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Berührungsfreie Dichtsysteme für Anwendungen im Fahrzeug- und Maschinenbau: Dissertation

. Institutsbericht (2005)275.

Abstract

Due to environmental protection, safety and cost effectiveness non-contacting seals are more and more used, if non pressurized shaft interfaces have to be sealed reliably and maintenancefree. The increasing of rotational speed, the demands of low power loss and long lifetime is often not to be achieved with contacting rotating shaft seals made of rubber. The maximum allowable circumferential speed of a rotating shaft seal made of fluoro elastomer and a shaft diameter of 80 mm is 30 m/s, according to a rotational speed of 7000 min-1, when all other operating conditions are optimal. Higher circumferential speed or disadvantageous operating conditions are leading to a higher abrasion of the sealing edge and finally to failure. By using non-contacting seals, there is no contact and for this reason no abrasion. Using non-contacting seals, there are unfortunately no standard systems in opposite to many contacting rotating shaft seals. Therefore it is essential to design and dimension a noncontacting seal for each new application. In practice, manageable solutions and guidelines exists only for sealing low viscous fluids with high run accuracy, for example in the working spindle of machine tools. Verified experimental solutions for high viscous fluids, smaller run accuracy which leads to dynamic changing gap heights, self induced air flow with resulting oil mist leakage are not known. This tends to result in, that non-contacting seals, for example for rail-mounted vehicle transmissions or transmissions in wind-powered devices are not being designed and dimensioned, but developed by trial and error with a high investment. The goal of this research work was, to examine the function of non-contacting seals under special operating conditions to be found in aggregates of vehicle and mechanical engineering, like: • sealing high viscous fluids, • appearance of dynamic changing gap height, • appearance of self induced air flow, • demand of small axial mounting space. Experimental results and design details are described in diagrams and illustrated figures. Most important for reliable sealing is the entrance zone. A well designed entrance zone prevents fluid to enter in the interior zone of non-contacting seals. When sealing high viscous fluids, the collecting chamber should be noble designed because of the worse flow behaviour. This is also valid for dynamic changing gap heights leading to higher incoming fluid flows. Self induced air flows could be verified, both by experiment and Finite Element Analysis (FEA). FEA was used to optimize the design of non-contacting seals. Resulting sealing design showed less or no air flows. So it was possible to avoid the leakage of oil mist by keeping primary sealing function. The results of this work are summarized in advanced design guidelines for each viewed item. It enables engineers to design reliably operating non-contacting seals for their specific application. Additionally, principal sketches show, how easy mountable sealing systems with axial mounting direction should be designed for inner and outer sealing.

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