Categories: Shaft Alignment,Machinery Maintenance,Other Topics

Reduce Force to Maximize L10 Bearing Life

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By on August 17, 2016

Simply put, L10 bearing life is the number of service hours that 90% of bearings will survive or conversely 10% of bearings will have failed. L10 life: is the preferred term in specifying bearing life and is defined by The American Bearing Manufacturers Association (ABMA).

A bearing life equation is:

L10a

This calculation assumes proper installation and lubrication, no shock or vibration, perfect alignment, debris free environment and temperatures that are not extreme. Obviously, all of these factors are important to maintenance personnel, however one of the critical factors of this calculation we can control with precision shaft alignment is FORCE.

If we simplify this calculation to:

L10b

it is apparent that the amount of force created by misalignment is very detrimental to bearing life.

For twice the misalignment;

L10c

For three times the misalignment;

L10d

“Perfect Alignment” is not practical as rotating machinery does not operate in a “perfect” world. IF it did maintenance personnel possibly wouldn’t be needed. Fortunately flexible couplings allow for machines to operate in less than “perfect” environments.

That being said, rotating machinery does need to be aligned to close shaft alignment tolerances, not coupling tolerances. See a previous blog on this subject. Misalignment creates forces at the coupling which are exerted on the shafts. This results in reduced bearing and seal life.

The force effects of misalignment can be simplified by considering the misalignment as a simple lever. Misalignment at the coupling creates a moment of force acting on an effort arm. This will create a first class or second class lever with either the inboard or outboard bearing acting as a fulcrum. The length of the motor shaft between its bearings is the resistance arm. The objective of shaft alignment is to minimize coupling forces by making two rotational axes form a single line while the machine operates.

Misalignment Forces

As the above simplified calculation illustrates, when the force is increased the reduction in bearing life is exponential.  Doubling the force reduces the L10 bearing life to 1/8. Tripling the force reduces the L10 life to 1/27.

So minimize “The Force” with precision shaft alignment for maximum L10 life so the bearings, seals, & etc. with “Live Long and Prosper”!

Save The Machine!

About the Author

Brad Case has been associated with VibrAlign since 1990, first as a manufacturer’s representative, than joining the company as a direct employee in 2005. He has over 35 years experience in aligning industrial machinery. Brad attended Texas Tech University, in Lubbock, TX.

Brad began his career in the automotive industry providing technical training, sales, and service for Murray Goldseal an aftermarket air conditioning component manufacturer. His background includes 25 plus years experience in sales, service and training, of Centralized Lubrication Systems, Couplings, Gearing, and Gear Reducers.

Brad and his wife currently live in Clifton, TX.

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