| abstract |
A hydraulic oil composition prepared by blending a base oil having a percentage CA value of 5 or below with (A) 0.01 to 5 % by weight of an amine antioxidant such as 4,4'-dioctyldiphenylamine, (B) 0.01 to 5 % by weight of a phenol antioxidant such as 2,6-di-t-butyl-4-methylphenol, (C) 0.01 to 5 % by weight of a phosphate ester such as tricresyl phosphate, and (D) 0.001 to 5 % by weight of a fatty acid amide such as isostearic triethylenetetramide and/or a polyhydric alcohol ester such as sorbitan monooleate, each amount being based on the whole composition. This composition is effectively inhibited from premature degradation or formation of sludge due to increase in the pressure and therefore can be used for a prolonged period. Further, the oil composition can solve the problem of chattering of cylinders [vibration or abnormal noise occurring in hydraulic working zones, e.g., those between a cylinder and a piston or between a rod and a guide (seal)] to exhibit stable working characteristics. |