Bearing failures and greasing arrangment

Have you double checked nominal speed and load configurations, possibility of contamination, working temperature, and the presence of unexpected loads like shaft bending, vibration, etc? I'd first try to determine exactly what the failure mode is instead of just deciding to change the bearing type blindly.

We are replacing bearings with the same ones as orignally fitted on these ABB motors.

Why some motors have external lubrication arrangment?

There could be many reasons for bearing failure,shaft misalignment? are these motors direct coupled or belted,are they driven by an electronic drive or ATL?,Drives can induce voltages in the rotor shaft,and they seek ground out through bearings,Belted loads if belt tension is to great can cause failure.

All above replies tried to address your problem quite good. Alternatively you can sough help of bearing manufacturer what type of bearing is recommended for that particular application. Cross check bearing replacement method; will liquid nitrogen more helpful than induction heating???

Motors are direct coupled and driving direct on line.

We are using same bearings as orignally fitted on these motors?

Can someone help us about differnt modes of bearing failure.

direct coupled to what?

drive or non drive end failure?

verticle?

operating amperage vs. nameplate amperage?

You may be cooking the grease or even softening the bearing in induction heating.

There is also a wide range of bearing quality - but carry the same numbers.

What is the make?

What exactly is the failure? Describe a failed bearing

ball or inner or outer race or cracking or flaking or one side of race, colouration, etc?

We are using skf induction heater and heating bearing only upto 100 deg C.

Bearing are of FAG.

Both ZZ broken and colourization. Bearings jammed badly.We have to cut bearings for removal.

In one case sudden bearing failure occured and rotor hit stator and breaker tripped.

Bearing housing are ok and fitting methods have been repeatedly checked, no mistake observed.

Have you checked;

rotor balance, shaft straightness?

bearing seats are true to shaft and each other and shaft centers?

Also;

coupling condition and alignment?

Good morning Guest: There is a general training tutorial on detecting bearing faults available from Sales@bearinglifeguard.com. It gives you some info on terminolgy and early detection and means for monitoring dynamic loads which may shorten your bearing life. It will detect early stages of lub breakdown and surface degradation and help you to avoid catastrophic failures. It won't answer the specific question on the lubrication but the bearing manufacturer should be your best source of assistance on that.

It will be better if you approach motor mfr for your application. ABB motors are good make also FAG bearings. It may be higher ambient temp which is melting the grease in the bearings. Normally motors are suitable for 40 deg C. For higher temp bearing grease should be suitable for such application i.e Graphite Grease.

Did you try c3 bearings? just an idea:is possible you change the original bearing for another that's not c3?;2) Are you using old very old bearings with old grease or even used recondicioned bearings ? is not so common in these days the zz bearings they were replaced by 2rs bearings.-

Not possible to give an opinion on why the bearings fail, but to answer your question, which to my understanding is:

Is there any advantage to changing from sealed bearings to non-sealed bearings and providing greasing facilities?

Yes and No. It depends on many things. Usually we would only use "greased for life" bearings with relatively small motors, say less than 30 kW or so (I avoid them like the plague except for really small ones - washing machines etc). Remember that if the greasing interval calculated for you bearings is say 6 months this will pretty much apply whether they are sealed bearings or not, so your decision is based, amongst many other things, on how often you want to grease them or strip them and replace them.

Note that for a sealed bearing, the life of the bearing is limited to the life of the grease. In a bearing that is re-greased at correct intervals the total bearing life is extended beyond the life of the first grease charge to the actual fatigue life of the bearing.

If the failures that you are experiencing are occurring after the re-greasing interval for your specific bearings in your specific motor, then you have two choices, replace the bearings more frequently or provide greasing facilities and grease according to a schedule with the right amount of grease.

If your bearings are failing within the greasing interval then changing the sealing arrangement will not improve matters and you will have to look elsewhere for you problem.

A motor with properly greased bearings should have a life of around 10 years. It would be most unlikely to get more than a fraction of this life out of a sealed bearing.

Motors are 45 kw rating installed in diesel engine based power plant. Motors installed in vertical position.

There are total 16 motors.

What is basic vibration tolerance for this rating motors i.e vertial , horizantal directions? Does grid rapid voltage or power surges have some bad effect on motor bearings due to rapid fluctuation of electromagnetic torque?

It may well be these bearings are not up to the axial load of vertical mounting plus any force via the coupling.

Check with the motor manufacturer and with the bearing makers for say angular contact style.

Vertical around 2 mm/s

Horizontal around 2-4 mm/s

What type of couplings are you using? Which bearing is failing and what type of bearing is it. In othere words are you failing the axial locating bearing or the "sliding" purely radial bearing and at which end of the motor are each of these located?

What are the dominant vibrations frequencies?

We are using rubber coupling. Motors upper side Non driving end bearing in most cases is causing problem.

You have not answered guest 18's questions with regard to bearing type and which one is fixed, so I will guess that the non-drive end bearing is the fixed bearing and that it is a deep groove ball bearing. With a 45 kW rotor hanging off it and it being a sealed bearing you would probably have to grease it every 4000 to 8000 hours (got to guess because you do not give information about the bearings). You can calculate this for yourself, just go to the SKF site (or FAG or many others) and do the greasing frequency calculations for yourself.

If you are not re-greasing at this sort of interval, and with zz bearings that means changing the bearings, you will get quite short life out of these motors. Your answer is probably as indicated by kyzine, look at angular contact bearing, C3 clearance and probably in X arrangement. You must then provide greasing facilities.

Contrary to popular belief, the most common cause of bearing failure is Over Greasing of the bearing.When pumping grease into a bearing, the motor should be running, and the grease drain plug removed for 5 minutes after greasing.This allows the grease to get out of the ball contact path.Too much trapped grease will churn, overheat, carbonize, and cause premature bearing failure.

Check your greasing proceedure.

Ah, but in the case of the OP we are looking at sealed bearings. No over-greasing problem here!

Well strictly speaking zz are shields and non contact, but I'm thinking this may be a pre-load conflict if the tail bearing is not free to move a bit.

Usually thrust is taken on front bearing.

The outer of the tail bearing should be a sufficient press fit to stop rotation, but still allow expansion and/or variables in front bearing wear or mounting.

Sometimes when tail bearings fail, they rotate in the casing, wearing, making the replacement bearing 'too loose', the temptation is to use locktite 'super bearing mount' which is far too strong - producing 'fighting bearings' - and the front one tends to win.

I'd be checking just exactly the fitters are doing things.

But; given it is a tail bearing and the motor is tail up, if I understand correctly, then using a z, or NR, shield or seal down, and maintaining a grease 'blob' under the cap, may go a fair way to solving total seizure side of this.

(z = 1 shield. zz = shields both sides (2z) NR = one side. 2NR = 2 sides)

(but you can just pop out one shield/seal of a zz or 2NR)

check this file

http://rapidshare.com/files/342900087/bearing_failure.pdf

contacting with bearing manufacturer will be very usefull