Mechanical due to friction to derivatives lubrication, friction can be divided into dry friction, boundary friction, liquid friction and mixed friction. Lubrication mechanism related with these different friction states .

A. mixed friction
Mixed friction also called mixture lubrication, it is to belong to an unstable lubrication. It already exists lubricating oil viscosity generated viscous resistance, it has a metal surface slightly convex body contact frictional resistance generated. In fact it is the above three friction has two kinds of friction in the presence of the situation, can be divided into half dry friction and half liquid friction.

B. boundary friction

Boundary friction also called boundary lubrication, it is to point to object on the friction between the existing by a lubricant consists of the boundary membrane was friction.
The boundary film is the nature of the main factors of influence boundary friction, by its form, can be divided into adsorption membrane and reaction film two kinds. The membrane is through the physical adsorption factors (molecular attraction) or chemical factors (electronic exchange produce chemical binding force), make the lubricant polarity molecules of the formation of the orientational a layer of film.

C. liquid friction

Liquid friction, also known as the liquid lubricant, as an object of the interface between the oil film is completely separated, the object relative motion produced by the friction that liquid friction.
Liquid friction, the object of the friction between the surface not directly contact, it besides boundary lubrication film outside, still have a flow of oil film. So the friction between only occurs in lubricating oil, motion resistance by lubricating oil molecule room only attractive (measured cohesion) formation, thus friction coefficient is small, generally in the scope of 0.01 to 0.001.

D. dry friction
Between the friction surface without lubricant exists cause friction, called dry friction.
 



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