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Hi Guys, 

Long time lurker, first time poster. Can you please give me a hand? 

I'm having trouble identifying if this is false brinelling or electical fluting. 

Right now, I'm leaning towards false Brinelling. Why? 

- The flutes do no go all the way around in the outer race; they fade in and out 

- The rolling elements are not pitted or marked, other than having a 'frosted' appearance. Same with the inner race 

- If it was electrical arc fluting I would expect a darker color flutes. These are very light in color. 

- The flutes are not narrow, they go almost the hole length of the rolling element. The pictures I've seen shows the electrical arc flute to be narrow compared to the width of the rolling element. 

Any links to materials or discussions on this topic would be greatly appreciated!

 

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Original Post

From Rexnord

”False Brinelling

Blog Content Image
 
False brinelling is caused by vibrations acting on the bearing while in a non-rotating state and may occur on new equipment which has been carelessly transported. The signs of this type of brinelling, as seen in the image to the right, are depressions and wear marks in the bearing raceway along the axial direction. These depressions cause more noise and eventual fatigue.’
 
Note in particular the use of β€œnon-rotating”.  Under such conditions the spacing of the distress areas approximates the spacing of the rollers.  Yours are not that way, hence I’m leaning toward β€œtrue brinelling.”  Having said that, while this unknown machine is shutdown, is the shaft truly stopped or is there some slight slow rotation?  Is a VFD invoved?
Last edited by John from PA

Thanks for the reply and I disagree about your definition. True brinelling is caused by exceeding the elastic limit of the material. False brinelling is anything looking like that, but isn't through excessive load. I did a quick search and copied some links for you.

https://www.linearmotiontips.c...-look-at-brinelling/

http://www.midpointbearing.com...ds-Take-Issue-18.pdf

I'm sure this is not true brinelling; the radial loads are not huge.

This is a gearbox for a pump. There is no flow to turn the pump when this unit is down. There is very little vibration in the surrounding structure.

 Edit:

John, I should have mentioned the specs of the machine. Sorry!

Bearing: High speed input @~1100rpm driven by VFD (sleeve bearings)

The bearing is from a gearbox that drives a pump.

 

 

Last edited by Oilsands87
Oilsands87 posted:

 

Bearing: High speed input @~1100rpm driven by VFD (sleeve bearings)

 

Ah, VFD, a key piece of information.  Hence why I said "Having said that, while this unknown machine is shutdown, is the shaft truly stopped or is there some slight slow rotation?  Is a VFD invoved?"

Go on over to https://www.skf.com/binaries/3...res---14219_2-EN.pdf and download a copy of the SKF guide to Bearing Damage and Failure Analysis.  In particular take note of the following:

page 30

page 56 figure 32

page 57 figure 34.

There may be additional information, this is what I quickly found searching on washboarding, an effect seen in VFD motors.

 

 

John from PA posted:
Oilsands87 posted:

Bearing: High speed input @~1100rpm driven by VFD (sleeve bearings)

Ah, VFD, a key piece of information.  Hence why I said "Having said that, while this unknown machine is shutdown, is the shaft truly stopped or is there some slight slow rotation?  Is a VFD invoved?"

Go on over to https://www.skf.com/binaries/3...res---14219_2-EN.pdf and download a copy of the SKF guide to Bearing Damage and Failure Analysis.  In particular take note of the following:

page 30

page 56 figure 32

page 57 figure 34.

There may be additional information in the SKF guide, this is what I quickly found searching the PDF on washboarding, an effect seen in VFD motors.

Another resource is the Timken Bearing Damage Analysis with Lubrication Reference Guide.  See page 21.

Now, another question, is the washboarding I see in your image just over part of the periphery?

 

 

Hi John,

I was actually looking at this very PDF (SKF and Timken), it's very good.

The damage on my bearing is not all the way around, and it fades in and out on some areas.

All the of the pictures of electrical arc fluting that I have found seem indicate that the damage is consistent, and all the away around the race. I was trying to find something in writing that confirms this.

 

I vote for "Electrical Fluting" known as Electrical Discharge Machining (EDM). The pattern is right, as I have seen on real machines. The fact that the machine has a VFD adds to the diagnosis. The fact that the entire race/ring circumference does not have a uniform pattern can be due to many issues including lubricant film, load on bearing, and electrical discharge path through bearing housing and structure. The real world is not always like the Diagnostic Charts and images and case history photos!

Walt

@Walt Strong posted:

I vote for "Electrical Fluting" known as Electrical Discharge Machining (EDM). The pattern is right, as I have seen on real machines. The fact that the machine has a VFD adds to the diagnosis. The fact that the entire race/ring circumference does not have a uniform pattern can be due to many issues including lubricant film, load on bearing, and electrical discharge path through bearing housing and structure. The real world is not always like the Diagnostic Charts and images and case history photos!

Walt

Thanks Walt, and company. 

The gearbox company rep contacted Timken, and Timken guys believe this is electric arc fluting as well. 

On my side, I've contacted Aegis to provide a shaft voltage analyzer, and a shaft ground solution. The guy I was talking to said this problem happens with 50% of VFD motors. I have confirmed this same damage on another gearbox, and I'm expecting to find the same damage on another I'm pulling out. 

https://www.est-aegis.com/index.php

 

"The flutes do not go all the way around in the outer race; they fade in and out"

My thoughts on this, "do not go all the way around", is, after looking closely at the pictures of the rollers and the outer race, it appears that the rollers were "arcing" on their large end ,based on the "dark or black" marks of that end of the rollers.

And it looks as though, on the outer race, the clearance was not properly set (too much clearance) and allowing the rollers to cease to make contact with the outer race when leaving the load zone, hence causing the "marks" to disappear.

The outer race also seems to show that the "marks'" are extremely far from the large end of the outer race while the smaller end of the rollers and "marks" are very close to the smaller end's edge, which in my opinion, could also basically show an indication that the clearance was too great and allowing the rollers to loose contact with the outer race.

Only my opinion and I could be totally wrong.

Thanks and Have a Great Day,

Ralph

Curious.....if i read your post correctly, you have an electric motor with sleeve bearings of unknown HP VFD driven, turning 1100 rpm attached to a gearbox with rolling element bearings which drives a pump?

Is everything direct coupled mtr/gbx/pump or are there belts? Have seen this type of pattern with an electric motor on a VFD with belt pull, side in constant contact showed the most amount of fluting

https://download.schneider-ele...&p_File_Ext=.PDF

Not normal for VFD to affect the gearbox, this is a good resource for checking if your machine or mtr/gbx/pump are properly grounded, kinda step one in why fluting happens

Attached is an example, before and after history of bearing change on a 200HP motor, VFD driven, less than 50' of cable to motor, took data recently and still no indication of fluting developing. This technology reduces significant short duration spikes in the voltage supply to the motor being caused by VFD. Just another piece of information on your quest for help

http://www.coolblue-mhw.com/co...ores/coolblue-video/

Dave

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Images (1)
  • Screen Shot 2020-05-30 at 7.56.16 AM

Curious.....if i read your post correctly, you have an electric motor with sleeve bearings of unknown HP VFD driven, turning 1100 rpm attached to a gearbox with rolling element bearings which drives a pump?

Is everything direct coupled mtr/gbx/pump or are there belts? Have seen this type of pattern with an electric motor on a VFD with belt pull, side in constant contact showed the most amount of fluting

https://download.schneider-ele...&p_File_Ext=.PDF

Not normal for VFD to affect the gearbox, this is a good resource for checking if your machine or mtr/gbx/pump are properly grounded, kinda step one in why fluting happens

Attached is an example, before and after history of bearing change on a 200HP motor, VFD driven, less than 50' of cable to motor, took data recently and still no indication of fluting developing. This technology reduces significant short duration spikes in the voltage supply to the motor being caused by VFD. Just another piece of information on your quest for help

http://www.coolblue-mhw.com/co...ores/coolblue-video/

Dave

Hi Dave.

5000hp motor (sleeve bearing on one, roller bearing on another, two different instances of the arc fluting on the gearbox) - gb - pump, direct drive. There is a disk pack style coupling between the motor and gearbox.

Very good info, thank you. I like the coolblue link.... might be worth to get a quote!

 

 

"The flutes do not go all the way around in the outer race; they fade in and out"

My thoughts on this, "do not go all the way around", is, after looking closely at the pictures of the rollers and the outer race, it appears that the rollers were "arcing" on their large end ,based on the "dark or black" marks of that end of the rollers.

And it looks as though, on the outer race, the clearance was not properly set (too much clearance) and allowing the rollers to cease to make contact with the outer race when leaving the load zone, hence causing the "marks" to disappear.

The outer race also seems to show that the "marks'" are extremely far from the large end of the outer race while the smaller end of the rollers and "marks" are very close to the smaller end's edge, which in my opinion, could also basically show an indication that the clearance was too great and allowing the rollers to loose contact with the outer race.

Only my opinion and I could be totally wrong.

Thanks and Have a Great Day,

Ralph

Ralph, that is a very good observation. I've had another guy on site also suggest this to me. I will have to review the bearing tolerances and fitment for these gearboxes.

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