Effect of Abrasive Size on Tribological Properties of HNBR for Reciprocating Seal

High-speed reciprocating friction experiments were carried out using UMT friction and wear tester in order to investigate the effect of abrasive particle size on the tribological properties of HNBR under oil lubrication. Before the experiment, the abrasive particles were analyzed by energy spectrum, and the particle size was counted by laser particle size analyzer. After the experiment, the surface wear morphology of HNBR was characterized by three-dimensional morphology instrument and scanning electron microscope, which supported the analysis of wear mechanism of abrasive particles. The surface of HNBR in pure lubrication group produced wear debris and small pits formed by filler shedding. The 300 mesh group produced a large number of scratches with a width of 4~7 μm. The depth of abrasive escape pitted in 150 mesh group was greater than that in 300 mesh group. In addition to pit and scratch, the 100 mesh group also included furrows and incomplete peeling caused by abrasive particles on the surface of HNBR. The EDS analysis of the wear zone showed that the tribochemical reactions of different sizes of abrasive particles on the surface of HNBR had different degrees. Wear morphology showed that there was a critical size between 300 mesh and 150 mesh for the transition from rolling to sliding. Abrasive particles participated in sliding friction and wear when the critical size was lower than the critical size, and rolling friction and wear when the critical size was higher than the critical size. Under the action of torque, some rolling abrasive particles were broken and below the critical size, which changed from rolling to sliding and formed scratches on the surface of HNBR, thus increasing the wear amount. The ability of rolling to form pits and crushing decreased with the decrease of abrasive particle size, and the ability of rolling to slip increased with the decrease of abrasive particle size. Below the critical size part of abrasive particles embedded in HNBR acted as a cutting tool and push non-embedded abrasive particles to produce scratches between friction pairs. It was found that there were two peaks with different sizes in each reciprocating period in the curve of friction force changing with displacement, and the difference of friction work in reciprocating process could be obtained by integration, so the difference of peaks reflected the instability of reciprocating friction. According to the integral meant value theorem and the continuous derivative property of function, the integral calculation of friction force was transformed into the analytical calculation of friction coefficient. The analysis results indirectly reflected the difference of reciprocating friction work and reflect the difference of reciprocating friction process. The second derivative of friction coefficient indirectly reflected the change trend of the difference of reciprocating friction work. In this way, the influence of abrasive particles with different sizes on reciprocating motion could be accurately described and analyzed. According to the time-varying curve of friction coefficient, the friction process could be divided into unstable and stable stages. In the unsteady phase of friction, abrasive particles increased the reciprocating friction work difference. The larger the abrasive particle size, the greater the difference in reciprocating friction work, and the slower it tended to be stable. Compared with the pure lubrication group, the sliding particles increased the reciprocating friction work difference, while the rolling particles decreased the reciprocating friction work difference. The larger the size of rolling abrasive particles, the smaller the reciprocating friction work difference.