Light duty slewing ring / Xuzhou Wanda slewing bearing

A slewing ring is a contained system of balls or rollers, caging, raceways, mounting provisions, and often, integral gearing as well. These large units are designed to transmit axial, radial, and tilting moment loads. And because they handle loads (and different combinations of them) in one assembly, these bearings eliminate weight, space, and cost penalties of other rotational designs.

The most suitable slewing ring for a design depends on static and dynamic loads, bolt requirements, and gearing specifications. How are loads on a slewing ring best calculated? By using the classical engineering approach of creating free-body diagrams and then solving for unknown variables using static equilibrium equations. (Such a sketch shows forces, their vectorial direction in terms of X and Y Cartesian coordinate values, and the X and Y perpendicular distances of these forces relative to the bearing center.) The bearing plane becomes a cut line for the free-body diagram dividing forces — left and right or top and bottom relative to the bearing plane. Bearing loads are simply the reaction forces at the cut plane. Equations of static equilibrium return reactionary forces at this plane are:

Σ Axial forces = 0

Σ Radial forces = 0

Σ Moments = 0

The directions of force and moment rotation are very important, indicating whether a value is positive or negative. Moment loads are calculated about the center of the ring — that is, where the center plane and rotation axis of the ring cross.

After loads have been calculated, product specification sheets can give basic data for choosing one or more possible bearing style for a particular application. To illustrate: Some rings are developed for use as fifth-wheel bogie steering pivots on trailer applications. Other slewing rings are common on general turntable applications; their moment capacity provides stability to turntables having diameters well in excess of the bearing diameter. Finally, slewing rings with high contact angles and increased internal clearance are suitable for thrust applications where the center of force remains within the raceway diameter.

Wire-race slewing rings are known for being very light and reliable. They're used in medical scanning equipment and radar antennas, and are appropriate where lightweight, replaceable raceways or ring material selection is an important consideration. However, self-selection is not recommended; manufacturers should be involved in the design process for slewing rings.

Listed raceway capacities are often static ratings. Since most large-diameter ring applications involve intermittent slewing and a broad spectrum of loads, it's prudent to select a ring based on its static capacity — and a recommended application service factor. Capacities listed are non-simultaneous: In other words, a catalog thrust capacity doesn't account for moment or radial loading. Similarly, moment capacity assumes no thrust or radial load, and listed radial capacity accounts for no thrust or moment. When applications involve a load combination, the load components must be combined into an equivalent load. (For static raceway calculations, this equivalent load is taken to be load as seen by the highest loaded rolling element.)

The exact machine duty cycle and the mounting structure design have tremendous influence on the durability of the ring. In high-cycle applications, dynamic capacity, rather than static capacity, may dominate the slewing ring selection.