Accelerated testing of Shaft Seals as components with complex failure modes

Radial Shaft Seals (RSS) are widely used in all fields of mechanical engineering for sealing of rotating elements. Up to now there has been no possibility to include Radial Shaft Seals adequately into the lifetime calculation of mechanical systems. In this paper the difficulties in accelerated life testing of RSS are presented and discussed. First of all, this involves the consideration of the RSS only as one part of a complex sealing system. Then, the influences on reliability and lifetime are specified and a definition of a failure itself is given. The main part identifies the major failure modes, the failure causes and the effects of these failures on the sealing system. All those points listed above result in a definition of testing parameters and first accelerated life tests of RSS. Finally an outlook based on the results of the first tests is given. In this paper the fundamentals to determine the reliability of RSS are given. Though the RSS is a simple looking mechanical element, there are complex sealing and failure modes that have to be taken in account when evaluating the lifetime. The effort for reliability testing is enormous, due to the many existing influencing factors. A main part of the reliability analysis, especially for RSS, is the determination of the failure modes, which can only be identified with different measurement methods. An evaluation of the reliability of RSS based on the failure time without taking the different failure modes in account leads to a mixed distribution. As shown in the last section accelerated testing normally leads to a change of the failure modes and needs a close examination of all components of the sealing system after a test run. Under the shown conditions accelerated testing of RSS is very demanding.