High performance sealing with CVD diamond self-mated rings

Abstract

A new system of mechanical seals based on CVD diamond coated silicon nitride (Si 3N 4) rings is proposed. This ceramic is chosen due to its proved adequacy to ensure optimal adhesion. Mechanical seals are machine elements specially designed to prevent fluid leakage from pressurized chambers in fluid (gas or liquid) transport systems or to avoid lubricant outflow in general equipment moving parts. Dense Si 3N 4 ceramics processed by pressureless sintering were diamond coated by microwave plasma chemical vapour deposition technique during 2 and 6 h, leading to different diamond grain size and nominal surface roughness. The CVD diamond self-mated sealing systems were tested in ring-on-ring configuration varying the internal water pressure, the rotating speed and the applied load, leading to P·V conditions ( P, the effective pressure and V, the linear speed) in the range 0.1–5.7 MPa m s −1. The finer grain sized diamond tribosystem could guarantee full sealing at P·V≈0.8 MPa m s −1, keeping a low stationary friction coefficient of 0.05, for very long running times of 430 h (5730 km) without measurable wear. Additional advantages of the diamond coated ceramic are the low density and the chemical inertness in aqueous media.