Define viscosity of oil8/30/2023 ![]() ![]() As mentioned, the viscosity is the primary contributor to film thickness during hydrodynamic and elastohydrodynamic lubrication. The lubricant then possesses film strength and boundary lubrication properties.įilm strength can be described as the lubricant’s ability to lessen the effects of friction and control wear by means other than the film thickness. The base oil and additives are carefully blended together to produce the specific lubricant product (either oil or grease), which is formulated to mitigate the anticipated boundary conditions. This support involves wear and friction-control additives. When the hydrodynamic or elastohydrodynamic lubrication prerequisites are not met, the base oil will require support during what is called boundary contact conditions. There may also be concerns when the temperature increases too much, causing the viscosity to decrease, or excessive contamination contributes to abrasive contact in the film gap. Most machine designs and operating parameters will require instances when insufficient velocity exists, such as starts and stops or changes in directional motion. But what happens if these film thickness conditions are not met, such as when there is insufficient relative velocity, inadequate viscosity or too much load? ![]() In practice, it is best to keep machine surfaces separated, with the film thickness providing the best opportunity for reduced friction and wear. A full film separation remains, albeit a very thin one. This is called elastohydrodynamic lubrication. The base oil’s pressure-viscosity relationship allows the oil’s viscosity to increase temporarily due to the higher pressures. In fact, these pressure points play an important role. In applications with rolling contact (and thus negligible relative sliding motion), film thickness between the metal surfaces can still occur, even with greater localized pressure points. When the film thickness is the result of a balance between these factors, it is called hydrodynamic lubrication. These three factors are also influenced by other elements such as temperature and contamination. ![]() For the base oil to provide separation in this situation, there must be a balance of three contributing factors: the relative velocities, the base oil viscosity and the amount of load. After all, the primary intent is to avoid metal-on-metal surface contact. When you think of lubrication, what comes to mind? It might be the base oil creating a film thickness to separate two metal surfaces. This article will discuss the importance of a lubricant’s film strength and what impacts its effectiveness. It is heavily influenced by the lubricant’s base stock and additives. Film strength is one of the most critical lubricant properties for protecting a machine’s internal components from wear and degradation. ![]()
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