Lubricants developments

All the models of mixed lubrication developed previously were based on a traditional idea, as schematically shown in Fig. 2, that the nominal contact zone, O, has to be divided into two different t3q>es of areas the lubricated area, 0,1, where two surfaces are separated by a lubricant film and the asperity contact area, where two surfaces are assumed to be in direct contact. The present authors and Dr. Zhu [16,17] proposed a different strategy for modeling... 

Eight in category C (Commercial) CA, CB, CC, CD, CE, CF, CG, and CH The chronology of engine, gear and automatic transmission lubricants development since 1930 (Copan and Richardson, 1999) is illustrated in Table 2, Appendix. 

Yarn lubricants. Self-emulsifled lubricants developed to meet specific low sling characteristics where atmospheric conditions warrant attention to oil vapor control. Possess excellent scourability properties for ease of removal by aqueous or dry cleaning methods. 

Another material of this kind is tungsten disulphide, originally developed by NASA for aerospace applications, now also applicable to specialty industries [58]. Ti3SiC2 is a thermodynamically stable, nano-layered, ternary carbide and part of a family of over 50 ternary carbides and nitrides, the MAX phases [62]. These phases are a new class of solids possessing unique combinations of properties they are readily machinable, relatively soft for ceramics, but elastically stiff, and electrically and thermally conductive. They combine the good properties of both metals and ceramics that could lead to this technology contributing to future lubricant developments. 

Because of these factors, the lubrication requirements of aircraft are generally very critical. Only in a few cases can lubricants developed for non-aircraft applications be used satisfactorily in aircraft. This has not always been the case the mineral oil or castor oil lubricants used in the earliest aircraft were all standard automotive or marine products. 

The introduction and development of gas turbine engines led to the development of new lubricants. While the early gas turbine engines ran successfully on mineral oil lubricants, and in fact many Russian aircraft engines still operate on such lubricants, the demand for higher specific thmst, with the concomitant high operating temperatures, needed lubricants with better thermal stability. Carboxylic esters were developed which, with yet further improvements, are still used today. These lubricants are also used in aero-derived industrial and marine gas turbines, meaning that for the first time lubricants developed for aircraft were used in other applications. 

An initial problem with lubricant development was that engine manufacturers regarded their individual products as unique by metallurgy, design and use. Individual manufacturers wanted special lubricant tests in addition to general lubricant... 

G. J. Bishop, Aviation Turbine Lubricant Development, J. Synth. Lubr., 1987, 4-1,25. Harlacher, E. A. Krenowics, R.A. Putnick, C.R. Alkylenzene Based Lubricants. Prep. 52D26P, 86th AlCHE national meeting, Houston, April 1-5 1979. 

Simultaneously, the developing mineral oil industry was finding new ways to make lubricants along with fuels, offering opportunities for advancement in lubrication technology. Many of the lubricants developed for these applications would have been considered advanced in their day, but are now long obsolete. 

It is instructive to consider the general process of lubricant development before tackling the topic of advanced lubricants. Figure 1 is a schematic of the process. Economic drivers in engineering equipment are efficiency, reliability, maintenance costs, productivity and longevity. The relative importance of these will depend on the user. For personal cars, reliability is likely to be top of the list - a car is not much use if it can t be driven. Fuel and maintenance costs are also important. For industrial equipment, all the above drivers will be important, but weightings will vary by industry and location. 

Figure I. Schematic of the lubricant development and formulation process.

Having differentiated between the preservation and tribology functions of a lubricant, it is now possible to explore the extent to which tribology research can impact lubricant development. 

Internal combustion engine designers and lubricant developers rely heavily on computer based analytical tools. The sophistication and functionality of these tools is growing rapidly. It is therefore important that the models, on which these techniques are based, are validated and continually improved by very reliable and accurate experimental techniques. 

Professor D. Dowson (Institute of Tribology, School of Mechanical Engineering, University of Leeds, UK). 1 enjoyed your excellent, comprehensive overview of lubricant development. 

I wonder if you could give an example or two to illustrate your point that lubricant developments can enable" new designs ... 

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