SKF 305704 C-2Z Laufrollen (20x52x20,6)

As a track or cam roller, this component runs directly on a mating track or cam surface. The dynamic load rating of 19.5 kN characterises this bearing. The static load rating is 12.5 kN. For a roller carried along by its track rather than driven, a low breakaway torque is not a convenience feature but an operating condition. This track roller is closed on both sides with shields that work without contact.

They narrow the gap far enough that the grease charge stays in the rolling chamber and coarse ingress from the track does not get in, but create no friction surface in doing so. For this design that is more than a convenience: the roller is not driven but set turning by the contact with its track, and too high a breakaway torque causes it to slide on the track instead of rolling on it — precisely the condition that wears running surface and track together and frequently becomes visible as a flat spot on the roller.

The limit of the shielding is just as clear: against moisture, splash water and fine abrasive dust it forms no tight closure, and where these are permanently present a bearing seal is preferable. Since the lubricant stays in the bearing and relubrication is frequently not provided for, the operating temperature and the load have a share in determining the service life of the grease charge.

The rest of the construction follows the design: the thick-walled outer ring, hardened through the running depth, takes the contact pressure from the track contact and rotates through the load in doing so, so that the most heavily stressed location travels over the whole circumference; the hardness, surface finish and course of the mating track have a share in determining the load capacity of the pairing; the profile of the running surface determines whether an angular error relative to the track forces the pressure out to the edge. Rings and rolling elements are made of standard bearing steel.