Lubrication regimes
Lubrication regimes describe the type of lubrication film that is created under certain operating conditions and are dependent on the degree of contact between these surfaces. There are three primary lubrication regimes: boundary lubrication, mixed lubrication and hydrodynamic lubrication.
Let's look at this using the example of the water-skiing in the video above.
Boundary lubrication
During boundary lubrication, the opposing surfaces meet with little or no oil film separation. In this regime, damage is prevented by protective additives that promote sliding rather than welding of surface asperities. This regime usually occurs at low speeds.
Imagine you are driving a speedboat. If you gave it a little throttle, the nose of the boat would rise, and the rear end would lean into the water. When half of the boat is still in the water, it creates drag. The same thing would happen to the water skis when you try to get going for the first time. This is a good example of boundary lubrication.
Hydrodynamic lubrication
During hydrodynamic lubrication, the moving parts are completely separated by a film of fluid. This regime typically occurs at high speeds.
Back to our previous example, now imagine that the boat has been at full acceleration for long enough to reach full speed. At this speed, the nose of the boat comes down and you are moving so fast that you barely skim the top layer of water. While we definitely do not recommend trying this at home, this example demonstrates hydrodynamic lubrication.
Mixed lubrication
Mixed lubrication occurs during the transition from low to high-speed operation, when boundary and hydrodynamic conditions coincide. In this regime the asperities of the boundary surfaces separate across the film and occasionally come into contact.
Finally, imagine that you accelerate your boat to full throttle. At first, the nose of the boat will drop a little as you accelerate, but you have not yet reached the maximum speed of the boat. At this point, the water skis have been balanced and the boat sails in conditions similar to those of mixed lubrication.
Understanding the difference between lubrication regimes is critical to selecting the right lubricant for an application, which will protect your component and prevent wear. Now that you understand the basics of lubrication regimes, you are ready to ask the right questions to select a lubricant for your application.
