The Composition of Surface Layers Formed in a Lubricated Cam/Tappet Contact

Abstract

The Composition of Surface Layers Formed in a Lubricated Cam/Tappet ContactThe frictional behavior of two oils was measured in a cam/tappet friction apparatus using a direct acting bucket tappet geometry. One oil contained a soluble molybdenum friction modifier. The tappet was equipped with a removable friction disk, which allowed the frictional surface to be easily removed for surface characterization using surface profilometry, reflection infrared and XPS spectroscopies. The films consisted of varying amounts of inorganic phosphates, sulfates and sulfides with zinc, magnesium, and possibly molybdenum as cations. MoS 2 , expected because additives containing molybdenum and sulfur were present, was not detected. The detection limit was less than 0.1 atom percent Mo. The film formed by the friction modified oil was thinner, smoother and contained small amounts of molybdenum. While the smooth surface finish could reduce friction by improving microelastohydrodynamic lubrication, friction reduction could not be tied to any of the chemical structures detected in these experiments. . Paper No. 90-Trib-17. Associate Editor: B. Bhushan. Experimental2.1 Test Apparatus. The cam/tappet friction apparatus is an improved version of equipment described previously (Willermet, Pieprzak and Dailey, 1989;. A cam/tappet module is driven by a variable speed 2 hp. DC motor with an attached flywheel. The torque required to rotate the cam shaft is measured with a torque meter positioned between the cam shaft and flywheel (Fig. 1). Torque Meter Attachment and Mounting.Solid split shell couplings are used to attach the torque meter. These solid couplings have much lower rotational inertia than flexible couplings. This reduction in inertia significantly increases the natural frequency of the system and reduces the amplitude of the natural frequency "noise." To make the use of solid couplings possible, a visco-elastic mount was incorporated to support and stabilize the torque sensor. Cam/Tappet Module.The cam/tappet module is essentially a temperature controlled aluminum box which can accommodate a variety of value train designs (Figs. 2 and 3). The drop-in components, which establish the test configuration, are located within ±0.05 mm via locating holes. The temperature of the module is controlled by circulating a

Tribofilms generated from ZDDP and DDP on steel surfaces: Part 2, chemistry

“…The infrared measurements suggested that there are polyphosphates in the films [6][7][8][9]. The XANES measurements have shown that the film has a bilayer structure with long chain Zn polyphosphates at the surface, and short chain polyphosphates in the bulk of the film [14][15][16]18] with little or no Fe oxide between the Fe and the phosphate due to digestion of the Fe oxide layer during phosphate formation [10].…”

“…Many advanced spectroscopic techniques have been applied to elucidate the chemical nature of tribofilms generated from antiwear agents. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) [1][2][3][4][5], reflectance infrared spectroscopy [5][6][7][8][9] and X-ray absorption near edge structure (XANES) spectroscopy [10][11][12][13][14][15][16][17][18] have played a major role to understand the mechanisms of formation of antiwear film on the rubbed surfaces. A good summary of the role of many of these techniques is given in a very recent paper [10].…”

Effects of Mo-Containing Dispersants on the Function of ZDDP: Chemistry and Tribology

“…Willermet et al pioneered the use of this molecular spectroscopy on cam and tappet parts from engines (Willermet,et al (5)- (8)). It was through this research that the existence of metal phosphates on the uppermost layers of the tribofilm was definitively established.…”

Thermal degradation behavior of zinc dialkyldithiophosphate in presence of catalyst and detergents in neutral oil

“…Investigation of the film chemistry using various surface analytical techniques has shown that it is the ZDDP decomposition products and not the ZDDP itself, which provide the wear protection [5][6][7]. A number of investigations have focused on the reaction of ZDDP in solution.…”