Smörjfilm

Smörjfilm, or lubricating film, is a thin layer of lubricant that separates two contacting surfaces to reduce friction and wear. It can form from liquids such as mineral oils, synthetic oils, esters, or grease and may exist in several lubrication regimes depending on conditions.

Lubricating films are categorized by their formation and load-bearing mechanism. Hydrodynamic lubrication occurs when relative motion and geometry generate a pressure field that supports the load, creating a relatively thick film. Elastohydrodynamic lubrication involves high contact pressures that deform the surface elastically, generating thicker films in highly loaded contacts. Boundary lubrication occurs when the film is so thin that adhesion and chemical interactions between surface asperities dominate, and additives in the lubricant become essential to reduce wear.

Film thickness, typically on the order of nanometers to micrometers, depends on viscosity, sliding speed, load, temperature, and surface roughness. The Stribeck curve summarizes transitions between boundary, mixed, and hydrodynamic regimes as these parameters change. Temperature changes alter viscosity and film stability, while contaminants can degrade film quality and cause wear.

Measurement and monitoring of a smörjfilm employ techniques such as interferometry, ellipsometry, or capacitance sensing, providing thickness estimates and revealing film uniformity. Additives—anti-wear, anti-corrosion, and viscosity modifiers—enhance performance, especially in boundary lubrication or high-load conditions.

Applications of lubricating films span machine elements like bearings, gears, pistons, and slideways, where they reduce friction, minimize wear, and aid heat dissipation. Proper selection and maintenance of lubricants ensure film integrity across operating conditions, extending equipment life and efficiency.