Dichtheit von Radial-Wellendichtringen auf Gegenlaufflächen mit mesoskopischen Strukturen

authored by

Mark Philipp Matus

supervised by

Gerhard Poll

Abstract

In other projects the reasons for occurring leakage were investigated. However there is no satisfying method to identify critical surface structures such as lead on shafts on the market yet. Furthermore reliable limits are not known. Also in a properly executed grinding process or in the further handling process, scratches on the micro or meso scale can occur on shaft surfaces. In practice it can happen that surfaces, even those identified as good or lead-free, can be a cause of leakage. To promote the current state of research, in this thesis the investigations were carried out in reverse. Good seal counterfaces, which otherwise could be sealed properly, were micro-structured in order to investigate their effect on the performance of radial shaft seals. The focus was on investigating critical scratch failures. For this purpose laser scratches with a variation in depth, orientation, and number were created on the seal counterfaces, and leakage tests were carried out. Test results carried out with mechanically scratches support the comparability with laser-scratches. Different radial shaft seal types, such as plain lip seals or seals with unidirectional sealing aids were tested on the scratches with regard to their capability to compensate failures and to prevent leakage. The micro structures were precisely measured with a 3D-laserscanning microscope. The test results show that depth, orientation, and number of the scratches can have a massive impact on the seal performance. Also the distance and orientation between the structures can affect the leakage-free operation of the sealing system. One important result can be pointed out, namely that a small number of scratches with depths in the order of magnitude of the tolerable surface roughness can lead to a significant amount of leakage and consequently the loss of the sealing system function. By superimposing the reverse pumping rate measured on failure-free counterfaces and the pump rate influenced by the scratches, the net pump rate of the scratches was estimated. An empirical model to estimate the net pump rate of scratches was introduced. Beside the experimental investigations theoretical investigations using computational fluid dynamics were carried out with the open source multiphysics software ELMER. Thus the fluid flow through the scratches was estimated and compared with the experimental results. The results obtained with different solvers (Reynolds vs. Navier-Stokes) were compared and the application limits regarding the calculation of the considered structure parameter combinations could be identified.

Organisation(s)

Institute of Machine Elements and Engineering Design

Type

Doctoral thesis

No. of pages

177

Publication date

2023

Publication status

Published

Sustainable Development Goals

SDG 3 - Good Health and Well-being

Electronic version(s)

https://doi.org/10.15488/14579 (Access: Open)