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Tuesday, 30 April 2013

What is lubrication exactly?

Have you ever tried to define what is lubrication?

We all have a pretty good idea of what lubrication is, but the term has come to mean a lot more than overcoming friction and wear. The official dictionary definition of what lubrication is, is; the application of an oily or greasy substance in order to diminish friction.

What is a lubricant?

Oil and grease are the most common lubricants. Grease is composed of oil and a thickening agent to obtain its consistency, while the oil is what actually lubricates.

Oils can be synthetic, vegetable or mineral-based as well as a combination of these. The application determines which oil, commonly referred to as the base oil, should be used. In extreme conditions, synthetic oils can be
beneficial. Where the environment is of concern, vegetable base oils may be utilized.

Lubricants have additives that enhance, add or suppress properties within the base oil. The amount of additives depends on the type of oil and the application for which it will be used.

For instance, engine oil might have a dispersant added to keep insoluble matter conglomerated together to be removed by the filter upon circulation. In environments that undergo extremes in temperature, from cold to hot, a viscosity index (VI) improver may be added. The only problem with additives is that they can be depleted, and in order to restore them back to sufficient levels, generally the oil volume must be replaced.

What are the functions of lubricants?

Reducing friction is a key function of lubrication, but there are many other benefits of this process:
  • Lubricating films can help prevent corrosion by protecting the surface from water and other corrosive substances. 
  • Controlling contamination within the lubrication system. The lubricant works as a conduit in which it transports contaminants to filters to be removed. 
  • Lubricants also aid in temperature control by absorbing heat from surfaces and transferring it to a point of lower temperature where it can be dissipated.

What are the types of lubrication?

 There are three different types of lubrication: 

  • Boundary. 
  • Mixed. 
  • Full film. 
Each type is different, but they all rely on a lubricant and the additives within the oils to protect against wear.

Full-film lubrication can be broken down into two forms:
  • Hydrodynamic lubrication occurs when two surfaces in sliding motion (relative to each other) are fully separated by a film of fluid. 
  • Elastohydrodynamic lubrication is similar but occurs when the surfaces are in a rolling motion (relative to each other). The film layer in elastohydrodynamic conditions is much thinner than that of hydrodynamic lubrication, and the pressure on the film is greater. It is called elastohydrodynamic because the film elastically deforms the rolling surface to lubricate it. 
Boundary lubrication is found where there are frequent starts and stops, and where shock-loading conditions are present.

Some oils have extreme-pressure (EP) or anti-wear (AW) additives to help protect surfaces in the event that full films cannot be achieved due to speed, load or other factors. These additives cling to metal surfaces and form a sacrificial layer that protects the metal from wear.

Boundary lubrication occurs when the two surfaces are contacting in such a way that only the EP or AW layer is all that is protecting them. This is not ideal, as it causes high friction, heat and other undesirable effects.

Mixed lubrication is a cross between boundary and hydrodynamic lubrication. While the bulk of the surfaces are separated by a lubricating layer, the asperities still make contact with each other. This is where additives again come into play.

The best definition of what lubrication is.

With a better understanding of this process, it should be easier to define exactly what lubrication is:

It’s a process of either separating surfaces or protecting them in a manner to reduce friction, heat, wear, and energy consumption. This can be accomplished by using oils, greases, gases or other fluids.

For the most effective lubrication contact Habot Synthetic Lubricants for advice on our range of high performance quality synthetic lubricants.