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Understanding the generation of third body particles and their contribution to the formation of tribofilms of MoS x thin films is still challenging due to a large number of influencing factors. Besides the structure of the as-deposited MoS x films, the environment and the conditions during the Ball-on-disk tests affect tribofilms and thus the friction. Therefore, the influence of the surface pressure and sliding velocity in air, argon and nitrogen environments on the generation of the third body particles and the tribofilm formation of randomly oriented MoS x films is investigated. A high surface pressure is one major factor to achieve low friction, especially under humid conditions, which is important considering the use in industrial applications, for example dry-running screw machines. However, the mechanisms leading to that frictional behavior are still affected by the surrounding environment. While low friction is caused by a more extensive tribofilm formation in air, in argon and nitrogen, large size third body particles dispensed all over the contact area contribute to a lower friction. Raman scattering reveal a different chemistry of these particles reflected in the absence of laser-or temperature-induced surface oxidation compared to the as-deposited film and the wear track. The Raman scattering results are discussed with respect to the wear particle size, its chemical reactivity and strain-induced bonding changes.

Subject of discussion are simulations and experimental investigations on the acoustic characterization of three single stage centrifugal pumps of different specific speed. In operation, these pump-types generate pressure pulsation at blade passing frequency, primarily due to rotor-volute-interaction. In order to determine the acoustic excitation it is necessary to know about the pumps’ acoustic transmission parameters. In this paper, a one-dimensional numerical model for transient time-domain simulation is presented, which takes into account the pump geometry as well as the volutes’ structural behaviour by means of the local effective speed of sound. Numerical results for the transmission characteristics of the three different pumps are shown in terms of scattering matrices and evaluated against parameters calculated from measurement results. The experimental analyses are carried out using dynamic pressure sensors in both the suction and the discharge pipe. Assuming solely plane wave propagation, the complex acoustic field on each side is evaluated independently. The so called “two source” method is then used to determine the transmission parameters of the pumps in standstill for a range of frequencies experimentally. Subsequently, the acoustic excitation at varying rotational speed is evaluated by means of measurements at the pumps in operation and presented as monopole and dipole source types for cavitation-free conditions.

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ZusammenfassungUnsynchronisierte, trockenlaufende Schraubenmaschinen weisen ein großes Potential auf, eine ressourcenschonende Alternative zu konventionellen Bauformen von Schraubenmaschinen zu liefern. Durch die Einsparung eines Synchronisationsgetriebes und den Verzicht auf ein flüssiges Schmiermittel ergeben sich ökonomische und ökologische Vorteile, da der Material‐ und Energieeinsatz reduziert werden. Die Reinheit des Prozessgases wird erhöht und die Umweltbelastung wird somit minimiert. Vakuumbeschichtungsverfahren stellen eine der Schlüsseltechnologien zur Realisierung einer unsynchronisierten, trockenlaufenden Schraubenmaschine dar. Durch die endkonturnahe Beschichtung und die Möglichkeit, die strukturellen Eigenschaften der Beschichtung gezielt zu verändern, lassen sich die Dünnschichten optimal konditionieren. Durch den Einsatz von MoS2‐Dünnschichten als Vertreter der Festschmierstoffe können die Reibeigenschaften der Schraubenmaschinen verbessert werden, sodass auch an dieser Stelle ein großes Potential vorliegt, die Reibung und somit den Energieeinsatz zu reduzieren.