A slewing bearing, slew ngring, or turntable bearing is a rotational

rolling-element bearing In mechanical engineering, a rolling-element bearing, also known as a rolling bearing,ISO 15 is a bearing (mechanical), bearing which carries a load by placing rolling elements (such as balls, cylinders, or cones) between two concentric, Groove ...

that typically supports heavy, slow-turning, or slowly-oscillating loads in combination. Slewing bearings are often used in horizontal platforms, such as conventional cranes,

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, and wind-facing platforms of horizontal-axis wind turbines. In other orientations (e.g. a horizontal axis of rotation), they are used in materials handling grapples,

forklift A forklift (also called industrial truck, lift truck, jitney, hi-lo, fork truck, fork hoist, and forklift truck) is a powered industrial truck used to lift and move materials over short distances. The forklift was developed in the early 20th c ...

attachments, and welding turnover

jigs The jig (, ) is a form of lively folk dance in compound metre, as well as the accompanying dance tune. It first gained popularity in 16th-century England, Ireland, Scotland, and other parts of the British Isles, and was adopted on mainland Eu ...

. Compared to a standard

ball bearing A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this ...

, slewing bearing rings are quite wide, and usually have holes drilled in them to provide fixation to a structure.

Seals Seals may refer to: * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impress an emblem, used as a means of a ...

can be provided between the rings to protect the rolling elements. Compared to other rolling-element bearings, slewing bearings are relatively thin. Slewing bearings' thinness means that the structure they are bolted to must be stiff enough to not distort the bearing. Slewing bearings range in size from as little as 100mm in diameter to well over 15,000mm. Large slewing bearings are often segmented for transport and handling. The slewing bearings on the Falkirk Wheel, for example, are 4 meters in diameter, and fit over a 3.5 meter

axle An axle or axletree is a central shaft for a rotation, rotating wheel and axle, wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In ...

. Slewing bearings are often made with

gear teeth A gear or gearwheel is a rotating machine part typically used to transmit rotational motion and/or torque by means of a series of teeth that engage with compatible teeth of another gear or other part. The teeth can be integral saliences or ...

integral with the inner or outer race used to drive the platform relative to the base. Slewing bearing designs range from single row ball or roller style, through double row ball or roller, triple row roller, combined (1 roller/ 1 ball) or wore guided raceways - each design having its own special characteristics and application. Old designs can have split rings to allow tight control on preload during assembly. As for other bearings that reciprocate, rather than rotating continuously, lubrication can be difficult. The oil wedge built up in a continuously rotating bearing is disrupted by the stop start motion of slewing. Instead, a

hydrostatic bearing Fluid bearings are bearings in which the load is supported by a thin layer of rapidly moving pressurized liquid or gas between the bearing surfaces. Since there is no contact between the moving parts, there is no sliding friction, allowing flui ...

with pumped oil flow may be used.

Standards

Most manufacturers of slewing rings have their own set of manufacturing standards. The

American Society of Mechanical Engineers The American Society of Mechanical Engineers (ASME) is an American professional association that, in its own words, "promotes the art, science, and practice of multidisciplinary engineering and allied sciences around the globe" via "continuing edu ...

(ASME) publishes the following standard: *ASME SRB-1 on Design, Installation, Maintenance, and Application of Ball Slewing Ring Bearings

References

{{Reflist Rolling-element bearings