What is the difference between bearing and bush?

Answer 1

A bearing consists of a series of rollers or balls that support a shaft whereas a bush is merely a sleeve.

The bearing works due to the principle of hydrodynamic lubrication - the rollers, as they roll, squeeze the lubricant to a certain pressure at which point the fluid supports them.

The bush works on the principle of fluid films, where the viscosity of the lubricant supports the mating surfaces.

Bearings fail catastrophically if the lubricant is missing, because the point loading of the balls or rollers is extremely high - this can dislodge the rollers or even lock up the shaft. This is why an automobile crank can be ruined very quickly if oil pressure fails - The oil gets squeezed out and when metal touches metal, it's disaster.

Bushes require a very minimal amount of lubrication to function, and in case of starvation, the bush does not self destruct, and continues to function with reduced efficiency. Bushes are usually made of bronze alloy which has a self lubricating effect, and does not friction weld unlike most alloys. Some low RPM applications use bushes which are dry or merely greased.