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Labyrinth seal design for space applications
(Elsevier, 2025-02-14) Pouzar, Josef; Košťál, David; Westerberg, Lars-Göran; Nyberg, Erik; Křupka, Ivan
Labyrinth seals, extensively used in space applications, serve to prevent the loss of liquid lubricants and shield satellite subsystems from contamination. These seals are essential for the reliable functioning of bearings and for protecting satellite subsystems from contamination. This study compares analytical predictions of lubricant loss against experimental measurements and computer simulations to optimize labyrinth seal configurations. Analytical models tend to overestimate mass loss by 5-8 times compared to experimental data, indicating limited reliability for complex seal geometries. Simulations using MolFlow+ and COMSOL Multiphysics align closely with experimental results, providing accurate mass loss predictions. Key findings highlight that labyrinth length, width, and surface roughness are critical factors in minimizing evaporative mass loss. Notably, stepped labyrinth seals with relief grooves and optimized step positioning effectively reduce molecular beaming effects and improve sealing performance compared to straight geometries. Effective sealing not only reduces mission failures but also helps to minimize space debris, thereby promoting safer satellite missions.
Effect of Surface Texturing on Friction and Lubrication of Ti6Al4V Biomaterials for Joint Implants
(Springer Nature, 2025-03-01) Ranuša, Matúš; Odehnal, Lukáš; Kučera, Ondřej; Nečas, David; Hartl, Martin; Křupka, Ivan; Vrbka, Martin
The number of endoprosthetic implants for both large and small joints is increasing at a steady rate, thereby creating a growing demand for durable products that closely replicate the functionality of human joints. Notwithstanding the aforementioned advancements, challenges pertaining to implant fixation and tribological surfaces persist. The advent of progressive technologies, such as three-dimensional printing, offers a promising avenue for addressing these challenges in implant design and surface engineering. The Ti6Al4V and CoCrMo alloys, renowned for their biocompatibility and osseointegration properties, represent promising printable materials, although they are susceptible to wear on articulating surfaces. In order to mitigate the effects of abrasion, it is essential to implement surface treatments to facilitate the formation of a robust lubricating film. This research investigates the potential of texturing and electrochemical polishing to enhance protein aggregation in the contact area. The study employs a reciprocating simulator and colorimetric interferometry to observe the contact area and measure the coefficient of friction (CoF) of modified surfaces. The findings demonstrate that textured surfaces and the combination of electrochemical polishing result in an increase in the thickness of the protein lubrication film, which may potentially reduce wear. These outcomes suggest the potential for the utilization of Ti6Al4V alloy implants with fewer elements manufactured by additive technology.
Case study: the influence of oil-based friction modifier quantity on tram braking distance and noise
(Serbian Tribology Society, 2017-06-21) Galas, Radovan; Omasta, Milan; Klapka, Milan; Křupka, Ivan; Hartl, Martin; Kaewunruen, Sakdirat
In the present study, the twin disc machine and the light rail system was employed in order to investigate the ability of oil-based friction modifier (FM) to optimize adhesion and to reduce noise. The risks associated with poor adhesion conditions after the application of FM were evaluated. Both laboratory and field experiments showed that if the contact is overdosed by FM, the poor adhesion, which results in the extension of braking distance, can occur. In contrast, the smaller quantities do not cause critical adhesion but the effect of FM on the noise reduction is negligible. This study indicates that it can be quite difficult to achieve a reasonable noise reduction without a significant impact on braking distance of tram when the oil-based FM is applied. The field experiments also showed that the carry distance of FM is rather limited, approximately 100 m.
Thickener Behaviour in Rolling Elastohydrodynamic Lubrication Contacts
(SPRINGER/PLENUM PUBLISHERS, 2024-06-04) Okál, Michal; Košťál, David; Sakai, Kazumi; Křupka, Ivan; Hartl, Martin
This paper focuses on the study of thickener behaviour in elastohydrodynamic contacts using fluorescence microscopy and optical interferometry. A standard Ball-on-disc configuration tribometer was used as well as a newly developed Ball-on-ring configuration tribometer mimicking the conditions in a 6314 deep groove ball bearing. Three types of custom-made greases were used with the same base oil and Coumarin 6 fluorescent dye on the thickener. These greases contained no additives and were of the lithium complex and alicyclic di-urea type. It was confirmed that the behaviour of the grease was directly influenced by both the structure and type of thickener, and the differences were successfully observed by fluorescence microscopy. The concentration of thickener was found to change due to the formation or breakdown of the deposited thickener layer on the track. At low speeds, the alicyclic di-urea forms a thickener layer on the track that is more pronounced than the lubricating film formed by the base oil alone. The thickener layer formation also occurs at higher speeds when fully flooded conditions are beneficial in building the layer. Experiments with a Ball-on-ring tribometer show that the natural replenishment of the real contact geometry is more effective than on a Ball-on-disc tribometer, but the formation of the thickener layer on the track is more limited than in a Ball-on-disc tribometer with artificial replenishment. At higher velocities, a smaller but stable layer is formed where the layer does not change much from a certain velocity.
Study on the wheel/rail adhesion restoration and damage evolution in the single application of alumina particles
(Elsevier, 2019-04-30) Shi, Lu-bing; Li, Qun; Kvarda, Daniel; Galas, Radovan; Omasta, Milan; Wang, Wenjian; Guo, Jun; Liu, Qi-Yue
The aim of this study is to explore the wheel/rail adhesion restoration performance of alumina particles and the comparison between the continuous and single application test strategies in twin disc simulation. The results indicate that the single application test strategy performs better on evaluating the adhesion restoring ability of solid particles. In the single application tests, the restored adhesion coefficient increases with the applied alumina quantity and final gets stable when the quantity exceeds 2 g (0.607 g/m). However, the increase of alumina quality could always extend the duration of restored adhesion. The alumina particles at the size in the range of 0.075–0.15mm showed the best adhesion restoration and the longest duration was achieved at the size of 0.15 mm. In addition, it is observed that the serious damage is mainly caused in the particles crushing process, and will be gradually ground off in the following long running to have no threat on the serving life of the wheel and the rail. and the rail.

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