NTN 51208 Kugellager (40x68x19)

As a thrust ball bearing, this bearing carries axial loads only and must not be loaded radially. The dynamic load rating of 47 kN characterises this bearing. The static load rating is 98.5 kN. The limiting speed is 3900 rpm. A second, radially carrying bearing must always be provided to guide the shaft — this design takes longitudinal forces alone.

The thrust ball bearing transmits force through balls between two flat washers and is therefore restricted to longitudinal loads; radial load must not be placed on this bearing but belongs at a separate radial bearing position. The set is separable, so the shaft washer and the housing washer can be fitted independently and handled individually during repair.

For the balls to roll rather than slide under all operating conditions, a permanently acting minimum axial force is required; without it at high speed, centrifugal force prevails and rolling contact is lost. The seating faces must be square to the shaft axis, because any out-of-square condition concentrates the load onto a few balls. Standard bearing steel is through-hardened and provides the raceway hardness and dimensional stability for the usual operating-temperature range; for the design, axial force, speed and the required minimum load should be assessed together.