Experimental Study of Surface Roughness on Improving the Tribological Performance of Sealing Pairs in Magnetorheological Damper

During the reciprocating dynamic sealing process, hydroxy iron powders suspended in magnetorheological fluid (MRF) enter the sealing interface under the combined action of hydrodynamic pressure and shear forces, which accelerating the friction and wear between piston rod and O-ring, eventually leading to the sealing leakage. This seriously endangers the working performance and even lifespan of magnetorheological damper. A self-made test device and a high-speed reciprocating friction wear testing machine were used to simulate the wear behavior of sealing pairs in magnetorheological damper. Through comparing the time-varying curve of friction coefficient formed in the reference medium methyl silicone oil, the influence of surface roughness on the tribological performance of sealing pairs under magnetorheological fluid is revealed. It should be pointed out that methyl silicone oil was the carrier fluid for the preparation of magnetorheological fluid and did not contain any particles. The purpose of choosing methyl silicone oil as the experimental benchmark in this article was to highlight the effect of hydroxy iron powders on the wear mechanism of sealing pairs. The results showed that the friction coefficient curves of sealing pairs under two experimental media were in sharp contrast, and the surface roughness reference range recommended by conventional hydraulic system was no longer suitable for the design criterion of magnetorheological damper sealing system. Specifically, the rough sample in magnetorheological fluid exhibited lower friction coefficient and material wear, which was mainly caused by three-body abrasive wear. While the curves corresponding to polished sample fluctuated sharply and wear seriously, primarily dominated by two-body abrasive wear. Moreover, the optimized sample T_opt ( \sigma _\mathrmo\mathrmp\mathrmt=3.2\text μm) obtained by the data fitting method showed excellent anti-friction characteristics and anti-contact fatigue properties. It revealed that the surface roughness of piston rod was close to average particle size in suspended iron powder, which helped to improve the sealing wear performance, and provided a reference for extending the service life of MR device sealing system. Based on the analysis of dynamic characteristics, the wear morphology of sealing pairs was observed by scanning electron microscopy (SEM) and ultra-depth-of-field microscope to explore the influence of surface roughness on the tribological performance of sealing pairs under magnetorheological fluid condition. It revealed that the instantaneous coupling between iron powders and rough texture weakened the hysterical friction generated by asperities on the O-ring surface, thereby avoiding premature sealing failure. In addition, element distribution characteristics of O-ring wear surface were analyzed by energy dispersive spectrometer (EDS). It was further proved that change of contact state (i.e. embedding and/or rolling), and movement pattern of iron powder in the seal gap caused by surface roughness were the main reasons for the difference in wear mechanism of sealing pairs.