The Effect of Abrasive Concentration on the Friction Characteristics of Fracturing Pump Plunger Seal Pair

In the oil and gas extraction process, the fracturing pump plays a pivotal role. Its primary function is to inject fracturing fluid into the well, facilitating the fracturing of oil and gas reservoirs. However, in actual operation, fracturing pump may leak fracturing fluid, which will cause hard quartz sand particles to enter the plunger friction pair, thus affecting its tribological performance. In order to study the influence of particle concentration on the tribological properties of plunger rubber, we chose hydrogenated nitrile rubber and 40CrNiMoA alloy steel as the research objects. Firstly, we prepared fracturing fluid containing solid particles, then changed the particle concentration by simulating the working environment and motion form of the plunger, and conducted reciprocating friction experiments with pin-on-disk specimens. Following the friction test, the rubber components were cleansed and dried, and then used a three-dimensional white light interferometer and a scanning electron microscope to analyze the surface morphology and chemical composition of the wear marks. The experimental results showed that with the increase of particle concentration, the surface wear of hydrogenated nitrile rubber became more and more serious, and there were great differences in the surface morphology of rubber under different concentrations. The fracturing fluid containing particles would increase the friction coefficient of the friction pair, and with the increase of particle concentration, the friction coefficient showed an increasing trend, and the growth rate increased first and then decreased. In scenarios with high particle concentration, the hindrance effect of particle accumulation induced fluctuations in the instantaneous friction coefficient. Moreover, as particle concentration increased, the frequency of these fluctuations intensified. When there were no particles in the lubricating medium, the surface morphology of rubber was mainly micro-pits caused by contact fatigue, and the wear mechanism was fatigue wear; when the particle concentration was low, the surface morphology of rubber was mainly grooves, pits, etc, and the wear mechanism was abrasive wear; when the particle concentration was high, with the further expansion of cracks, layered structure appears; when the particle concentration continued to increase, the density of cracks and layered structure increased, and the particle accumulation phenomenon became more serious, resulting in more particles breaking or even embedding into the rubber matrix under the interaction. Particle embedding in cracks would lead to crack propagation, and crack propagation would lead to more particle embedding, which promoted each other, forming a positive feedback mechanism, which significantly aggravated the wear. When the particle concentration increased, the particle aggregation and accumulation increased, and the elastic deformation increase would lead to more energy loss. The energy loss of rubber was composed of adhesion and hysteresis terms, but the influencing factors of these two terms were different in different stages of particle concentration.