Study on Stick–Slip Friction of Reciprocating O-Ring Seals Using Acoustic Emission Techniques

Abstract

The stick–slip friction of the reciprocating O-ring seal in reactor coolant pumps (RCPs) has significant effects on the characteristic of the stationary ring and dynamic behaviors of the entire sealing system and has always been somewhat difficult to study due to the fact that entrance into the contact area is almost impossible and only indirect measurements can be used.

The acoustic emission (AE) technique is a direct measurement method and is sensitive to the microstructural changes within the material and is used in this article to study the four typical states of the stick–slip friction of the reciprocating O-ring seal, including standstill, partial slip, transition from static to dynamic friction, and slip of low amplitude.

Experiments investigating the stick–slip friction of the specimens of the O-ring seal were performed using an SRV friction and wear tester and an AE device. From the experimental results, the following relationships were discovered: the frequency-domain characteristic of the AE signals of the O-ring seals of ordinary materials, the correlations of the AE root-mean-square (RMS) voltage with the friction coefficient and the stick–slip friction, and the influence of the normal load and precompression ratio of the specimen on the AE activities. The article focuses on how the AE activities associated with the different friction states could be connected with the tribological behaviors of the frictional pair. The AE technique is proven to be effective in characterizing the various states of stick–slip friction and helpful in monitoring the conditions of the reciprocating O-ring seal in operation.

KEY WORDS:

• Reciprocating Seals
• Stick–Slip
• O-Rings
• Acoustic Emission
• Mechanical Seals
• Seal Online Monitoring

ACKNOWLEDGEMENTS

The authors acknowledge financial support from the National Basic Research Program of China (973 Program, No. 2009CB724304), the Key Research Program of the State Key Laboratory of Tribology of Tsinghua University (No. SKLT08A06), and the National Natural Science Foundation of China (No. 50975157).

Review led by Richard Salant