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What is Lubrication?
Lubrication is the process or technique of using lubricants to reduce contact friction and wear between two surfaces. Lubricant research is a field of study in the field of chemistry.

Lubricants can be solids (such as molybdenum disulfide MoS2), solid/liquid dispersions (such as grease), liquids (such as oil or water), liquid-liquid dispersions, or gases.

Fluid lubrication systems are designed so that the applied load is carried partially or completely by hydrodynamic or hydrostatic pressure, which reduces solid interactions (and thus friction). friction and abrasion). Depending on the degree of surface separation, different lubrication modes can be distinguished.

Adequate lubrication allows machine components to operate smoothly, continuously, reduces wear rates, and prevents excessive stress or shock in bearings. When lubricants break down, components can rub destructively against each other, causing heat, localized welding, destruction and failure.

Understanding Lubrication

Lubrication is the control of friction and wear by creating a friction-reducing film between moving surfaces in contact. The lubricant used can be liquid, solid or plastic.

Although this is a valid definition, it fails to realize all that lubrication actually achieves.

Many different substances can be used to lubricate surfaces. Oils and greases are the most common. Grease consists of oil and thickener to get the consistency, while oil is actually a lubricant. Oils can be synthetic, vegetable or mineral as well as combinations of these.

The application determines which oil, often referred to as the base oil, should be used. In severe conditions, synthetic oils can be beneficial. Where environmental concerns are a concern, vegetable-based oils may be used.

Lubricants contain oils with additives that enhance, supplement or eliminate the properties within the base oil. The amount of additive depends on the type of oil and the application in which it will be used. For example, motor oil may have added dispersants.

Dispersants keep insoluble substances clumped together for removal by filtration during recirculation. In environments with extreme temperatures, from cold to hot, viscosity index (VI) improvers may be added. These additives are long organic molecules that stick together in cold conditions and separate in hotter environments.

This process changes the oil's viscosity and allows the oil to flow better in cold conditions while still maintaining its high temperature properties. The only problem with additives is that they can be depleted, and to restore them to adequate levels, often the oil quantity must be replaced.

The Role of Lubricants

The main functions of lubricants are:

- Reduce friction
- Prevents wear
- Protects equipment from corrosion
- Temperature control (heatsink)
- Contamination control (carries contaminants to filter or tank)
- Power transmission (hydraulic)
- Provides a liquid seal

Sometimes the functions of reducing friction and preventing wear are used interchangeably. However, friction is the resistance to movement, and wear is the loss of material due to friction, contact fatigue, and corrosion. There is a significant difference. In fact, not everything that causes friction (e.g., fluid friction) causes wear, and not everything that causes abrasion (e.g., gravitational erosion) causes wear. causes friction.

Reducing friction is the primary goal of the lubrication process, but there are many other benefits to the process. A lubricating film can help prevent corrosion by protecting the surface from water and other corrosive substances. Additionally, they play an important role in controlling contamination in the system.

The lubricant acts as a conduit in that it transports contaminants to the filters for removal. These fluids also aid in temperature control by absorbing heat from surfaces and transferring it to a point of lower temperature where it can be dissipated.

Lubrication Classification

There are three different types of lubrication: boundary, mixed, and total. Each type is different, but all rely on lubricants and additives in the oil to protect against wear.

- Fluid film lubrication
- Elastohydrodynamic lubrication
- Lubricate the boundary
- Mixed lubrication

1. Fluid Film Lubrication

Fluid film lubrication is a mode of lubrication in which, through viscous forces, the load is completely supported by the lubricant in the space or clearance between moving parts relative to another object (the part being lubrication), and avoid solid-solid contact.

In hydrostatic lubrication, external pressure is applied to the lubricant in the bearing to maintain the fluid lubricating film where it would otherwise be forced out.

In hydrodynamic lubrication, the movement of the contact surfaces, as well as the design of the bearing, pumps lubricating gear oil into the gearbox to maintain the lubricating film. This design of the gear can wear out when starting, stopping or reversing due to the breakdown of the lubricant film.

The basis of the hydrodynamic theory of lubrication is the Reynolds equation.

2. Elastohydrodynamic Lubrication

Mostly for unconformable surfaces or higher load conditions, bodies deform elastically upon contact. Such tension creates a load-bearing zone, creating an approximately parallel gap for the fluid to flow through.

Just as in hydrodynamic lubrication, the movement of the contacting parts creates flow-induced pressure, which acts as a bearing force on the contact area. In such high pressure regimes, the viscosity of the fluid can increase significantly.

When fully lubricating the elastohydrodynamic film, the lubricating film is created that completely separates the surfaces. Due to the close coupling between the hydrodynamic behavior of the lubricant and the elastic deformation upon contact with the solid, this lubrication regime is an example of fluid structure interaction.

Classical elasticity theory considers the Reynolds equation and the elastic deflection equation to deal with pressure and deformation in this lubrication regime. Contact between raised solid features, or thicknesses, can also occur, leading to mixed lubrication or boundary lubrication regimes.

3. Boundary Lubrication

Hydrodynamic effects are negligible. Bodies come into closer contact with each other as they age; The heat developed by the local pressures causes a condition known as stick-slip, and some of the dormant parts break off.

Under high temperature and pressure conditions, the chemically reactive components of the lubricant react with the contact surface, forming a highly durable layer or film on the moving solid surface (the boundary film). world) is capable of withstanding loads and abrasion or breakage is avoided. Boundary lubrication is also defined as the mode in which the load is carried by the surfaces instead of by the lubricant.

4. Mixed Lubrication

This mode is between the full elastic lubrication mode and the boundary lubrication mode. The lubricant film created is not sufficient to completely separate the bodies, but the hydrodynamic effects are significant.

Uses of Lubrication

Lubrication is necessary for the correct functioning of mechanical systems such as pistons, pumps, cams, bearings, turbines, gears, industrial chains, cutting tools, etc. In the absence of lubrication, the pressure between adjacent surfaces will create enough heat for the surfaces to rapidly deteriorate, which in rough conditions can weld the surfaces together, causing convulsions.

In some applications, such as piston engines, the membrane between the piston and cylinder wall also seals the combustion chamber, preventing combustion gases from escaping into the crankcase.

If an engine requires pressure lubrication, such as a plain bearing, there will be an oil pump and an oil filter. On early engines (such as Sab marine diesel engines) where the feed pressure was not necessary splash lubrication was sufficient.

Source: Collector