System-Based Monitoring Approach for Mechanical Seals Using Excited Mechanical Resonances by an Electromagnetic Acoustic Transducer

Mechanical seals are widely used today for sealing applications in the field of hydraulic fluid machinery. The main components of the seal are the stationary ring and the rotating ring. After the seal is assembled, the sealing gap is formed between the rings. The solid-state contact situation in the gap is crucial for the service life of the seal. To avoid unexpected machine stoppages due to seal failures, monitoring of the seal is required. In this paper, a new approach to seal monitoring is presented. In this approach, the stationary ring is considered as a mechanical system and a specific mechanical resonance of the stationary ring is excited with an electromagnetic acoustic transducer and measured with an accelerometer. The mechanical resonance is influenced by the solid-state contact situation in the sealing gap and the resulting mechanical coupling between the rings. A specially developed test rig is used to press the rings together gradually, thus changing the contact situation in the sealing gap. The changes in the calculated magnitude and phase of the system are evaluated in terms of the ring compression. The results clearly show that the presented approach is suitable to measure the interaction between the two rings, as the magnitude shows a relative change of up to 75 % and the phase increases by 48° when the mechanical coupling is increased by gradually pressing the rings together. These results show that the excited mechanical resonances can be used to indicate mechanical changes in the seal and thus provide the basis for a novel monitoring approach.