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Lubrication of plastic gears
Hartl, Petr ; Čermák, Jan (referee) ; Křupka, Jiří (advisor)
The work deals with the process of lubrication of gears from a combination of materials that have significantly different material properties. The experimental measurement is performed on a tribometer in simulated gear contact with a ball-disk configuration. The Chromatic Optical Interferometry method is used to measure the formation of a lubricating film in contact. The purpose of this work is to clarify the process of film thickness formation and compare experimental measurements with predictions, which are valid in Soft EHL regime.
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Experimental Study of Lubrication Films Formation During Start-up and Reversal Motion of Rubing Surfaces
Svoboda, Petr ; Dzimko, Marián (referee) ; Čermák, Jan (referee) ; Dobeš, Petr (referee) ; Křupka, Ivan (advisor)
This dissertation is focused on the effects of both artificially produced and real roughness features on mixed lubrication film formation during start-up and reversal of non-conformal contacts operated under rolling/sliding conditions. The start-up operation of mixed lubricated contacts represents one of the transient conditions that bring the risk of the surface damage because of asperities interactions. Chromatic interferograms captured by CMOS high-speed camera during start up of the motion enabled to observe the detailed changes in lubrication film caused by surface features. The observation of the effects of surface dents artificially produced on the ball surface helped to understand better the behaviour of real surface topography. It was found that the presence of shallow surface features can help to separate mixed lubricated rubbing surfaces more efficiently than it could be suggested from the results obtained with smooth surfaces. It can be suggested from the obtain results that properly designed topography of the rubbing surfaces can help to reduce the asperities interactions under transient operational conditions.
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Design of Artificial Hip Joint Test Rig
Dočkal, Kryštof ; Košťál, David (referee) ; Vrbka, Martin (advisor)
In this thesis, is described one of possible approachs to the design of the hip joint simulation rig, primarily designed for analysis of the lubricant film thickness at the contact of two conformally curved surfaces (femoral head and acetabulum). In relative motion of those two components of artificial hip joints is necessary to observe the behavior of lubrication film between them. The observation is also related to choice of appropriate observational method. In the design of the artificial hip joint is today primarily used wear simulations on smulations rig with very accurate simulation of kinematics of biological hip joints. For description of the behavior of the lubricants between conformall surfaces is used a simplified kinematics along with optical interferometry. The simulation rig will be able to study behavior of lubricant layer using optical inteferometry,
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Film thickness distribution during the start-up of smooth surfaces.
Manga, Martin ; Křupka, Ivan (referee) ; Svoboda, Petr (advisor)
Bachelor thesis is engaged in experimental study of start-up of smooth surfaces under the conditions of mixed and elastohydrodynamic lubrication. Start-up is non-stationary process, whereat the surface doesn’t need to completely separated with lubrication film. Therefore it exists a real risk of failure. Study summaries all present studies and extends with own experiment on the equipment of tribological laboratory. The evaluation of the experiment was made by chromatic interferometry. This method is used to measure thin lubrication films. Experiment for miscellaneous values of acceleration confirms the findings of previously studies.
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Surface texturing of rubbing surfaces
Chlachula, Petr ; Čermák, Jan (referee) ; Křupka, Ivan (advisor)
Surface texturing of rubbing surfaces represents the way how to increase tribological performances by improving the lubrication film formation and diminishing friction and wear. Its application in machine components requires detailed understanding of the mechanism taking place between rubbing surfaces in microscopic scale. This diploma thesis is focused on the processes taking place in tribology systems to consider the possibility of surface texturing applications in highly loaded machine parts operated under transient operational conditions.
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In-situ Study of Surface Topography Changes in Elastohydrodynamic Contact
Šperka, Petr ; Dzimko, Marián (referee) ; Návrat, Tomáš (referee) ; Dobeš, Petr (referee) ; Hartl, Martin (advisor)
This dissertation thesis deals with elastohydrodynamic lubrication (EHL) of surfaces with real roughness. Systematic study of surface harmonic components behaviour, during their passage of the EHL contact, by other authors led to retrieval of a uniform principle according which individual harmonic components deform inside the contact. Although the amplitude attenuation model can provide rapid tool for more accurate surface assessment in design process it has not been validated on real surfaces till now. The thesis represents pioneering work on quantitative analysis of real surfaces EHD measurements. It contains original and new results with real and model roughness features that in many cases confirm theoretical expectations. Deeper understanding of surface roughness behaviour inside EHL contact, which is typical for machine parts like bearings, gears, cams etc., can help to improve design process of the components and ultimately enable machines and equipment to work with lower energy requirements and higher durability.
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Study of lubrication films formation under starved lubrication conditions
Košťál, David ; Hartl, Martin (referee) ; Křupka, Ivan (advisor)
The purpose of this thesis is to reveal production mechanisms of lubrication films between non-conformal surfaces in situations, when is not possible to designate lubrication regime as fully flooded elastohydrodynamic contact. Under certain conditions of lubrication volume, rolling speeds, temperatures, lubrication properties or loads could lubrication film decrease under values determined by fully flooded formulas. This regime is designated as starvation at it includes risk of increased wear. In this thesis the methodology and the new simulator of starving contact are described. Obtained film thickness results are compared with existing numerical models.
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Study of Correlation between Grease Film Formations and Mechanical Losses on Various Surfaces
Sakai, Kazumi ; Glovnea, Romeo (referee) ; Gonçalves, David (referee) ; Křupka, Ivan (advisor)
Tato disertační práce se zaměřuje na studium závislosti mezi reakčním momentem ložiska mazaného plastickým mazivem s lithným mýdlem a vlastnostmi maziva, jako například tloušťka vytvářeného mazacího filmu, jeho reologie, struktura zpevňovadla, trakční vlastnosti či vliv topografie povrchu. Typ maziva poskytujícího nižší odpor závisí na podmínkách provozu ložiska, zejména rychlosti. Chování mazacího filmu za nízkých rychlostí má vliv na reakční moment ložiska v nízkých rychlostech. Mez toku a trakční chování koreluje s momentem ložiska za vysokých rychlostí. Schopnost zpevňovadla vstupovat do kontaktu má vliv na tloušťku filmu, vzhled kavitační oblasti na výstupu kontaktu a chování hladovění. Důvod vstupu zpevňovadla do kontaktu je jeho chemická struktura. Vysoká polárnost hydroxylových sloučenin zpevňovadla podporuje jeho vtažení kontaktními povrchy. Mazivo s nejvyšší polaritou prokázalo na površích obsahujících denty nejčastější vstup do prostoru dentů. Na základě předchozích pozorování je navržen popis principu mechanismu mazání.
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The effect of surface grooves on point contacts lubrication
Matoušek, Kamil ; Čermák, Jan (referee) ; Šperka, Petr (advisor)
This diploma thesis deals with experimental study of the effect of surface grooves on distribution of lubricant film in elastohydrodynamic lubricated point contact. Lubricant film thickness was measured by ball-on-disc apparatus using an optical interferometry technique - thin film colorimetric interferometry. The effects of groove geometry, lubricant and operating conditions were studied in this diploma thesis. The effects of these variables are evaluated based on newly suggested parameter Rgi (groove influence ratio). Groove influence ratio is defined as an influenced film thickness influenced by groove divided by film thickness for smooth surfaces.
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The effect of lubricant contamination and degradation on lubricating film behavior
Strnad, Jan ; Dzimko, Marián (referee) ; Omasta, Milan (advisor)
Lubrication contamination and degradation is one of the major causes of unexpected failure of tribological nodes. As a result, different levels of maintenance are introduced in practice, leading to a longer service life of the lubricated node. These systems often include sophisticated on-line diagnostic tools that can be used to evaluate a sample of a lubricant using certain variables such as viscosity, number of particles, humidity, dielectric constant, etc. Based on changes of these variables some systems can make corrective measures such as filtering or complete replacement of lubricant. Therefore, the aim of this experimental thesis is to determine the influence of lubrication contamination (solid particles, moisture) and degradation (oxidation) on the lubricating film behavior with respect to its limit bearing capacity. To examine the thickness of the lubricating film, friction and wear, an optical and MTM tribometer, in the ball-on-disc configuration, was used.
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