The Development of Zinc-Free Anti-Wear Hydraulic Oil: Doubling Useful Service Life

The excellent anti-wear (AW) and oxidation inhibition properties of Zinc Dialkyl Dithio Phosphates (ZDDPs) have resulted in their extensive use in modern AW hydraulic oils. However, increasingly compact hydraulic systems utilizing high service-pressure pumps (>300kg/cm²), has lead to operating temperatures (>250°C) that have been shown to thermally degrade ZDDP into insoluble sludge ^[1]. This paper chronicles the development of a non-ZDDP AW hydraulic oil, and evaluates its performance relative to a ZDDP oil in the areas of sludge generation, oxidation, and AW properties. The formulation reduces sludge by 85 to 99.5%; retains more viscosity; reduces metal wear by 04-06%; and extends useful service life to at least twice that of the ZDDP-based hydraulic oil.