Oxidation Stability and Tribological Behavior of Vegetable Oil Hydraulic Fluids

Abstract

The new generation of vegetable oil hydraulic fluids has a price advantage and provides field longevity comparable to synthetic esters at moderate temperature.

This article investigates the oxidation stability and tribological behavior of fully formulated vegetable oil hydraulic fluids. Differences in origin (canola, soybean, and sunflower oil) and the degree of unsaturation are studied. Modified ASTM D943 (Dry TOST) was found reliable to evaluate the impact on oxidative stability of various additive packages in vegetable oils. Tribological testing utilized laboratory hydraulic pumps such as the Vickers V 104C, Vickers 20VQ, and Vickers PFB-5 under a variety of temperatures, pressures, pump outputs, and speeds. The conditions of aging fluids were monitored by evaluation of TAN, viscosity, wear rate, and depletion of antioxidants. Voltammetric technique was applied to determine the concentration of antioxidant in systems. Based on analysis of antioxidant consumption, the main degenerative process in vegetable oils under demanding pump operations is similar to pyrolytic degradation, rather than oxidation.

By selecting the appropriate synergistic additive packages, a remarkable pump longevity can be obtained for each vegetable base stock studied.

Keywords:

• Hydraulic Fluids
• Vegetable Oils
• Oxidation
• Pump
• Voltammetric Technique
• Antioxidant
• Antiwear
• Extreme Pressure Additives

Acknowledgments

Presented at the STLE/ASME Tribology Conference in Ponte Vedra Beach, Florida October 26-29, 2003

Final manuscript approved November 13, 2003

Review led by Paul Bessette

Notes

^a The cam ring, vanes, and rotor used in the Vickers V-104C were manufactured by Conestoga USA, Inc.