Lubricating Composites

In some publications bonded coatings are described as composites, and technically the description is correct, but it is convenient to use the term composite only for materials in three-dimensional or bulk form in order to differentiate clearly between them and bonded coatings. Composites can generally be described in terms of one or more dispersed phases in a continuous solid matrix, although there are some, such as resin-impregnated fabrics, which are not readily described in this way. 

The two purposes, of lubricant supply or friction reduction, are of course not entirely distinct, since continuing friction reduction requires a continuing supply of lubricant. The difference lies in the fact that the amount of lubricant required to maintain low friction of the composite itself is relatively small, probably restricted to a film which may be only a few molecules thick. The more general lubrication of a bearing system will require an additional supply of lubricant which is at least sufficient to provide an equivalent film on all the bearing surfaces involved. With the inevitable wastage inherent in movement of lubricant to other surfaces, the lubricant demand will be much greater than for self-lubrication alone. 

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Lubricants. TeUurides of titanium, 2irconium, molybdenum, tungsten, and other refractory metals are heat- and vacuum-stable. This property makes them useful in soUd self-lubricating composites in the electronics, instmmentation, and aerospace fields (see Lubrication and lubricants). Organic teUurides are antioxidants in lubricating oUs and greases. 

J. F. Argillier, A. Audibert, P. Marchand, A. Demoulin, and M. Janssen. Lubricating composition including an ester-use of the composition and well fluid including the composition. Patent US 5618780,1997. 

The main cause of DPF ageing (and thus of its functional characteristics) is the accumulation of lubricant residues, which is directly proportional to the engine lubricant consumption and to the lubricant composition (ashes rate). 

Obtain specific properties using, for example, a self-lubricating composite insert. Discontinuous fibre reinforced thermoplastic composites can also be overmoulded onto GMT sheets. 

Dithiyl radicals seem to be especially attractive because they can form extended homopolymer films. If one uses a simple compound that is capable of forming dithiyl radical, then that can open a way for formulation of a lubrication composition. For example, a poly(disulfide) was obtained as a result of a two-electron transfer to 2,5-di(thiocyanato)thiophene (Scheme 8.16) (Todres et al. 1979, Todres 1991). 

Uses Ibr lampblack include Black pigment for cements, ceramic ware, monar. inks, linoleum, surface coaling, crayons, polishes, carbon paper, soap, etc. ingredient of insulating compositions, liquid-air explosives, matches, fertilizer, furnace lutes, lubricating compositions, carbon brushes reagent in cementation of siccl. 

The model explains many lubrication phenomena in which antiwear and extreme-pressure additives are involved. It spurs the design of new additives and lubricating compositions. 

The tribofilms consist of amorphous, short-chain phosphates (ortho- and metaphosphates), with some evidence of sulfur incorporated into the phosphate chain structure. Tribofilm structure depends not only on the lubricant composition of the substrate material, but also on the severity of the rubbing contact. The ZDDP typically forms phosphates under antiwear conditions, whereas sulfides and sulfates are typically formed under severe or very severe conditions, li > 0.8 (Willermet et al., 1997). 

Today, a modified bearing service life calculation is increasingly in use. It takes into account the possible use of special materials, special production qualities, lubricant composition and purity, as well as operating temperatures. With the measures commonly used today, modified bearing service life can be approx. 2.5 times the LhlO service life. However, to obtain similar values, it is advisable to adopt the LhlO value when assessing a bearing design. 

This was also a period of great interest in lubrication associated with the needs of the machinery of the Industrial Revolution. Dowson mentions several patents for lubricant compositions of considerable complexity which were granted between 1800 and 1850. Nevertheless the next references to the use of molybdenite as a lubricant are by gold miners in the Colorado gold rush of 1858-62, who are said to have used it to lubricate the axles of their wagons. This can hardly be considered a new development, since it was probably only a repetition of use in primitive times. 

The general problem of resupplying a system with a solid lubricant is discussed elsewhere in this book, and various possible techniques are mentioned, but resupply by transfer from some form of reservoir is the most successful technique, and the only one which has been used commercially. It has been used in spacecraft, and in terrestrial applications for vacuum or for very high or very low temperatures, while rolling bearings lubricated by solid lubricant composite retainers or cages have been commercially available for over thirty years. 

Janes, Neumann and Sethna ° reviewed the general subject of solid lubricant composites in polymers and metals. They pointed out that the reduction in mechanical properties with higher concentrations of solid lubricant can be offset by the use of fibre reinforcement. Glass fibre is probably the most commonly used reinforcing fibre, with carbon fibre as a second choice. Metal and ceramic fibres have been used experimentally to reinforce polymers, but have not apparently been used commercially. To some extent powders such as bronze, lead, silica, alumina, titanium oxide or calcium carbonate can be used to improve compressive modulus, hardness and wear rate. 

Apart from the lubricant area fraction, the actual dimensions of the recesses are also important. Deep, narrow pockets are inherently likely to give strong support and retention of the lubricant material, but, as shown previously, deep pockets are wasteful of lubricant, while narrow pockets are susceptible to blocking with wear debris. On the other hand, wide shallow pockets are likely to provide poorer support and retention for the lubricant material. Wide recesses will also lead to a gross lack of uniformity in the surface strength of the bearing surface because the lubricant composite and the metal matrix are likely to have very different moduli. 

Martin and Murphy ° compared twenty-five different solid lubricant composites for use in small arms. The best performance was obtained with a composite of molybdenum disulphide in molybdenum with niobium and copper. This had a lower wear rate (0.224 x 10 mm /Nm) and lower coefficient of friction (0.05 - 0.15) than any of the twenty-one polymer-based composites. 

Mizutani et al ° carried out a review of some of the problems of metal-lubricant composites, and in particular the difficulty caused by the fact that sintering temperatures are limited by the thermal stability of the lubricant. The result of this is that either softer metals must be used, or lower sintering temperatures which result in lower structural strength due to brittleness. This led them to investigate metal-lubricant composites in which the lubricant is synthesised in situ. The result was the ternary alloy of iron, molybdenum and sulphur which was described in Chapter 9, and which had the characteristics of a slightly sulphur-depleted molybdenum disulphide composite. 

The retainer may be completely fabricated from a composite material, or may consist mainly of a composite with reinforcement by metal rings. Alternatively it may be conventionally fabricated of steel or other suitable metals, with composite components bonded, rivetted or pressed onto it, or with holes or grooves filled with the lubricant composite. 

Tsuya, Y., Shimura, H. and Matsunaga, M., A Study on Some Metal-Base Self-Lubricating Composites Containing Tungsten Disulfide, Lubric. Eng., 29, 498, (1973). 

Gardos, M.N. and McConnell, B.D., Development of a High-Load, High-Temperature Self-Lubricating Composite - Parts I to IV, Proc. ASLE-ASME Lubrication Conference, New Orleans, LA, (5-7 October, 1981). ASLE SP-9. 

Lavik, M.T, and Hopkins, V., Development of Self-Lubricating Composites Utilising Carbonised Phenolic Matrix, AFML-TR-75-175-PT. (1975). 

Suzuki, M., Moriyama, M., Mishimura, M. and Hasegawa, M, Friction and Wear of Self-Lubricating Composites at Temperatures to 450 in Vacuum, Wear, 162-164, 471, (1993). 

Wu, Y., Wang, F., Cheng, Y. and Chen, N., A Study of the Optimization Mechanism of Solid Lubricant Concentration in Ni/MoSj Self-Lubricating Composite, Wear, 205, 64, (1997),... 

Boes, D.J. and Bowen, P.H., Friction-Wear Characteristics of Self-Lubricating Composites Developed for Vacuum Service, ASLE Trans., 6, 192, (1963). 

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