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Understanding the three types of lubrication

Lubricants like oils, fluids and grease are produced by leading manufacturers across the world, such as Aeroshell, Quaker-Houghton and Castrol, and have been designed to keep equipment operating smoothly. These oils have been cleverly developed to answer the demand of a wide range of equipment, from passenger vehicles to stationary agricultural machinery. Lubricant makers often work alongside equipment manufacturers to create oils specially designed for products that not only meet the requirements of machinery specs, but also the intense industry demands and conditions they must operate efficiently under.

When lubricant producers engineer a grease, oil or fluid, it will always fall into one of three categories of lubrication: full film, boundary or mixed. In the following passages, we explore what each category entails:

Full film lubrication

Hydrodynamic and elastohydrodynamic are the two forms of full film lubrication. Hydrodynamic lubrication is defined when two individual surfaces, relative to one another, are in sliding motion and are kept entirely apart by a fluid-based film.

While similar to hydrodynamic lubrication, elastohydrodynamic lubrication is instead described by the action of surfaces relative to one another that are involved in a rolling motion, with a film of fluid separating them. The layer of film for elastohydrodynamic lubrication conditions is far thinner than properties found in hydrodynamic lubrication, and the film is put under far more intense pressure. The name elastohydrodynamic is used to describe this form of full film due to the way the film deforms the rolling surfaces so it can lubricate them effectively.

Even among the smoothest and most polished surfaces of machine parts, some irregularities can be found. On a microscopic scale, these imperfections create peaks and troughs in the surface. The peaks are referred to as asperities. For the required conditions for full film to be answered effectively, the lubricant film needs to be thicker than the asperities length. Full film lubrication is the best type of lubricant for protecting surfaces efficiently.

Boundary lubrication

Boundary lubrication is used in conjunction with equipment that features frequent stops and starts, and where protection from sudden shocks is critical. When factors like load and speed mean that a full film lubricant is not possible to achieve, some oils will be infused with additives for anti-wear and extreme pressure to provide further protection for surfaces.

These powerful additives adhere to metal surfaces, forming a protective layer for the metal, defending it against wear during operation. Boundary lubrication works when two surfaces make contact, and the additive layer provides sole protection. This scenario, however, is not ideal, as it can cause extreme heat and high levels of friction, among other unwanted effects.

Mixed lubrication

A cross between hydrodynamic and boundary lubrication, mixed lubrication offers a middle ground. For the most part, the majority of surfaces enjoy the protection of a lubricating full film layer, although to some extent the asperities will make contact with one another and will rely on the extreme pressure and anti-wear additives for enhanced protection.

While each of the lubrication types differ from one another, they all depend on a dedicated lubricant, like an oil, and a carefully balanced additive formula that offers additional protection from wear.

1 thought on “Understanding the three types of lubrication

  1. Very well explained. Lubricants have one main function: to reduce friction. In addition to reducing friction, lubricants help keep moving parts from getting stuck or wearing out too quickly.

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