Browsing by Author "Feuchtmüller, Oliver"

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    An empirical study on the friction of reciprocating rod seals at predefined lubrication conditions and shear rates
    (2022) Feuchtmüller, Oliver; Hörl, Lothar; Bauer, Frank
    A key factor influencing the friction of rod seals is a thin oil film, which is dragged into the sealing gap at outstroke and instroke. Accurate determination of oil film thickness in the sealing gap of rod seals is a challenging task since it is only in the range of a few nanometers. A novel measurement procedure to analyze the friction of common reciprocating sealing systems in direct relation to the shear rate and film thickness is introduced in this paper. Results from a first empirical study with film thicknesses in the range of a few nanometers and shear rates up to γ˙=107 s−1 were used to compare the friction of practically relevant polyurethane U-cups. The U-cups differ in their geometry and surface roughness. It is seen that even at such thin films, the measured friction of those seals can be approximated by Newtonian fluid friction (speed, film thickness, viscosity, contact area). In general, the novel measurement procedure is useful in a scientific and technical context, since it offers a new perspective on tribological mechanisms at thin film lubrication conditions.
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    An empirical study on the wear of reciprocating hydraulic rod seals using 15 different oils
    (2022) Feuchtmüller, Oliver; Hörl, Lothar; Bauer, Frank
    Hydraulic oils differ in their chemical composition and viscosity substantially. Their influence on the wear of rod seals is neither fully understood nor can be predicted precisely. The primary objective of this study was to evaluate the influence of various oils and their wetting properties on the wear of rod seals. In an empirical study, the wear of 30 commercially available polyurethane U‐cups was investigated with 15 different oils using a recently built test rig. The wear of rod seals increased with lower viscosity and higher polarity of the oil. Both oil properties are combined in a new parameter which helps to assess the lubricity of oil and the wear of rod seals.
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    Remarks on modeling the oil film generation of rod seals
    (2021) Feuchtmüller, Oliver; Dakov, Nino; Hörl, Lothar; Bauer, Frank
    The oil film generation of a U-cup rod seal and the oil film thickness on the rod after outstroke were analyzed analytically, numerically, and experimentally. The analyzed sealing system consists of an unmodified, commercially available U-cup, a polished rod, and mineral oil. The inverse theory of hydrodynamic lubrication (IHL) and an elastohydrodynamic lubrication (EHL) model - both based on the Reynolds equation for thin lubricating films - were utilized to simulate the oil film generation. In the EHL analysis, physical parameters and numerical EHL parameters were varied. Both the analytical and numerical results for the varied parameters show that the film thickness follows a square-root function (i.e., with a function exponent of 0.5) with respect to the product of dynamic viscosity and rod speed, also referred to as the duty parameter. In comparison to the analytical and numerical results, the film thickness obtained via ellipsometry measurements is a function of the duty parameter with an exponent of approximately 0.85. Possible causes for the discrepancy between theory and experiments are discussed. A potential remedy for the modeling gap is proposed.
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    Zur Schmierfilmbildung und Reibung von Stangendichtungen
    (Stuttgart : Institut für Maschinenelemente, 2024) Feuchtmüller, Oliver; Bauer, Frank (apl. Prof. Dr.-Ing.)
    Rod seals are crucial machine elements for hydraulic and pneumatic cylinders. During the outstroke and instroke of a cylinder, the piston rod drags a thin oil film into the sealing gap forming a lubrication film. The oil film formation and tribological mechanisms in the sealing gap are of great technical interest due to their influence on friction, wear and leakage. In empirical tests with different sealing systems and operating conditions, the oil film formation and friction of rod seals were analyzed. The film thickness was measured using ellipsometry. For the friction measurements, a common test arrangement described in ISO 7986 was used. Additionally, a new measurement procedure, which combines film thickness measurements and friction measurements, is introduced. Different polyurethane U-cups and different lubricants were used for the empirical tests. Based on the results, the influence of operating conditions (rod speed, pressure, temperature) and properties of the sealing rings (hardness, surface energy, roughness) and lubricants (viscosity, surface tension) on the oil film formation and friction are discussed. It is remarkable that the analysis of the oil film formation in the nanometer range was successful, and the measured friction can be approximated by Newtonian fluid friction (speed, film thickness, viscosity, contact area). A correlation between wetting properties and the friction of the rod seals was not observed.