WE are using combination of Ball bearing & a Roller bearing ad DE side & single Roller bearing at NDE side of HT motor ( 200 kw to say 4000Kw) upto 4 pole speed.

Many of the cases NDE beraing gives noise problem. On opening , scoring marks are observed on inner race ans as well on rollers.
What can be the cause of such problem & how to avoid. Bearings are grease luricated.

The first question has to be, are these bearings "manufacturer" fitted or are you fitting them in house? If so, how do you fit bearings? What is your workshop practise? Do you use hot oil bath/bearing heater method?

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scoring marks are observed on inner race ans as well on rollers.

Sounds like there might be some overheating involved here when they are "heated" for expansion to allow them to be installed on the shaft, especially if the outer race is showing no signs of problems and the heating is done through a magnetic type heater or some other type heater that heats through the inner race or even with a torch (hope not).

But then again, what is the definition of "scoring"? Can you show us a picture? "Driving" the bearings on the shaft by stiking against the inner race, this is not what is happening is it?

Like the ole saying "a picture is worth a thousand words".

We are heating ineer race of roller bearing on induction heating machine for about 3-4 minutes , till it attains temp. of approx. 120 deg. cent., then fitting on shaft, outer race alongwith rollers is fitted after cooling of inner race on shaft.

Normally problem starts with noise from NDE , sometimes followed by high vibrations, sometimes brg. seizes on shaf with in no time. .

I have always favoured an oil bath heating method. That way you get an even temperature rise throughout the whole bearing. With an induction heater you tend to heat the inner race first. When this expands it can remove the internal clearances and force the balls against the outer race, possibly causing microscopic dents in the race/balls. It doesn't take much to damage these high precission pieces of equipment!

I have a question for cheddar caveman.What's reason that is favoured oil bath heating method?

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We are heating ineer race of roller bearing on induction heating machine for about 3-4 minutes , till it attains temp. of approx. 120 deg. cent., then fitting on shaft, outer race alongwith rollers is fitted after cooling of inner race on shaft.

Am I reading this correctly? Seems like you are refferring to a NUXXXX bearing when you say
"We are heating ineer race of roller bearing on induction heating machine for about 3-4 minutes , till it attains temp. of approx. 120 deg. cent., then fitting on shaft, outer race alongwith rollers is fitted after cooling of inner race on shaft."

Does the NDE have an NU type bearing? Is this the type bearing that is failing? Do the rollers slip easily onto the inner ring after cooling down? Has the shaft been measured to see if it the correct size for the bearing used?

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Normally problem starts with noise from NDE , sometimes followed by high vibrations, sometimes brg. seizes on shaf with in no time. .

What does "seizes on shaft" mean? Is the bearing actually loose on the shaft or does the bearing lock up internally? Does this always happen on the NDE?

Hello Dinesh Kumar :

Your roller bearing scoring marks are most likely caused by your bearing installation practise. Please read the following instructions recommended for installation of NU type cylindrical roller bearings:

Prevention of Scuff-Marks when assembling Cylindrical Roller Bearings.
Before assembly the inner race is located on its journal on the shaft. The outer race, containing the roller elements, is inserted in the bearing housing which is part of the end shield ( in case of a motor or generator ). The end shield is suspended from a crane. When slipping the outer race over the inner race the end shield must be positioned perfectly perpendicular to the shaft which is in general difficult to achieve. If it is not perfectly perpendicular the leading edges of the rolling elements can ( and often will ) produce scuff marks and scratches in the exposed surface of the inner race. To avoid this kind of damage , which will remain undetected until the machine is put into operation, we machined a sleeve from a solid block of white nylon. Using a lathe, a hole is drilled to match the shaft diameter for a snug fit. The outer dimension of the sleeve is machined to match the outer diameter of the bearing’s inner race ( perhaps a few thousands of an inch larger ). The finished sleeve is pushed over the shaft extension until it touches the inner race. Now, when assembling the two halves of the bearing, the rolling elements are gently guided by the sleeve into a perfectly perpendicular position, and when the leading edges of the rollers touch the inner race they cannot cause any scuffs or scratches.

Hullo ungereng,
Thank you for sharing a nice practical idea!

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Originally posted by Dinesh Kumar:
WE are using combination of Ball bearing & a Roller bearing ad DE side & single Roller bearing at NDE side of HT motor ( 200 kw to say 4000Kw) upto 4 pole speed.

Many of the cases NDE beraing gives noise problem. On opening , scoring marks are observed on inner race ans as well on rollers.
What can be the cause of such problem & how to avoid. Bearings are grease luricated.

Scoring marks on bearings are indicative of contamination of lubriacants. I have personally experienced so many examples in motors as well as pumps.Use packed use and throw type grease guns now supplied by SKF. Also, take care that V rings or felt are intact top prevent ingress of contaminants in grease .

What you decribed could be caused by roller skidding. Especially the roller type bearings require minimum load which can be calculated from SKF catalog. If this load is not achieved the rollers will be skidding making marks and overheating. It could be the issue of too "beefy" bearing for the application.

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WE are using combination of Ball bearing & a Roller bearing...

First, is that the OEM bearing configuration, as an early poster queried?

Is the ball bearing a thrust bearing?
Is the roller bearing cylindrical roller, not tapered?

I presume "yes" to both questions.

Can you clarify these most-basic questions first?

Bearings, from the smallest to the largest, are all brothers in what they will do and in how they will die.

I have a simple, small (1/6th HP) vent fan motor working in the attic roof above where I'm typing this note. It's a GE made motor, USA manf, date of install, by myself, 1983.

This is 2007. The motor has been in operation for fully 24 years now, without pause except during times of power failure. I oil it once every five years. This is no rare sort of record for bearing life--some ancient machinery has run for decades longer without wear or failure.

If bearings are properly selected, installed, kept clean, they last well.

Oh--this small fan motor's bearings have lasted this well because they are sleeve bearings, not even ball bearings, and so there is no wear-out to them, because of the hydrodynamic principle.

I enjoy learning about bearing technology and hope that I can learn more about big ball and roller bearing behaviours in heavy industrial service.

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Bearings are grease lubricated

It might be fair to note that IF clean and stable oil lubrication can be obtained, oil is the best lubricant for any bearing. Grease is a practical expedient; a second-best choice. Grease is metallic soap and oil. But it is oil that best maintains/allows for, the hydrodynamic film which, at speed, prevents micro seizures, galling, etc. Just a general fact from ancient textbooks on the topic; I don't suppose any of this has altered by time or engineering advance: good grease is good stuff, but if oil can be maintained in the bearing, clean oil, oil is the best bearing lubricant.