Paper 7: A Comparative Examination of Some Potential Inorganic Lubricants on the Shell Four-Ball Tester and on a Crossed-Cylinder Wear Machine

Several workers have reported the use of mixtures of solid lubricants in dry film systems and, in particular, combinations of various metallic sulphides with molybdenum disulphide (MoS₂) in the dry state have been shown to be successful. Here, data obtained using a Shell four-ball tester is presented in which selected inorganic sulphides and oxides dispersed in oil have been examined; the variation in the size of wear scars with load in the range 20 to 800 kg is shown. Examples are also given of the variation in the wear-load curve with concentration of dispersed solid, where it is shown that the amount of wear decreases with increasing concentration of solid up to an optimum concentration of approximately 0·7 per cent by volume, with the exception of sulphur, which performs equally well at all concentrations between 0·2 and 20 per cent by volume.

The same solids have also been examined in the form of dry rubbed films in three atmospheres on a crossed-cylinder wear machine, and only MoS₂ has been found to provide effective lubrication as a dry unbonded film.