Analysis of Dynamic Characteristics of Mixed Lubrication Mechanical Seals Under Impact Conditions Considering Three Dimensional Fractal Contact

Severe load fluctuations in fluid machinery during variable operating conditions significantly affect the reliability of mechanical seals. To address the problem of dynamic failure in mechanical seals under impact conditions, such as pressure fluctuations, this paper establishes an impact response analysis model. The model is based on three dimensional (3D) fractal contact and mixed lubrication theory, taking into account the axial motion of the seal face and thermo-mechanical deformation. The accuracy of the model is validated by an impact response test rig. A direct numerical simulation method is employed to solve the model and investigate the effects of the peak value and duration of half-sine impact loads on the dynamic characteristics of the mechanical seal. The results indicate that impact conditions induce a pumping effect on the seal faces, causing a positive cumulative offset of the equilibrium position, which is the root cause of dynamic failure. When the impact peak increases from 4% to 28% of the steady-state opening force, the maximum positive offset of the equilibrium position increases by approximately nine times. Under long-duration impact, the seal faces develop an irreversible opening state, leading to leakage failure. In contrast, under short-duration impact, the seal faces exhibit high dynamic stiffness; the impact peak is permissible up to 70–80% of the steady-state opening force. However, for long-duration impact, the peak must be limited to within 50% of the steady-state opening force to prevent cumulative leakage failure. These results offer data and theoretical insights for designing high-stability seals under impact.