Gränsskiktfriktion

Gränsskiktfriktion, or boundary layer friction, refers to the resistance to motion that occurs when two solid surfaces are in close contact, and the intervening lubricant film is very thin. In such conditions, the lubricant is unable to fully separate the surfaces, leading to direct contact between asperities (microscopic high points) on each surface. This direct contact results in significant frictional forces.

The phenomenon is primarily governed by the adhesive forces between the surface materials and the shearing of the lubricant that does exist. It is distinct from fluid friction, where a continuous film of lubricant prevents solid-to-solid contact. Gränsskiktfriktion is characterized by high friction coefficients and can lead to wear, damage, and increased heat generation.

Factors influencing gränsskiktfriktion include the surface roughness of the materials, their chemical composition, the presence of adsorbed layers or chemical films on the surfaces, the load applied, and the relative speed between the surfaces. Extreme pressure (EP) additives are often incorporated into lubricants to mitigate the effects of gränsskiktfriktion. These additives form protective films on the metal surfaces under high-pressure conditions, reducing direct asperity contact and preventing seizure. Understanding and controlling gränsskiktfriktion is crucial in tribology for designing efficient and durable mechanical systems, such as bearings, gears, and engines.