Lubricated wear

The effect of such operating parameters as load and rubbing speed on the quantitative relation of dry and lubricated wear is neither simple nor obvious. Table 13-4 shows two direct comparisons one of data from the work of Kerridge and Lancaster [15] and the other of unpublished data 

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Luengo G, Israelachvlll J N and Granick S 1996 Generalized effects In confined fluids new friction map for boundary lubrication Wear 200 328-35... 

Yoshizawa H, Chen Y L and Israelachvili J N 1993 Recent advances in molecular level understanding of adhesion, friction and lubrication Wear 6B 161-6... 

The data of Zink et al. (1998) illustrate the measurement by NRA of near-surface composition profiles in isotopically labelled polymer blends. If a mixture of polymers is adjacent to a phase interface (e.g. a solid or an air surface), often one of the components is preferentially attracted to the surface and will segregate to it, and this phenomenon will influence the tribological behaviour the interface (lubrication, wear and adhesion). 

It is fairly obvious that other factors such as lubricants, wear debris, ageing of the surfaces and humidity can also affect friction and, once again, test conditions must be chosen that resemble those found in service. 

UHMWPE possesses a unique combination of mechanical and technological properties and enjoys a variety of special applications based on low friction (solid lubricant), wear resistance (protection of metal surfaces), excellent chemical stability, as well as radiation and neutron resistance. UHMWPE is used in chemical processing, food and beverage industries, foundries, the lumber industry the electrical industry, as medical implants and in mining and mineral processing sewage treatment, and transportation. 

Specialty Chromium-Plating Baths. Chromic acid baths using sodium chromate and sodium hydroxide to form a tetrachromate (92) have had limited use. Porous chromium is used in lubricated wear applications, and is made by chemically etching regular chromium plate, sometimes with light grinding after the etch. Black chromium is used on solar collector surfaces (see PHOTOVOLTAIC CELLS Solarenergy). Baths are sulfate-free, and include fluosilicic acid or acetic acid (91). 

Table 2.7. Performance of synthetic and mineral lubricant oils. Relative evaluation of viscosity, stability (thermal, oxidation, hydrolytic, volatility), lubricity (wear protection and fatigue) and environmental impact...

Lubricity - wear protection and fatigue. The coefficient of friction is a measure of lubricity of a lubricant. The esters, being more polar, are attracted to the metal surfaces and form monolayers. These thin layers reduce the coefficient of friction at the surface. The surface phenomena that determine the behavior of boundary lubricants can be described in the following terms physically and chemically adsorbed layers and tribochemically formed films. 

Boundary and Mixed Lubrication Science and Applications (Dowson et al., Editors) Tribological Research and Design for Engineering Systems (Dowson et al.. Editors) Lubricated Wear - Science and Technology (Sethuramiah)... 

McCain, J.W., A Theory and Tester Measurement Correlation About MoSj Dry Film Lubricant Wear, SAMPE Journal, p. 17, (1970). 

Clow, W.L., Relation Between Inorganic Binder Wettability and Solid-Film Lubricant Wear-Life, ASML-TR-68-313, (Nov. 1968). 

Sanes J, Carridn FJ, Jimenez AE et al (2007) Influence of temperature on PA 6-steel contacts in the presence of an ionic liquid lubricant. Wear 263 658-662... 

Jimenez AE, Bermudez MD (2008) Imidazolium ionic liquids as additives of the synthetic ester propylene glycol dioleate in aluminium-steel lubrication. Wear 265 787-798... 

Kulczycki, A. (1985) The correlation between results of different model friction tests in terms of an energy analysis of friction and lubrication. Wear 103 67-75. 

P. A. Molian, B. Janvrin, and A. M. Molian, Laser chemical vapor deposition of fluorinated diamond thin films for solid lubrication. Wear, 165(2) 133-140 (1993)... 

Furthermore, additive action should become more effective in decreasing the lubricated wear rate with increasing concentration of additive. 

A somewhat more explicit example is found in the following expression obtained from C. N. Rowe s analysis of a model for lubricated wear [60],... 

The preceding chapter was devoted to the development of the fundamental concepts of mechanical wear and to the examination of generalized wear phenomenology in relation to these concepts. The same basic mechanistic processes govern both unlubricated and lubricated wear. The role of the lubricant in lubricated wear is essentially to ameliorate wear by modifying the extent and the rates of those basic processes that exert the critical influences in whatever particular case is under examination. Unlubricated wear is not necessarily simpler or more elementary than lubricated wear in fact, unlubricated wear is more likely to be so destructive under severe conditions that it may be effectively impossible to specify what occurred at a given stage of the wear process. 

In the discussions of Chapter 13 there was no categorical separation of unlubricated and lubricated wear. Given the existence of an unbroken film of liquid lubricant between two surfaces, it is generally expected that no wear will occur. This is not always so transmission of hydrostatic pressure through the film can plastically deform the bodies which it separates, and tangential tractive forces in the film can do the same. These are wear phenomena as defined in Chapter 13, and since they occur in the presence of lubricant they can be formally classified as lubricated wear. However, in this chapter we shall not concern ourselves with these particular aspects of lubricated wear. We shall be concerned instead with the course of wear in situations where the behavior of the lubricant does not. conform fully with the laws of hydrodynamics or elas-tohydrodynamics. The inference, of course, is that the lubricant at the rubbing surfaces is not there as an unbroken film. 

Such being the case, further inferences about the nature of the wear process follow. A disrupted fluid film allows localized contacts at the rubbing surfaces, and it is the mechanistic processes at these contacts that determine the course of lubricated wear. When the wear process is abrasive, it is most likely influenced directly by fluid film thickness and surface roughness, whereas processes such as adhesion, transfer, oxidation, additive reaction and the like are responsive to surface conditions at the contacts as well as to the number of contacts. These are the aspects of lubricated wear that are emphasized in this chapter, from the viewpoint of phenomenology, mechanisms and modeling. 

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