bearing running hours 1

[redlinej]

Hi guys,
i would like your opinion on this problem,we use radiator to cool the water on our 17 MW diesel generator and i am trying to find out is there a specific running hours for the motor bearing to be changed,the product manual say to grease at 15,000 to 30,000 hours and the generator is only 36,000 hour so do u guys think the bearing need to change basic on running hours or conditions thank you .

 

[Artisi]

what bearings are you talking about?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[redlinej]

the NDE and DE ball bearing for the 3 phase electric motor

 

[Artisi]

and what 3 phase electric motor is that? are you talking about the drive motor for the water pump of the cooling system?
Sorry but the crystal ball is a bit hazy at the moment.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[redlinej]

the cooling fan motor ,sorry thought you guy know that the cooling pump is engine driven in a diesel power plant

 

[Artisi]

...... "thought you guy know that the cooling pump is engine driven in a diesel power plant", so are many cooling fans engine driven. Assume nothing, no misunderstanding then.

Anyway back to the question, if it were me, I would ask the electric motor manufacturer what L10 bearing life was used in the design, having this info you can then make an informed decision about bearing replacement periods.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Walterke]

sorry thought you guy know that the cooling pump is engine driven in a diesel power plant

I guess you also think we know what size motor you're using, what the nominal drive speed is, what kind of bearings you installed and what kind of lubrication you use?

As said before, ask your manufacturer to find out for what lifetime they were designed, and change them accordingly.

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[redlinej]

Sorry for the late reply here is the spec for the motor KW 8.6,V-380,A-21,rpm-870,P-3,AMB-40c,rise-80c,DE bearing-6309c3,NDE bearing-6307c3,the motor is vfd operated depending on engine load/temperature.grease is unirex n3.

 

[Walterke]

http://webtools3.skf.com/BearingCalc/

NX 7.5.5.4 with Teamcenter 8 on win7 64
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[Tmoose]

L10 is a prediction of the life 90% of bearings will exceed. It's kind of a shame to throw away all that unused life.

For more than a decade SKF and FAG have been saying that ball bearing life can be infinite at some low-ish load level, if lubrication quality and cleanliness can be maintained.

Exchanging bearings on a schedule can bring real danger of poor overall reliability when infant mortalilty strikes less than perfectly executed repairs.

Methods exist to evaluate a ball bearing's condition and get the most life out of a bearing, and avoid failure. Vibration analysis is a favored and effective method.

 

[Artisi]

Tmoose, in complete agreement, but L10 is usually far in excess of the failure rate from poor maintenance, over lubrication, water ingress etc - this has been my observations within the pump game.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[tbuelna]

Artisi- Your point about bearing L10 values is excellent. When calculating rolling element bearing L10 life, there is an "unadjusted" value and an "adjusted" value. The unadjusted L10 only takes into account loads and cycles. The adjusted L10 also takes into account factors such as material quality and lubrication conditions. And these material and lubrication adjustment factors can have a huge impact on predicted L10 bearing life.

In reality, the speeds and loads this fan bearing are subject to in normal service are probably quite modest. In theory, if this bearing were kept free from moisture and debris, and were properly lubricated, it would have a virtually unlimited life. Moisture intrusion is probably the most problematic issue with grease lubricated rolling element bearings. Heating/cooling cycles of the engine can cause any humidity trapped within the sealed bearing space to condense into droplets, and the droplets then causes corrosion pitting on the race surfaces. These corrosion pits on the race surfaces quickly lead to spalling failures.

The easiest, cheapest, and most effective way to ensure long life for this particular bearing would be to lubricate it every 500 hours rather than every 15,000-30,000 hours. When lubricating the bearing, it is essential that sufficient fresh grease is added to ensure that all of the existing grease within the bearing is displaced, along with any trapped moisture or debris.