If the bearing is not submerged,
a seal should be inplace.
Bearings are made to reduce the
rolling friction. The oil or
grease creates a film between
the rolling contact surfaces and
help to reduce the friction.
What type or kind of bearing are
you asking about?
thanks, I am asking axial and radial bearing , I need the mechanisim of this film and how the pressure droped at the bearing as bearing turbine and how keep the oil inside this bearing
The main function of the bearing is generally to support the rotor.
Oil is used for lubrication and sometimes heat removal.
There are many different configurations for retaining the oil: grease was mentioned, oil bath (not suitable for all types bearings), oil-ring lubricated, forced oil, hydrostatic lubrication.
The two basic types of bearings are rolling-element (anti-friction) and sliding bearings.
In all bearings the force is transmitted somehow through the oil since oil is between the metal parts preventing metal to metal contact.
In sliding bearings such as sleeve, tilting pad, there is generally hydrodynamic lubrication which relies on the viscosity of the oil to prevent contact.
In rolling element bearings there is generally elastohydrodynamic lubrication (I think that's thre right word). The viscosity of the oil goes up greatly under pressure.
Try some searches on google and try to form more specific questions.
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Oil is never kept in the bearing, there is always a flow whether it is splash lubricated or forced lubrication. Sealed bearings are used with grease to keep the grease in.
The fluid film is based on the operating viscosity of the oil, you need to select the proper oil viscosity to keep the fluid film thick enough based on the diameter and speed of the bearing. FAG has a very good tehcnical article on anti-friction bearing lubrication on their website. Go to
Never say never. Rolling bearings often have up to half of the lowest rolling element submerged (see page 15/16 of above referenced document). We have vertical motor Kingsbury thrust bearings where thrust pads are completely submerged and radial pads are one half submerged.
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I stick by my statement, the oil is still circulated through the bearing in the submerged or partially submerged situation. As the bearing rolls, it pulls in fresh oil from the sump.
There are vertical shaft applications where the oil level is well above the bearing, in these cases there is a ring mounted on the shaft to promote oil circulation.
