## Selection of Rolling Element Bearings – Part 6

written by: kkaarthic • edited by: Lamar Stonecypher • updated: 11/13/2008

This is the sixth part in the series for the selection of rolling element bearings. This article deals with the Dynamic Load Capacity of the bearing and its influence on the life of the bearing.

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Dynamic Load Capacity of a bearing

Till now we have discussed broadly on the various aspects of bearing selection. The dynamic load capacity of a bearing any bearing can be selected from the bearing catalogue where all details pertaining to the particular bearing are given. The dynamic load capacity of the bearing is unique and has been determined based on various empirical formulas which the manufacturer has developed based on the years of experience and research carried out. See Selection of Rolling Elements – Part 5 to locate the dynamic load capacity of a bearing in the bearing catalogue.

The dynamic load capacity is a value which has a unit of ‘N’ or ‘kN’ (Newtons or Kilo Newtons). The Dynamic Load capacity can be defined as the load that will give a life of one million revolutions of the inner race. The dynamic load rating hence plays a vital role for the bearing life. The relation between the bearing life and the dynamic load capacity is expressed as follows:

L = (C/P) ^3 - for Ball bearing

L = (C/P) ^10/3 – for Roller bearings

Here L = Bearing L Life,

C = Dynamic Load capacity of the bearing, Newtons

Since we normally know the expected life for a bearing and the equivalent radial load on the bearing, it would be easy for us to determine the value of C, the dynamic Load capacity of the bearing. All that we need to do is to select a bearing, whose dynamic load capacity value, C is greater than the value calculated.

The static load capacity of the bearing is denoted by Co. The unit is Newtons (N). This value is given to ensure that the equivalent radial load does not exceed the static load capacity of the bearing. This denotes the amount of load the bearing will be able to withstand in standstill condition without creating any deformation in the bearing i.e. to the inner race, outer race or the rolling elements. By experiments it has been concluded that when a bearing is subjected to this load i.e. the maximum of the Static Load capacity, it tends to produce a deformation of 0.0001 times the diameter d of the rolling element.

These two steps form the basis for the selection of the bearing on all the data we have gathered. We will look into the constructional aspects and capabilities of different types of bearings in the forthcoming articles.

#### Selection of Rolling Element Bearings

This article deals with the important terminologies we need to know about for the selection of a rolling element bearing. These terms like axial and radial loads, Static Load carrying capacity, Dynamic Load carrying capacity, etc are explained in detail.
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