Ein Simulationsmodell zur Analyse des Schmierfilms von Stangendichtungen

Abstract
Even though the most important parameters that influence the performance of a rod scal are known today, it still remains very difficult to measure or predict certain characteristic parameters such as the flm thickness between the scal and the rod. This leads to two prolems: On the one hand, simulation models for rod scals are usually quite complicates due to the complexity of the tribological phenomena and the soft clastomeric materials used for the scals. This also causes extensive computing times to obtain results. On the other hand, it is very difficult to validate the developed model due to the complicates measurements.
Thus, it is no big surprise that only few of the simultaion models for rod scals which habe been developed in the past thwo decades have been validates with actual measurements. Therefore, no quantitative prediction of the seal performance is yet possible but he analysis of the qualitative bahavior of the rod scals is feasible. Yet, these possibilities are mostly restricted to very few people at universities or research departments due the complexity of the simulation programs. Also, apart from one exception, no simulation approach exists to treat starved conditions of rod scals although many seals operate at least partly in such lubrication conditions.
In the present thesis, a model based on the theory of inverse hydrodynamic lubrication in steady state conditions was developed. This theory requires an inflexion point in the contact pressure distribution between the seal and the rod. However, in many practical casses this inflection point cannot be found. The maximum of the calculated pressure gradient, which is often uses in these cases, strongly depends on the mesh density of the FEA calculation of the pressure distribution. The gradient is thus determined by a boundary condition of the simulation and not by the physical problem. In this work, the pressure build-up in the converging gap before the contact, the "booster zone", is calculated and iterativly merged with the static contact pressure distribution between seal and rod. This approach is very fast and shows a good agreement with highly sophisticated models that couple the film thickness in the contact and the change in contact pressure due to the fluid film.