Research Into The Technology Of Magnetic Fluid Seal At Stern Shaft

The stern shaft seal is a special kind of seal due to the preventing both the leakage of lubricating oil out of the ship and the entrance of seawater into the stern shaft system. Not only leakage and pollution are the consequences of improper sealing design, but the operating safety of robots will be affected as well. Magnetic fluid seal has the characteristics of long life, zero leakage, simple structure, fitting high-speed rotation, etc, making it an effective new technology of sealing at the stern shaft of ships.The paper begins with the preparation process and method of magnetic fluid. The magnetic particle, base fluid and surface activating agent are rationally chosen. The water base, oil base and ester based Fe₃O₄ magnetic fluid are prepared by chemical method and their hydrophobic and oleophobic performances are investigated. The effects of preparation technique on the magnetization characteristics, viscosity characteristics and suspension stability of the prepared Fe₃O₄ magnetic fluid are also discussed. Then, the research target in the experiment of this paper—oil based Fe₃O₄ magnetic fluid, is confirmed through analysis and compare.Based on the research objective of the experiment of magnetic fluid seal at stern shaft, the overall plan of the experimental devices is put up with and the experimental facility is designed. The material choices and main parameter design and calculation of each component are carried out, ensuring the improvement of the pressure differences of magnetic fluid, under the precondition of the same magnetic fluid characteristics and the same volume of permanent magnet.From the point of view of magnetic circuit, the characteristics of the magnetic fluid of the stern shaft sealing device are analyzed and the model of magnetic fluid seal is built. According to the magnetism of particles, and combining the possible concentration distribution model of magnetic particles in the magnetic field, the pressure-bearing formula of the corresponding magnetic fluid seal is deduced.Furthermore, the pressure-bearing power of the Fe₃O₄ magnetic fluid is studied and the main factors that could affect the pressure-bearing power of magnetic fluid sealing devices are analyzed. Results show that the pressure-bearing power has a negative relationship with the sealing clearance and the rotating speed of the rotation shaft, but has a positive relationship with the intensity of saturated magnetization of the magnetic fluid.The research findings in the paper have provided the theoretical basis and credible experimental data for the application of magnetic fluid seal technology at stern shaft of ships. Simultaneously, these results have laid a foundation for the subsequent researches.