Theory analyses and experimental study on starting torque and seal capacity of field-control magnetic fluid seal

Abstract

Magnetic fluid seal(MFS) is one of the most mature applications of magnetic fluid(MF) and is widely used in numerous fields. The permanent magnet is an integral component of the classic MFS and provides a stable and robust magnetic field. However, this leads to a high initial torque requirement and a noticeable separation between ferromagnetic particles and the base liquid in the presence of such a strong magnetic field. This situation results in starting difficulties and impedes the normal device startup, particularly in low-temperature environments. Moreover, a constant magnetic field fails to address fluctuating pressure. To address these issues, we have introduced a novel design for the field-controlled MFS. Through theoretical and finite element analyses(FEA), we derived the magnetic field distribution within the seal gap. Additionally, we established the theoretical range for the sealing capacity of the field-control MFS. Experimental results demonstrate that the magnetic field, sealing capacity, and starting torque all increase with higher coil currents. The reduction in starting torque is particularly pronounced at lower temperatures. By manipulating the magnetic field, the starting torque can be reduced by over 50%. The field-controlled MFS exhibits a 0.24 MPa sealing capacity without requiring cooling equipment, representing a 33% improvement in sealing capacity compared to the classic MFS without a coil.