Lubrication and Sealing Performance of O-Ring for End Face Dynamic Seal

O-ring is one of the most widely used standard seals, whose sealing characteristics are of interest to many researchers. In the past years, the theory of elasto-hydrodynamic lubrication was applied to performances analysis of a sealing system. However, most of the associated studies have been conducted on the O-ring in reciprocating system, or end face seal system without O-ring. There is a lack of researches on the end face dynamic sealing system with O-ring for pitch control propellers. The present study provided a method to analyze the lubrication and sealing performances of O-ring in end face dynamic sealing system considering the effect of eccentricity. The sealing system was simplified into four parts, including O-ring, sealing groove, sealing cover and drive shaft. The tangential and normal velocities of the dynamic seal interface between O-ring and sealing cover were analyzed. The static pressure was obtained using the finite element method, and the pressure of rough contact was solved through Greenwood-Williamson model. In doing so, a steady-state two-dimensional Reynolds equation in the cylindrical coordinate system considering tangential and normal velocities was derived based on the Navier-Stokes equation, the continuity equation and the oil film velocity boundary conditions, and the Jakobsson-Floberg-Olsson (JFO) cavitation condition was considered. Using the sealed oil pressure as the inlet oil pressure, the finite difference method was used to solve the Reynolds equation. In contrast to the traditional scheme of using semi-infinite bodies to simulate elastic deformation in one-dimensional model, the oil film thickness was updated by solving the Greenwood-Williamson model in reverse. In order to verify the model, the fluid pressure and rough pressure obtained by the program in this paper were compared with the corresponding results in the literature. After obtaining the film thickness and pressure, the structural leakage was calculated. The numerical results showed that the eccentricity between sealing cover and O-ring caused fluctuations in the oil film thickness and pressure in the sealing area along the circumferential direction, and the fluctuation becomes obvious with the eccentricity increase. The change in contact speed would cause the sealing area to experience the process of ‘forward leakage and oil return’ when the contact point rotated from a position closer to the rotational center to a position away from the rotational center. Increasing the compression rate of O-ring was conducive to improve the sealing performance, but it significantly increased the rough contact pressure and leaded to a nonlinear increase in friction torque, meaning a decrease in tribological properties of O-ring. The self-sealing property of O-ring allowed it to increase the sealing pressure appropriately, which increased the static contact pressure and rough contact pressure, and caused the sealing interface shift to move outward, reducing the amount of outward oil leakage when the eccentricity occurred. However, the sealing pressure exceeded a certain value, which would directly lead to seal failure of O-ring.