Bearing life

Calculating Bearing Life: Bearing Loads & Speeds

Bearing life is mostly often measured using an L10 or L10h calculation. The calculation is basically a statistical variation of individual bearing lives. A bearing’s L10 life as defined by ISO and ABMA standards is based on the life that 90% of a large group of identical bearings will attain or exceed. In a nutshell, a calculation on how long 90% of the bearings will last in a given application.

Understanding L10 Roller Bearing Life

L10h = Basic rating life in hours

P = Dynamic equivalent load

C = Basic dynamic load rating

n = Rotational speed

p = 3 for ball bearings or 10/3 for roller bearings

L10 – basic load rating-revolutions

L10s – basic load rating in distance (KM)

 

As you can see from the equation above, in order to determine the L10 life of a specific bearing the application radial and axial loads are needed as well as the application rotational speed (RPM’s). The actual application loading information is combined with the bearing load ratings to identify the combined load or Dynamic equivalent load that is needed to complete the life calculation.

Calculating & Understanding Bearing Life

P = Combined Load (Dynamic Equivalent Load)

X = Radial load factor

Y = Axial load factor

Fr = Radial load

Fa = Axial load

Notice that the L10 Life Calculation does not consider temperature, lubrication and a host of other key factors crucial to achieving the designed application bearing life. Proper treatment, handling, maintenance and installation are all simply assumed. This is why it is extremely difficult to predict bearing fatigue and why less than 10% of bearings ever meet or exceed their calculated fatigue life.

What Determines a Bearing’s Service Life?

Now that you have a good understanding of how to calculate the basic fatigue life and expectancy of rolling bearings, let’s focus on other factors that determine life expectancy. Natural wear and tear are the most common cause of bearing breakdown, but bearings can also prematurely fail due to extreme temperatures, cracks, lack of lubrication or damage to the seals or cage. This type of bearing damage is often the result of selecting the wrong bearings, inaccuracies in the design of the surrounding components, incorrect installation or lack of maintenance & proper lubrication.