Selecting the Right Bearing
A lot goes into selecting a bearing. First you must think of application, and then after that you need to think about bearing life.
Bearing applications vary widely. From small Yo-Yos to large indsutrial electrical motors, bearings have many uses. Selecting a bearing for a given application depends first on the requirements of the bearing's application such as speed, misalignment capabilities, and bearing valve. These requirements and more will determine which bearing style – single row deep groove bearings, double row angular contact ball bearings, etc. – will be selected.
Once the style is nailed down, the top considerations in selecting the right bearing is the predicted life of a bearing under a certain load, and whether or not that bearing fits the given space in an application.
The most common way to determine bearing life is by using the load ratings of the bearing and the loads required by the application. The common measurement is “L10” life, defined as the number of revolutions before metal fatigue first appears on 10% of a large group of similar bearings. This is referred to as basic rating life, or fatigue life. The equations for calculating L10 life are:
- For ball bearings: L10 = (C/P)3
- For roller bearings: L10 = (C/P)3
Where P is the bearing equivalent load and C is the basic load rating.
If the bearings run at a constant speed it’s possible to determine L10 life in terms of hours. This equation is expressed as:
- For ball bearings: L10h = 1,000,000 / 60n (C/P)3
- Where L10 is rating fatigue life in hours and “n” is RPM.
Other considerations come into play when determining bearing lifespan. Running temperature and its effect on basic load rating must be considered, as well as adjustments to fatigue life rating. After bearing life has been predicted, the final consideration is cost of the bearing.