The research and study area of tribology is one of the most interdisciplinary areas in science today. In short, tribology is the study of interacting surfaces in relative motion. The interaction of surfaces, and the interfacial properties between surfaces, govern the properties of many systems. Therefore, the tribology of the system is one of the most important factors of a given system.
Surfaces, whether they are stand-alone, interacting or just in the same environment as one another, are important for many applications and industries. As surfaces, no matter how small, are always present, the study of tribology is widespread, interdisciplinary and a fundamental consideration across many areas of science.
These principles also stand true for the many industries that use oils in their product and/or mechanical system, be it lubricants, greases or some other oil-based formulation. As oils are used in many applications and are required for long-term use, the analysis and maintenance of these oils is a common procedure to make sure that they are up to the manufacturers standard. There are many methods to analyze oils and tribology plays a role in all of them. Within this article, we cover what tribology is and how it is crucial for many oil environments and applications, many of which require regular maintenance to be effective.
What is Tribology?
Tribology is the science of interacting surfaces in relative motion and includes multidisciplinary areas such as friction, lubrication, contact mechanics, surface damage processes and surface optimization. The principles of friction, wear and lubrication are the most important in tribology and are often engineered to optimize the efficiency, performance and reliability of a tribological system. There are currently many applications that rely on the effects discovered from tribological studies.
Tribology can be used for two or more surfaces that come into contact with each other in a number of ways. These types of interaction can take the form of frictional forces, surfaces coming together, surfaces being kept apart and stress or strain at a surface contact point.
Why is Tribology a Crucial Factor in Oil Environments
The tribology of an oil-based system is important for the functional working of the system and for analyzing whether it is still suitable through various tests. Whilst the tests incorporate some use of tribology, the greatest effects of tribology are actually found within the oil(s) themselves and how the tribology of the oil is useful for various application environments. Tests, such as viscosity, elemental concentration determination etc. can call upon the interaction of the oil surface with other molecules. However, many applications that use oil are mechanical in nature (automotive engines, wind turbines etc.) and it is within these applications that the tribology of the oil system is important for long-term efficiency, reliability and long-term usage.
Within a mechanical system, how the oil acts with itself or the surrounding components is of great importance. Within a system, the forces of two surfaces coming together/apart is commonplace, as is many of the other potential interactions- frictional forces, wear effects, stress and strain and lubricative environments.
When two surfaces come together, the tribology is important, because to most observers the surface is smooth. But at the molecular level, every surface has roughness, even if it is at the Angstrom level. When an oil layer comes together with another oil layer, or an external surface, the contact is not made along the whole surface, but at certain points known as asperities (i.e. the points of roughness). The localized roughness points can cause local adhesion in oil systems, which may or may not be beneficial depending on the degree of lubricity required within the system.
The mechanism of lubricity itself can be explained through tribology and is the act of keeping two surfaces apart, namely component-component interfaces. Lubricity is achieved by placing layers of oil between the two surfaces, which then enables the two surfaces to slide over one another with a reduced friction and wear.
Wear is another product of tribology. Wear in an oil-based system (be it the oil or the lubricated components) occurs when the asperities of two surfaces come into contact with each other. The more contacts, the greater the wear. So, in an ineffective lubricant system, old oil system, or a wrong type of lubricant system, the amount of wear can increase if the lubrication is not as effective as it could be. That’s why oil is tested regularly as the wear is a direct result of the tribological effects.
Wear can be affected in three different ways. The first is through adhesive wear, where the breaking of the asperities occurs, and material detaches itself from the component. The second is abrasive wear and is where grooves end up in the softer of two materials, but no material is ejected into the oil system. The third and final type of wear is erosive, and is the most dangerous to many oil systems. It is the reason for why many oils require frequent changes after regular maintenance tests. Erosive wear occurs when particles (or even water droplets) that have gotten into the oil system break off other particles of the surrounding components, leading to a large increase of abrasive particulates within the lubricative oil system.
All the above processes have implications for many types of oil-based system and help to govern how the system performs a specific function, be it for lubricants, greases, for the automotive industry, for wind turbines, or otherwise. As the tribological effects within an oil system are so important, their analysis and maintenance are also important and the effectiveness of these tribological effects can be studied to determine whether an oil is still fit for purpose.
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Leonardo Centre: http://www.leonardocentre.co.uk/about-us/what-is-tribology
Imperial College London: http://www.imperial.ac.uk/tribology