Treatment and restoration of used Mineral-Oil-Based hydraulic fluids from different machines. Part 1: Dewatering, filtration and effect of viscosity modifier

Abstract

ABSTRACTIn this work, characterization and treatment of used hydraulic oil samples were performed in three steps. In the first step, the physical and the chemical properties of fresh and used hydraulic mineral oil samples from various centrifugal casting and pipe drawing machines were investigated according to ASTM D 6158. Results show that water content, solid particles count and depletion of additives have considerably affected most of the oil properties. Used oil samples failed in the appearance, thermal stability, oxidation stability, foaming tendency, water content and particles count.In the second step, a simple methodology for dewatering and filtration was adopted. This methodology involved settling, followed by dry-air bubbling for oil dehydration and finally vacuum filtration. Such process successfully removed considerable portion of solid particles and water in used oil samples. Appearance, pour point, water content, particles count, and acid number were restored to the allowable limits. While water separability, oxidation stability, thermal stability and foaming tendency still failed the limits after treatment. It is obvious that additives will be needed to restore the latter properties.In the third step, viscosity modifier additive was added to the oil samples to enhance viscous properties. A linear increase in kinematic viscosity was witnessed at 100°C, while at 40°C, an initial linear increase at low viscosities was followed by lower slopes at higher viscosities.