L. Deters

An axisymmetric hydrodynamic interface element for finite-element computations of mixed lubrication in rubber seals

This paper presents an elegant way to compute hydrodynamic lubrication in machine parts, especially in highly deformable dynamic seals. In such tribologic systems, the sealing and frictional behaviour is highly related to the interaction between the hydrodynamic lubrication and the structural deformation of the seal. In this work, a hydrodynamic interface element is developed in order to achieve a strong coupling of the fluid dynamics and the deformation of the solid structure. The fluid flow is represented by the two-dimensional steady-state Reynolds equation, the structural deformation by standard finite-element procedures. This method enables the application of arbitrary, non-linear material models provided by finite-element programs. Furthermore, a model for mixed lubrication, including frictional effects, is presented.

Simulating transient wear characteristics of journal bearings subjected to mixed friction

This article describes a calculation model for the simulation of the transient wear characteristics of journal bearings subjected to mixed friction. For predetermined time steps the local wear is calculated for circumference and width. The resulting changes to the gap geometry then flow directly into the further calculation process. The solid contact load ratio and boundary friction ratio in the mixed friction area are calculated on the basis of real rough surfaces. Modifications to the rough surfaces resulting from the running-in process are taken into consideration. In addition the microhydrodynamic effects, elastic deformations of the bearing environment and mass conserving cavitation are also recorded. The calculation model’s potential is demonstrated by means of an unsteady loaded conrod bearing.

Oscillating thrust bearing at fuel lubrication

As part of an FVV research project (ref. no. 920) tests were conducted on a diesel injection pump’s oscillating selfaligning thrust bearing at Otto von Guericke University Magdeburg. Combining tests under mixed and boundary lubrication conditions with simulation of the contact conditions deepened knowledge and understanding of the tribological processes that occur.

Calculation of a Stribeck curve of a journal bearing

Abstract The Stribeck curve can be used to describe a range of different states of friction and lubrication of lubricated journal bearings as a function of their macroand microgeometry (roughness), lubricants and operation conditions. In the calculation model presented, fluid friction is determined on the basis of established solutions. Solid friction is determined by using an energy approach. For this approach it is assumed that solid friction can be calculated from the sum of various energy conversion processes. A measured and a calculated Stribeck curves are compared, and the results obtained are discussed. The calculation shows that, unlike for plain surfaces, the minimum film thickness tends to a finite value rather than tending to zero.

Reibung, Verschleiß und Schmierung

Reibung und Verschleis sind haufig unerwunscht. Wahrend Reibung den Wirkungsgrad von Maschinenelementen, Maschinen und Anlagen verschlechtert und damit den Energiebedarf erhoht, mindert Verschleis den Wert von Bauteilen und Baugruppen und kann zum Ausfall von Maschinen und Anlagen fuhren. Andererseits wird bei vielen technischen Anwendungen eine hohe Reibung angestrebt, Tabelle 10.1. Auch Verschleis kann in Sonderfallen in begrenztem Umfang nutzlich sein, so z.B. bei Einlaufvorgangen.

Lagerungen, Gleitlager, Wälzlager

Lagerungen im Maschinenbau ermoglichen Relativbewegungen von Maschinenteilen und stellen somit im Sinne der Getriebelehre die konkrete Ausformung von Gelenken dar, Abb. 11.1.: Linearlager erlauben translatorische Relativbewegungen Drehlager ermoglichen rotatorische Relativbewegungen Gelenklager lassen Drehbewegungen um beliebige Achsen zu Drehlager, die in sich axial verschiebbar sind, bilden Dreh-Schubgelenke

Self-lubricating dry rubbing bearings-fundamentals and methods of calculation

Following a general discussion about the construction and the lubrication mechanisms of compound bearings made of a steel backing with a porous bronze layer filled with a PTFE/solid lubricant mixture, problems in conjunction with the use of pU diagrams are pointed out. Instead of pU values parameters such as the overlap ratio, the compressive strain or the shear stress ratio for example which are imporant, for a reliable design of dry rubbing bearings are represented then. As basis for the friction calculation a relationship between the shear stress ratio and the quotient of the compressive strain and the overlap ratio was experimentally found and the temperature-dependent curves of the Youngs modulus and of the shear strength of PTFE are shown. After that, the contact angle influenced by deformation, wear and temperature rise is examined and an approximation equation for determining the contact angle is introduced. A method for calculating temperature, friction and working life of dry rubbing bearings that is based on theoretically and experimentally established data is offered afterwards. In addition the positive effect of a wear particle trap is demonstrated. Finally, calculation examples show the mode of operation of the calculation method.

Calculation of EHL contacts in mixed lubrication regime

A calculation model is presented for machine elements operating under mixed lubrication regime. The following conditions are assumed: elastohydrodynamic point contact; stationary rough surface to study pure sliding conditions; non-Newtonian Ree-Eyring fluid model; linear-elastic, ideal-plastic material behaviour and isothermal conditions. Under these constraints some detailed investigations within the mixed lubrication regime are made.

Manganhartstahl im Stoßverschleißtest

Die Schlagleisten in Prallbrechern unterliegen einem hohen Verschleis. Um den Prozess des hauptsachlich auftretenden Stosverschleises zu simulieren, wurden Modelluntersuchungen mit einer speziellen Prufeinrichtung durchgefuhrt. Dabei konnten 11 verschiedene Chargen von Manganhartstahl, die sich im wesentlichen in ihrer chemischen Zusammensetzung unterschieden, untersucht werden. Die unterschiedliche chemische Zusammensetzung der einzelnen Chargen fuhrte zu unterschiedlichen Ergebnissen hinsichtlich der Verschleisbestandigkeit der einzelnen Modellschlagleisten. Hierbei ist ein signifikanter Zusammenhang zwischen der Verschleisbestandigkeit und der Makroharte der Manganhartstahle zu erkennen. Die Umfangsgeschwindigkeit des Rotors der Prufeinrichtung beeinflusst ebenfalls das Verschleisverhalten, und zwar fuhrte eine hohere Umfangsgeschwindigkeit zu hoherem Verschleis. Mikroskopische Untersuchungen an geschadigten Probekorpern zeigten ein Einbetten von kleinsten Partikeln aus Beton im oberflachennahen Stoffbereich der Metallmatrix. Manganese steel in impact wear testing Beating arms in impact crushers show high wear. In order to simulate the process of the mainly occuring impact wear, experimental investigations with a special test device were carried out. With this 11 different charges of manganese steel differing in their chemical composition were tested. The different chemical composition of the charges led to different results concerning the wear resistance. A significant interrelationship between wear resistance and macro-hardness of the charges of the manganese steel could be detected. With a faster rotor speed a considerable increase of wear could be determined as well. Microscopical investigations on worn test pieces exhibit a typical embedding of small particles of concret into the metal matrix.

Normen, Toleranzen, Passungen und Technische Oberflächen

Normen, Toleranzen und Technische Oberflachen haben eine grundlegende Bedeutung fur die Beschreibung und Definition von technischen Gegenstanden. Daher ist es notwendig sich mit diesem Inhalten vertraut zu machen, bevor einzelne Konstruktionselemente betrachtet werden.