Lubrication

Introduction

The rubbing action of the components causes an excessive amount of heat to be generated. Whenever oil is poured between two surfaces, it generates a fluid film between them, which helps to keep the two pieces separated from one another and minimises the amount of friction.

It is a well-known truth that all machines or engines are made up of a collection of components, some of which are in motion and in contact with one another, and which perform relative actions to one another. Frictional forces are generated as a result of the motion, resulting in a loss of power, excessive wear of components, and eventually failure of the components.

Lubricants involving oil contain additives that improve, increase, or reduce the qualities of the base oil in which they are incorporated. The amount of additives used in an oil is determined by the type of oil used and the use for which it is intended. Adding a dispersion to engine oil, for example, is common practice.

A dispersant helps to keep insoluble materials conglomerated together so that it can be removed by the filter when the water is circulated. A viscosity index (VI) improver may be used in areas where temperature extremes occur, ranging from cold to hot, to improve viscosity. When exposed to freezing temperatures, these chemicals remain tightly bundled together, but when exposed to higher temperatures, they become disorganised.

As a result of this process, the oil’s viscosity is altered, allowing it to flow more freely in cold temperatures while retaining its high-temperature qualities. The only issue with additives is that they can become depleted over time, and in order to restore them to adequate levels, the oil volume must be changed in most cases.

Lubrication in brief

In a situation where two surfaces are in contact with each other and have relative motion with each other, lubrication is the process of making them smooth. This is accomplished by adding a material known as lubricant into the system, which reduces frictional forces. In reality, lubrication minimises the amount of energy required by a machine by minimising the frictional force between two machine components that are in relative motion with one another..

Although one of the primary goals of lubrication is to reduce friction, there are numerous other advantages to this process. Lubricating films can aid in corrosion prevention by shielding the surface from contact with water and other corrosive chemicals. Furthermore, they play a critical role in the prevention and management of contamination within systems.

The lubricant performs the function of a conduit, transporting pollutants to filters where they can be removed. Temperature control is also made possible by these fluids, which collect heat from surfaces and transmit it to a place of lower temperature where it may be dissipated.

Principle of Lubrication

When two machine components come into contact with each other and move in the same direction as each other, even though the metal surface has been smoothed by machining, there is always a significant amount of friction present.

Whenever the machine components are loaded while lubricating oil is being introduced into them, the load will attempt to drive the lubricating oil layer out of the surface, which will result in metal-on-metal contact between the two components. Based on the fact that when a shaft rotates in a bearing, it is lubricated by the addition of lubricating oil, this is a straightforward concept. Some amount of clearance is always supplied between the two sides of the shaft and the bearing for a variety of technical reasons. Because of centrifugal forces, when the shaft rotates, the lubricant has a tendency to rise up the shaft and into the bearing. The lubricant is sandwiched between two surfaces in a somewhat eccentric position.

Classification of Lubricants

There are three forms of lubrication: boundary lubrication, mixed lubrication, and full film lubrication. Each type is distinct.

Full-film lubrication:  Full-film lubrication can be divided into two types: hydrodynamic lubrication and elastohydrodynamic lubrication. It is possible to achieve hydrodynamic lubrication when two surfaces in sliding motion (relative to each other) are completely separated by a layer of fluid.

Elastohydrodynamic lubrication:  Elastohydrodynamic lubrication is similar to hydrodynamic lubrication, except it occurs when the surfaces are in a rolling motion instead (relative to each other). Because the film layer is significantly thinner than that of hydrodynamic lubrication, the pressure exerted on the film layer is larger in elastohydrodynamic conditions than in hydrodynamic lubrication. The term “elastohydrodynamic” refers to the fact that the film elastically deforms the rolling surface in order to lubricate it.

Boundary lubrication: Shock-loading circumstances and frequent starts and stops are two characteristics of boundary lubrication that are seen in many applications. If complete films cannot be achieved due to speed, load, or other causes, certain lubricants contain extreme-pressure (EP) or anti-wear (AW) compounds that can assist in preserving surfaces.

In addition, these chemicals attach to metal surfaces, where they produce a protective coating that shields the metal from wear and tear. Boundary lubrication occurs when two surfaces come into contact in such a way that only the EP or AW layer serves to prevent them from further contact. High friction, heat, and other unpleasant effects result as a result of this practice, which is not recommended.

Mixed lubrication:  Boundary lubrication and hydrodynamic lubrication are combined to provide mixed lubrication. Despite the fact that the majority of the surfaces are separated by a lubricating layer, the asperities remain in contact with one another. This is when the additives come back into play once more.

Conclusion

There are a plethora of various compounds that may be used to lubricate a surface. The most frequently encountered substances are oil and grease. Grease is made up of oil and a thickening agent to give it its consistency, while the oil is the one that actually lubricates the joints and machinery. Oils can be made from synthetic, vegetable, or mineral sources, or a combination of these sources.

The application decides which oil should be used, which is generally referred to as the base oil in the industry. Synthetic oils can be quite beneficial in harsh situations. Where the environment is a concern, vegetable base oils may be used instead of mineral base oils.