Influences of trace water in hydrogen and argon on the tribological properties of pure iron

Tribological properties of pure iron were studied in argon environments containing trace water which is controlled at the value between 1 and 10,000 ppb and virtually no oxygen. The experimental data were compared with those obtained in our previous study with the same conditions of experiment but in hydrogen. The influences of trace water were recognized in both gases and confirmed not peculiar to a hydrogen environment. The coefficients of friction and specific wear rates were different to some extent between argon and hydrogen environments. The differences were supposed to be attributed to the influences of hydrogen atoms which chemisorbed on pure iron atoms appeared on the nascent surface made by sliding. Whether hydrogen and water have synergy effect on influencing tribological properties was not clarified in this study

Experimental Study of Starvation and Flow Behavior in Grease-Lubricated EHD Contact

This paper describes an experimental study of starvation and flow behavior in grease-lubricated elastohydrodynamic contact. Rolling tests were conducted with four grease samples with different thickeners and base oils in a conventional ball-on-disk test rig. The EHL central film thickness was determined with SLIM, the Spacer Layer Imaging Method, and grease flow around the conjunction and the flow pattern on the track of the disk specimen were observed with CCD cameras. The grease track included some thickener deposited on the track and a corrugated fingerlike flow pattern outward from the center of the track. It was found that the flow pattern varied with grease type and test conditions, and that the average interval between fingers decreased with the entrainment speed. At higher speeds, inlet starvation occurred and the finger pattern was deformed and gradually ruptured. The speed of the finger-loss was higher than the speed at which starvation started. It was also found that the starvation speed was greater with greases having lower apparent viscosity at lower shear rate and higher apparent viscosity at high shear rate. This implied that the replenishment and entrainment of the greases depended on the viscosity characteristics of the greases

On the Magnitude of Load-Carrying Capacity of Textured Surfaces in Hydrodynamic Lubrication

This paper investigates the magnitude of the load-carrying capacity enabled by textured feature in hydrodynamic lubrication. The numerical model is a two-dimensional fixed pad bearing with a single dimple. The Reynolds equation was numerically solved using the Elrod algorithm. Two boundary conditions at the inlet and outlet were compared: a periodic boundary condition and an atmospheric boundary condition. The load-carrying capacity for the atmospheric boundary condition is negative while that for the periodic boundary condition is positive when a dimple is located at the centre of the lubricated area. The atmospheric boundary condition, when a dimple is located on the inlet side and is opened to the outside, exhibits greater load-carrying capacity than that in the enclosed dimple case

The role of synthetic oils in controlling hydrogen permeation of rolling/sliding contacts

Bearing steels suffer from a degradation of mechanical properties when atomic hydrogen diffuses into the steel from the contact surface. In rolling contact fatigue tests this can lead to a significant reduction in fatigue lives of the specimens as the amount of hydrogen diffused into the steel increases. To mitigate this challenge synthetic oils of different chemistry have been studied so as to identify their efficiency and mechanism of retarding or preventing hydrogen permeation. Thrust bearing type tests were conducted with three synthetic base oils. The effect of base oil chemistry on hydrogen generation and permeation in bearing steel was explored by relating the concentration of hydrogen species in specimens with changes in the surface and subsurface of the wear track and the condition of the oil