Oxidation and Corrosion Characteristics of Vegetable-Base Biodegradable Hydraulic Oils

To adapt biodegradable hydraulic oils to heavy-duty construction machines, we have investigated eight commercially available vegetable-based biodegradable hydraulic oils for an oxidation stability and corrosion characteristics by laboratory tests and an axial piston pump rig test.

From the laboratory tests, it became clear that all vegetable hydraulic oils show poor oxidation stability and two vegetable hydraulic oils show strong corrosion to bronze materials. Three vegetable hydraulic oils, which contain 0.7 %, 0.25 % and 0% sulfur, have been tested by a high pressure axial piston pump. The 0.7 %S vegetable hydraulic oil resulted in rapid viscosity increase and serious bronze corrosion in the 32 MPa x 95°C pump test. In the 32 MPa x 80°C pump test, the oxidation and corrosion of the 0.7 %S vegetable hydraulic oil were much lower. To compare the vegetable hydraulic oils, 42 MPa x 80°C pump tests were conducted. The 0.7 %S vegetable hydraulic oil caused similar heavy corrosion to that in the 32 MPa x 95°C pump test. The 0.25 %S vegetable hydraulic oil also caused light corrosion. The 0 %S vegetable hydraulic oil did not cause corrosion. These oxidation and corrosion characteristics and related phenomena are discussed.