Were the bearings greased before they were installed. The grease may have obstructed the flow from oil mist lubricator. Would also check and clear the lines. Another recommendation if you are run the bearing at high RPM to switch to hybrid bearing. The cermet balls in a hybrid bearing will run much cooler with to no lubrication.

Hello Fahad,

Is it possible to take more pictures of whole bearing pedestal? You wrote that the high temperature left the visible signs on the rotor shaft - no proper lubrication and, what is strict linked, no cooling. There is the other issue you should take into consideration. Have you done the run out measurement of the rotor during the repair activity? I suspect that high temperature could affect the rotor in such way that it is bent just now, so it means the problems during start up and further work. If the rotor works at high speed the run out measurements results should be very small. Certainly, there is no problem to make the rotor straight, a couple of methods exist ...

I will try to have more picture. there is coolant. runout checked and found is it ok. speed id 1800rpm

you also might need to consider a constant flow of oil as opposed to a mist - simialr problem sovled this side in this way. The flow of oil acts as a lubricant as well as a coolant, carrying heat away from the shaft...

thanks a for suggestion,

Hi Fahad,

"Oil mist manifold get full in short period,"

Where is this manifold located? upstream or downstream to the bearings.

If getting full, this is likely blocked lines so no longer any lubrication - as indicated above in the other post.

Are both bearings lubricated independently?

How is axial preload and axial compliance (spring?) to be sure that there is always full contact of balls to raceways?

Better to look at pressure and velocity in oil-mist duct lines.

Best to monitor lubrication film thickness (noncontacting measurement), we had developed this and tested in a variety of high quality ball-bearings, can be made on reqest.

RHABE

Where is this manifold located? upstream or downstream to the bearings.

upstream.

Are both bearings lubricated independently?

there is one oil mist manifold supply both bearing.

How is axial preload and axial compliance (spring?

i don't understand your question

we had developed this and tested in a variety of high quality ball-bearings, can be made on request

please send me more info about it

Lubricant Film Thickness Measurement System:

If good lubrication is existing then the balls (rollers) are separated completely from the raceways by a lubricant film.

This film usually has a thickness of 1 to 3 µm if well established but may be much thinner depending on geometry, speed and viscosity of lubricant. Any thickness above the combined roughness of contacting elements is possible and may be good.

The film thickness is not sufficient to separate the contacts at too low speed, too much dirt in the lubricant or bearing, overload or nontrivial errors as retainer squealing.

I developed a non-contacting (capacitive) coupling of low level electrical signals to the bearings or shaft, the signals are returned to the housing by passing through inner-ring-ball-outer-ring.

The capacitive coupling and the first electronic are requiring very special stability requirements so need adaption to any new measurement task.

There are 2 contacts for each ball. These contacts act as resistive and capacitive elements although the resistivity of the oil may be very high.

The total resistivity will be complex from all the balls/rollers in parallel.

If one of the contacts is not fully separated this can be detected - although at considerable speed this condition may exist only for some micro-seconds.

The system can detect lift-off-speed, rising (with speed or viscosity) lubricant-film-thickness, failures of whatever origin.

There was an earlier system from SKF named Lubcheck that worked not good as there was sliding contact to the shaft that produced a lot of electrical noise that spoiled the signal.

We tested our system in a lot of demanding applications: turbo-molecular-pumps, inertial-guidance-gyros, high quality small servo-motors, momentum-wheels for satellite stabilisation and more.

All these worked beautiful and gave a lot of insights how to avoid loops in bearing-assembly development and how to do best quality insurance.

We published the results in the Draper Lab: International Rolling Element Bearing Symposium, San Diego, 1994.

Anybody who wants to have a copy may get one, please send your email address (by the mail system of CR4, not open in the forum) and indicate the allowable size of an email as this comes as pdf from a scanned article. Delivery of film-thickness measurement system is possible on request and discussion. (Not working with ceramic balls.)

Below one of the measurements from a high speed bearing that failed to generate a good lubricating film at medium speed. (22mm OD ball-bearing)

RHABE

Hallo Fahad,

I agreed with some of the comments regarding to this issue. You should put more photos of failed bearing, because it will discribed more story,will help us to gate more information.

Bearing failure is more difficult to determine compared to other components failure. Because bearing can be failed in many ways and many reasons.

These turbine bearings are getting less quantity of lubricating oil per minute, that is lub flow rate is less, increase it by 25% more from the existing flow rate.Do you any cooler for the lub. oil to cool?

from

GVS

yes there is cooler

Is it possible that the oil is being over heated due to insufficient flow? Given what I have seen of over heated oils, they will "cook" down to a caramel-like consistency, or worse, turn into a sludge that resembles a greasy brownie. Either way, the picture isn't pretty for the items being lubricated.

Should the flow be good, then I would look into alignment based loading issues for the cause of the overheat condition.

Well, you bring something i was not considered it. I was thinking what could be the source of the black caramel! Please look to the picture...

you really need to provide much more details and pictures if you want us to help you diagnose your bearing failure correctly. Bearings are extremely complicated relative to their function. You can have water in your lubricant, solid particle contamination, failure due to vibration, corrosion and pitting, brinelling, false brinelling, fatigue; could even be electrical arcing (doubt it, but possible), I could go on forever. Hell even excessive lubricant can be as much of a problem as inadequate lubrication. And what kind of bearing is it? I don't remember seeing, axial, radial, maybe thrust? More details please.

it is ball bearing single row SKF 6310Z/C3 used on both side DE and NDE

I can see some discoloration on the shaft - just abobve the finger. However picture quality is poor. (only 9KB). What is the discoloration on the balls/ race-way?

Is it possible that the bearing is not properly shrunk into the shaft and this discoloration is due to sliding of the race over the shaft?

Check for the cleanliness of the lube oil line. The typa of contaminant looks like solid particle. Rub on fingers and try to find out. Any oil cracking should be very fine carbon particles where as this one at least looks like as if it has been picked up from some where. Check the Lube oil line cleanliness.

In some cases I have seen the casting (especially cast iro) shedding their particles and contaminating the oil. So can many other things. These particles are very much likely to choke the nozzle and may result in the lube failure.

Do you have either temperature pick-up or at least flow monitor on the lines? these will give you indications of failures.

See whether you can go for circulating oil lubrication instead of the mist lubrication. This will avoid the choking problem, but in a lot of cases you will land up in lube oil leakage through the seals/glands, not designed to handle this quantity- most probably you will have labyrinth seals.

What is the system filtration ?

Guest # 15 may have a point. If the inner race of the bearing is not properly seated on the shaft and is slipping, especially if it's intermittent, this will make for all kinds problems with the bearings. You will need to measure the OD of the shaft with precision and compare it to the ID of the bearing. They should be very close.

yes the shaft has worn out at bearing area, but is it as consequences of bearing failure or it is from the Beginning that I am not sure! for that I have recommended to do hard chroming and shaft interference fit will be 0.001"

The journal diameter ? I remember it was 50mm or so isn't it? The ball bearings are simple journal or thrust/combined ?

The size is too small for my comfort (normally we are on roller / white metal bearings, almost never on ball bearings).

However normal cases the fit of m5 or worst case m6 is the recommended one - so 0.02mm (0.001") interference is OK.

The second question is the housing - just check that it gets a precision sliding fit. I am not sure the recommendation, but is is likely to be on the J6 or K6 range.

Assuming it is not a pure journal, just see that the required thermal expansions are not blocked off.

But these are the normal fitting practices, primarily as I said, check the contamination, feel it, if required get it analysed and act accordingly. If it is oil cracking, change the lubricant with some with EP additives ( hopefully you are not working with normal hydraulic oil).

Also based on the RPM and the load, check the oil viscosity grade recommended. Low viscosity oil will transfer you from EHD to mixed or even boundary lubrication system and that will result in your bearing seizing and eventual failure. (BTW the oil viscosity is based on your actual operating temperature)

GA - first person to address the possibility that "mist" is not flowing - hence lack of lubrication and heat. Manifold full means no mist!

What lubricant are you using. Have you done an oil analysis?

Pure Oil mist

Naphthenic based oils are usually recommended so the use of the word "Pure" really has no meaning as to what is actually being utilized. I'm sure everyone would imagine that you're not recycling left over cooking oil for this application.

One stray thought that I had is that the bearing that you mentioned, a SKF Size 6310 , Z= single shielded-metal, C3 normal tolerance, is being installed with the shield to the outboard side so the mist can get inside the races. It is a deep groove bearing so I'm figuring that it's capable of the thrust being generated but if installed incorrectly could create failure since it would be blocking off the mist internally.

I still question whether it's entering the housing in any meaningful quantity based on your pictures showing the gooey tar like residue.

The term "Pure" in this case refers to the method of lubrication and has nothing whatsoever to do with the purity or otherwise of the oil.

Just trying to inject a little humor as well as some oil mist.

If this is an environmentally friendly (closed system) Fahad may want to check the return line to make sure it isn't blocked. That too would create a back pressure in the housing preventing the mist from entering.

I am asking for the manufacturer of the oil, and the product number, ISO number, and any other information you may have.