Lubrication oils variation

Lubricating oil used in intermittent service must show the least possible variation in viscosity with respect to temperature and must be changed at frequent intervals to remove the foreign matter collected during service. The stabiUty of such oil is therefore of less importance than the stabiUty of oil used in continuous service for prolonged periods without renewal. Lubricating oil for continuous service must be extremely stable because the engines in which it is used operate at fairly constant temperature without frequent shutdown. 

The on-line measurement of viscosity under plant conditions poses particular difficulties. This is due to the wide range of viscosities that can occur within a process plant, to the difficulty of obtaining reliable measurements (particularly for non-Newtonian fluids) and to the accuracy that is often required (e.g. better than within 1 per cent for lubricating oils). Variables which can affect the measured viscosity are the temperature, pressure and rate of flow of the sampled stream— quite apart from the normal errors that can occur in any similar instrument (e.g. due to variations in supply voltage and frequency, sample contamination, sample not being representative of the bulk fluid, etc.). Automatic temperature compensation is always required and, in the case of multiphase systems, the difficulty of obtaining a representative sample is considerable (see Section 6.9). In this instance... 

A variation in the time of flow when the walls of the tube are covered with an immiscible liquid, such as oleic acid, is really due to changes of surface tension, which are iniportant with some types of viscometer. It is possible, however, that some slip may occur with some lubricating oils, due to the regular reflexion of large molecules from the walls, as contrasted with the diffuse scattering of smaller molecules by irregularities of molecular dimensions in the walls. ... 

Due to variations of properties of crude oils from around the world it is difficult to obtain an ideal standard crude oil sample that could be used as a control standard. Fortunately, base oil blends with high viscosity and low viscosity free of metals are available from MBH (Conostan, London). These oils, which are representative of a wide range of crude and lubricating oils, are used to study analytical methods in terms of solubility, precision and accuracy using ICP-OES. Table 5.4 lists the properties of two such oils that are used as part of this study. 

Many contaminants and oil constituents contain metallic elements that can be measured to determine relative concentration. The most effective and least costly method for measuring metallic content of lubricating oils is by elemental spectroscopy for which there are several variations. 

For most purposes, a comparison is made between spilled samples and suspected source candidates. In the case of a ship being the suspected source, it is essential that reference samples be taken of all the oils carried on board the vessel, which might include cargo oils, fuel oU, lubricating oils and waste oils. In many cases attempts may be made to imply that not all the oU pollution came from one source, careful and detailed examination of contaminated sites such as beaches should be made to determine the uniformity of the spilled oil deposit. Any apparent variation in the type of oil should be sampled, the extent noted and supported by photographs. 

The oil-bath or oil-disk casing is used with the bath and disk methods of lubrication, with variations from the standard casing available depending on the chain speed and shaft center distances (Fig. 5.95). The second type of casing is used in outdoor applications when water. 

The costs for processing heavy oils such as neutral oils and cylinder stock are even less consistent. The great variation in these costs is due to the inherent differences in lubricating-oil stocks and the variety of treating and dewaxing operations that may be used. 

Figure 22 shows variation of the him thickness with velocities. The three curves in the hgure are results from the EHL solution, experimental data, and TFL solution, respectively. The maximum Hertzian contact pressure is 0.125 GPa and the atmosphere viscosity of oil is 0.062 Pa s. While the velocity is higher than 100 mm s, i.e., the him is thicker than 50 nm, all the results from EHL, TFL, and experimental data are very close to each other, which indicate that when in the EHL lubrication regime, bulk viscosity plays the main role and the results of three types are close to each other. When... 

Typical emission factors for metals cannot be derived from baseline characterization of auto exhaust by dynamometer tests, as performed by EPA, since attempts are made to keep variability of additives, oils, and lubricants to a minimum. Emphasis is placed rather on the eflFect of emissions as a function of variations in operating conditions. The data cited in Table X reflect this because test cycles identified as FTP, HWFET, and CFS differ significantly in the average speed (19.9, 49.9, and 35.0 mph, respectively) and in the extent of variability in operating mode (acceleration, deceleration, and cruise). 

Regional performance demand Different geographical regions have different market requirements. European oils tend to be for longer drain applications, up to 30,000 miles between oil drains, whereas North American market lubricants tend to be changed every 3000-10,000 miles. Additionally, differences between developed and developing markets have an effect on the required lubricant performance and hence the formulation and the lubricant drain interval. Local fuel variation also needs to be considered, e.g. the sulphur content of diesel, overall fuel quality based upon refinery processing and contamination of fuel. 

Oils and greases provide a relatively simple means of lubrication in spacecraft applications. They can give low torque variation and good thermal transfer properties when correctly specified. There are some fundamental problems with operation in vacuum and zero gravity, however, which should always be borne in mind. 

High-temperature coking resistance is checked by the panel coker test where an aluminium plate, held at temperatures ranging from 275 to 350°C, is splashed with lubricant and the deposited coke is weighed and rated. This procedure has many variations including methods to measure the effect of the oxidising effect of fuel oil contamination on lubricant stability. 

As developed by Dean and Davis, this empirical method expresses viscosity variation with temperature numerically, initially on a simple scale of 0 to 100, based on two sets of reference distillate fractions. These oils were from two crudes whose distillates had not been refined in any manner (i.e., they had not been dewaxed or solvent refined). The viscosity changes with temperature of the 0 reference oil fractions were large, while those of the fractions from the 100 reference were small. These assignments of 0 and 100 were of course arbitrary and reflected experience at that time. It was assumed in developing the method that all distillation fractions from each of these reference crudes had the same VI (and that approximately agreed with the current knowledge) and that this was true for all other crudes and their lubricant fractions. A further assumption was that the Vis of all oils would fall between 0 and 100. 

No longer the tools of today, these methods and their variations are common throughout the lubricant literature and familiarizing oneself with these methods is worthwhile. Results from these methods are still quoted today, but mainly for naphthenic oils. 

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