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Selection of Rolling Element Bearings - Part 5

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

This article is a continuation of the series for the selection of rolling element bearings. The Bearing Life or Median life of the bearing is discussed in detail here in this article.

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    Bearing Life:

    Before we look into the dynamic and static load capacity of the bearing, one must be very much aware of the bearing life. Just like every mechanical element, the bearings are selected based on the criterion of expected life from the bearing. Why is bearing life so important?

    Let us see the technical aspect of the bearing life, Bearing Life indicates the total number of revolutions or the number of hours at a given constant speed, the bearing is required to work for before signs of failure set in.

    A Bearing under load is subjected to contact hertzian stress in the roller balls, inner race and outer race. A bearing which is provided with dirt free lubrication, operated at reasonable temperatures and taken proper care of, can only fail by means of fatigue. The bearing life here hence refers to the fatigue life of the bearing.

    Many manufacturers of bearings have carried various tests to see how the bearings fail. Based on the results obtained they we able to arrive at a common terminology to denote the life of the bearing known as L life of the bearing. This is typically explained in the graph below. L life of the bearing denotes that when a group of bearings are operated at typically similar conditions, 90% of the bearings will exceed or complete the cycles before the fatigue failure of the bearings set in. The typical L life of the bearing is One Million revolutions. Click here to see the graph of bearing life expectancy. Under tests carried out by bearing manufacturers it has been found out that the start of fatigue failure initiates with spalling and pitting of the load carrying surfaces.

    The bearing life or the fatigue rating life of the bearing hence has a vital role for the selection of the bearing. A bearing which is selected should hence be able to complete the L life criterion. This is governed by the Dynamic Load Capacity of the bearing. Well let us see how this Dynamic Load rating is specified in the bearing catalogue. Click here to see.

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.
  1. Selection of Rolling Element Bearings – Part 1
  2. Selection of Rolling Element Bearing - Part 2
  3. Selection of Rolling Element Bearings - Part 3
  4. Lubrication of Rolling Element Bearings
  5. Selection of Rolling Element Bearings - Part 4
  6. Selection of Rolling Element Bearings - Part 5
  7. Selection of Rolling Element Bearings – Part 6