The surface chemical evidence of the tribofilms is measured by electrical contact resistance and SEM/EDS surface chemical analysis []. Theory of Boundary Lubrication Boundary and extreme-pressure regimes of lubrication often coexist in tribological situations where hydrodynamic, mixed and elasto-hydrodynamic lubrication are ineffective. In this case, the occurring lubrication mechanisms include adsorption, sacrificial films, amorphous layers etc. on the contacting surfaces. These interacting mechanisms ensure that the machinery is kept in operation. Tribologists continue to develop the understanding of boundary lubrication mechanisms because of their practical importance in automotive contacts such as piston cylinder liner, and steel gears. Also, metal-working tools employ at least one of these mechanisms for prevention of seizure, severe wear and high coefficients of friction []. The additives in the lubricant control the boundary lubrication mechanisms. The cost of the additives is usually very low compared to that of the machinery being lubricated. Therefore, the additives can be sacrificed for large tribological benefits. The additives form protective layers that reduce coefficients of friction and wear loss. The lubricating mechanisms are related to the load capacity and interfacial frictional temperature. The principle of boundary lubrication is explained, based on coefficient of friction []. The coefficient of friction, COF or µ, is defined as the ratio of the frictional force and the normal load applied to the surface. ‘F’ ‘W’ = µ Equation 34 Interfacial contacts occur at asperities peaks which are somewhat dry. Therefore, the true total contact area is sum of the individual contact areas between the asperities. If the adhesion component of friction is the main friction mechanism between the asperities, and that other effects like ploughing are low; then the frictional force is: F = Equation 35 Where: F is the frictional force, N At is the true contact area, m2 is the effective shear stress of the material, Pa The applied load can be expressed in terms of contact area, i.e.:
The surface chemical evidence of the tribofilms is measured by electrical contact resistance and SEM/EDS surface chemical analysis []. Theory of Boundary Lubrication Boundary and extreme-pressure regimes of lubrication often coexist in tribological situations where hydrodynamic, mixed and elasto-hydrodynamic lubrication are ineffective. In this case, the occurring lubrication mechanisms include adsorption, sacrificial films, amorphous layers etc. on the contacting surfaces. These interacting mechanisms ensure that the machinery is kept in operation. Tribologists continue to develop the understanding of boundary lubrication mechanisms because of their practical importance in automotive contacts such as piston liner, and steel gears. Also, metal-working tools employ at least one of these mechanisms for prevention of seizure, severe wear and high coefficients of friction []. The additives in the lubricant control the boundary lubrication mechanisms. The cost of the additives is usually very low compared to that of the machinery being lubricated. Therefore, the additives can be sacrificed for large tribological benefits. The additives form protective layers that reduce coefficients of friction and wear loss. The lubricating mechanisms are related to the load capacity and interfacial frictional temperature. The principle of boundary lubrication is explained, based on coefficient of friction []. The coefficient of friction, COF or µ, is defined as the ratio of the frictional force ‘F’ and the normal load ‘W’ applied to the surface. µ = Equation 34 Interfacial contacts occur at asperities peaks which are somewhat dry. Therefore, the true total contact area is sum of the individual contact areas between the asperities. If the adhesion component of friction is the main friction mechanism between the asperities, and that other effects like ploughing are low; then the frictional force is: F = Equation 35 Where: F is the frictional force, N At is the true contact area, m2 is the effective shear stress of the material, Pa The applied load can be expressed in terms of contact area, i.e.: cylinder