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Analysis, Modelling and Simulation of Wear at Multiple Scales for Span Time Prediction at Shaft Seals Made of PTFE-Compound

Rotary shaft seals made of Polytetrafluorethylene (PTFE) exceed the sliding velocity and the chemical resistance of elastomeric seals. Wear is the only failure mode, which limits the life span. PTFE possesses an extremely low frictional coefficient due to its unique molecular andmorphological structure. PTFE itself has a relatively poor wear resistance due to its soft nature. To use PTFE for sealings it is usually filled with particles, small plates or fibres for example. These fillers affect the tribological behaviour and improve the wear resistance. Filled PTFE is called a PTFE-compound. The subject of this thesis is the numerical description of the tribological system shaft seal. It consists of a shaft seal made of PTFE-compound, a steal shaft and an intermediate lubricant. The PTFE-compound itself, the tribological counterpart, the lubrication state and the operating conditions influence friction and wear; thus they must be taken into consideration. Solely one length scale is not sufficient to describe and simulate such complex interactions. A multi scale approach was set up.

Three scales were taken into account to formulate a bottom-up-approach; from the smallest to the biggest scale:

  • The meso scale model is set up between the nano and micro scale. It contains an energetic approach for the calculation of the wear rate. It considers temperature-dependent compression and shear strengths using dimensionless parameters. The apparent energy density takes the lubrication state into account.
  • The micro scale model calculates thermal material properties using a representative volume element.
  • The macro scale model includes a geometric model of the sealing and the wear algorithms. These algorithms reduce the shaft seal model volume to simulate wear. A finite element framework is used to integrate the meso- and micro scale model.

Extensive experimental work was performed to characterise the thermo-mechanical and tribological material behaviour. These experiments are the basis for the multi scale modelling. A computer tomography scanner was used to analyse the material composition and its microstructure. Hardness and nano indentation techniques were used to identify tribological parameters.Tensile, compression and shear tests were performed on an universal testing machine to describe the thermo-mechanical stress-strain-relation. A ring-on-disc test rig was coupled with a thermal imaging camera to measure friction, wear and the temperature nearby the friction contact.

Lesen Sie die deutsche Zusammenfassung auf Kunststoffe.de
Author
 André Daubner

André Daubner
Institut für Maschinenelemente
Universität Stuttgart

Information

Free keywords: Wear, Wear Smulation, Span Time Prediction, Multiscale Approach, Tribology, PTFE, Polytetrafluoroethylene, Sealing Technology, Shaft Seal Ring
Institute / chair: Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik der Universität Stuttgart
Language: German
Technical consultant for expert services: Prof. Dr.-Ing. habil. Werner Haas (Betreuer), Prof. Dr. rer. nat. Siegfried Schmauder
Publication year: 2014
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) / Kunststoffe.de

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