When to choose a plain bearing over a rolling one?

When the motion oscillates or is very slow, when impacts occur, when the space is tight, or when lubrication cannot be provided. Under small-angle oscillation a rolling bearing works the same spot of the raceway all the time and brinells it.

Do maintenance-free designs really need no grease?

Correct — the composite layer transfers material onto the journal and forms a sliding film. They must not be greased „just in case”: grease collects dust and forms an abrasive paste that destroys the working layer faster than dry running.

Plain bearings | e-Feniks

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Plain bearings have no rolling elements — surface slides on surface. They therefore take high loads at low speeds, damp vibration and tolerate impacts that would dent the raceway of a rolling bearing. They work in cylinders, construction machinery joints, hinges and anywhere motion is oscillating rather than rotating.

There are two families: designs requiring lubrication (bronze, steel-bronze, with grease grooves) and maintenance-free ones with a PTFE composite layer that run dry. Spherical plain bearings and rod ends form a separate group, carrying load while the axis tilts.

What to look at when selecting

Oscillating motion and low speed favour a plain bearing; continuous high-speed rotation favours a rolling bearing.
Maintenance-free PTFE where there is no access to a grease nipple or where grease would collect dust.
Check the permissible pressure–velocity product (p·v) — that, not load alone, sets the limit.
Journal hardness and surface finish must suit the bush material, otherwise the bush is destroyed within hours.

Common questions

When to choose a plain bearing over a rolling one?: When the motion oscillates or is very slow, when impacts occur, when the space is tight, or when lubrication cannot be provided. Under small-angle oscillation a rolling bearing works the same spot of the raceway all the time and brinells it.
Do maintenance-free designs really need no grease?: Correct — the composite layer transfers material onto the journal and forms a sliding film. They must not be greased „just in case”: grease collects dust and forms an abrasive paste that destroys the working layer faster than dry running.