Slewing bearing cages
A "slewing" bearing is a rotational rolling-element bearing that typically supports a heavy but slow-turning or slow-oscillating load, often a horizontal platform such as a conventional crane or the wind-facing platform of a horizontal-axis windmill.Compared to other rolling-element bearings, slewing bearings are thin in section and are often made in diameters of a metre or more. Slewing bearings often use two rows of rolling elements. Slewing bearings are often made with gear teeth integral with the inner or outer race, used to drive the platform relative to the base. Assembly is completed by fitting a cage to the balls to maintain their positions relative to each other. Without the cage, the balls would eventually drift out of position during operation, causing the bearing to fail. The cage carries no load and serves only to maintain ball position.