Can a Misaligned Shaft Affect Bearing Performance?

[asteorit]

Hello,

I want to ask if the shaft is mounted on bearings, it is possible that the shaft can misalignment? Since the bearings have "free angle of misalignment".
As such it then misalignment determine or calculate?


For every answer thank you in advance.

 

[Astronuc]

There should be a tolerance on straightness of the shaft and perpendicularity of the bearing and bearing housing.

It is possible to misalign a shaft (or set of shafts), either laterally (horizontally or vertically), or angularly. Usually that has to do with the orientation of the housing, so it is important to set a turbomachinery housing or coupling properly.

 

[asteorit]

and when we consider that the bearings are stored perfect, perpendicularity of shaft is also perfect. And we will consider only the will, which is in the bearing.

 

[SteamKing]

Bearings can be misaligned due to thermal effects and deflections due to other loadings on the bearing supports.

 

[asteorit]

Yes, I understand, are all external conditions for the deployment of the shaft bearings.
But I would like to know how to deflect the shaft mounted between two bearings, bearing me the simple radial play, axial play, free angle of misalignment. .
For example as shown in fig.

 

[Q_Goest]

Hi asteorit. I assume English is not your native language. Your questions are very difficult to understand.

I think what you are asking is how you could mount a shaft on bearings but still allow for the shaft to be displaced at some angle. Do you need to shift the axis of the shaft by some angle as you show in your first picture here?

If so, what angle do you need to shift the axis by? Right now the picture you posted just says: X^oX'
Is this angle the one you need to shift the axis of the shaft by?
If so,

• can you give an aproximate angle?
• does the shaft need to be supported with 2 sets of bearings as you show in the picture? Or can you use just 1 bearing such as a spherical roller bearing which would allow some small angular movement as you show.

Ref: Spherical Roller Bearing

 

[asteorit]

I apologize for my bad English. It's not my native language.
I do not want to deflect the shaft axis. I want the shaft axis is perpendicular to the base.
I want to know whether it can deflect the shaft axis? Inasmuch as the bearings have the clearances.

I mean as follows: The shaft with bearings assembled as shown. And some small force (eg only handle) I will push the shaft axis. And I will measure the misalignment the shaft axis micrometer. Of course we consider that all components except deposits are perfectly rigid. A precision machined surfaces is also perfect.

It is a proposal for an electric motor. A must withstand indicated loads.
Think that such a choice is correct bearings?
Insure lower ball bearing also on the stator? (Axial)

XU080264 : http://medias.schaeffler.de/medias/en!hp.ec.br.pr/XU*XU080264

 

[Q_Goest]

Hi asteorit. I'm still having a bit of trouble understanding you, so I'll try and explain what I believe you are asking. If I'm confused, please feel free to correct me.

I believe you are asking how much deflection the bearings might contribute or add to the deflection of a shaft when a force is exerted perpendicular to the shaft axis as shown in your last drawing. That force you show is 10000 N. The bearing's contribution to the deflection of the shaft will be minimal. I would suggest you neglect the contribution of the bearings to the shaft deflection. If the remainder of your hardware (motor, shaft, etc...) is sufficiently rigid to prevent excessive shaft deflection, the bearings will work fine.

I believe you are also asking if the bearing selected is suitable for the loads given. You show a 10000 N load that is 600 mm from the rear bearing and the bearing in question (crossed roller bearing) 150 mm from the rear bearing. You should be able to sum the moments around the rear bearing and conclude that the crossed roller bearing will have roughly 40000 N of radial load. You also show an axial load of 1960 N. The bearing you provide a link to has a dynamic load rating in the radial direction of 54000 N, so the short answer is no, the bearing is not suitable for this application. It will fail rapidly. In fact, it shows the "maximum permissible radial load against friction lock" is only 21000 N, but even that high a load will cause the bearing to fail rapidly.

Take a look at the SKF bearing life calculations here:
http://www.skf.com/group/products/bearings-units-housings/roller-bearings/principles/selection-of-bearing-size/selecting-bearing-size-using-the-life-equations/basic-rating-life/index.html

That tells you how many times a bearing can rotate before a certain percentage of them will wear out. As a rule of thumb, and this is a sweeping generality, I would suggest looking for a dynamic load rating on your bearing roughly 10 times higher than the load it has to support. Depending on how fast it rotates, how long you need it to last and how sure you are of the actual loads in service, you may not need a bearing with a dynamic load rating 10 times higher than the load being supported, but you should be doing a calculation based on bearing life and actual conditions.

Bearings can be tricky to properly select. You need to take into consideration the interference fit on the shaft and in the bore, how to lubricate it, how fast it rotates, etc... There's a lot to consider. I'd suggest talking to a bearing manufacturer or supplier if you're not familiar with them. If you'd like some suggestions I might be able to show you a way to properly support this using a sketch tomorrow. Let me know if I've understood you correctly though.

 

[asteorit]

I thought of something else. Probably do not speak English so well, to explain what I want. But thank you anyway for your reply.
My professor changed his mind and wants to use a different solution. He decided to use only one large bearing. What do you say?

 

[Q_Goest]

Well, I don't know how you can support a motor shaft with just one bearing. Generally a motor is not a simple disk, it has some axial length to it. So if it has any axial length and if you have a force which is not in line with the bearing, you will produce a moment around the bearing which the bearing is not designed to resist. Or maybe I'm just misunderstanding what your professor is trying to suggest. Good luck!

 

[asteorit]

I can not even imagine how I will it work with one bearing.
I'm thinking of still the shaft deflection.