Frictional Performance of Water-Glycol Fire-Resistant Hydraulic Fluid

With the continuous development of industrial technology, hydraulic systems have become an indispensable part of modern industry, and hydraulic oil is the core element of hydraulic systems. Traditional oil-based hydraulic oils are gradually becoming unsuitable for modern hydraulic systems due to their environmental pollution, flammability, and other reasons. In addition, the current hydraulic system is gradually developing towards high pressure, high speed, and high temperature. Traditional oil-based hydraulic oils are prone to combustion, causing safety hazards and property damage. Therefore, water-based hydraulic fluids are gradually dominating the market with their environmental advantages, good flame resistance and stability. Water–glycol fire-resistant hydraulic fluids (HFC) is the most widely used type of water-based hydraulic fluid, and HCF is now widely used in marine equipment, aviation, and mining fields. In order to research the tribological performance of water–glycol fire-resistant hydraulic fluids under different working conditions, this paper studied the effects of different loads, speeds, and temperatures on the tribological performance of HFC using a four-ball friction and wear testing machine, and the variation of viscosity of HFC with temperature was tested using a rheometer. The surface parameters of the wear area of the friction pair under different working conditions were analyzed using VHX-6000 optical microscope and ZYGO three-dimensional white light interference surface morphology instrument, and the corresponding wear rate was calculated. In addition, the microstructure and chemical composition of the wear area of the friction pair were analyzed using a field emission environment scanning electron microscope. X-ray photoelectron spectroscopy (XPS) was used to analyze the elemental changes in the wear area under different working conditions. The results indicate that with the increase of load and speed, the average friction coefficient and wear rate first decreased and then increased. When the load reached to 588 N, the wear rate of the specimen increased by 168% compared to 392 N. When the speed increased to 2400 r/min, the wear rate increased by 142% compared to 1200 r/min. As the temperature increased, the friction coefficient and wear rate also increased. When the temperature reached to 85 ℃, the wear rate reached 1.17×10⁻⁸ mm³/(N·m), an increase of 328% compared to 25 ℃. When the working conditions were 400 N, 1200 r/min, and 25 ℃, water–glycol fire-resistant hydraulic fluids had the best lubrication performance, the lowest friction coefficient and wear rate. The wear mechanism of the system at low load, low speed and low temperature was mainly abrasive wear. When the working condition reached high load (588 N) or high speed (2400 r/min) and high temperature (85 ℃), the wear mechanism changed to adhesive wear and fatigue wear. This work was of great significance for improving engineering applications, extending equipment life and preventing failures.