odd marks on journals / bearings

[TonyCro]

Hello Guys,

I've been sent through some photographs that show odd longitudinal marking on the journals and bearings :-( I suspect that they're caused by the journal roundness, but would appreciate any views (apologies for the quality of the photographs)

Thanks
Tony.






Clickable photographs back to 800x600 image

 

[byrdj]

Does the rotor have some type of low speed drive. I'm thinking like turning gear. And thus marks would be chatter from low speed rotation before a film is established or oil to hot to establish a film.

 

[TonyCro]

hi byrdj,

Thanks for replying. I wondered the same thing, although it uses a gas turbine as prime mover, there is no barring equipment attached to generator :-(

Tony

 

[sms]

What part of the machine train are these from? The gas turbine, gearbox, or generator?

It is hard to tell, I assume that the top photo the bearing surface? What does the thrust look like?

My first thought was that it might be electrical discharge... but that would be fairly rare (although not impossible) on a gas turbine generator train. Have you had any electrical problems with the generator? If this is a generator bearing, are the bearing(s) properly insulated?

Might also be acid etching. Take a lube oil sample and get the TAN and water content checked.

How deep are the marks? can you feel them with your finger nail? Have a look with a magnifying glass. Do they look like pits with melted bottoms?

"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970

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[Tmoose]

I've seen many new shafts with ground journals with similar patters visible after pressing bearings on and off. We attributed it to being finished with a grinding wheel with runout or out of balance.

Field service vibration analysis for several New England grinding houses often was in search of similar visual patterns. Often grinding wheel trim balancing improved the situation.

 

[electricpete]

Just a clarification in terminology. I think the marks you are referring to are the circumferential marks, not the longitudinal remarks, correct?

http://en.wikipedia.org/wiki/Longitudinal

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[electricpete]

Well maybe it is not just a clarification in terminology. It may help to clarify which marks.

I see longitudinal (axial) marks on the bearing.

I see circumferential marks on both the bearing and the journal.

I suspect the original poster is talking about the circumferential marks since he said both bearing and journal.

I am under the impression that the comments about machining of the bearing are referring to the axial marks.

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[electricpete]

also so the axial marks resemble what I might associate with bearing currents (although I'm not too sure about it)

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[electricpete]

ok, now I see very faint axial marks on the journal also. If it were on both the journal and the bearing, it might point more toward bearing current than to machining.

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[byrdj]

Have you counted the number of marks around the journal and bearing.

I guess it looks like 80 per rev on the journal, but more like it would be a 160 on the journal

 

[dimjim]

I wonder if these are fretting corrosion marks caused by
high vibration while the bearing is simply not turning or at rest.

 

[Skogsgurra]

More on terminology.

Do journal bearings also have rolls in them? I always thought that no. But these marks look like they were typical, although weak, EDM marks in a roller bearing.


Gunnar Englund

http://www.gke.org

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[sms]

No, journal bearings do not have rolls.

Just an oil filled clearance..

"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[Skogsgurra]

Thanks sms. Then it is a mystery to me.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[rmw]

I take it that this is a generator bearing or is it a power turbine bearing?

If generator, does the generator have jacking oil?

Are the bearings insulated? Is either of them (hopefully not both) grounded? Or, should I ask are they both grounded or neither insulated?

IF it doesn't have jacking oil, is it a unit subject to lots of starts?

rmw

 

[TonyCro]

Hi Guys,

Thanks for the all the replies

The shell and journal are the DE of a 5MW 4pole sych generator coupled to a Gearbox and then a GT - again I apologize for the poor quality photographs and especially having the shell photo upside down :-(

We were called to check the generator bearing insulation and shell condition after 'somebody' looked into the g/box and saw bluing of the teeth which was attributed to low generator bearing IR ?, unfortunately that is all the detail I have on that discussion:-(.

but to answer some of the questions;

Well maybe it is not just a clarification in terminology. It may help to clarify which marks

Hi Pete, Apologies for the confusion, I am discussing the marks that along the length (the long axis of the rotor) of the journal and shell, not the ones that are circumferential.

Might also be acid etching. Take a lube oil sample and get the TAN and water content checked.

How deep are the marks? can you feel them with your finger nail? Have a look with a magnifying glass. Do they look like pits with melted bottoms?

I haven't been to site, but the report back is that these indications cannot be felt; but please me tell more about acid etching in a bearing, this is new to me.

The unit dose not have jacking oil
but is not subject to a high number of starts, industrial generator which provides a base load to the plant.
and the bearing IR is good.

again thanks for the all the comments

Cheers
Tony.

 

[byrdj]

Would the number of journal marks coencide withthe number of driven gear teeth?

posibly the transfe of some teeth contact force on the journal. wouldn't the DE bearing be grounded?

 

[strokersix]

Agree with tmoose. I've also seen similar markings that have been produced by a grinding operation. Grinding wheel dressing, balance, machine or fixture rigidity, have been implicated as causing these type of marks. I can't explain why the marks are on both surfaces. Perhaps an impression from one to the other at startup.

 

[sms]

Acid etching or contact staining is common with machines that start and stop a lot. You get moisture into the bearing, and the water and contamination combine to acid etch the surfaces, Each stop is a differnt place so you get lots of marks over time...

"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[jet1749]

Longitudinal marks on journal look very much like grinding wheel marking, possibly from "blinded" wheel or excessive load applied to wheel. Has the journal been refinished at some point?
regards
John