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Turbo Machine Contact of Bearing Liner with Shaft

06/28/2020 2:59 AM

These are both radial bearing liner removed from turbo machine after one year of service. Bearing liners are fitted in solid metal carrier.One bearing(NDE ) diameter is 140 mm DE diameter is 160 mm. Please discuss about its touching contact with shaft. Shaft journal is round without any step but bearing lower half shows that there is not complete touching contact with shaft. There in no touching contact on upper half as usual .We find same observation on every inspection of bearing. DDiscussion is that Why there is not complete touching contact on bottom of bearing lower liner half.

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#1

Re: Turbo machine.Contact of bearing liner with shaft.

06/28/2020 3:12 AM

Looks like a lubrication issue to me....

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#2

Re: Turbo machine.Contact of bearing liner with shaft.

06/28/2020 4:10 AM

It would appear from the pictures that the area of contact is pretty much in the centre of the bearing. This would not be the normal running area at full speed. The formation of varnish appears to be slightly offset from the centre line which, depending on direction of rotation of the shaft, would be a more normal load point.

Pictures are not clear enough, but this looks very much like slow roll damage either during startup, coast down or barring.

Knowing what kind of "turbo machine" this is would be useful.

Again, from the picture, I would not be terribly concerned. Question is, why was it inspected after only one year?

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#3

Re: Turbo machine.Contact of bearing liner with shaft.

06/28/2020 7:35 AM

There should be NO touching.The shaft should be supported by a thin film of oil.

Insufficient oil pressure,contaminated oil, shaft imbalance,shaft out of round,improper torque during installation,vibration,dirty metal carrier to which liner mounts causing uneven pressure on liner.The discoloration indicates excessive oil temperature.Could be uneven pressure, or oil getting behind the support and being churned due to excessive clearance between bearing and support.Lack of lubrication is indicated by the shiny surfaces.Starting before oil pressure is sufficient can cause this.Foaming due to overfilling can cause oil film failure.Check all oil passages and flush the entire oil system with clean oil before reassembly.

Cleanliness is critical...think brain surgery.

Please include an image at X10 magnification for better information.

Check shaft for roundness, run out, and check assembled clearances using Plastigauge.

https://www.plastigaugeusa.com/

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#4
In reply to #3

Re: Turbo machine.Contact of bearing liner with shaft.

06/28/2020 10:55 AM

Is there an issue of improper crush height? There is no contact in center in line of cut for lube oil entry. ........................j

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#5
In reply to #3

Re: Turbo machine.Contact of bearing liner with shaft.

06/28/2020 12:16 PM

there are touching marks on both lower half in the center 20 to 25 mm segment has no mark.

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#6
In reply to #5

Re: Turbo machine.Contact of bearing liner with shaft.

06/28/2020 12:23 PM

What is your lubrication type and method? How is it maintained?

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#7
In reply to #6

Re: Turbo machine.Contact of bearing liner with shaft.

06/28/2020 9:00 PM

force feed with rotary pump along with cooling annd filteration system.

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#8

Re: Turbo Machine Contact of Bearing Liner with Shaft

06/28/2020 10:35 PM

Turbine jacking pump? google ->

https://www.google.com.au/search?rlz=1T4GGHP_enAU411AU411&source=hp&ei=ZlL5XreTF7iQ4-EPt7u9oA4&q=turbine+jacking+oil+system&oq=turbine+jacking&gs_lcp=CgZwc3ktYWIQARgAMgIIADICCAAyBggAEBYQHjIGCAAQFhAeMgYIABAWEB4yBggAEBYQHjIGCAAQFhAeMgYIABAWEB4yBggAEBYQHjIGCAAQFhAeOgUIABCxAzoECAAQClCoO1jZcWCllAFoAXAAeACAAZ8BiAG6EZIBBDAuMTWYAQCgAQGqAQdnd3Mtd2l6sAEA&sclient=psy-ab#spf=1593397881354

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#9

Re: Turbo Machine Contact of Bearing Liner with Shaft

06/28/2020 11:02 PM

It looks like the film strength is sufficient to support the journal in the center of the bearing, due to the friction of the exit passage to either side. As you get closer to each edge of the bearing, the film thins due to the lack of flow resistance, at least while the shaft is at rest. The wiping action observed likely only occurs as you roll the shaft from rest, the shaft floats completely while running at speed.

The fact that both bearings show a symmetrical pattern and identical patterns at either end is encouraging, at the very least.

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#10
In reply to #7

Re: Turbo machine.Contact of bearing liner with shaft.

06/28/2020 11:24 PM

There doesn't seem to be enough pressure...or it may be a lack of, or excess, viscosity...Even if the turbine is shut down, the oil pump should start before the turbine and lift the shaft off the bearing maintaining a liquid barrier between the shaft and bearing...The viscosity should be matched to the operating temperature, and tested periodically for breakdown and contamination....

https://www.machinerylubrication.com/Read/1863/lubricant-failure

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#11
In reply to #10

Re: Turbo machine.Contact of bearing liner with shaft.

06/29/2020 4:12 AM

The oil pump for turbo machinery does not usually lift the shaft off the bearings prior to startup. Lift off occurs due to the formation of an oil wedge once the shaft starts to rotate.

Some very heavy rotors that are driven by relatively slow starting drivers have jacking pumps to lift the rotor during startup.

As far as I can see from the pictures there is no damage to the bearing. The shiny bit at the centre is typical and can be caused during slow roll. Can even be caused during something as simple as rotation during alignment.

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#12

Re: Turbo Machine Contact of Bearing Liner with Shaft

06/29/2020 9:02 AM

As indicated above, these are pressure fed bearings and, when you go onto your turning (barring) gear, there is no oil film. So one has rubbing, for part of the first revolution. From then on, there is no more babbet damage.

The darkened patch is varnish, which shows overheating.

The "contact line" should ideally be either uniform "down the middle" or maybe a bit heavier on the inboard edge, since the rotors get a bit straighter, in operation. Generally, there is a "ball fit" or other adjustment somewhere in the bearing support to address any "twist and / or tilt" misalignment.

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#13
In reply to #5

Re: Turbo machine.Contact of bearing liner with shaft.

06/29/2020 9:08 AM

Look at the journal and bearing diameters, in this area, every inch, or less, and every 45 degrees, as a minimum. My guess is that the shaft is not round and the bearing is not elliptical. Few bearings will round, of course.

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#14
In reply to #11

Re: Turbo machine.Contact of bearing liner with shaft.

06/29/2020 2:31 PM

I find it hard to believe that anybody would design a heavy rotating mass with metal to metal contact in the bearings...This to me is clearly a lubrication failure ...or a design failure...or ill fitting parts...besides how often is this turbine stopped?

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#15
In reply to #14

Re: Turbo machine.Contact of bearing liner with shaft.

06/29/2020 11:20 PM

All high load capacity bearings essentially have metal to metal contact at rest, ball, rollers, sleeve.

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#16
In reply to #15

Re: Turbo machine.Contact of bearing liner with shaft.

06/30/2020 5:07 PM

Well if it's kept at rest then you don't need any lubrication, because there won't be any wear...If on the other hand you plan to rotate that mass, metal to metal contact is going destroy the bearing/shaft assembly....

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#17
In reply to #14

Re: Turbo machine.Contact of bearing liner with shaft.

07/01/2020 3:16 AM

Had there been lubrication failure one would see major signs of heat and a molten mass of bearing metal.

You would be hard pressed to find any rotating equipment that does not have contact between shaft and bearing at standstill. That is one of the reasons why the bearing materials are chose as they are.

In hydrodynamic bearings the oil wedge that forms between the journal and the bearing preventing the shaft from contacting the bearing requires the shaft to rotate in order for it to form. (Jacking oil is used in some cases as I said above).

Note that the bearing is "flooded" with oil so lifts off pretty quickly once it starts to rotate.

This is not the best video, but it may help.

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#18

Re: Turbo Machine Contact of Bearing Liner with Shaft

07/01/2020 10:18 AM

Shiny spots indicate a lack of lubrication.Uneven contact indicates improper tightening of the journals or out-of-round shafts or warped journals.

The dark spots indicate excessive heat,which could be oil churning under the insert.

The assembled clearances need to be checked.

A rule of thumb is .001" to .003", (.0381-.0762mm) but check manufacturer's specs.

The most accurate method I know of is Plastiguage.

It will show the assembled clearance of the bearing and the shaft.

It is very inexpensive and very accurate,as you can see the clearance across the whole contact area of the bearing.

It is used by professional race engine builders and has a long track record for accuracy.

I have used it myself many times and was very satisfied with the results.

I do not have any financial interest in the company.

Here is a link:https://www.plastigaugeusa.com/how.html

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#19
In reply to #17

Re: Turbo machine.Contact of bearing liner with shaft.

07/01/2020 11:00 AM

Note that in the video the sacrificial layer on the race is provided in case of lubrication failure, and if properly lubricated should last forever... There could certainly be a problem with the shaft causing this problem, but that should have already been checked at this point...and lubrication failure is much more common...

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#20
In reply to #11

Re: Turbo machine.Contact of bearing liner with shaft.

08/06/2020 12:06 PM

what will happen if crush height is not proper?.and how mush crush height is required for bearing of 140 and160 mm shaft diameter while thickness of bearing liner is 5.3 mm.

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#21
In reply to #18

Re: Turbo Machine Contact of Bearing Liner with Shaft

08/06/2020 12:11 PM

plastic gauge is better for clearance check but measrement of bearing ia much required. check with plastic gauge is good to verify the fitting of bearing .

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