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 rating life definition), "comparative" load ratings calculated by the same non-ISO method are given in the product tables for double direction tapered roller thrust bearings as these bearings are frequently used in rolling mills.
These comparative load ratings may only be used together whit the life and equivalent load equations specified below; they may not be used to calculate an ISO rating life.

Comparative life determination

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

LF10 = 90 (CF/PF10/3

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 which gives a rating life of 90 million revolutions, kN
PF=equivalent dynamic bearing load, kN (PF = Fa)
n=constant operating speed, r/min
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