposure to air.

Key Points are:

  • rolling element / raceway contact areas
  • micromovements / elastic deformation
  • vibrations
  • corrosion/wear shiny or reddish depressions
  • when stationary: at rolling element pitch
  • when rotating: parallel “flutes”

Abrasive wear. Most of the time, real abrasive wear occurs due to inadequate lubrication or the ingress of solid contaminants. Abrasive wear is generally characterised by dull surfaces. Abrasive wear is a degenerative process that eventually destroys the microgeometry of a bearing because wear particles further reduce the lubricant’s effectiveness. Abrasive particles can quickly wear down the raceways of rings and rolling elements, as well as cage pockets. Under poor lubrication conditions, the cage may be the first component to wear.

 

Bearing Inspection: Motor Drive End Bearing – FAG X-life NU324-E-TVP2-C3

Image 1 is of the poor grease condition from the bearing.

Image 1:

 

Image 2 is an image of the false Brinelling indetention on the inner raceway.

Image 2:

 

Image 3 is a microscopic image of a false Brinelling depression on the inner raceway. Rust at the bottom of the depressions. This is caused by oxidation of the detached particles

Image 3:

 

Image 4 is a microscopic image of the inner raceway showing the over roll of particles.

Image 4:

 

Image 5 is an image of the outer raceway in the load zone showing the false Brinelling. This is only present in the load zone.

Image 5:

 

Image 6 is a microscopic image of a false Brinelling depression on the outer raceway.

Image 6:

 

Image 7 is a microscopic image of a rolling element. Here you can see the flat spot from the false Brinelling. In addition the ring that is around the inner and outer raceway is due to over roll of particles and poor lubrication condition. Flat spot from the false Brinelling Ring of over roll of particles

Image 7:


 

Vibration Data: 

The comparison below show Fan 1 (in blue) and Fan 2 (in green). This highlights the very high destructive levels of the drive end bearing and that it was close to failure.

 

The PeakVue spectrum plot below confirmed that it was a bearing defect and highest at the outer raceway.

Hi All, this is the last post for 2017 – Enjoy

Background:
We were called to inspect a gearbox as the client had reported an abnormal sound. This was a very large old extruder high torque gearbox with a single input and dual output shafts.

Executive Summary:
Through onsite vibration analysis we were able to pinpoint the shaft that was generating the abnormal noises, this enabled the bearings for the shaft to be pre-ordered so they arrived at the repair shop the same time as the gearbox. This ensured a quick turnaround was completed with minimal production loss.

On Site Initial Assessment:
The gearbox vibrational levels as measured under full load conditions were >20mm/s RMS. This is considered “Vibration Causing Damage” as per ISO 10816-3. The Acceleration Peak to Peak impactions at Gearmesh #1 was excessive at 162G’s. There was also indications of misalignment on the 1st intermediate shaft and considerable looseness present. The 1st intermediate shaft ‘binds’ for 1/4 to 1/3 of a revolution when turned by hand.

Vibration Data:
The Input shaft high frequency Acceleration spectra clearly shows a high 2x gearmesh frequency for the gearmesh 1. This indicates there is misalignment within the gearing setup. The sidebanding at 19.20Hz indicates that it is relative to the 1st intermediate shaft.

The plot above is the Acceleration Spectrum from the Gearbox NDE Horizontal.

The Peak to Peak measurements on the Acceleration Time Waveform below indicates the Acceleration forces are within the 1st Intermediate shafting. The total reading of 162G’s is highly destructive and is impacting at 19.2Hz, the 1st intermediate shaft speed.

The Velocity spectrum taken from the NDE of the 1st intermediate shaft shows a considerable amount of run speed harmonics attributed to the shaft speed. This is an indication of looseness.

Cause of Failure:

On inspection the tab washer on the first intermediate shaft outer bearing had failed. In addition the suspected gear on the 1st intermediate shaft was extremely loose. It was found that this shaft had been previously repaired with metal spray and this had failed. On closer inspection the stress raiser appears to be around the keyway, as there was no strengthening welds around the keyway to support the metal spray.

Strip Down Images:

This is an image of the gearbox internal layout.

Images of the failed tab washer found in the bearing cap from the 1st Intermediate shaft.

Image of the key that supported the 1st intermediate gear that was loose.

Metals spray coating that was under the 1st Intermediate shaft gear. This failed initially at the metal spray coating at the keyway.

 

 

%d bloggers like this: