MRO Magazine


How to meet your bearings’ life expectancies

Question: “We recently received a shipment of L10-rated bearings. Can you explain the meaning of the L10 designation?”

Rotating-element bearing manufacturers measure reliability using a “load–life” calculation rating known as the L10 rating life. To achieve this rating, the manufacturer assumes the bearing will be run in a clean operating environment that provides an adequate lubricant film (adequate described as a film equal to, or greater than, the composite roughness of the two mating surfaces) of the correct viscosity for the designed maximum bearing speed and operating temperature ratings.

The L10 rating is given to bearings manufactured with cleaner, degassed steels (usually manufactured in an electric arc style furnace) and represents a percentage probability that under ideal conditions 90 percent or more of all L10-rated bearings will achieve the published life expectancy.

As maintainers, we have great influence over whether a bearing will achieve its design life expectancy. The following points illustrate the basic dos and don’ts for ensuring a long and healthy bearing life:

• Store bearings in a clean, dry, temperature-controlled place in their original wrapping until required for use: This will eliminate contamination and ensure it is “factory fresh” when put into service

• Don’t handle bearings with bare hands when unwrapping and preparing for use: Always use clean gloves as debris from dirty hands will contaminate the bearing surfaces, and transferred sweat can cause the bearing to oxidize (rust).

• Check for factory lubrication: According to specification, some bearings come pre-lubricated while others do not. Ensure it is lubricated to approximately 40 percent of its open area, but do not over lubricate!

• Use recommended tools and techniques when installing bearings: Forcing one in place by hitting it with a blunt instrument is a recipe for premature failure.

• Establish a lubrication regimen according to load, speed, duty and environment: Lubricating it with the right lubricant, with the right amount, in the right place, at the right time, with the right contamination-avoidance practices will ensure it outlives its host. Establish a lubrication regimen according.

Contact Ken Bannister at (519) 469-9173 or by email at