Experimental research on static and dynamic magnetic powder sealing used by micro-nano composite magnetic particles

•Based on the static pressure curves, the microstructure models of different magnetic powders in the sealing gap are proposed.•The dynamic sealing capability of powders with different proportions also prove the rationality of the microstructure hypothesis.•It is concluded that different microstructures have different fracture and recombination abilities under the action of shear stress and external magnetic field.•The thermal effect caused by the friction between the shaft and magnetic powder makes the magnetism of magnetic powder decrease and reduces the sealing ability. The focus of the paper is the experimental study of static and dynamic magnetic powder sealing by preparing micro-nano hybrid magnetic powders with different proportions. The magnetization curves of the magnetic powders are measured, and the formula for calculating saturation magnetization of mixed magnetic particles is fitted. In the static seal test, the maximum pressure resistances of magnetic powders are studied. It can be concluded that the nanoparticles can achieve a stable pressure resistance under low pressure and the micron particles have higher pressure resistance, but there is a small amount of leakage due to the microcavities between particles. The nanoparticles are introduced into the micron particles’ microcavities to form a hybrid magnetic powder, which significantly improves the pressure resistance. The microstructure models of magnetic powders in the sealing gap are proposed based on the static pressure curves. However, in the dynamic magnetic powder seal test, its pressure characteristic curve is different from that of the magnetic fluid seal. The relationship between the pressure resistance and the rotational speed of the shaft is studied. It is concluded that different microstructures’ fracture and recombination abilities under shear stress and external magnetic field in seal clearance are different. The thermal effect caused by the friction between the shaft and magnetic powder makes the magnetism of magnetic powder decrease and reduces the sealing ability. Experimental studies prove the application potential of magnetic powder seal.