Impact of Vibration on the Sealing Interface Stability of Spiral-Magnetic-Fluid Composite Seals in Roller-Cone Bits

Summary

This study addresses some limitations of traditional macroscale simulations in investigating the vibration-induced interfacial behavior of cone-bit seals and strengthens the connection between microscopic mechanisms and experimentally observed phenomena. It provides insights into the microscopic behavior of magnetic-fluid sealing interfaces under vibrational loading and its relationship with macroscopic interfacial responses. By integrating molecular dynamics (MD) simulations with simplified vibration experiments, this work investigates the interfacial evolution of cone-bit spiral-magnetic-fluid composite seals under controlled vibration conditions. Unlike previous studies that primarily focused on macroscale behavior or solid/solid and solid/liquid interfaces, this study constructs a molecular model of the liquid/liquid interface between the magnetic fluid and drilling fluid, representing a key interface relevant to downhole sealing conditions. The results reveal the vibration-induced displacement and dispersion of magnetic-particle aggregates at the microscale, suggesting that aggregate destabilization is an important factor contributing to interfacial mixing. Using a self-developed vibration testing system with adjustable amplitude and frequency, a cross-scale comparison was conducted between the simulated microstructural changes and the experimentally observed interfacial responses. This comparison indicates associations among the applied vibration conditions, magnetic-particle aggregate evolution, interfacial mixing, and seal interface stability, suggesting a possible interfacial evolution process from aggregate migration and dispersion to increased mixing and reduced interface stability. Under the tested combinations of vibration parameters, the interfacial mixing thickness tended to approach a plateau in the higher-frequency tests, while greater mixing thicknesses were observed in the larger amplitude tests. These trends are qualitatively consistent with the vibration-induced destabilization of magnetic particle aggregates observed in the simulations. This study provides a theoretical and experimental basis for understanding the vibration-induced interfacial behavior of magneticfluid composite seals and may contribute to their preliminary vibration-resistant design for cone-bit applications.