2pl Motor in V1 2

[Feg]

Hi Guys

Can you give me your opinion on the following: 90Kw 2pl 400V 3ph IP55 280 frame in V1 position. This motor will have a roller bearing NU314 on the drive end and a thrust bearing 7314 on the NDE. This motor is on a fan application with a belt drive being started twice a day by VSD. The pulley is 10" dia driving 13". The motor was supplied to me with std ball& ball bearing set up. I have changed to the roller & thrust set up because of the loads being applied by the belts and the thrust to due to the rotor weight. My question is would you be happy with this set up. I don't have any more application info other than this. Thanks in advance Feg

 

[aolalde]

The array you have selected is the best option for the application described if do not exceed 3000 rpm. Certainly 3000 rpm motors are not the best option for pulley and belts, coupling to the load and if you add the vertical position the application is a big challenge. Your set up must work if manufactured with precision, the maximum allowed speed for yor roller bearing is 3600 rpm grease lubricated; your 10" dia pulley works at 7854 FT/min when the shaft spins at 3000 rpm.

 

[electricpete]

I am a little uneasy with that setup not because I have any firm basis but only because I have never seen it before.

Some questions might be:
- Is the weight of the rotor sufficient to prevent the upper thrust bearing from skidding?
- The belt applies radial load to bottom bearing. Ideally the lower bearing acts like a pivot and shaft acts like a lever with force times distance to upper bearing equal to force times distance to lower bearing. In this ideal situation there is force on lower bearing but no moment taken by the lower bearing. But if the upper thrust bearing allows some motion of the rotor in response to belt force, then we end up with the bottom bearing taking some moment (or alternatively induces some misalignment of lower bearing which being a cylindrical roller bearing is not tolerant). I don't know if the motion at the top bearing is enough to be a concern but certainly a thrust bearing has lower radial stiffness than a ball bearing and thus more concern.

Two questions out of curiosity.
- What was the original ball bearing and what is weight of the rotor?
- With a vfd why is there need for a belt. Is the machinery physically not able to be positioned for direct coupling?

There is also a bearing forum on this site.

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[electricpete]

"Ideally the lower bearing acts like a pivot and shaft acts like a lever with force times distance to upper bearing equal to force times distance to lower bearing"

should have read as follows:

"Ideally the lower bearing acts like a pivot and shaft acts like a lever with force times distance to upper bearing equal to force times distance to sheave"

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[aolalde]

The main risk for this array is found when axial thrust is lost or reduced to a point in which the upper bearing (angular contact) loses radial alignment. The magnetic radial pull of the stator could make the rotor rubb against the stator or the shaft seals.