bearing tolerance

[autoguru]

Must the rollers in a bearing be grounded to fine tolerance?

What will happen if a "rough" roller gets used in order to save cost?

Will the wear out quickly?

 

[Pressed]

As your name suggests,this is an automotive application? Most auto bearings are ground to some tolerance which is designated by a bearing class. I don't think a rough bearing would make it into a an auto application. Check the bearing manufactures website, they are packed with data.

The lowest class of bearings are for low speed applications like a lazy susan. They also get used in agriculture for the low speed and dirty environment, where a precision bearing would not be a benefit. These are abused and cheap to replace.

As far as wear, the higher the class of bearing the closer the size of the rollers/balls, the better distribution of load, the less wear. Going in the opposite direction, you get more wear.

A more detailed post will probably get a more detailed responce.

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[autoguru]

So how long can a bearing usually last?

I know there is something called a L10 life where 10% of the bearing fails. That's usually 100 million revolutions. Right?

And the "average" life of a bearing is usually 5 times the L10, which is 500 million revolutions.

So if I know the rpm, I can calculate the hours the bearing can last.

Is that right? I really don't know what I'm talking about.

By the way, can a bearing be made to last "forever"? Steel have something called a "endurance limit" so if the load is under the endurance limit, it should last forever. Or is it not practical?

Thanks

 

[Pressed]

Some bearing companies have an engineering book/catalog that you can use to determine the life of a bearing based on all the specific details of the application. I suggest you do that.

If a bearing had little load and floated on oil, I guess it could last a while, but is this practicle? Bearings get hot, that is from friction, they are going to wear.

_______________________________________
Feeling frisky.........

http://www.tailofthedragon.com

 

[ischgl99]

How long can a bearing last? From a few minutes to a few decades, it all depends on your operating conditions.

The rollers are precision ground to a tight tolerance, depending on the class of the bearing. Cheap bearings have looser tolerances then the higher quality aerospace and precision bearings and a price tag to match. The better the surface finish the higher load rating the bearing can have and this corresponds to a longer life expectancy at similar loads.

The life of a bearing is dependant on many factors. The L10 life is a theoretical life for the fatigue failure. Most failures occur for other reasons such as contamination, improper installation, vibration, etc. To calculate the L10 life you need to know the nominal rating of the bearing and the load it will see, from that you can calculate the L10 life. You will also need to use correction factors for the environment it is in, heat, oil/grease quality, etc. These can be very subjective and lead to wrong estimates if you do not properly factor the environmental conditions.

A bearing can be sized for infinite life, but this depends on properly calculating your loads and operation conditions. But in reality, every bearing will fail at some point, it is just a matter of what fails first, the bearing or the machine is scrapped.