SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING For plain ball bearings, radial load ratings in pounds(as given in catalogs) are based upon a given rpm and a given number of hours of life with 90% survival. The product rpm X 60 X hr life is then equal to 106. Round per minute Other manufacturers give rated loads on the basis of 106 revolutions instead of hours of life(again, 90% survival). In that case, the number of hours of life can be found by dividing10° by rpm×60. It will be clear from the foregoing that, for a given load, changes in rpm(within the design limits as given by the manufacturer) affect life in hours inversely, thus n,/n,=H,/H 6.5 where n=rpm and H=life (hr ) Changes in load, on the other hand, affect life in revolutions exponentially: thusSCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING For plain ball bearings, radial load ratings in pounds (as given in catalogs) are based upon a given rpm and a given number of hours of life with 90% survival. The product rpm × 60 × hr life is then equal to 106 . Other manufacturers give rated loads on the basis of 106 revolutions instead of hours of life (again, 90% survival). In that case, the number of hours of life can be found by dividing 106 by rpm × 60. It will be clear from the foregoing that, for a given load, changes in rpm (within the design limits as given by the manufacturer) affect life in hours inversely; thus, n1 /n2 =H2 /H1 6.5 where n=rpm and H=life (hr.). Changes in load, on the other hand, affect life in revolutions exponentially; thus, Round per minute