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Schaeffler has developed a high-capacity cylindrical roller bearing for wind turbine gearboxes, which offers higher load ratings and reduced friction due to a new cage design. Schaeffler’s FAG high-capacity cylindrical roller bearings have a new sheet steel cage, which enables a much more compact design compared to a conventional solid brass cage. This more slimline cage leaves space for at least one additional rolling element in the bearing, which increases the load rating. Due to the new cage, the high-capacity bearing has a lower friction than full-complement cylindrical roller bearings with maximum basic load rating.

The ‘self-retaining’ cage also simplifies bearing mounting because the rolling elements are retained even when the ring is removed. Most current planetary stages of wind turbine gearboxes use full-complement cylindrical roller bearings. These bearings have no cage, the function of which is to guide the rolling elements and to maintain a set distance between them. These full-complement bearings have the highest load ratings, since more rolling elements are fitted to bearings that have no cage. However, full-complement roller bearings have relatively high friction because the rolling elements are in direct contact with each other.

These kinematic conditions cause higher friction losses. In contrast, cylindrical roller bearings with conventional solid brass cages have lower friction, but often do not achieve the required load ratings due to the reduced number of rolling elements. Schaeffler’s new FAG high-capacity cylindrical roller bearings incorporate a sheet steel cage, which ensures low friction and provides sufficient space for an additional roller element in the bearing (due to very narrow crosspieces). The cage comprises two cage rings lying one inside the other and joined together. The crosspieces of the inner cage guide the roller elements. At the same time, these retain the roller elements in the bearing, even when the bearing ring is removed.

This means that the bearing is much easier to mount, as no separate device is required to help prevent the roller elements from falling out. In addition, the special geometrical shape of the cage pockets improves lubricant flow, which reduces friction and prevents damage to the bearing. The basic static (C) and dynamic (Co) load ratings of the high-capacity cylindrical roller bearing are six per cent higher than those of a conventional cylindrical roller bearing with a solid brass cage. This means that the rating life is increased by more than 20 per cent. The new bearings are currently undergoing trials in various customer applications. Schaeffler plans to commence volume production of the bearings in 2011.