To prolong the life of a back-up bearing for a cluster mill.
A recess 5a is formed in an outer surface of a sealing plate 5 for closing both ends of the clearance between an inner ring 1 and outer ring 2 of the back-up bearing. By driving a knock pin 8 into the inner ring 1 from the recess 5a and preventing slip-off with a bolt 9, the slip-off from the inner ring 1 of the sealing plate 5 and the joint rotation with oil seal 6 are surely prevented without shortening the length of a roller 3, thereby preventing the occurrence of faulty lubrication. By forming a carburized nitriding layer containing a right amount of residual austenite on the surfaces of the inner ring 1 and roller 3, the surface starting point flaws in the inner ring 1 and roller 3 are prevented. By applying right compression stress onto the surface of the outer ring 2, a split damage caused by a surface crack in the outer ring 2 is prevented. By so doing, the life of the back-up bearing is increased.
DAIKO MAKOTO
Higashio Masahiro
Torii Kazuhisa