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Effect of surface roughness on lubrication of plain bearings
Vaněk, Tomáš ; Hartl, Martin (referee) ; Šperka, Petr (advisor)
This work investigates the influence of surface roughness on the lubrication of axial hydrodynamic bearings with convergent wedge gaps. It focuses on situations where operational conditions allow for full separation of surfaces by the lubricating film, as well as the transition to mixed lubrication. The aim is to understand the impact of surface roughness on the hydrodynamic lubrication process and whether their proper selection can affect the friction and load-carrying capacity of the bearing. Experimental measurements are used to determine the influence of parameters, where the thickness of the lubricating film is captured through fluorescence microscopy, along with the friction force at the contact between the pin and the test sample. The samples form a wedge gap with a rotating saphire disk, and the investigated surface roughness parameters include orientation, height Sq, and skewness Ssk (i.e., the relative ratio of depressions and protrusions). According to the obtained results, the orientation, height, and shape of roughness are key factors influencing hydrodynamic lubrication. However, the orientation alone does not determine the contact behavior, and additional roughness parameters must be considered for a complete understanding of the phenomenon. Increasing surface roughness negatively affects lubrication, but the proper combination of Ssk and orientation can minimize this effect. This work represents one of the first experimental measurements examining the influence of surface roughness on hydrodynamic lubrication. The findings have applications not only in plain bearings, but also in other components such as wet couplings or other sliding interfaces using hydrodynamic lubrication.
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The effect of surface texture on friction and lubrication of axial plain bearings
Knotek, Jan ; Hartl, Martin (referee) ; Šperka, Petr (advisor)
This paper deals with the influence of textures on friction and lubrication of axial plain bearings. Targeted texturing has the potential to affect the performance of mechanical components, where the main parameter is the friction coefficient and the thickness of the lubricating layer. Many experimental studies have been published so far, but few of them lead to a more detailed understanding of the function of textures on parallel surfaces and their interaction with a wedge-shaped gap. The problem was modeled in this work using a pin-on-disk configuration operated with controlled tilt in the hydrodynamic lubrication regime. In contrast to previously published studies, the thickness of the lubricating film was measured in real-time during the experiment using fluorescence microscopy, along with the friction coefficient. It has been demonstrated that textures are generally more beneficial in conditions with parallel surfaces compared to conditions with wedge-shaped gaps. For the case of parallel surfaces, the influence of partial texturing was identified, where the surface textured with a quarter of its area located at the entrance to the contact in the centerline led to the most positive results. In addition to partial texturing, the influence of texture size and the pattern of their distribution on the contact surface was confirmed. Parallel surfaces showed a high sensitivity of results to small changes in surface tilt. However, with increasing tilt, the effect of the wedge-shaped gap dominated over the effect of textures, and their contribution was typically in the range of single-digit to low double-digit percentages.
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