Ultra-low friction of sintered silicon carbide in aqueous tribological environment of mechanical seals

The ultra-low friction (ULF) phenomenon between the water lubricated silicon carbide (SiC) surfaces presents unique natures: little-wear, extremely low friction coefficient (<0.01), thin lubricant film (approx. 100 nm), etc. This ULF state could be an appropriate running state in mechanical seals due to the balanced performance between leakage and wear. However, the understanding on its lubrication mechanism and the controlling methods are still insufficient. In this book, a modified surface-contact reciprocating test method was used to study this ULF phenomenon. The necessities for building the ULF state were proposed. However, the ULF state is neither possible to be reproduced manually, nor to be inherited from another running-in. The main reason is attributed to the unavailable operation precision when assembling two tribo-surfaces. Thus, a running-in period is unavoidable to build an ULF state. A unique method was proposed and verified effective to optimize the running-in procedure for building the ULF state. Comparing to the non-optimized tests, the same stable ULF state was built. The running-in duration was shortened by 80%, meanwhile the severe abrasive wear was prevented. This optimization method means tremendously to the ULF's industrial application. To obtain a pair of seal faces in mechanical seals, it is not necessary to polish the surfaces and then to assemble them precisely. Instead, a pair original sintered SiC surfaces can be directly pressed onto each other and then proceed to an optimized running-in. After this running-in, a pair of precisely mated tribo-chemically smoothened surfaces without severe abrasion can be naturally obtained.