Why Accurate Cage Selection is Essential for Reliable, Long-term Bearing Operation

December 3, 2018

Looking back a few posts, we seem to be missing a critical part of a bearing’s anatomy. The glossy races and structure rings are there, as are the hardened and ultra-smooth rolling elements. The cage, though, where is this roller retaining section? Correcting this oversight, let’s see which cage types are most viable. Using that last statement as an article segue, here’s why accurate cage selection guidelines are important.

The Role of the Bearing Cage

If only we could view a conventional bearing in some fantastical manner that wasn’t normally possible. Viewed in some kind of cutaway mode, the polished races and ring of concentric ball bearings come into focus. Only, there’s a retaining structure surrounding those lubricated rolling elements. This is the bearing cage. Its job is to evenly space out the balls and to keep them rolling in a radially symmetrical fashion. If that structure was left out of the bearing, the whole device would fly apart as soon as it begun to spin. Transient loads, thrust forces and angularly applied energies, they’re all kept under control by an optimally selected bearing cage.

Weighing the Cage Selection Considerations

By intelligently selecting a dimensionally accurate cage size, the engineer is preemptively offsetting the problems listed in the previous paragraph. The inner and outer rings lock together, the rolling elements spin in-line, precisely within the race pathways, and there are no power-impeding oblique forces impacting the rings. They’re retained, held to that one spinning line. Imagine if that weren’t the case. Even if the rings were engineered so that their geometries locked the balls in place, they would perform terribly. The balls wouldn’t be spaced, so they’d contact each other, generate micro welds, and produce large quantities of thermal energy. The entire device would also wobble uncontrollably, with the rolling components staggering incrementally from one side of the ring edge to the other side. Noise, a squealing, squeaking cacophony would radiate loudly.

Thinking about accurate bearing cage selection, when the cage is properly sized, it satisfies a range of challenging engineering specs. High-tolerance dimensionality eliminates noise. There’s no ball rubbing, no micro welds, no damaged race surfaces, and very little thermal loss. Now, with the rolling elements laterally held in-check that previously mentioned wobble factor is zeroed out and the high-performance lifespan of the caged bearing is maximized. Incidentally, the above problems and solutions are influenced by ring circumferences, but they’re also impacted by cage types. Among them, there are one-piece steel crowns, hemispherical metal and nylon types, and many more element-retaining options. These, too, require careful selection.

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