Lubricants performance

Lubricating performance Extreme pressure and anti-wear properties Oil separation... 

Porous bron2e and iron, a variety of plastics, carbon—graphite, wood, and mbber are widely used in dry sliding or under conditions of sparse lubrication. These materials have commonly allowed design simplifications, freedom from regular maintenance, reduced sensitivity to contamination, and good performance at low speeds and with intermittent lubrication. Although these materials are often used dry or with sparse lubrication, performance normally improves the closer the approach to full-film lubrication. 

An ATE requires high lubrication performance, high levels of oxidation stability to withstand the locally high operating temperatures, a degree of fluidity that ensures... 

Operational behavior in hydraulic systems (lubrication performance, temperature range and seal compatibility, for example) ... 

Two factors militate against the universal use of water-based fluids. Very severe machining operations call for a lubrication performance that is beyond the capacity of such fluids, and the design of some machine tools means that water cannot be used because of the risk of cross-contamination with machine lubricants. In these instances, neat cutting oil is the only fluid that can provide the required performance. 

With the increased speed and horsepower capabilities of modem chain drives, the role of lubrication has increased in importance. The precision roller chain is actually a series of connected journal bearings and it is essential that lubrication minimizes the metal-to-metal contact of the pin/bushing joints of the chain. Many factors affect lubrication performance and chain life including heat, improper lubrication, windage, contamination, and oil viscosity. 

When the length scale approaches molecular dimensions, the inner spinning" of molecules will contribute to the lubrication performance. It should be borne in mind that it is not considered in the conventional theory of lubrication. The continuum fluid theories with microstructure were studied in the early 1960s by Stokes [22]. Two concepts were introduced couple stress and microstructure. The notion of couple stress stems from the assumption that the mechanical interaction between two parts of one body is composed of a force distribution and a moment distribution. And the microstructure is a kinematic one. The velocity field is no longer sufficient to determine the kinematic parameters the spin tensor and vorticity will appear. One simplified model of polar fluids is the micropolar theory, which assumes that the fluid particles are rigid and randomly ordered in viscous media. Thus, the viscous action, the effect of couple stress, and... 

Huang, R, Wang, H. Z., Xu, L. G., Meng, Y. G., and Wen, S. Z., Numerical Analysis of the Lubrication Performances for Ultrathin Gas Film Lubrication of Magnetic Head/Disk with a New Finite Difference Method, Proceedings of IMECE05, Paper No. IMECE2005-80707,2005. 

Lubricity Additive - used to help prevent wear of high-pressure fuel injection equipment. Use is not permitted in aviation gasoline and can be used only by permission in civil jet fuel. Use is mandatory in military jet fuel grades. Topically, the corrosion inhibitor also functions in providing adequate fuel lubricity performance. 

Since the introduction of low-sulfur diesel fuel, much study has been completed to determine the lubricity properties of this fuel. Comparison of low-sulfur diesel with high-sulfur diesel has clearly revealed that fuel sulfur has a dramatic impact on the ability of fuel to provide a higher level of lubricity performance. A comparison of the lubricity performance of a typical high-sulfur diesel low-sulfur diesel and low-aromatic, low-sulfur diesel is shown in FIGURE 5-3. 

FIGURE 5-3. Comparison of the Lubricity Performance of Typical High-Sulfur Diesel Low-Sulfur Diesel and Low-Aromatic, Low-Sulfur Diesel Fuel... 

Certain compounds which have the ability to film or adsorb onto a metal surface are effective at improving fuel lubricity performance. These compounds include modified fatty acids, modified fatty amines, and other amine=based compounds. For years, the lubricity performance of jet fuel has been improved by treatment with organic acid based corrosion inhibitors. 

In recent years, the concern over fuel lubricity has led to the use of a high concentration of corrosion inhibitors to improve diesel fuel lubricity performance. The film formed on the metal surface by fatty acid type corrosion inhibitors improves fuel lubricity. However, the result of this overtreatment may lead to sticking of injection pump parts. 

Tests showed that liquid lubricants do not even provide adequate lubrication in the lower Vacuums of space simulators. Solid lubricants, such as molybdenum disulfide, tungsten disulfide. and the soft metals have given better results. However, the known data about space lubricants are results of simulator measurements made in the pressure range of 10 s to 1C6 torr which does not simulate real space conditions, and therefore, these available data cannot be considered completely valid. It can be expected that definite data on lubricant performance in a vacuum will be obtained by conducting tests in a simulator that reaches the low 10"10 torr range. At this press level, the monolayer formation time is increased to at least several hours which will result in a sufficient time span for observing the metal... 

Some thermally degraded byproducts react tribochemically with the friction iron surface to produce sulfide FeS. This is seen, for example, when elemental sulfur reacts tribochemically with the rubbing surface however, much greater quantities of elemental sulfur release are seen from dibenzyl DBDS than diphenyl DPDS disulfide, thus qualifying DPDS as a better lubrication performer (Plaza, 1987c and 1989 Plaza at al., 1997, 1999 and 2000). 

The final chapter, "Environmental issues , addresses lubricant performance and suggests ways to improve fuel efficiency of engines by the use of lower viscosity grade oils and the use of modifiers to reduce metal-metal friction. 

Lubricity and Abrasion Resistance. Specific plastic materials offer outstanding self-lubricating performance and abrasion resistance. 

Molybdenum is in Sub-Group VI A/B of the Periodic Table, and in the second series of transition elements. Transition elements are those which have an incomplete inner orbit in their atomic structure (see Table 3.1), and such an incomplete orbit is less stable than a filled orbit. The result is that the transition elements, and their compounds, show resemblances to each other and peculiarities in comparison with non-transition elements. It is therefore interesting that a number of compounds of other transition elements have been studied for solid lubricant use, and some of them have been found to be very effective, but no-one has yet shown any particular relationship between transition element structures and lubricating performance. The electron orbital assignments for these various elements are shown in Table 3.1. 

Molybdenum dioxide is highly abrasive, and its formation would be a serious disadvantage to lubrication performance, but in practice it seems clear that the formation of the dioxide is transitory or exceptional, and that the oxidation process normally produces the more harmless trioxide. 

Vacuum in itself has no harmful effects on the lubrication performance of molybdenum disulphide. The effect of conventional atmospheres containing oxygen and water vapour is to increase the friction and decrease the wear life of molybdenum disulphide lubricants. It follows that in high vacuum, where such contaminants are absent, the friction and wear behaviour are generally improved. 

Table 9.7 Some Organo-Molybdenum Compounds Studied for Lubricant Performance...

The lubricating performance of the lamellar crystal structure is strongly dependent on the inter-lamellar separation and bonding, and these can be modified by the intercalation of other substances between the lamellae. The general subject of intercalation will therefore be discussed before proceeding to descriptions of the individual lamellar solid lubricants. 

In 1970 Jamison and Cosgrove reported an interesting study of the relationship between the crystal structure and the lubrication performance of the sulphides and selenides of several of the transition metals in Groups 4, 5, 6 and 7 of the Periodic Table (see Table 14.2). They showed experimentally that satisfactory film formation and low friction were only obtained within certain closely-defined limits of crystal structure. It is not proposed here to attempt to present full details of the rather complex crystallographic considerations, but only to give a simplified version of the essential aspects of their findings. 

In the case of the equivalent niobium compounds, the same electronic effects are not present. He postulated that in pure stoichiometric niobium disulphide this results in poor lubrication. When good lubrication behaviour is observed, it is probably caused by additional niobium atoms intercalated between the lamellae, which contribute non-bonding electrons. On the basis of this theory, non-bonded atoms intercalated between the lamellae can increase the inter-lamellar spacing, whereas bonded intercalated atoms increase the resistance to inter-lamellar shear, and therefore the friction. However, an alternative interpretation is that certain intercalated atoms alter the interaction between the niobium atoms, allowing rearrangement to the 2H structure of molybdenum disulphide, and it is the favourable structure which provides good lubrication performance. 

Jamison found that low concentrations of intercalated copper or silver in niobium disulphides and diselenides promoted good lubricating performance. Higher concentrations increased the resistance to inter-lamellar shear, and therefore the friction, but improved high temperature performance due to the reduced intracrystalline shear and some sacrificial oxidation of the intercalated metals. 

Jamison, W.E., Structure and Bonding Effects on the Lubricating Performance of Crystalline Solids, ASLE Trens., 15, 296, (1972). 

Fleischauer, P.D., Fundamental Aspects of the Electronic Structure, Material Properties and Lubrication Performance of Sputtered M0S2 Films, Thin Solid Films, 154, 309, (1987). 

McConnell, B.D. and Mecklenburg, K.R., Solid Lubricant Compacts - an Approach to Long Term Lubrication Performance in Space, Lubric. Eng., 33, 544, (1977). 

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