Friction and wear

The main characteristic properties of asbestos fibers that can be exploited in industrial appHcations (8) are their thermal, electrical, and sound insulation nonflammabiUty matrix reinforcement (cement, plastic, and resins) adsorption capacity (filtration, Hquid sterilization) wear and friction properties (friction materials) and chemical inertia (except in acids). These properties have led to several main classes of industrial products or appHcations... 

Eunctional or hard chromium plating (169,175) is a successfljl way of protecting a variety of industrial devices from wear and friction. The most important examples are cylinder liners and piston rings for internal combustion engines. Eunctional chromium deposits must be appHed to hard substrates, such as steel, and are appHed in a wide variety of thicknesses ranging from 2.5 to 500 ]Am. 

Although these resins have been on the market for a number of years, volumes and appHcations remain low in spite of favorable properties including high temperature resistance, excellent wear and friction properties, good electrical properties, chemical inertness, and inherent nonflammability. ProcessibiHty and price may be the limiting factors. 

Material Characteristics Strength and Sliffness Toughness Short-Term Heat Resistance Long-Term Environ-Heat menial Resislance Resistance Dimensional Accuracy in Molding Dimensional Stability Wear and Frictional Properties Point Subtotal Cost Point Total... 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

Li, Y. and Bhushan, B., Wear and Friction Studies of Contact Recording Interface with Microfabricated Heads," Wear, Vol. 202,1996, pp. 60-67. 

BN is used for reinforcing ceramics and alloys to reduce wear and friction and thus obtain self-lubricating parts [109-111]. 

ETFE resins are very often compounded with varied ingredients, such as glass fibers and bronze powder, to attain certain mechanical properties. For example, glass fibers are added at 25 to 35 wt% levels to increase modulus and improve wear and friction characteristics. By adding 25% glass fibers, for example, the dynamic coefficient of friction is reduced from about 0.5 to about 0.3 69... 

Tanaka, K., Uchiyama, Y., Nakagawa, T. and Matsunaga, M., Wear and Frictional Behaviours of Molybdenum Disulfide Pellets, and Steel Lubricated with Molybdenum Disulfide Powder, Proc. 3rd Inti. Conf. on Wear of Materials, ASME, p. 637, (1981). 

Matsunaga, M., Nakagawa, T. and Tennicki, M., The Wear and Frictional Behaviour of Molybdenum Disulfide Compacts, ASLE Trans., 26, 64, (1983). 

Crump, R.E., Factors Influencing Wear and Friction of Solid Film Lubricants, Product Eng., 28, p. C24, (Oct. 1957). 

Asbestos has been used in a broad variety of industrial applications which draw upon its low cost and desirable properties such as heat and fire resistance, wear and friction characteristics, tensile strength, heat, electrical and sound insulation, adsorption capacity, and resistence to chemical and biological attack. At the peak of its demand, about 3,000 applications or types of products were listed for asbestos. In most of its applications, asbestos is bonded with other materials such as Portland cement, plastics, and resins. In other applications, asbestos is used as a loose fibrous mixture or woven as a textile. 

Lower wear and friction (Wear is reduced by a factor of 5-6 the coefficient of friction is reduced by 20-30%.)... 

Special considerations high temperature treated carbon fiber requires treatment to increase adhesion by, for example, oxidation wear and friction grades usually contain combination of graphite, carbon fiber, and PTFE... 

Joly-Pottuz L, Vacher B, Ohmae N, et al. Anti-wear and friction reducing mechanism of carbon nano-onions as lubricant additives. Tribol Lett 2008 30 69-80. 

Equations of this type can describe both the physical dipole/dipole interactions and the subsequent desorption from the film. Since ka and k have different temperature coefficients, increasing temperature can lead to either increased, decreased or unchanged surface coverage. Provided that a critical minimum surface is maintained, wear and friction can be controlled. But once 0 falls below this critical value, believed to be approx 0.5, friction and wear will rise. The adsorption of dilinoleic acid [4], a series of organic sulphur compounds [5] and a ZDDP (zinc dialkyldithiophosphate) [6] has been described in these terms. 

The model for film formation described above suggests that interactions between basestock and film-forming additives, which retard their adsorption, will have a detrimental influence on wear and friction. For instance, highly napthenic basestocks are good solvents for polar species whilst paraffinic basestocks are relatively poor solvents for polar species and will therefore enhance film-forming activity. Clear evidence of this effect has been shown for molybdenum chemistries [7] and for ZDDPs [8, 9]. 

Both low friction and low wear can be achieved if these films of friction modifier are laid down on thicker films of, say, ZDDP. The anti-wear and friction properties of several classes of additives have been described together with the influence of... 

A complementary study of steel/steel contacts (100Cr6) [47] used an oscillation wear and friction tester to screen ionic liquids in the boundary lubrication regime at 30, 100 and 170°C at 200 N load. Results are summarized as follows (i) some promising ionic liquids gave lower friction and wear at all temperatures, compared to reference lubricants, (ii) chemical structures of ionic liquids have a high impact on their physico-chemical as well as on tribological properties and (iii) careful selection of both cation and anion, as a tailor-made ionic liquid, enables adaptation of ionic liquid structures to specific applications. 

Lubrication > Introduction of any of various substances between sliding sur- faces to reduce wear and friction. a... 

TABLE 9-9. EFFECT OF DIISOPROPYL DITHIOPHOSPHATES ON WEAR AND FRICTION... 

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