CHARACTERIZATION OF FILMS FORMED AT A LUBRICATED CAM TAPPET CONTACT/

The surfaces of tapper inserts subjected to lubricated, moving contact in a cam/tappet friction apparatus have been analyzed by IR reflectio n-absorption, X-ray photoelectron and Auger electron spectroscopies. T he two lubricants used were similar fully formulated oils. One contain ed a soluble molybdenum friction modifier additive while the other did not. Thin inorganic films were formed across the contact area during the cam/tappet experiment. Regardless of the lubricant used, these fil ms consisted of varying amounts of inorganic phosphates, sulfates, sul fides, and perhaps thiophosphates, with zinc and magnesium as cations. Molybdenum would also be a cation in the case of the friction modifie d oil. The films generated during the wear process differed in thickne ss, composition and surface coverage as a function of wear time, conta ct position and Lubricant composition. The films formed by the frictio n modified oil were thinner and less continuous as compared with films formed from the unmodified oil.