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Types of lubrication

Hydrodynamic lubrication (full fluid film) 

(1) Moving surfaces are separated completely by the pressure of a continuous unbroken film or a  layer of lubricant, generated by the movement of the two surfaces relative to each other. 
(2) Essential requirement is formation of a wedge of lubricants between surfaces. 
(3) Thickness of film 0.025 – 0.10 mm. 
(4) Lubrication for Journal Bearing, Bottom End Bearing, Tilting Pad Thrust Bearing

Boundary lubrication 

(1) It exists when a full-fluid film lubrication is not possible. 
(2) The sliding surfaces are separated by only a thin film of lubricant. 
(3) High friction between the surfaces and some degree of metal to metal contact occurs 
(4) Lubricant oil film decreases, until asperities of mating surfaces touch 

Hydrostatic lubrication 

(1) A form of thick film lubrication, but instead of being self- generated, it is supplied from an  external source by oil under pressure from a pump. 
(2) Lubrication for Crosshead Bearings, with attached pump. 

Elasto-hydrodynamic lubrication

(1) Applies to line contact or nominal point between rolling or sliding surfaces, such as rolling  contact bearings and meshing gear teeth. 
(2) Thin film or squeeze film lubrication limits metal to metal contact. 
(3) Elastic deformation of the metals occurs, and there is effect of high pressure on the lubricant.

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