Bearing life calculation tool -Contents of HELP in New Life Calculation Equation-

Explanation of L_able

NSK new life calculation equation (NSK ABLE FORECASTER) introduces Fatigue load limit (P_u), which does not cause flaking less than that,

in addition to the load applied to bearing, Contamination factor(a_c), which indicates the level of contamination for lubricant, and Life adjustment factor (a_NSK),

which is calculated by considering viscosity ratio (κ) representing the ratio between the viscosity of the lubricant and necessary   viscosity lubricates bearing normally.

It is shown as below.

Explanation of a_NSK

The a_NSK adjustment factor of the NSK life calculation equation is defined as a function of the load parameter

and the a_c contamination factor, which reflects both contamination levels of the lubricant,

and includes the lubrication parameter κ (viscosity ratio).

 Explanation of ISO 281: 2007

     L_nm  =  a₁   a_ISO  L₁₀

 where,

     L_nm  =  ISO281 modified rating life

                 However, in case that calculated life exceeds 200 000 hours, it is indicated "over 200 000"

     L₁₀  =  basic rating life

     a₁  =  life modification factor for reliability

     a_ISO  =  life modification factor, based on a system approach of life calculation

 However, this equation can not apply to following operating conditions

     · In case of very large load imposes to the bearing (More than C₀  or more than 50% of C)

     · In case of very light load imposes to the bearing

     · In case of exceeding limiting speed

     · In case of water intrudes to the bearing or lubricant

     · Bearings with the occurrence of abnormalities such as wear, corrosion, or electric erosion

     · In case that there is a large misalignment between inner and outer rings

     · In case of very large and hard foreign debris intrudes to (Life is shorter than the calculation result)

     · In case that viscosity when driving is 10% or less of necessary dynamic viscosity

Explanation of reliability factor a₁

Bearing fatigue life is defined as the basic rating life with a statistical reliability of 90% (Basic rating life L₁₀).

Depending on the machines in which the bearings are used, sometimes areliability higher than 90% may be required.

The life adjustment factor for reliability, a₁, is listed in following table:

It is possible for ABLE and ISO 281: 2007 to calculate bearing life up to 99% reliability.

Explanation of contamination factor a_c

When foreign debris enters the bearing interior during operations, small dents are generated on the rolling contact surface.

Flaking occurs due to concentration of stress at the periphery of the dents.

The NSK life calculation equation (NSK ABLE Forecaster) divides lubricating conditions into five stages to determine the contamination factor a_c

Explanation of contamination factor e_c

When the lubricant is contaminated with solid particles, permanent indentations in the raceway can be generated when these particles are over rolled.

At these indentations, local stress risers are generated, which will lead to reduced life of the rolling bearing.

This life reduction due to contamination in the lubricant film is taken into account by the contamination factor e_c .

Guide values for the contamination factor can be taken from from the following table, which shows typical levels of contamination for well lubricated bearing.

In the case of severe contamination (ec  →0), failure may be caused by wear, and the life of the bearing can be far below a calculated modified rating life.

Explanation of Load factor f_w

When a radial or axial load has been mathematically calculated, the actual load on the bearing may be greater than the calculated load

because of vibration and shock present during operation of the machine.

The actual load may be calculated using the followingequation:

     F_r  = f_w  · F_rc                            Note:    F_rc= radial load

     F_a  = f_w  · F_ac                                        F_ac= axial load

where

     F_r  ,F_a  : Load applied on bearing ( N )

     F_rc , F_ac : Theoretically calculated load ( N )

     f_w : Load factor

The values given in below table are usually used for the load factor fw

* Radial load and axial load, which are used in this program, are frc , and  fac respectively.

Explanation of Bearing material / Special specification

About calculation of sealed bearings.

Sealed bearing life (bearings with seals or shields on both sides) is calculated using grease lubrication.

If operated using oil lubrication, please consult NSK for further information.