Abstract: Magnetic fluid seal is one of the most mature applications of magnetic fluid. It is found that the anti-pressure capacity of the static or dynamic magnetic fluid seal may rise over time. If it is a dynamic seal, the starting torque will increase. These phenomena are investigated through experiment. Then the concept of yield stress of magnetic fluid is introduced to explain qualitatively the phenomena. And the formulas of anti-pressure capacity and torque are improved. The results show that the yield stress of magnetic fluid is the main factor inducing the increase in the anti-pressure capacity and torque of magnetic fluid seal. The greater the yield stress is, the higher the anti-pressure capacity is, and the larger the starting torque is. The results provide a design basis to reduce the starting torque and improve the anti-pressure capacity of magnetic fluid seal.

Key words: mechanical design, seal, magnetic fluid, yield stress, starting torque, anti-pressure