Machine Design

Segmented bearings overcome limitations in conventional geometry

Hollow-cylindrical bearings, rolling-ring linear actuators, and self-aligning bearings are some of the topics covered in this bearings reference guide.

Edited by Lawrence Kren and Victoria Reitz

Segment technology assembles a number of individual, self-contained segments to form a ball-bushing bearing. Each segment consists of a plastic retainer and lid that holds and retains the plate and balls. Subsequently, the segments are joined to create a complete bearing.

Two extruded members provide smooth relative motion, low drag, and minimal deflection without significantly modifying the extrusions. The annulus between the inner and outer extrusions is too small to permit use of standard bearings without extra components. The new custom segments are distributed within the assembly to use the extrusion as part of the bearing.

When most people think of recirculating rolling elements, they think of traditional ball-bushing bearings. However, recent expansions into segment-bearing technology address applications where conventional ball-bushing or other rolling-element bearings never dared to go. Segmented bearings have a ball retainer assembled from several self-contained ball-retainer segments. Each segment includes at least one ball track with a load-bearing portion and a return portion. Now segments with recirculating ball technology can be designed and placed to accommodate the most un-usual shapes, as well as dramatically reduce envelopes.

Traditionally, users requiring the high-load capacity and low friction of rolling element bearings were forced to conform to standard bearing configurations and envelope restrictions. Segments can be configured to fit within the annulus constraints of two components to provide low-friction smooth linear motion, minimum deflection, and long life. They have self-adjusting features that 'forgive' temperature fluctuations and housing variations, and maintain a consistent preload over their life.

Segmented bearings reduce design constraints and provide a low-friction alternative for high-drag applications where part configuration prevents use of standard bearings. Recirculating bearing technology can now be employed where only plain bushing bearing technology could be used previously.

Segmented bearings are recommended for retained (nonpress fit) or light press-fit applications. The units can also be used as core or steel-sleeve bearings for heavy press fits with housings, or in applications with bearings held in place by a setscrew.

This information supplied by Frank Dalessandro, manager, Product Engineering, Thomson Industries Inc., Port Washington, N.Y.

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