Si3N4 and Si3N4/SiC composite rings for dynamic sealing of circulating fluids

Abstract

Silicon nitride (Si 3 N 4) and silicon nitride/silicon carbide (Si 3 N 4 /30 wt.% SiC) seal rings were tested as self-mated pairs and dissimilar sealing systems against grey cast iron. The tribological experiments were conducted in a ring-on-ring tribometer at V ≈ 4 m s −1 of linear speed, in the range of 0.3-1 kN of applied load, under a pressure of 2 × 10 5 Pa of a mixture of 20 vol.% of hydrogen peroxide in deionised water, which gives an effective pressure (P) between 0.2 and 1.3 MPa. The homologous tribosystems are ineffective to seal due to catastrophic abrasive wear. The system with better performance is the dissimilar pair Si 3 N 4 /grey cast iron, that presented wear coefficient values of K = 4.2 × 10 −8 mm 3 N −1 m −1 for the ceramic ring and K = 1.3 × 10 −7 mm 3 N −1 m −1 for the metallic ring, in tests driven for about 60 h and 890 km, with full sealing. An amorphous passivating film of silica protects the ceramic surface. This system still presents an excellent combination K × PV ≈ 0.1 m h −1 , this product being a measure of the surface loss of a machine component for a given time of service.

Functionality Diagrams for Hybrid Mechanical Seals with Silicon Nitride Rings

“…This layer afforded third‐body protection to the ceramic ring surfaces, keeping the wear coefficient values in the acceptable range of 10 −9 –10 −8 mm 3 /N/m (Table I). The thickness of this tribolayer is higher in the inner contact area where the fluid has access, as previously discussed 5 . A remarkable value of 2.9 × 10 −9 mm 3 /N/m is presented by the SN10SC ring when sliding against the WC/Co counterpart.…”

“…Several materials were selected to produce rings for tribological characterization: (i) silicon nitride, Si 3 N 4 (SN); (ii) silicon nitride/carbide composites, Si 3 N 4 /10 wt% SiC (SN10SC) and Si 3 N 4 /30 wt% SiC (SN30SC); (iii) GCI BS grade 200 (GCI); and (iv) hardmetal ISO grade GD05, WC/5 wt% Co (WC). Details on the composition, sintering procedure, and mechanical properties of the Si 3 N 4 ‐based ceramic materials are described elsewhere 5 . Before testing, the working surfaces were polished, giving rise to initial roughness values ( R a ) presented in Table I and to the typical microstructures shown in Fig.…”

“…Silicon carbide, alumina, zirconia, and silicon nitride are the most common ceramics used as mating surfaces 2–4 . The latter is an attractive choice because of its relatively high fracture toughness and low processing cost, compared with the other ceramics 5 . Only a few works report on the tribological performance of Si 3 N 4 ‐based seals.…”

Mechanical and fatigue strengths of silicon nitride ceramics in liquid aluminum alloys

“…For the applications of the ceramic, the fundamental study of the material properties of Si 3 N 4 was performed by many researchers, and the useful experimental data have been obtained. [1][2][3][4][5][6][7][8][9][10][11] Mechanical seals protect the environment from product leakage in various equipments, including engines and turbines, with rotating shafts or alternative moment parts. It appeared from the recent studies that a high extent dynamic sealing (or wear) of Si 3 N 4 is obtained as sealed with a grey cast iron rings 1 compared with the silicon nitride/silicon carbide rings, because of the protection by a tribolayer com- * Corresponding author.…”

Silicon-incorporated diamond-like coatings for Si3N4 mechanical seals

“…Furthermore, a demanding technology is needed to fully densify SiC, as very high sintering temperatures are required, which makes this ceramic an expensive and laborious product. Therefore, more recently a new system of ceramic mechanical seals based on silicon nitride (Si 3 N 4 ) has been proposed [12].…”