Viscosity of lubricating oil

Volarovich MP (1944) The low-temperature viscosity of lubricant oils. Moscow Ed USSR Acad Sd (in Russian)... 

The viscosity of lubricating oil is a measure of its flow characteristics. It is generally the most important controlling property for manufacture and for selection to meet a particular application. The viscosity of a mineral oil changes with temperature but not normally with high stress and shear rate (ASTM D-5275, ASTM D-5481,ASTM D-5684, IP 294), unless specihc additives that may not be shear stable are included to modify the viscosity-temperature characteristics. Explosions can also result when lubricating oil is in contact with certain metals under high shear conditions (ASTM D-3115). 

The increase in Staudinger index with temperature is technologically made use of in the case of the so-called viscosity improvers (VI). The viscosity of lubricating oils decreases as the temperature rises. This increase in fluidity is not always desirable, so macromolecules are added to the lubricant such that they dissolve in the oil and are in the theta state, approximately, at the lowest application temperature. With increasing temperature, the viscosity of the lubricating oil indeed falls. The Staudinger index [f/] of the added polymer, on the other hand, increases. With a suitable choice of one or more polymers as additives, a compensation of both effects can be attained, as seen by writing equation (9-139), with = ( — i)/ i. in the form... 

TWo limiting conditions exist where lubrication is used. In the first case, the oil film is thick enough so that the surface regions are essentially independent of each other, and the coefficient of friction depends on the hydrodynamic properties, especially the viscosity, of the oil. Amontons law is not involved in this situation, nor is the specific nature of the solid surfaces. 

A number of higher n-alkyl methacrylate polymers have found commercial usage. The poly-(n-butyl-), poly-(n-octyl-) and poly-(n-nonyl methacrylate)s have found use as leathering finishes whilst polyflauryl methacrylate) has become useful as a pour-point depressant and improver of viscosity temperature characteristics of lubricating oils. 

Lube oil extraction plants often use phenol as solvent. Phenol is used because of its solvent power with a wide range of feed stocks and its ease of recovery. Phenol preferentially dissolves aromatic-type hydrocarbons from the feed stock and improves its oxidation stability and to some extent its color. Phenol extraction can be used over the entire viscosity range of lube distillates and deasphalted oils. The phenol solvent extraction separation is primarily by molecular type or composition. In order to accomplish a separation by solvent extraction, it is necessary that two liquid phases be present. In phenol solvent extraction of lubricating oils these two phases are an oil-rich phase and a phenol-rich phase. Tne oil-rich phase or raffinate solution consists of the "treated" oil from which undesirable naphthenic and aromatic components have been removed plus some dissolved phenol. The phenol-rich phase or extract solution consists mainly of the bulk of the phenol plus the undesirable components removed from the oil feed. The oil materials remaining... 

This technology has been utilized by BP Chemicals for the production of lubricating oils with well defined characteristics (for example, pour point and viscosity index). It is used in conjunction with a mixture of olefins (i.e., different isomers and different chain length olefins) to produce lubricating oils of higher viscosity than obtainable by conventional catalysis [33]. Unichema Chemie BV have applied these principals to more complex monomers, using them with unsaturated fatty acids to create a mixture of products [34]. 

Viscosity is one of the most important properties of lubricating oil. The actual viscosity of oil samples is compared to an unused sample to determine the thinning of thickening of the sample during use. Excessively low viscosity will reduce the oil film strength, weakening its ability to prevent metal-to-metal contact. 

An important point to remember with over-slung worm gears is that they are not immersed in the lubricant and the oil must be fed to the point of contact. The viscosity of the oil is important here, as it must not drain too quickly from the contact area. Manufacturers because of the particular lubrication problems involved with worm gears often prefer a mineral oil compounded with fatty oil. 

The unit of Pf here is MPa is the kinetic viscosity of lubricant in mm /s u is the velocity in mm/s, for the oil without polar additives, k is 23.5 X 10". If the tribo-pairs need to be lubricated with the fluid film in the TFL and EHL regime, the lubricant and the rolling speed should be chosen according to the pressure applied as Eq (9) so as to make that the liquid factor L is larger than the failure fluid factor L. Otherwise, the liquid film caimot be maintained under the pressure added. 

The materials used to be employed for making tribo-pairs are metals or metal oxides that belong to a high-energy surface so that it will exert influence on the arrangement of lubricant molecules nearby the solid surfaces. This contributes mainly to the viscosity variety of lubrication oil near to the solid surface. 

Roelands, C. J. A., Vlugter, J. C., and Waterman, H. I., "The Viscosity Temperature Pressure Relationship of Lubrication Oils and Its Correlation with Chemical Constitution, ASME J. Basic Eng., 1963, pp. 601-610. 

The contact ratios for lubricants with different viscosities are plotted in Fig. 37 as a function of speed. The decreasing rates vary significantly due to the difference in viscosities. For the maximum viscosity of tested oil 13606 (100 mm /s), the decreasing rate of contact ratio with speed is highest, and the contact ratio becomes zero at the speed lower than 2 mm/s. For the lower viscosity of lubricants such as oil... 

There have been some examples of the use of LDMS applied to the analysis of compounds separated via TLC, although not specifically dealing with polymer additives [852]. Dewey and Finney [838] have described direct TLC-spectroscopy and TLC-LMMS as applied to the analysis of lubricating oil additives (phenolic and amine antioxidants, detergents, dispersants, viscosity index improvers, corrosion inhibitors and metal deactivators). Also a series of general organics and ionic surfactants were analysed by means of direct normal-phase HPTLC-LMMS [837]. Novak and Hercules [858] have... 

Applications Over the last 20 years, ICP-AES has become a widely used elemental analysis tool in many laboratories, which is also used to identify/quantify emulsifiers, contaminants, catalyst residues and other inorganic additives. Although ICP-AES is an accepted method for elemental analysis of lubricating oils (ASTM D 4951), often, unreliable results with errors of up to 20% were observed. It was found that viscosity modifier (VM) polymers interfere with aerosol formation, a critical step in the ICP analysis, thus affecting the sample delivery to the plasma torch [193]. Modifications... 

Important applications of liquid-liquid extraction include the separation of aromatics from kerosene-based fuel oils to improve their burning qualities and the separation of aromatics from paraffin and naphthenic compounds to improve the temperature-viscosity characteristics of lubricating oils. It may also be used to obtain, for example, relatively... 

Lube oil solvent refining includes a collection of subprocesses improving the quality of lubricating oil stock. The raffinate or refined lube oils obtain improved viscosity, color, oxidation resistance, and temperature characteristics. A particular solvent is selected to obtain the desired quality raffinate. The solvents include furfural, phenol, sulfm dioxide, and propane. 

Twenty-five years ago the dewaxing processes available to the refiner of lubricating oils were the cold pressing method applicable only to low viscosity distillates and the cold settling and centrifuge methods applicable to certain residual oils. A vast amount of... 

While most bearings depend on the viscosity of the oil for the formation ol a lubricating film (0.01)01 lo 0.11020.0(125 to 0.051 nun thick), iherc arc many cases where this is not feasible and successful lubrication depends on the formation of veiy thin films t III to It) A thicki. This was geneiallr thoughl to occur through preferential adsorption by the solid surface of polar compounds (c.g.. naplhihenic acids, sulfur compounds) present m small ainounls In the otl. 

Since the viscosity-temperature coefficient of lubricating oil is an important expression of its suitability, a convenient number to express this property is very useful, and hence, a viscosity index (ASTM D-2270) was derived. It is established that naphthenic oils have higher viscosity-temperature coefficients than do paraffinic oils at equal viscosity and temperatures. The Dean and Davis scale was based on the assignment of a zero value to a typical naphthenic crude oil and that of 100 to a typical paraffinic crude oil intermediate oils were rated by the formula ... 

The equation uses molar mass and specific temperature as the input parameters and offers a means of estimation of the viscosity of a wide range of petroleum fractions. Other work has focused on the prediction of the viscosity of blends of lubricating oils as a means of accurately predicting the viscosity of the blend from the viscosities of the base oil components (Al-Besharah et al., 1989). 

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