Machine Design

Hard bearing is soft inside

Standard spherical plain bearings use through-hardened 52100 steel for the spherical inner ring and the outer ring. The steel resists wear, but is somewhat brittle. This makes it easy to fracture the outer ring, a necessary manufacturing step that lets the inner ring slip into the split outer ring. But under harsh loads and sudden impacts, the brittle steel can fracture and break on impact.

To solve this problem, engineers at RBC Bearings in Fairfield, Conn., make their ImpactTuff spherical bearings out of carburized 8620 steel. They case harden the outer surface of the bearing and ring to RC 60, while keeping the inner core relatively ductile at RC 40. This lets the outer shell take the brunt of the impact, while the softer inner core absorbs and distributes the load to prevent cracks and fracturing. A patented notch machined in the outer ring permits controlled fracturing of the ring, which facilitates bearing assembly.

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