Stribeckkäyrän

The Stribeck curve, named after Richard Stribeck, is a graphical representation of the relationship between the coefficient of friction, the lubricant viscosity, and the relative speed of two sliding surfaces. It illustrates how friction changes under different lubrication regimes.

At very low speeds or high loads, the lubricant film is thin, and the surfaces are in close contact, leading to boundary lubrication. Here, friction is high due to direct surface-to-surface interaction and the shearing of the lubricant molecules. As speed increases, the lubricant begins to separate the surfaces, and the coefficient of friction decreases.

This downward trend continues until a minimum point on the curve is reached, known as the Stribeck minimum. At this point, hydrodynamic lubrication is established, where the relative motion of the surfaces generates sufficient pressure in the lubricant to create a complete film that fully separates them. Friction is at its lowest in this regime.

Beyond the Stribeck minimum, if the speed continues to increase while the load remains constant, the lubricant film thickness increases. However, the viscous drag of the lubricant itself starts to become a dominant factor in friction. This leads to a gradual increase in the coefficient of friction as speed rises further, entering the region of hydrodynamic lubrication where friction is dominated by viscous shearing.

The Stribeck curve is a fundamental concept in tribology and is crucial for understanding and designing lubrication systems, selecting appropriate lubricants, and predicting wear in mechanical components. It helps engineers to operate systems within the most favorable lubrication regime to minimize friction and wear.