What is the L10 life of the bearing and how to determine it?

Ever wonder how long a bearing will last before it needs replacing? Dive into the world of bearing durability with an exploration of L10 life—learn what it is, how it’s determined, and why it matters in ensuring smooth machinery operation.

What is L10 Life?

The L10 life of a bearing refers to the calculated fatigue life expectancy of a group of identical bearings operating under identical conditions. It’s the number of revolutions or hours that 90% of a group of identical bearings are expected to complete before the first evidence of fatigue occurs.

L10 Life Chart

The Equation for L10 Life

Terms and Definitions

• L10 Life: The calculated fatigue life expectancy of a group or identical bearings under identical conditions.
• Basic Dynamic Load Rating (C): The constant load under which a bearing will achieve a rating life of 1 million revolutions.
• Equivalent Dynamic Bearing Load (P): The load acting on the bearing that produces the same life as if the load were purely radial or purely axial.
• Exponent (p): An exponent used in the calculation of L10 life, typically ranging from 3 to 10, depending on the type of bearing and operating conditions.
• Revolution: The complete rotation of the bearing inner ring relative to the outer ring.
• Hours: The duration of the operation in terms of time.
• Fatigue: The process of material degradation due to repeated loading and unloading cycles.
• 90% Reliability: The probability that 90% of a group of identical bearings will achieve or exceed their calculated L10 life.

Symbols:

• L10: Calculated fatigue life (in millions of revolutions or hours).
• C: Basic dynamic load rating of the bearing.
• P: equivalent dynamic bearing load.
• p: Exponent used in the L10 life calculation.

Derivation:

• Basic Dynamic Load Rating (C): This is the load that the bearing can withstand for a theoretical life of one million revolutions without exhibiting fatigue failure. It’s determined experimentally by bearing manufacturers.
• Equivalent Dynamic Bearing Load (P): In real-world applications, bearings often experience complex loads that are not purely radial or axial. The equivalent dynamic bearing load represents a combination of radial and axial loads acting on the bearing, converted into an equivalent load that would produce the same fatigue life as the actual load.
• Exponent (p): This exponent is used to account for the different stress distributions within the bearing components. It varies based on the type of bearing and operating conditions.
• L10 Life Equation: The L10 life equation is derived from empirical data and statistical analysis of bearing performance. It relates the basic dynamic load rating (C) to the equivalent. dynamic bearing load (P) and the desired life expectancy (L10) of the bearing. The exponent (p) is included to adjust for different bearing designs and operating conditions.

Factors:

Safety Factor

The safety factor, also known as the safety margin or design factor, is a ratio used to ensure that a component or system can withstand loads and operating conditions beyond those expected in normal operation.

It represents the ratio between the calculated L10 life and the desired or required life expectancy. For example, if a bearing is expected to operate for 100,000 hours under specific conditions, but its calculated L10 life is 200,000 hours, the safety factor would be 2.

A safety factor greater than 1 indicates that this bearing is expected to exceed the desired life expectancy under the specified operating conditions. It provides a margin of safety against uncertainties in load, speed, lubrication, and other factors that could potentially reduce the bearing’s life.

Choosing an appropriate safety factor depends on various factors, including the criticality of the application, the consequences of failure, and the level of reliability required. Common safety factors range from 1.5 to 5, with higher values providing greater assurance of reliability but potentially resulting in overdesign and increased costs.

• Minimum Load Notice : ensures that the bearing is always subjected to a minimum load to prevent skidding or sliding.

• Heavy Load Notice: advises against exceeding certain loads that could cause premature bearing failure or damage.

Shaft/Rail Hardness Factor, fH

Takes into account the hardness of the shaft or rail on which the bearing operates. Harder surfaces generally result in a longer bearing life.

Required Lifetime (km) Factor, fL

Adjusts the bearing’s rated life expectancy based on the required lifetime in kilometers. This factor accounts for the relationship between bearing life and the distance traveled.

Reliability Factor, fR

Adjusts the calculated bearing life to achieve the desired level of reliability. Higher reliability requires a higher factor, which typically corresponds to a longer calculated bearing life.

Short Stroke Factor, fSS

Accounts for the effect of short stroke lengths on bearing life. Short strokes can result in higher stress concentrations and may require adjustments to the calculated bearing life.

FAQs

• What Determines a Bearing’s Service Life?

A bearing’s service life is primarily determined by factors such as proper lubrication, load, speed, operating temperature, and environmental conditions.