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You spin me right round

01 July 2019

Slewing ring bearings have been in use for many years and are often associated for rotating heavy and slow-turning or slow-oscillating loads on a horizontal platform, such as on a crane. In this article, however, dry-tech director, Robert Dumayne, focuses on the ‘Lazy Susan’ type of slewing ring bearings for fast rotary movements in confined spaces.

Compared to other rolling-element bearings, slewing ring bearings are thin and often use two rows of rolling elements. They usually include three race elements, such as an inner ring and two outer ring "halves" that clamp together axially. They also tend to feature gear teeth on the inner or outer race, which drive the platform relative to the base. As for other bearings that reciprocate, rather than rotating continuously, lubrication can be problematic. The oil build-up in a continuously rotating bearing is disrupted by the stop/start motion of slewing. To overcome this problem, a hydrostatic bearing with pumped oil flow can be used. An alternative is to use lubrication-free polymer slewing ring bearings, which are maintenance-free and particularly wear-resistant. 

Polymer slewing ring bearings are suitable for a wide spectrum of applications, wherever high cycle rates and loads are key requirements. They come in a range of sizes with inner diameters from 20 to 300mm and many assorted designs, from light (solid) plastic versions and driven slewing ring bearings, to split bearings for difficult installation situations and toothed slewing ring bearings. High-temperature versions are also available. For confined spaces and medium load applications, such as automation or stage technology, an ultra-low-profile version is available. 

Read the full article in the July issue of DPA

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