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The effect of real condition of a rail on friction between the wheel and rail
Škubna, Michal ; Hajžman, Michal (referee) ; Omasta, Milan (advisor)
The aim of this master’s thesis is to determine the influence of the friction layer formation conditions on the rail surface on the coefficient of adhesion. Currently, laboratory studies of adhesion are carried out on simplified contact models using tribometers in a two-disc device configuration or in a ball-to-disc configuration, which does not correspond to the real behavior of the wheel-rail interface. The experiments described in this work were carried out in a laboratory environment on a sample of a real rail using a tribometer to achieve variable slip. This made it possible to measure the entire traction curves for the specific rail surface condition. Several experiments were carried out to determine the influence of climatic conditions – especially relative humidity and the effect of water on the development and composition of friction layers naturally formed on the rail. To do this, several procedures were used to achieve the individual friction layers. In addition to the influence of climatic conditions, the influence of simulated passages of rolling stock using a contact simulator was also implemented. The output of the thesis is a draft article describing the methods of preparation of friction layers and the results achieved.
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Design of a sample grinding jig
Potoček, Samuel ; Čípek, Pavel (referee) ; Omasta, Milan (advisor)
Friction analysis using the device Mini-Traction-Machine (PCS Instruments) leaves a minor amount of surface and subsurface damage on the test surface of samples. Samples like this cannot be used for further testing. This thesis deals with the design of a grinding head that can be mounted on an existing manual grinder owned by BUT FME. In the first, research part of this thesis can reader learn about methods and machines commonly used for metallographic grinding and polishing, which inspired the design of this device. In the next chapter were proposed 3 concept designs of a sample holder, from which was one chosen to be further expanded in the last part of the thesis. The result of this thesis is a design of a grinding head able to work in a semi-automatic manner, working with more samples at the same time. The device regrinds or repolishes the damaged samples so that the samples can be reused for more friction testing. This in turn reduces the costs of test samples.
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Contactless temperature measurement in sliding contacts
Knoth, Tomáš ; Hajžman, Michal (referee) ; Omasta, Milan (advisor)
This work deals with the implementation of infrared thermography for detailed temperature mapping in conformal sliding contacts in a pin-on-disc configuration. The implemented method is then applied for study of textured sliding contacts. This method can bring unique insights into the temperature distribution in contacts with textured surfaces, where thermal phenomena play a crucial role. The current state of knowledge in this area relies mainly on numerical simulations, which is why the absence of experimental knowledge is a fundamental gap in knowledge. The research questions are devoted to the temperature distribution in contact and the demonstration of the occurrence of the so-called viscosity wedge effect. Hypotheses are built on the basis of works that study the issue using numerical simulations. The implementation of the method is based on the calibration and measurement procedure from the area of point contacts, where the ball-on-disc configuration is used. This method of calibration was confronted with applications on conformal textured surfaces and subsequently modified according to identified needs. In the second part of the work, contacts with textured surfaces are analyzed using the implemented method. The subject of interest here is parallel and near-parallel contacts. On the correction of the Stribeck curve according to the actual temperature of the lubricant, it is demonstrated that knowledge of the actual temperature of the lubricant in contact is essential for its study. However, the occurrence of thermal phenomena could not be proven in the range of experimental conditions.
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Design with respect to production costs
Homola, David ; Omasta, Milan (referee) ; Svoboda, Petr (advisor)
This bachelor’s thesis analyse general principles of Design for cost strategy in parts manufacturing. Compared manufacturing processes are Machining, Casting, Welding and 3D Print. Each process is rated based on production costs which are influenced by amount of manufactured parts, material, shape complexity, achieved tolerances and surface quality. Those informations are than applied in construction design of chosen part for each process separately. Each design is than compared based on production costs for specific amount of manufactured parts.
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Research on the textured journal bearings for engines in automotive
Svoboda, Martin ; Hartl, Martin (referee) ; Omasta, Milan (advisor)
The aim of this thesis is to describe the effect of surface textures of radial journal bearings with polymer coating on friction and damage development using experimental tests. Wear and friction tests of real bearings with different texture geometries and surface materials were performed. It was found that the wear deterioration of the textured aluminum sliding bearing surface and neutral or positive effects on the wear of the textured bearing with polymer coating. The reason for the improvement is the good resistance to high pressures of the polymer coating and the preservation of the texture dimensions throughout the bearing run. The friction test showed an improvement in the frictional properties of the textured surfaces when the amount of lubricant in contact was insufficient. At the same time, a positive effect on tribological properties was demonstrated by reducing the lateral lubricant discharge.
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Guide roller scraper
Šmíd, David ; Omasta, Milan (referee) ; Frištenský, Miroslav (advisor)
This bachelor thesis deals with doctors, that play essential role in paper, food, or chemical industry. These devices have effect on economy and quality of manufacturing process. Analysis discusses usage of this device in paper making industry and it mainly focuses on individual structural nodes. From this analysis are created three possible designs, from which author of this paper selected one, that works on the principle of pressure caused by the weight of the doctor, which is further elaborated and made into drawing documentation. The work analyses the basic parameters for the doctor and checks possible critical points of the construction. The end summarizes results of these inspections and the final design of the construction. Solution can be only used on particular guide roll, which it was designed for.
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Optimization of hydrostatic bearing recess shape
Kopřiva, David ; Omasta, Milan (referee) ; Michalec, Michal (advisor)
This bachelor's thesis deals with the problem of optimizing the recess shape of a hydrostatic bearing. It describes the principle of operation of hydrostatic bearings, their use and previous recess optimizations. A circular recess is considered as the reference geometry. This is firstly investigated by analytical calculation and CFD simulation. The results from the analytical calculation and from the calculation using the CFD simulation are then compared in terms of accuracy of CFD simulation. After verifying the CFD settings, three types of geometry are proposed based on research and previous studies, and with the help of CFD, these geometries are examined with respect to hydrostatic bearing load capacity and recess pressure. All proposed geometry types are then compared with the reference geometry. The results show that the reference geometry has the best results in terms of bearing load capacity and recess pressure. From the point of view of asymmetrical loading and damping, the use of the proposed geometries seems to be more appropriate. This thesis describes a detailed procedure for setting up the CFD and can serve as a basis for further optimization.
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Design of test rig for measurement of adhesion and noise in wheel-rail contact
Gabriel, Tomáš ; Robenek, Dětřich (referee) ; Omasta, Milan (advisor)
This master’s thesis is dedicated to the design of an experimental rig that allows investigation of causes for noise during tram’s passing of a track curve and the developement of means to mitigate this noise. The opening section of this thesis contains theoretical background for the tribological mechanics of wheel-rail contact with emphasis on the process of noise generation, followed by an overview of laboratory tst rigs with similar purpose. Design itself is centered around the implementation of the dynamic model of wheel-rail contact using real tram wheel. Resulting test rig allows measurement of the adhesion characteristic in tangential and lateral directions and recording of the generated noise while an angle of attack is set.
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Conceptual design of device for application of anti-icing agents on overhead catenary
Rohánek, Tomáš ; Kvarda, Daniel (referee) ; Omasta, Milan (advisor)
This bachelor’s thesis deals with icing of overhead contact lines. Relevant patents and existing commercial systems for applying anti-icing agents are comprehensively described and evaluated in the thesis. Based on that, two new concepts for public transportation are proposed. Compared to the existing systems, these concepts bring improvement in operational parameters and expand the number of products offered at the market. Afterwards, both concepts are critically assessed.
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