Weight Loss under Fretting Conditions

Loose molybdenum disulphide powder does not have a strong tendency to adhere to surfaces, and can be easily scraped off unless the conditions are such that the powder is burnished onto the surface. This probably occurs in rolling or 

Some of the difficulties in applying free powder to a surface can be overcome by dispersing the molybdenum disulphide in a volatile liquid. This enables it to be applied uniformly, in controlled quantity, and with much less tendency to escape from the desired working space. Evaporation of the liquid carrier then leaves a film of powder of remarkably uniform thickness on the surface. 

The usual commercial forms of molybdenum disulphide powder are not readily wetted by water or by some organic liquids. They tend either to float on the surface of the liquid or to sink to the bottom, and do not form satisfactory dispersions. The technique of floating powder on the surface of water, and lifting it off onto a surface, has been used experimentally to produce uniform films by Matsunaga and others, as described in Chapter 6. Such films can be very uniform, but are usually too thin for practical applications. 

An alternative method of improving wettability was first described by Groszek , and has been described in Section 7.6. This is the production of oleophilic molybdenum disulphide by ball milling in oil. The product is readily wetted by organic liquids, and can in fact be used as a grease thickener. Groszek described dispersions in several different organic liquids and it is clear that the improved wettability leads to the formation of much more stable dispersions. 

Dispersions can be applied to a bearing surface by brushing, dipping or spraying. The most suitable process depends on the size and shape of the component, and the viscosity and concentration of the dispersion. The liquid then evaporates, with or without the use of heat or enhanced airflow, leaving a thin but uniform and often adherent film of molybdenum disulphide powder. The adherence 

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Table 9.3 Weight Loss under Fretting Conditions (Ref.223)...

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