Wassereinzug über ölhydraulische Stangendichtsysteme

  • Water entrainment via oil-hydraulic rod sealing systems

Mielke, Tobias; Schmitz, Katharina (Thesis advisor); Bardow, André (Thesis advisor)

Düren : Shaker Verlag (2019, 2020)
Book, Dissertation / PhD Thesis

In: Reihe Fluidtechnik. D Band 98
Page(s)/Article-Nr.: 1 Online-Ressource (XXIX, 117 Seiten) : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2019


Hydraulic systems are indispensable in many areas of mechanical engineering, where those systems provide the necessary forces and moments. At the same time, hydraulic systems are subject to a trend towards cost reduction and increased efficiency, which means, among other things, that the tanks of the systems are reduced in size or in some cases completely omitted. As a result, the pressure medium in the circuit cannot rest sufficiently and foreign matter, such as particles or foreign liquids, cannot be separated or can only be separated incompletely. The entry of these foreign substances must therefore be effectively prevented in advance in order to guarantee a sufficient service life of the systems. An example of the introduction of such foreign substances is the entrainment of water, which can enter via the dynamic sealing area between the sealing body and the piston rod of a hydraulic cylinder. A distinction can be made between the entry of free water and the entry of water dissolved in the lubricating layer. In the first part of this work, the mechanisms of the entry of dissolved water via rod sealing systems are systematically investigated. Based on the underlying models of the sealing mechanism, the entrainment of water dissolved in the lubricating film is modelled. The basis for the model is the knowledge of the water dissolving capacity of the pressure fluids as well as the properties of the fluids as a function of the dissolved water content. Furthermore, the absorption mechanisms of water into the lubricating film are investigated and the saturation process is modelled, parameterised and validated by experimental tests. In the second part the entrainment of free water is investigated. Based on the sealing mechanism, the entrainment is modelled. The model is validated by means of a test bench and common sealing systems are systematically measured for different operating points. Subsequently, the influence of wipers on the water entrainment is investigated. The results obtained are then transferred to the application case of a mini-excavator, which makes it possible to estimate the amount of water entrained.