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# viscosity of lubricants under elastohydrodynamic conditions.

Written in English

Edition Notes

M.Sc. thesis. Typescript.

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The Physical Object ID Numbers Series Theses Pagination 1 vol Open Library OL13730977M

Chaohui Zhang, in Advances in Ceramic Matrix Composites (Second Edition), Elastohydrodynamic lubrication (EHL) Elastohydrodynamic lubrication (EHL) is the typical regime for friction pairs having elastic contact under very high pressure in unconformal contact, such as ball bearings and gears.

EHL is a development of hydrodynamic lubrication, which takes into account the. The different regimes of behaviour in the elastohydrodynamic lubrication of rollers are displayed on a chart whose rectangular co-ordinates express the influence of elasticity of the solids and variation of viscosity of the lubricant with pressure by: A technique is described for solving the inverse lubrication problem under point contact elastohydrodynamic conditions, i.

the calculation of a film thickness and. to know lubricant behavior at high stresses and under fast changing conditions. A significant progress in studying high pressure lubricant rheology and lubricant viscosity is done in [Bair, ].

For many lubricants their viscosity significantly increases with pressure and decreases with Size: KB. Elastohydrodynamic lubrication (EHL) is a mode of fluid-film lubrication in which hydrodynamic action is significantly enhanced by surface elastic deformation and lubricant viscosity.

Sadeghi, in Tribology and Dynamics of Engine and Powertrain, Introduction. The formation of a thin lubricant film between the mating surfaces of rolling/sliding non-conformal machine elements is commonly referred to as elastohydrodynamic lubrication, which is abbreviated as EHL or major factors influencing EHL are the elastic deformation of the contacting bodies due to the.

The stringent and often competing requirements of high fuel economy and low emissions are placing increasing emphasis on the selection of appropriate base oils for modem engine lubricants.

Two properties now recognized as important in engine oil design are the elastohydrodynamic (EHD) traction coefficient and the pressure-viscosity coefficient. bean (SBO), and jojoba (JO) seed oils under elastohydrodynamic (EHD) conditions were investigated to determine whether differ-ences in their chemical and physical properties affect their EHD properties.

Polyalphaolefin (PAO), whose EHD properties have been reported before, was used as the reference synthetic oil. The. The viscosity of an industrial oil is usually specified at 40 0C ( F). However different formulations may result in two oils that have identical viscosities at C, but very different viscosities at another temperature, e.g., C (00F) This difference in the rate of change is because the two oils have different “viscosity indexes” (VI.

Under these pressures, it would appear that the oil would be entirely squeezed from between the wearing surfaces. However, viscosity increases that occur under extremely high pressure prevent the oil from being entirely squeezed out.

Consequently, a thin film of oil is maintained. The impact of lubricant to the vibration of gearbox is concerned. Using average equivalent curvature radius and Reynolds equation, the elastohydrodynamic lubrication model for helical gearbox is established.

Simulation result shows that the vibration of gearbox increases with the reduction of lubricant viscosity and the lubricant viscosity is lower the impact is bigger.

Therefore, under slow speed, low film thickness conditions, the contact effectively operates within a viscous boundary layer, generating an elastohydrodynamic-type film much thicker than predicted from the viscosity of the bulk lubricant.

As the speed is raised the contact emerges from this boundary layer and reverts to elastohydrodynamic. Elastohydrodynamic Lubrication (EHL) is commonly known as a mode of fluid-film lubrication in which the mechanism of hydrodynamic film formation is enhanced by surface elastic deformation and lubricant viscosity increase due to high pressure.

It has been an active and challenging field of research since the s. Increasing efforts to reduce frictional losses and the associated use of low-viscosity lubricants lead to machine elements being operated under mixed lubrication. Consequently, wear effects are also gaining relevance. Appropriate numerical modeling and predicting wear in a reliable manner offers new possibilities for identifying harmful operating conditions or for designing running-in procedures.

The ability to calculate and precisely predict pressure-viscosity data of lubricants is important for the characterization of friction in machine components that operate in the elastohydrodynamic lubrication regime.

Elastohydrodynamic lubrication involves friction pairs having elastic contact under very high pressure in nonformal contact. Fig. 1: Pressure-viscosity dependence curve under isothermal conditions (at C) for a lubricant, α* is the slope of the secant between 0 and GPa (data collected from Sergeant Jr.

[]). Table 1: Empirical models for lubricant’s pressure-viscosity characteristics (Sargent Jr. []). This review of elastohydrodynamic lubrication (EHL) was derived from many excellent sources (Refs. 1–5). The review of Blok’s flash temperature theory was derived from his publications (Refs.

6–9). An excellent general reference on all aspects of tribology is the Encyclopedia of Tribology (Ref. 10). "Elastohydrodynamic lubrication (EHL) is a relatively new area in the development of lubrication theory and practice.

This monograph is devoted to selected performances of liquid lubricants, particularly mineral oils and synthetic fluids. combines asymptotic and numerical techniques to solve EHL problems for line and point contacts. Under some conditions, such as in the elastohydrodynamic lubrication state, the density of a lubricant should be considered to be variable.

Viscosity varies significantly with temperature and pressure. In elastohydrodynamic lubrication, both the viscosity and density of a lubricant significantly vary with temperature and pressure.

As mentioned, the viscosity is the primary contributor to film thickness during hydrodynamic and elastohydrodynamic lubrication.

When the base oil viscosity is insufficient to overcome metal-to-metal surface contact, the base oil and additive chemistry work together to create a. Book Search tips Selecting this option will search all publications .fluid The more recent NEMD works provided insights into shear localization and heat transport in lubricants under elastohydrodynamic conditions.

36–38 J. “ Nonempirical free volume viscosity model for alkane lubricants under severe pressures. There is an ongoing debate concerning the best rheological model for liquid flows in elastohydrodynamic lubrication (EHL). Due to the small contact area and high relative velocities of bounding solids, the lubricant experiences pressures in excess of MPa and strain rates that are typically $$10^5{-}10^7\,\text {s}^{-1}$$.The high pressures lead to a dramatic rise in Newtonian viscosity.

To optimize the balance between low wear and low friction, machine designers specify a lubricant with a viscosity suffi cient to generate hydrodynamic or elastohydrodynamic oil fi lms that separate the machine’s interacting surfaces, but not too high to induce excessive viscous drag loss.

Under these conditions, liquid lubricants can exhibit properties very different from those observed under ambient conditions and even low molecular weight organic liquids can be non-Newtonian.

Knowledge of the rheological behaviour of lubricants in EHD contacts is crucial for accurate prediction of friction, wear and fatigue life of engineering. Lubrication properties of refrigeration lubricants were investigated in high pressure nonconforming contacts under different conditions of temperature, rolling speed, and refrigerant concentration.

The program was based upon the recognition that the lubrication regime in refrigeration compressors is generally elastohydrodynamic or hydrodynamic, as determined by the operating conditions of the.

The first is a high performance base oil with a low traction coefficient, which translates to low viscosity under high pressure conditions. This decreases the shear resistance between sliding surfaces under elastohydrodynamic lubrication (EHL) conditions, which contributes in improving the fatigue life of bearings and other components.

primarily used for elastohydrodynamic lubrication because they exhibit pressure-dependent viscosity, also known as piezo-viscosity. Mixed lubrication is the regime where the conditions are between hydrodynamic and boundary, either because the viscosity or velocity are too low, or the load is too high to permit complete separation of the surfaces.

Conditions equivalent to using solid materials of bronze, steel, and silicon nitride, and lubricants of paraffinic and naphthenic mineral oils are considered in obtaining the exponent on the. Elastohydrodynamic lubrication (EHL) – a difficult word to pronounce – is effectively the secret to how we at ExxonMobil approach lubrication.

The most important aspect of lubrication is viscosity – oil’s resistance to flow or “thickness.” Finding the right viscosity for. triboﬁlms, as well as of the shearing of the lubricant ﬁlm.

Elastohydrodynamic lubrica-tion (EHL) is a lubrication regime which is characteristic for contacts found in machine and further developed to enable the study edge effects under variable operating conditions the viscosity and volume of the lubricant.

The model was utilized. Despite the fact that the synovial fluid viscosity is relatively very high under the initial rest conditions ($\mu_0 = 5 \text{Pa}\cdot\text{s}$), the early time response exhibits a much lower viscosity, closer to that of water (Figure 6a).

This occurs because the peak fluid film velocity is on the order of $15 \, \text{m}/\text{s}$ and the. The rheological behaviour of the lubricant in an elastohydrodynamic contact depends upon the properties of the fluid and the imposed conditions of load, speed and temperature.

For a lubricant of known rheological properties, it is shown how a ‘map’ can be constructed in which different areas of the map correspond to different regimes of. This paper describes an experimental study on dimple formation under elastohydrodynamic lubrication (EHL) conditions.

The oil film thickness between a ball surface and a glass disk was measured using optical interferometry, and the temperatures of both the surfaces and of the oil film averaged across it were measured using an infrared emission technique.

@article{osti_, title = {Elastohydrodynamic Lubrication with Polyolester Lubricants and HFC Refrigerants, Final Report, Volume 2}, author = {Gunsel, Selda and Pozebanchuk, Michael}, abstractNote = {Lubrication properties of refrigeration lubricants were investigated in high pressure nonconforming contacts under different conditions of temperature, rolling speed, and refrigerant concentration.

Predicting friction by simply knowing the viscosity of the lubricant is rather difficult. Therefore, tribometers with friction measuring system are generally used to examine the relationship between friction and viscosity for a specified system operating in mixed, starved, boundary, or elastohydrodynamic lubrication condition (see Figure 1).

The book thoroughly addresses all aspects of the topic, from viscosity and rotor-bearing dynamics to elastohydrodynamic lubrication and fluid inertia effects. Fully worked examples, analytical and numerical methods of solutions, practice problems, and detailed illustrations are included in this authoritative reference.

the oil viscosity changes with temperature, the better its lubricating performance at high and low temperatures and the higher its VI. Generally, higher VI is preferred for lubricants. To increase the viscosity index of a lubricant, high-molecular-weight VI-improving additives are sometimes added to the lubricant.

The calculation results show that, under the pure rolling condition, temperature rise of oil film temperature is mainly caused by the compression work and shear heat at inlet and the heat in contact zone mainly comes from the inlet and the heat conduction around; the temperature rise results in oil viscosity lower and the lubricating film.

Ehret P, Dowson D and Taylor C () On lubricant transport conditions in elastohydrodynamic conjuctions, Proceedings of the Royal Society of London.

Series A: Mathematical, Physical and Engineering Sciences,(), Online publication date: 8-Mar This study provides quantitative insight into the use of ester-based lubricants for low friction through the entire lubrication regime (boundary to full film) by utilization of suitable type and size of the ester base stocks.

KW - elastohydrodynamic lubrication. KW - ester. KW - friction. KW - synthetic base stocks. KW - viscosity. The essential function of oil is that of keeping moving elements separated.

The amazing feature of oil is how it does this by its capacity to increase in viscosity under heavy load conditions. This is called elastohydrodynamic lubrication and it happens when the rolling element and mating surface (ball and race) elastically deform to enlarge.Understanding Basic Lubrication Regimes.

A lubricant’s primary function is to provide a durable film that controls friction and wear between surfaces; however, the level of protection it provides is dictated by the condition or “regime” it works under.In this study the lubricants were tested between a hard and soft surface under a defined load, with frictional force plotted over a range of sliding speeds.

Fig. 4: Stribeck curves reveal boundary, mixed and elastohydrodynamic lubrication regimes.

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