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Improving friction of lubricated contacts by modifying thermal conductivity
Šnevajs, Matěj ; Hartl, Martin (referee) ; Šperka, Petr (advisor)
This thesis deals with an experimental study regarding the effects of the thermal conductivity of contact bodies on the friction, lubricant film thickness and temperature distribution in EHL contact. The thesis focuses on the configuration of the ball on disc contact. The contact body materials are characterized by a wide range of thermal properties. New contact pairs are proposed and used in the study in order to make the contact bodies’ thermal properties dependent on the behaviour of EHL contact. The colorimetric interferometry method is used to measure the lubricant film thickness and the infrared thermography method is used to observe the temperature distribution in EHL contact. The author presents the assumed mechanism of heat transfer within EHL contact on the basis of different heat transfer mechanisms. The same conditions – such as the Hertz pressure, mean entrainment speed, sliding speed and ambient temperature – are induced for all the contact pair combinations. That is why the differences in the results are attributed to the different thermal phenomena in the contact, caused by the thermal properties of the contact bodies. In the case of contact bodies with a reduced heat dissipation capability, a reduction of the friction coefficient of up to 50 % is observed, which is attributed to an increase in the lubricant temperature, resulting in a decrease in its viscosity. This is confirmed by the infrared thermography method, whereby a significantly higher lubricant temperature is observed in the case of a combination of contact materials with a lower heat dissipation capability.
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Off-board systems for top-of-rail lubrication
Málek, Jan ; Kvarda, Daniel (referee) ; Galas, Radovan (advisor)
This bachelor’s thesis is focused on rail off-board lubrication system. The main part of this thesis is explaining of function and design few certain lubrication systems. In this thesis are explained aspects of wheel-rail contact, such as types and parts of rail, adhesion, slip, creep–traction diagram. Another part of this thesis is description of few certain lubrication system for top of rail and gauge face application. In this thesis are explained product of major companies of friction management industries such as SKF-Lincoln, Whitmore, Loram. Additional part of this thesis speaks about usage and development of this devices in Czech Republic. Output of this thesis is conclusion about advantages and disadvantages these certain devices.
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Elastohydrodynamic Film Study under Impact Loading and Lateral Vibrations
Frýza, Josef ; Bakolas, Vasilios (referee) ; Habchi, Wassim (referee) ; Křupka, Ivan (advisor)
Disertační práce se zabývá chováním a odezvou elastohydrodynamického (EHD) mazacího filmu za neustálených provozních podmínek. V úvodní části práce jsou shrnuty poznatky z oblasti EHD mazání; od jeho historie, přes základní mechanismy mazání a používané experimentální metody, až po nedávno publikované studie zaměřené na transientní podmínky. Hlavním cílem práce bylo experimentálně objasnit vliv provozních parametrů a reologických vlastností maziv na chování mazacího filmu v bodovém kontaktu při jeho nárazovém zatěžování a vystavení příčným vibracím. Za tímto účelem byla vyvinuta laboratorní zařízení umožňující měření rozložení mazacího filmu a tření za kontrolovaných nestacionárních podmínek. Experimenty odhalili zásadní roli přibližovacích a zatěžovacích rychlostí na formování stlačených mazacích filmů při nárazovém zatěžování. Výsledky byly srovnávány s nedávným teoretickým řešením. Bylo ukázáno na jeho nedostatky, jež byly následně odstraněny implementací empirických vztahů zohledňujících reologii maziv. V případě příčných vibrací byly nalezeny hranice selhání mazacího filmu a určeny vztahy popisující vliv příčných vibrací na centrální tloušťku filmu a její fluktuace jednotně pro všechny maziva. Závěrečná část práce poskytuje nový pohled na reologii maziv pomocí inovativního přístupu měření třecích reakcí maziva současně ve dvou směrech kontaktu za podmínek příčných vibrací. Tyto původní výsledky rozšiřují pochopení mechanizmů EHD mazání a mohou být použity k dokonalejším návrhům strojů, a vylepšit tak jejich účinnost, spolehlivost a životnost.
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Multiphase Ti-Ni layer on Ti6Al4V substrate by local nickel alloying
Barančíková, Miriama ; Havlík, Petr (referee) ; Jan, Vít (advisor)
This bachelor's thesis comprises two main parts. The first part consists of a theoretical study on the Ti6Al4V alpha-beta titanium alloy and on the possibilities of adjusting its tribological properties. The second part deals with experimental work with the aim of improving tribological properties of Ti6Al4V by alloying nickel into its surface, creating a hard and homogeneous surface layer with superior tribological properties. In order to achieve these goals, a nickel layer was created on a Ti6Al4V substrate by electrical deposition. The layer was later melted with an electron beam, thus creating a Ti-Ni alloy. Several different parameters of the electron beam were used to create a homogeneous surface layer. This layer was then tested for its mechanical properties. The evaluation of its microstructure was conducted as well. The experiment resulted in the creation of a surface layer with hardness and tribological properties superior to the base material.
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Mechanical activation of chemical reactions at interfaces of MDF composites
Matoušek, David ; Másilko, Jiří (referee) ; Šoukal, František (advisor)
The thesis deals with study of mechnochemical activation of chemical reactions at interphase of MDF composites. MDF composites are high-perspective composite materials on polymer-cement base. They excel especially in terms of flexural strengths. High flexural stregth is caused by binding interactions between the polymer and the cement. This interactions arise due to mechanochemical activation of raw material mixture at the stage of production. This work focuses on the creation of artificial cement-polymer interphase by contacting the surfaces of two molded tablets (polyvinyl alcohol and monocalcium aluminate), activation of chemical reactions at interphase by means of specially designed appartus, which achieves good plane-parallelism of activation surfaces and good definability of activation conditions (shear rate, pressure). After experiments under different conditions, the activated surfaces are analyzed by SEM, EDS, XPS and FT-IR.
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Tribotechnical diagnostics of oils
Pokorný, Ondřej ; Frýza, Josef (referee) ; Svoboda, Petr (advisor)
The purpose of this bachelor’s thesis is compile an overview of currently used sensors for real-time oil analysis. The paper contains a record of knowlenge in field of wear and tribotechnical sensors and determines the appropiate behavior of the tribological system for predictive maintenance. In the next part of the thesis are evaluated the introduced sensors and with help of obtained informations is assembled diagnostic for monitoring the state of gearbox of wind power plants.
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The introduction of metrological procedures for determining the eligibility of gauges in tribology
Rozlílková, Lada ; Harčarík, Matej (referee) ; Šrámek, Jan (advisor)
This bachelor thesis deals with metrological procedures in determining the capability of measuring instruments in production in a company operating in the field of precision engineering. The main goal of each business is its competitiveness in the industry and the satisfaction of customer. Therefore in companies is a great deal of emphasis on modernizing and optimizing the production process, logistics, and reducing the enviromental impact. The customer's demands are constantly increasing and that is why the accuracy of the product is emphasized. So it is not only necessary to produce the product correctly and accurately, but also to check its quality, whether it fits within the given tolerances and meets the customer's requirements.
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Experimental Study of the Lubricant Film under Starved Conditions
Košťál, David ; Čermák, Jan (referee) ; Dzimko, Marián (referee) ; Ali, Fadi (referee) ; Křupka, Ivan (advisor)
The dissertation thesis deals with an experimental study of an elastohydrodynamic contact under insufficient lubricant supply. Theoretical studies published in this research area focus mainly on the development of theoretical models and there is an insufficient number of experimental studies which validate these models. There are two basic methods of starvation severity control in published theoretical models: by positioning of an inlet meniscus and by setting the thickness of an oil layer in the vicinity of contact inlet. The second method is more suitable when considering a wide range of operating conditions, however it is difficult to ensure experimentally. This thesis presents original experimental results and aims to describe the starvation severity level as a function of the inlet film thickness. Deeper understanding of fundamental processes in starved elastohydrodynamic contacts enables the development of more precise models, better ability of prediction of the starvation and improves the ability to avoid starvation in the early design process of key tribological components.
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Piston Ring Tribology in Internal Combustion Engines
Orbán, Tomáš ; Maršálek, Ondřej (referee) ; Raffai, Peter (advisor)
The theme of the thesis is tribology of piston rings for internal combustion engines. The work is divided into seven chapters. The first chapter deals with the piston rings, piston rings requirements, describes the main functions of piston rings, types of piston rings, compression rings and oil control rings. Finally, this chapter provides information about the kinematics of piston rings. The second chapter presents the mechanism of friction and lubrication of piston rings, is dedicated to tribology, friction, friction observation history, mechanism of friction and friction suitability. In addition, the work contains information about lubrication, specifically about a lubrication way of internal combustion engines and lubrication regimes. The third chapter deals with hydrodynamic lubrication. The theme of the fourth chapter is boundary lubrication. The fifth chapter provides information about mixed lubrication. Friction in the oil film is the theme of the sixth chapter. Last seventh chapter deals with dry contact friction due to surface roughness contact.
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Lubricant film formation in oil impregnated sintered metal parts
Látal, Roman ; Polach, Pavel (referee) ; Omasta, Milan (advisor)
This thesis deals with the experimental study of the formation of the lubricating film used for sintered metal parts impregnated with oil. The thickness of the lubricating film in a line contact is measured by the method of optical interferometry of thin lubricating films. In this thesis, the effects of various operating parameters on the formation of the lubricating film are described. The usage of impregnated lubricant leads to insufficient supply of lubricant to the contact. Individual results are significantly influenced by the degree of flooding of the contact area.
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