# Comparative load ratings

For rolling mill applications, load ratings are often used which are not calculated according to ISO 281:1990 but by a different method based on a rating life of 90 million revolutions (500 r/min for 3 000 operating hours). As a direct comparison of these load ratings with ISO load ratings is not possible, even if they are converted for 1 million revolutions (ISO life definition), "comparative" load ratings calculated by the same non-ISO method are given in the product tables for double row tapered roller bearings as these bearings are frequently used in rolling mills.
These comparative load ratings may only be used together with the life and equivalent load equations specified below; they may not be used to calculate an ISO rating life.

## Comparative life calculation

The comparative life is calculated using the comparative load rating CF as follows

LF10 = 90 (CF/PF) 10/3

or

LF10h = (CF/PF)10/3 (1 500 000/n)

where

 LF10 = comparative rating life [million revolutions] LF10h = comparative rating life [operating hours] CF = comparative dynamic load rating to give a rating life of 90 million revolutions [kN] PF = equivalent dynamic bearing load (for conditions please refer to table) [kN] n = constant operating speed [r/min]

For load cases 1a) and 1b), see table, it is necessary to use the load rating for one roller row when using PFL. This load rating (for 1 row) can be obtained from

CF (row) = 0,58 CF (bearing)