The lubrication mechanism of fully submerged sliding point contacts of AISI 52100 steel has been studied as a function of surface roughness and oxygen content of the lubricant. Strong indications are found that, at relatively low values of normal load and sliding speed, a partial elastohydrodynamic lubricant film (incompletely) separates the surfaces. This film survives asperity contacts because newly formed contacts oxidize rapidly. Collapse of the lubricant film occurs if oxidation can no longer keep ahead of the formation of new asperity contacts. Increasing surface roughness and decreasing oxygen content of the lubricant both cause a reduction in load carrying capacity. Depending upon the value of the speed of sliding, collapse of the EHD film either leads to “incipient scuffing” or to severe wear (scoring). This effect is probably associated with a metallurgical transformation in the steel at a particular value of the conjunction temperature.
The effect of running-in under low speed - high load conditions on the load carrying capacity at high speed of sliding crossed cylinders of steel AISI 52100, thin film lubricated with a marine diesel engine oil of 60°C, is described for three values of the initial composite roughness Rc, i.e. 0.14 μm, 0.42 μm and 0.71 μm. It is shown that—irrespective of the initial surface roughness—the surface of the (smaller) stationary cylinder becomes very smooth (Ra ≤ 0.1 μm), that of the (larger) rotating cylinder remaining virtually unaffected. As the local radius of curvature increases as a result of running-in, the load carrying capacity, expressed in terms of total force on the contact, increases considerably, i.e. 600 percent at Rc = 0.14 μm, 500 percent at Rc = 0.42 μm and 150 percent at Rc = 0.71 μm. This is not accompanied by a correspondingly large increase in Hertzian contact pressure at film collapse, pHc. In fact pHcincreases 45 percent at Rc = 0.14 μm and 15 percent at Rc = 0.42 μm and decreases 20 percent at Rc = 0.71 μm. It is further found that run-in surfaces show the phenomenon of delayed EHD-film collapse, meaning that the transition from the (partial) EHD to the scuffing regime may take from 1 to 40 s after application of the normal force. The test method should contribute significantly to the functional characterization of lubricants and—more in particular—running-in fluids, as candidates for use in concentrated contact situations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.