Lubricating composition

Abstract

A substantially zinc-free hydraulic fluid is provided. The substantially zinc-free hydraulic fluid contains a calcium detergent, an ashless antioxidant, and a metal-free phosphorous containing anti-wear agent. In one embodiment, the fluid contains at least 90 weight percent of a base oil having less than 500 ppm sulfur, a calcium detergent in an amount to deliver 5 ppm to 200 ppm calcium to the fluid, at least one metal-free phosphorus containing anti-wear agent to provide 10 ppm to 150 ppm phosphorous, and one or more ashless antioxidants. A method of lubricating a hydraulic system with the substantially zinc-free fluid is also provided.

1 . A hydraulic fluid comprising (a) at least 90 weight percent of a base oil having less than 500 ppm sulfur, (b) a calcium detergent in an amount to deliver 5 ppm to 200 ppm or 5 ppm to 150 ppm or 5 ppm to 100 ppm calcium to the fluid, and (c) at least one metal-free phosphorus containing anti-wear agent, and (d) one or more ashless antioxidants, wherein the hydraulic fluid has 10 ppm to 150 ppm phosphorus and where in the hydraulic fluid is substantially free of zinc. 
     
     
         2 . The hydraulic fluid of  claim 1 , wherein the calcium detergent comprises an alkylated aromatic sulfonate salt. 
     
     
         3 . The hydraulic fluid of  claim 2 , wherein the calcium detergent comprises a neutral salt or an overbased salt of alkylated aromatic sulfonic acid. 
     
     
         4 . The hydraulic fluid of  claim 3 , wherein the calcium detergent comprises or consists of a neutral salt of an alkylated aromatic sulfonic acid. 
     
     
         5 . The hydraulic fluid of  claim 1 , wherein the alkylated aromatic sulfonic acid comprises an alkyl group containing 6 to 20 carbon atoms. 
     
     
         6 . The hydraulic fluid of  claim 5 , wherein the alkyl group is branched. 
     
     
         7 . The hydraulic fluid of  claim 5 , wherein the alkyl group is linear. 
     
     
         8 . The hydraulic fluid of  claim 1 , wherein the calcium detergent comprises or consists of a neutral salt of alkylated naphthalene sulfonic acid. 
     
     
         9 . The hydraulic fluid of  claim 1 , wherein the calcium detergent further comprises a calcium phenate detergent, a calcium salicylate detergent, or a calcium salixarate detergent. 
     
     
         10 . The hydraulic fluid of  claim 1 , wherein the total base number of the calcium detergent is less than 10 mg KOH/g according to ASTM D4739. 
     
     
         11 . The hydraulic fluid of  claim 1 , wherein the metal-free phosphorus-containing anti-wear agent comprises or consists of a (thio)phosphate ester. 
     
     
         12 . The hydraulic fluid of  claim 1 , wherein the fluid comprises 0.02 weight percent to 3.0 weight percent or 0.03 weight percent to 1.5 weight percent or 0.05 weight percent to 0.5 weight percent of the antioxidant. 
     
     
         13 . The hydraulic fluid of  claim 1 , further comprising an ashless surfactant. 
     
     
         14 . The hydraulic fluid of  claim 13 , wherein the ashless surfactant comprises or consists of an ashless polyisobutenyl surfactant. 
     
     
         15 . The hydraulic fluid of  claim 14 , wherein the ashless polyisobutenyl surfactant comprises or consists of a substituted polyisobutenyl compound. 
     
     
         16 . The hydraulic fluid of  claim 15 , wherein the substituted polyisobutenyl compound comprises or consists of a polyisobutenyl succinimide derived from aromatic polyamine. 
     
     
         17 . The hydraulic fluid of  claim 13 , wherein the fluid comprises 0.025 to 0.75 weight percent of the ashless surfactant. 
     
     
         18 . The hydraulic fluid of  claim 1 , wherein the fluid has an ISO Viscosity Grade of 22 cSt or 32 cSt or 46 cSt or 68 cSt. 
     
     
         19 . The hydraulic fluid of  claim 1 , wherein the fluid contains less than 10 ppm or even less than 5 ppm zinc. 
     
     
         20 . A method of lubricating a hydraulic system, comprising supplying to said hydraulic system a hydraulic fluid composition as recited in any of  claim 1 . 
     
     
         21 . The method of  claim 20 , wherein the hydraulic system is operated at pressures at or above 300 bar. 
     
     
         22 . The method of  claim 20 , wherein the hydraulic system comprises a pump operating at a speed at or above 2500 revolutions per minute. 
     
     
         23 . (canceled)