Study On The Fretting Damage Of Nbr/metal Interface Of Mechanical Seal Auxiliary Components

Mechanical seals not only possess the advantages of high reliability, long service life and low leakage, but also can adapt to many harsh conditions such as high temperature, high pressure and various strong corrosive media. Therefore, mechanical seal is widely used in high technical fields such as aerospace, nuclear power generation. The auxiliary seal which has the ability of axial compensation is the second most important component apart from the surface seal(the main seal). With the service life of the main seal improved quickly, the fretting failure problem on the contact interface of auxiliary seal(usually rubber/metal material counterparts) becomes more obvious than ever and it has now become an important limit factor in the development of mechanical seals to higher reliability and long service life. So there are important theoretical values and engineering meanings to study the fretting tribological behaviors of rubber O-ring used in mechanical seals.In the present study, UMT-3 tribo-tester was used to study the tangential fretting wear characteristics of NBR which was the most common used material in reality. Test results showed that(1) because of the hyperelasticity of rubber, even when the displacement amplitude increased to few millimeters, it still ran in fretting regimes, while for metal the order of magnitude of fretting was usually micron;(2) the tangential fretting of NBR followed the theory of fretting maps; with the increment of displacement amplitude, NBR ran in the partial slip regime(PSR), mixed fretting regime(MFR) and slip regime(SR), respectively;(3) in different fretting regimes, the friction coefficient of NBR showed varied change laws and the surface damages also varied with the increment of displacement amplitude;(4) Abrasive wear, fatigue wear and adhesive wear were the main wear mechanisms for the NBR elastomer before the sticky layer formation; then, the damage mechanism was dominated by plastic deformation and fatigue delamination after a great deal of sticky layer formed;(5) both XPS and FTIR spectroscopy con?rmed that only a simple mechanical rupture of rubber molecules occurred during the fretting process, the chemical modi?cations observed on the worn surface can be attributed to the mechanochemical effects, deformation and fracture of NBR elastomer in the friction zone, rather than a thermo-oxidation process;(6) the surface roughness values of stainless steel influenced the fretting running regimes greatly; the experimental results showed that when Ra≤0.41 μm, the area of PSR and MFR decreased and the boundaries of PSR/MFR and MFR/SR moved to smaller displacement amplitudes with the increment of surface roughness values, which meant that it was easier for NBR to slip; when Ra increased to 2.16 μm, the area of MFR increased and the areas of PSR and SR decreased accordingly compared to that of 0.41 μm; the variation of friction coefficient was influenced by surface roughness differently at varied fretting running regimes; in different fretting running regimes, the surface morphologies of worn NBR and its wear mechanisms varied little.In order to better explain the surface damage of NBR, finite element software ABAQUS was adopted to simulate NBR O-ring under test conditions and the simulation results were compared with those of the experimental ones, so the surface damage of NBR could be better explained; the results of numerical simulation showed that media pressure and displacement amplitude played an important role in the tangential fretting behavior of NBR O-ring; with the increment of displacement amplitude, fretting ran in stick state, mixed stick-slip state and slip state, respectively; the results of experimental tests and simulation ones agreed each other quite well.