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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.

 

 

G,day all, here is another interesting job I got called to

 

Background:

This pump and motor had a history of reliability failures from bearings, shaft shearing and pipework flanges leaking. This was a pair of pumps on separate base frames but secured to the same concrete floor with a pipework common outlet.

I performed vibration analysis with phase analysis and diagnosed a foundation and structural problems as the root cause.

 

Vibration Data:

Pump Vibration Data:

Figure 1 shows the overall Velocity vibration trend from our first visit and second visit. This is gathered at the motor DE.

From this trend you can see a marked increase in the velocity vibration levels from 6.304 mm/s RMS and 8.388 mm/s RMS.

Fig 1:

 

Fig 2 compares the acceleration time waveforms from the motor drive end bearings

From this comparison you can see the lower levels of pump A (Blue Plot) and the very high impacting from pump B (Green Plot)

Fig 2:

 

Fig 3 is the vibration data from the motor drive end bearing

There is high impacting form the motor bearing and damage to the inner and outer raceway

Fig 3:

 

Pump B – Motor Bearing Inspection

Failure Mode:

From inspection the failure mode as per ISO 15243:2004 is 5.3.3.3 False Brinelling.

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”

 

Findings:

  1. Depressions appearing at rolling element pitch indicating damage while the pump was in standby stationary bearing (Image 1)
  2. Indications of oxidation of the detached particles, which have a large area in relation to their volume, as a result of their exposure to air.

 

Bearing Inspection: Motor Drive End Bearing – FAG X-lite NU319E.TVP2

Image 1 is the outer raceway, and displays depressions appearing at rolling element pitch which indicates damage to the bearing when the motor was stationary

Image 1:

 

Image 2 is a close up of the depression at rolling element pitch on the outer raceway, this is from the load side of the bearings and also shows the roll over.

Image 2:

 

Image 3 is a microscopic image of a depression on the outer raceway.

Image 3:

 

Image 4 is an image from the inner raceway, this also displays the depressions at the pitch of the rolling elements.

Image 4:

 

Image 5 is a microscopic image of a rolling element.

Image 5:

 

 

Motion Amplification

Even with this vibration data the client was not convinced so I had to use another technology to show the client how the structural and base was causing them their reliability headache.

 

This first video shows how the pipe work was moving, this was the cause of the stress and strain to the flange joints that led to the leaks

 

This second video is of the base plate, this showed the true motion of the pump and how these failures were being induced.

This was a first for me in 17 years! It was one of those with the right experienced people at the right place at the right time beauties!

We were called to a site when the operators reported an unusual sound from a 4 Pole 1500RPM fan motor. We attended and through vibration analysis and temperature measurements recommended stopping the motor and checking the connections in the motor terminal connection box. This enabled the site electrical team to quickly pin point the defect.

The vibration data indicated a dominant 100Hz electrical noise, the motor felt like it was hunting or pulsing and in addition the whole motor was hot with the motor DE housing was over 100oC.

It would be interesting if anyone else has ever found a defect like this?

Vibration Data:

The overall velocity Increased from a normal level of 1mm/s RMS to 3.9mm/s RMS and then in two days increased to 8.88mm/s RMS.

The velocity spectrum below displayed a new peak at 100Hz:

This is a single frequency 100Hz Trend, and shows a marked increase at 100Hz:

The PeakVue spectrum displayed dominant 100Hz and harmonics.

The acceleration 10 KHz spectrum displayed two mounds of activity with 100Hz sidebands:

We then decided to look at the auto correlation data and found the following.

10 KHz Acceleration time waveform circle plot with four main peaks and inner lower peaks:

 

PeakVue Acceleration Time waveform circle plot showing 4 clear peaks:

And this is what was found. (Note cable broke when it was lifted for photo.)

We were surprised the motor was still running (very badly with high vibration) in this condition !!!!!

Hi all,

Here is an interesting one. History is a worm wheel conveyor drive (Radicon Type). This operates in a rough environment and it ran for 8 months after maintenance and started to make a lot of audible noise.

It has a MJT 2 ¾ and a LJT 3 ½ on the input shaft. Coupling was the rubber pin type.

On inspection, there looks to be poor worm/wheel contact with some hair line surface cracks in the wheel gear. The gearbox input worm shaft NDE bearing has very bad damage.

We are thinking three possibilities for the root cause: Impact during mounting resulting in spalling at ball pitch and/or Spalls (Hertzian Fatigue) due to excessive thrust loading due to assembly or alignment errors. Also the possibility of transportation/storage damage. 

Anyone got any input?

Vibration Trends:

 

Acceleration trend showing increase after maintenance and the sharp increase.

 

 

PeakVue Trend showing a similar increase as the Acceleration trend.

 

 

Velocity Spectrum with high BPFI matches.

 

On Inspection Gear:

Incorrect gear meshing indications.

Visual surface hair line cracks.

 

Visual Inspection Outer Raceway:

Top left of image looks to be a hole in the raceway, there were two at 180 degrees opposite.

 

Microscope image of the outer raceway defect.

 

Visual Inspection of the Inner Raceway:

Images from around the inner raceway.

 

Microscope image of the inner raceway defects.

 

Visual Inspection of the Rolling Elements:

Two of the rolling elements, they all have various level of similar damage.

Microscope images of the rolling elements defects.

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