EP2274408A1 - Polyalkylene glycol-based wind turbine lubricant compositions - Google Patents

Abstract

A lubricant composition that is especially useful under extreme conditions, such as in wind turbine gearboxes, comprises a mixed feed glycol; a polyol ester; two particular antioxidants; a phosphorus-based extreme pressure additive; a yellow metal passivator; and at least one specified corrosion inhibitor. The composition passes testing according to ASTM D665B even at 168 hours from initiation, and/or the SKF-Emcor Test Method DIN 51802:1990.

Description

POLYALKYLENE GLYCOL-BASED WIND TURBINE LUBRICANT COMPOSITIONS

Cross-Reference to Related Applications

This application is a non-provisional application claiming priority from the U.S. Provisional Patent Application No. 61 /048,410, filed on April 28, 2008, entitled "POLYALKYLENE GLYCOL-BASED WIND TURBINE LUBRICANT COMPOSITIONS," the teachings of which are incorporated by reference herein, as if reproduced in full hereinbelow.

[0001] This invention relates to lubricant compositions. More particularly, the invention relates to a polyalkylene glycol (PAG)-based lubricant composition that may be useful under extreme environmental and mechanical conditions, such as those experienced in wind turbine gearboxes.

[0002] Although known for thousands of years, wind turbines now receive increasing interest with rising costs of coal and oil-based energy sources. This interest has become particularly intense since the 1970's, when the Organization of Petroleum-Exporting Countries (OPEC) first declared an oil embargo that resulted in a dramatic increase in the price of oil. Today, countries such as Germany, Spain, Denmark and the United States focus more and more on generating a significant portion of their energy needs using wind turbines, which offer substantial electrical generation, in some locations rivaling that of nuclear generating plants, with relatively minimal environmental impact. [0003] A typical wind turbine includes, among other parts, a gearbox that houses gears connecting a low-speed shaft to a high-speed shaft. These shafts enable rotational speeds to vary from 40 rotations per minute (rpm) - 60 rpm to 1 ,500 rpm - 1 ,800 rpm, the latter range representing a rotational speed required by most generators to produce electricity. Although wind turbines have an impressive record of reliability, when failures occur, they are often traced to gearbox bearing failure. The bearings must undertake extremely high loads, with constantly changing performance requirements. For example, under some operating conditions the bearings need to carry medium-sized loads at low speeds, while elsewhere the bearings need to carry much lower loads but at far higher speeds. Furthermore, light winds require bearings to carry high loads at low speeds. These constantly varying conditions within the gearbox combine with often harsh environmental conditions, such as high temperatures, water, oxygen, and salts that contribute to corrosion and wear of bearings, with undesirable results. Either the lubricants break down, that is, kinematic viscosity (KV) decreases, and a contact fatigue failure results, or the system requires an undesirably short oil drain interval, meaning that the turbine spends an unacceptable amount of time offline.

[0004] In general, lubricant formulations for wind turbine gear boxes now include synthetic, rather than natural oils. Synthetic oils generally use esters, polyalphaolefins (PAOs), combinations of PAOs and esters, and polyalkylene glycols. The PAOs often provide a high viscosity index (Vl) and low pour point, which supports wide ranges of operating temperatures. PAGs offer improved resistance to micropitting, but may in some cases be incompatible with coatings and/or seal materials. Recent approaches to the challenge may include the following.

[0005] One approach, disclosed in United States Patent Application Publication (USPAP) 2005/009409 to Devlin et al., is a lubricant composition comprising a sulfur- containing compound, a phosphorous-containing compound, an alkylene amine friction modifying compound, a dispersant compound containing basic nitrogen, and a diluent or base oil.

[0006] Another approach, disclosed in USPAP 2006/0276355 to Cary et al., is a lubricant composition comprising at least (>) two base stocks, preferably synthetic base stocks, one with a kinematic viscosity at 100 degrees Centigrade (^QC) (Kv100^QC) of more than (>) 100 centistokes (cSt) and a second with a Kv100^QC of less than (<) 10 cSt. The compositions may include a variety of additives such as those available in various commercial gear oil packages.

[0007] USPAP 2005/0090410, also to Devlin et al., discloses lubricant compositions described as suitable for use in wind turbine gearboxes. The compositions comprise a sulfur-containing compound, a hydrocarbylamine compound, an alkylphosphorothioate compound, a friction modifier compound, and a diluent or base oil. [0008] While the described art represents attempts to meet requirements of wind turbine applications, performance expectations are still not routinely met by products on the market. Oil drain intervals are still shorter than desired, a particular problem where offshore wind turbines are addressed. Corrosion, wear, and viscosity breakdown continue to challenge this high-growth, rapidly evolving industry.

[0009] In one aspect, this invention is a lubricant composition comprising an effective amount of (1 ) a PAG based on ethylene oxide (EO) and propylene oxide (PO), wherein at least 30 percent by weight (wt percent) of the PAG is EO units; (2) a polyol ester; (3) N- phenyl-1 ,1 ,3,3-tetramethylbutylnaphthalen-1 -amine, as a first antioxidant; (4) an alkylated diphenylamine formed from the reaction product of N-phenyl-benzenamine and 2,4,4- trimethylpentene, or a mixed octylated and butylated diphenylamine, as a second antioxidant; (5) a phosphorus-based extreme pressure additive; (6) a yellow metal passivator; and (7) at least one corrosion inhibitor selected from a group consisting of (a) an amine salt of an aliphatic phosphoric acid ester; (b) an alkenyl succinic acid half ester in mineral oil; (c) an amine salt of an alkyl phosphoric acid combined with a dithiophosphoric acid derivative; (d) a combination of barium dinonylnaphthalene sulfonate and dinonylnaphthalene carboxylate in a hydrotreated naphthenic oil; and (e) combinations thereof.

[0010] In a related aspect, this invention is a lubricant composition comprising

(1 ) 80 percent by weight of a random or block copolymer polyalkylene glycol based on ethylene oxide and propylene oxide, wherein 60 percent by weight is ethylene oxide units and 40 percent by weight is propylene oxide units, having an ISO viscosity grade of 460;

(2) 15 weight percent of a pentaerythritol ester of an alkanoic acid;

(3) 1 weight percent of N-phenyl-1 ,1 ,3,3-tetramethylbutylnaphthalen-1 -amine, as a first antioxidant;

(4) 1 .3 weight percent of an alkylated diphenylamine formed from the reaction product of N-phenyl-benzenamine and 2,4,4-trimethylpentene, as a second antioxidant;

(5) 1 .5 weight percent of an isopropylated triaryl phosphate combined with dodecyl phosphate and triphenyl phosphate as an extreme pressure additive;

(6) 0.1 weight percent of tolyltriazole as a yellow metal passivator; and

(7) 0.6 weight percent of at least one amine salt of an aliphatic phosphoric acid ester as a corrosion inhibitor.

[0011] The lubricant composition appears to have utility in both land- and sea-based uses, and in a variety of extreme environmental and mechanical conditions. Such applications include, for example, wind turbine gearboxes, subsea hydraulics, compressors, and other uses where stable viscosity, corrosion inhibition, wear reduction, and long life are particularly necessary. For example, the lubricant composition preferably passes SKF-Emcor Test Method DIN 51802: 1990 (ISO 1 1 007) with distilled water and with salt water (0.5 weight percent sodium chloride, based upon total weight of the salt water) with a rating of zero. In order to pass such testing, a composition must have a rating of no more than one. The lubricant also preferably passes ASTM D665B for at least 168 hours after initiation.

[0012] PAGs suitable for use in the above lubricant compositions are, in some non- limiting embodiments, selected from random and block copolymer glycols based on a mixed EO and PO feed. Because of their pour points, random copolymer glycols may be particularly useful herein. One or more PAGs may be used, but the overall EO unit content preferably ranges from 30 wt percent to 95 wt percent, based on the total PAG weight, the remainder being PO units. The EO unit content more preferably ranges from 50 wt percent to 85 wt percent, and still more preferably from 60 wt percent to 70 wt percent, based on the total PAG weight, the remainder being PO units. The PAGs may be monols, diols, triols, tetrols, higher polyfunctional alcohols, or combinations thereof. In some non-limiting embodiments diols may be selected.

[0013] By way of illustration, but not by limitation, preparation of a suitable PAG may be by any means or method known to those skilled in the art. For example, ethene and propene may be oxidized to EO and PO, respectively, using, for instance, dilute acidic potassium permanganate or osmium tetroxide. Hydrogen peroxide may alternatively be used, in a reaction transforming the alkene to the alkoxide. EO and PO may then be polymerized to form random PAG co-polymers by simultaneous addition of the oxides to an initiator such as ethylene glycol or propylene glycol and using, for example, a base catalyst, such as potassium hydroxide, to facilitate the polymerization. [0014] One may instead purchase a PAG copolymer base fluid. For example, SYNALOX™ and UCON™ lubricant fluids are available from The Dow Chemical Company. In some non-limiting embodiments, those having a viscosity in the ISO viscosity range of 22 to 1000 (that is, a KV of from 22 cSt to 1 ,000 cSt at 4O⁰C) may be particularly effective, though a viscosity ranging from 220 cSt to 680 cSt at 4O⁰C may be selected for some applications. In some particular but non-limiting embodiments, an ISO viscosity grade of 320 may be selected. It may also be desirable to select a copolymer base fluid that is water soluble, rather than water insoluble, as a water soluble base fluid may provide improved friction control in certain applications.

[0015] Polyol esters may be formed by the reaction of polyols (for example, neopentyl glycol; pentaerythritol, trimethylol propane) with acids. Commonly used acids include mono-acids having from 5 carbon atoms (C₅) to 18 carbon atoms (C₁₈), such as C₅ (valeric acid), C₁₀ (decanoic acid) and C₁₈ (oleic acid), and di- and tri-acids. Synthetic Lubricants & Functional Fluids, ed. by Ronald Shubkin provides teachings about manufacturing synthetic esters, including polyol esters. The polyol ester is preferably a pentaerythritol ester of an alkanoic acid.

[0016] Alkylene oxide polymers and interpolymers and derivatives thereof with terminal hydroxyl groups modified by esterification may be employed in place of some or all of the above polyol esters. These may be exemplified by mono- and polycarboxylic esters thereof, for example, the acetic acid esters, mixed C₃-C₈ fatty acid esters, esters formed from reaction with anhydrides, for example, maleic anhydride and succinic anhydride, and combinations thereof. [0017] Also useful in certain non-limiting embodiments of the invention are esters of dicarboxylic acids (for example, phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, alkenyl malonic acids, etc.) with a variety of alcohols (for example, butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol diethylene glycol monoether, propylene glycol, etc.). Specific examples of these esters include dibutyl adipate, di(2- ethylhexyl) sebacate, di-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azealate, dioctyl phthalate, dodecyl phthalate, dicicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid, and the like. [0018] Additional useful esters include those made from C₅ to C₁₂ monocarboxylic acids, polyols and polyol ethers, such as neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, and tripentaerythritol, polymeric tetrahydrofurans, combinations thereof, and the like. Also included are polyol esters and diesters, such as di-aliphatic diesters of alkyl carboxylic acids such as di-2-ethylhexylazelate, di- isodecyladipate, and di-tridecyladipate, commercially available under the brand name EMERY™ 2960 by Emery Chemicals, described in U.S. Pat. No. 4,859,352. Other suitable polyol esters are manufactured by Exxon-Mobil Chemicals. Exxon-Mobil Chemical's polyol ester P-43, NP343 containing two alcohols, and M-045, and Hatco Corporation's HATCO™ 2939 may be employed in some non-limiting embodiments.

[0019] Diesters may be selected, such as aliphatic diesters of a dicarboxylic acid, or a dialkyl aliphatic diester of an alkyl dicarboxylic acid, such as di-2-ethyl hexyl azelate, diisodecyl azelate, di-tridecyl azelate, di-isodecyl adipate, di-tridecyl adipate. For instance, Di-2-ethyl hexyl azelate is commercially available from Emery Chemicals under the brand name of EMERY™ 2958.

[0020] Also useful are polyol esters such as EMERY™ 2935, 2936, and 2939 from Cognis and HATCO™ 2352, 2962, 2925, 2938, 2939, 2970, 3178, and 4322 polyol esters from Hatco Corporation, described in U.S. Pat. No. 5,344,579, and MOBIL™ ester P 24 from Exxon-Mobil Chemical. Exxon-Mobil esters, such as made by reacting dicarboxylic acids, glycols, and either monobasic acids or monohydric alcohols, may be used. The polyol ester for use herein may, in certain particular but non-limiting embodiments, have a pour point of -100⁰C or lower to -2O⁰C and a viscosity of 10 cSt at 100⁰C or lower. [0021] The selected ester may be aliphatic or aromatic in nature, and may include, for example, diesters, phthalates, trimellitates, pyromellitates, dimer acid esters, polyols and polyoleates. In a particular non-limiting embodiment, the ester is a pentaerythritol ester of an alkanoic acid (for example, HERCOLUBE™ J, available from Hercules Incorporated). In certain other non-limiting embodiments, the ester is a hydrophobic ester which may be generally obtained by reacting a carboxylic acid with a polyol of formula C((CH₂)_n0H)₄ where n is an integer between 1 and 3, inclusive. These polyols are referred to herein as pentaerythritol homologs.

[0022] The esters may be manufactured in any manner, such as by the process of McNeil, U.S. Pat. No. 2,961 ,406, which describes the manufacture of the mono- pentaerythritol (PEOH) tetraester and the di-PEOH hexaester through a reaction between one or more alkanoic acids and a blend of mono- and di-PEOH. Suitable acids described therein include acetic acid, propanoic acid, butanoic acid, 2-methylpropanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid and nonanonic acid.

[0023] Alternatively to McNeil, the alkanoic acid or mixture of acids may be reacted, for example, with separate batches of the mono- and di-PEOH, the resultant batches of tetraester and hexaester being later combined. Also, more generally than McNeil, which teaches the use of alkanoic acids, the acid or mixture of acids may be selected from carboxylic acids; these acids may be normal or branched, saturated or unsaturated, aliphatic or aromatic, or any combination thereof.

[0024] Useful mono- and di-PEOH esters include a hydrocarbyl group, including normal and branched hydrocarbyl groups, saturated and unsaturated hydrocarbyl groups, and combinations thereof. Hydrocarbyl groups include aliphatic, cycloaliphatic, and aromatic groups, such as alkyl, alkenyl, alkynyl, cycloalkyl, aryl, aralkyl, and alkaryl groups. Hydrocarbyl groups also include both nonsubstituted hydrocarbyl groups and substituted hydrocarbyl groups, the latter referring to a hydrocarbyl portion bearing additional substituents, besides the carbon and hydrogen; correspondingly, aliphatic, cycloaliphatic, and aromatic groups are understood as including both nonsubstituted aliphatic, cycloaliphatic, and aromatic groups, and substituted aliphatic, cycloaliphatic, and aromatic groups, with the latter referring to the aliphatic, cycloaliphatic, and aromatic portion bearing additional substituents, besides the carbon and hydrogen.

[0025] Hydrocarbyl groups may include at least one hydrolytically stable heteroatom group, with "hydrolytically stable" meaning that the group does not undergo hydrolysis in the presence of an aqueous medium. Suitable hydrolytically stable heteroatom groups include ether, ester, amide, sulfide, sulfone, sulfoxide, and tertiary amine linkages, as well as halogenated hydrocarbyl groups (for example, chlorinated or fluorinated alkanes). [0026] A PEOH ester may comprise any combination of substituent groups, provided that a resulting mixture of PEOH ester is hydrophobic. Substituent groups independently, preferably comprise hydrogen or C₁-C₂₂ hydrocarbyl or alkyl groups, more preferably hydrogen or C₁-C₁₄ hydrocarbyl or alkyl groups, even more preferably C₄-C₉ hydrocarbyl or alkyl groups, and still more preferably saturated C₄ -C₉ alkyl groups (that is, mono- and di- PEOH esters of C₅ -C₁₀ monobasic saturated acids, preferably a blend of monobasic C₅ - C₁₀ normal saturated fatty acids).

[0027] Examples of acids that may be reacted with the polyol include, but are not limited to, formic acid, acetic acid, propanoic acid, propenoic acid, buytric acid, isobutyric acid, malonic acid, valeric acid, glutaric acid, caproic acid, adipic acid, caprylic acid, capric acid, decandioic acid, palmitic acid, dodecandioic acid, palmitoleic acid, stearic acid, oleic acid, linolenic acid, behenic acid and erucic acid.

[0028] Useful PEOH esters include those commercially available from Hercules Incorporated as HERCOLUBE™ and HERCOFLEX™ synthetic esters. These synthetic PEOH esters are essentially mixtures of mono- and di-pentaerythritol esters of C₅ -C₁₀ fatty acids. Tri-PEOH ester and esters of higher PEOH oligomers may also be present. Preferably, < 1 wt percent of the PEOH ester comprises impurities. Specific products include HERCOLUBE™ F, HERCOLUBE™ J, HERCOLUBE™ 202 and HERCOFLEX™ 707A, all available from Hercules Incorporated. Alternative commercially available esters include SYNATIVE™ ES TMP and TMTC unsaturated and saturated TMP esters, and saturated NPG/PE esters from Cognis.

[0029] Additional information may be found in Kirk-Othmer Encyclopaedia of Chemical Technology, (4^th ed. 1994), vol. 9, pp. 781 -812, which is incorporated herein by reference in its entirety.

[0030] The lubricant compositions include N-phenyl-1 ,1 ,3,3-tetramethylbutyl- naphthalen-1 -amine as a first antioxidant. The first antioxidant is commercially, available from Ciba Chemicals Corporation as IRGANOX™ L06.

[0031] The lubricant compositions include an alkylated diphenylamine as a second antioxidant. The alkylated diphenylamine may be a reaction product of N-phenyl benzenamine and 2,4,4-trimethylpentene, a mixture of octylated and butylated diphenylamines, or a combination thereof. A commercial example of the reaction product of N-phenyl benzenamine and 2,4,4-trimethylpentene is IRGANOX™ L57, available from Ciba Chemicals Corporation. A commercial example of mixed octylated and butylated diphenylamines is VANLUBE™ 961 , available from RT. Vanderbilt Company, Inc. [0032] The lubricant compositions also include a phosphorus-based extreme pressure additive, examples which include isopropylated triaryl phosphates, amine-phosphates; phosphor-thionates, acid phosphates, alkyl phosphates (for example, dodecyl phosphate), and combinations thereof. DURAD™ 310M, commercially available from Chemtura, is a combination of isopropylated triaryl phosphates with small amounts of dodecyl phosphate and triphenyl phosphate. Other extreme pressure additives include VANLUBE™ 719, 761 1 , 727, and 9123 from RT. Vanderbilt Company, Inc.

[0033] The lubricant compositions further include a yellow metal passivator. As used herein, "yellow metal" refers to a metallurgical grouping that includes brass and bronze alloys, aluminum bronze, phosphor bronze, copper, copper nickel alloys, and beryllium copper. Typical yellow metal passivators include, for example, benzotriazole, tolutriazole, tolyltriazole, mixtures of sodium tolutriazole and tolyltriazole, and combinations thereof. In one particular and non-limiting embodiment, a compound containing tolyltriazole is selected. Typical commercial yellow metal deactivators include IRGAMET™-30, and IRGAMET™-42, available from Ciba Chemicals Corporation, and VANLUBE™ 601 and 704, and CUVAN™ 303 and 484, available from RT. Vanderbilt Company, Inc. [0034] The lubricant compositions still further include at least one corrosion inhibitor selected from. (1 ) an amine salt of an aliphatic phosphoric acid ester (for example, NA- LUBE™ 61 10, available from King Industries); (2) an alkenyl succinic acid half ester in mineral oil (for example, IRGACOR™ L12, available from Ciba Chemicals Corporation); (3) an amine salt of an alkyl phosphoric acid combined with a dithiophosphoric acid derivative (for example, NA-LUBE™ 6330, available from King Industries); (4) a combination of barium dinonylnaphthalene sulfonate and dinonylnaphthale necarboxylate in a hydrotreated naphthenic oil (for example, NA-SUL™ BSN, available from King Industries); and (5) combinations thereof.

[0035] Other potential corrosion inhibitors include IRGACOR™ L17, IRGACOR™ DSSG, IRGALUBE™ 349, and SARKOSYL™ O from Ciba Chemicals Corporation, and VANLUBE™ 601 , 601 E, 704, 692 and 719 from RT. Vanderbilt Company, Inc. [0036] The lubricant compositions include each specified component, but such components may vary over a range of proportions relative to one another while providing an overall lubricant composition with desirable properties. The PAG preferably ranges from 50 wt percent to 99 wt percent, preferably > 70 wt percent, more preferably > 80 wt percent. The polyol ester preferably ranges from 10 wt percent to 20 wt percent, and is more preferably 15 wt percent. The first antioxidant preferably ranges from 0.1 wt percent to 5.0 wt percent, more preferably > 0.5 wt percent and still more preferably > 1 .0 wt percent. The second antioxidant ranges from 0.5 wt percent to 5.0 wt percent, more preferably > 1 .0 wt percent and still more preferably > 1 .3 wt percent. The extreme pressure additive preferably ranges from 0.1 wt percent to 3 wt percent, more preferably > 1 .5 wt percent and still more preferably > 2 wt percent. The yellow metal passivator preferably ranges from 0.01 wt percent to 0.5 wt percent, more preferably from 0.05 wt percent to 0.1 wt percent. Corrosion inhibitors preferably range from 0.1 wt percent to 1 .0 wt percent, more preferably from 0.2 wt percent to 0.75 wt percent, and still more preferably from 0.5 wt percent to 0.6 wt percent. Each wt percent in this paragraph is based upon total lubricant composition weight.

[0037] The lubricant compositions may also include one or more conventional lubricant additives in addition to components specified above. Such additives include defoamers such as polymethylsiloxanes, demulsifiers, antioxidants (for example, phenolic antioxidants, hindered phenolic antioxidants, additional sulfurized olefins, aromatic amine antioxidants, secondary amine antioxidants, sulfurized phenolic antioxidants, oil-soluble copper compounds, and mixtures thereof), copper corrosion inhibitors, rust inhibitors, pour point depressants, detergents, dyes, metal deactivators, supplemental friction modifiers, diluents, combinations thereof, and the like. The conventional lubricant additives, if present, typically range from 100 parts by weight per million parts by weight (ppm) of lubricant composition to 2 wt percent, based upon total lubricant composition weight, [0038] The lubricant compositions may be prepared via any method known to those skilled in the art. For example, typical blending equipment includes impeller mixers, tumble blenders, paddle and plow mixers, and single or double shaft mixers. Protocols generally prescribe charging first with a base fluid, herein a combination of PAG and polyol ester, followed by components that are used in relatively small proportion, herein antioxidants, extreme pressure additive, yellow metal passivator, corrosion inhibitor(s), and any additional additives that have been selected, in any order.

[0039] While potential applications of the lubricant compositions appear to be unlimited, they are particularly useful for extreme conditions, including, for example, extreme environmental and mechanical conditions. American Society for Testing and Materials (ASTM) test D665B provides a means of evaluating lubricant compositions for such applications. The lubricant compositions described herein may pass this test with overwhelming success, in many cases showing no significant signs of failure even at 168 hours after initiation.

[0040] The above description and examples that follow illustrate, but do not limit, various aspects or embodiments of this invention.

[0041] "Comprising" may, unless stated to the contrary, include any additional additive, adjuvant, or compound whether polymeric or otherwise. In contrast, "consisting essentially of" excludes from the scope of any succeeding recitation any other component, step or procedure, except those that are not essential to operability. "Consisting of" excludes any component, step or procedure not specifically delineated or listed. Unless stated otherwise, "or" refers to the listed members individually as well as in any combination. [0042] Testing done according to the examples and the comparative examples hereinafter adheres to the following standards.

[0043] Perform rust-prevention testing in accord with the ASTM D665: Standard Test Method for Rust-Preventing Characteristics of Inhibited Mineral Oil in the Presence of Water. ASTM D665A tests with distilled water, while ASTM D665B tests with salt water. Submerge a steel test rod or pin in a beaker of oil and 10 wt percent water at 14O⁰F. After 24 hours, evaluate the rod or pin and report results as pass or fail, depending on degree of pitting and corrosion. In examples and comparative examples that follow, extend testing to 168 hours, reporting results in approximate 24 hour intervals.

[0044] Prepare a lubricant composition, termed "Control Composition," by combining 81 .1 wt percent of a 60/40 ethylene oxide/propylene oxide (weight/weight) mixed feed glycol (SYNALOX™ 40D300, The Dow Chemical Company), 1 wt percent N-phenyl- 1 ,1 ,3,3-tetramethylbutylnaphthalen-1 -amine as a first antioxidant (IRGANOX™ L06, Ciba Corporation), 1 .3 wt percent of a reaction product between N-phenyl-benzeneamine and 2,4,4-trimethylpentene (IRGANOX™ L57, Ciba Corporation) as a second antioxidant, 15 wt percent of a pentaerythritol ester of an alkanoic acid (HERCOLUBE™ J, Hercules Incorporated), 1 .5 wt percent of an isopropylated triaryl phosphate (DURAD™ 310M, Chemtura) as an antiwear additive, and 0.1 wt percent of tolyltriazole as a yellow metal passivator, each wt percent being based upon composition weight and totaling 100 wt percent. The Control Composition also includes, 0.002 pbw, based upon 100 pbw of the aforementioned Control Composition, of polydimethylsiloxane as an antifoam additive. See Table 1 for Control Composition makeup

[0045] Mix the Control Composition on a mixing plate using a stir-bar, while heating for 60 minutes at a temperature of 6O⁰C. Test the Control Composition according to ASTM D665B, and summarize results in Table 2. Example 1

[0046] Replicate preparation of the Control Composition, but substitute 0.6 wt percent of a mixture of amine salts of aliphatic phosphoric acid esters (NA-LUBE™ 61 10, King Industries) as a corrosion inhibitor for an equal amount of the mixed feed glycol. This formulation is shown in Table 1 and the testing results are shown in Table 2. Example 1 also passes testing according to the SKF-Emcor Test Method DIN 51802:1990 (ISO 1 1 007) with distilled and with salt water (0.5 weight percent NaCI), having a rating in that test of 0 where a maximum rating of 1 is allowed to pass the test. Example 2 [0047] Replicate preparation of the Control Composition, but substitute 0.25 wt percent of an alkenyl succinic acid half ester solution in mineral oil (IRGACOR™ L12) as a corrosion inhibitor for an equal amount of the mixed feed glycol. Example 3

[0048] Replicate preparation of the Control Composition, but substitute 1 wt percent of amine salts of alkyl phosphoric acids and dithiophosphoric acid derivatives (NA-LUBE™ 6330, King Industries) as a corrosion inhibitor for an equal amount of the mixed feed glycol. Example 4

[0049] Replicate preparation of the Control Composition, but substitute 0.5 wt percent of barium dinonylnaphthalenesulfonate/carboxylate in hydrotreated naphthenic diluent oil (NA-SUL™ BSN, King Industries) as a corrosion inhibitor for an equal amount of the mixed feed glycol.

Example 5 (Comparative)

[0050] Replicate preparation of the Control Composition, but substitute 1 wt percent of a proprietary preparation of amine phosphate and heterocyclic derivative chemistry (NA- LUBE™ 6220, King Industries) as a corrosion inhibitor for an equal amount of the mixed feed glycol. Comparative Example 5 fails 24 hour testing. Example 6 (Comparative)

[0051] Replicate preparation of the Control Composition, but substitute 0.2 weight percent of dodecyl dimethyl ammonium bicarbonate/carbonate (CARBOSHIELD™ 1000, Lonza, Inc.) as a corrosion inhibitor for an equal amount of the mixed feed glycol. Comparative Example 6 fails 24 hour testing. Example 7 (Comparative)

[0052] Replicate preparation of the Control Composition, but eliminate the pentaerythritol ester of an alkanoic acid (HERCOLUBE™ J), increase the mixed feed glycol by an equal amount to offset the eliminated material, and change the mixed feed glycol to SYNALOX™ 40D220 (The Dow Chemical Company) to maintain a base fluid viscosity of 320 cST at 4O⁰C in the absence of the HERCOLUBE™ J. Comparative Example 7 fails 24 hour testing.

Table 1

1 SYNALOX 40D220 is a random 60/40 EO/PO copolymer having a typical kinematic viscosity of 320 cSt at 4O⁰C.

2 SYNALOX 40D300 is a random 60/40 EO/PO copolymer having a typical kinematic viscosity of 460 cSt at 4O⁰C.

3 DCF200-12500 is a polymethylsiloxane antifoam agent, available from Dow Corning Corporation.

Table 2

1 P indicates passes ASTM D665B.

2 F indicates fails ASTM D665B.

3 n/a indicates not applicable, testing was stopped following failure.

4 N indicates no haze is visible.

5 Y-haze indicates a yellow/white haze is visible.

Claims

What We Claim Is:

1 . A lubricant composition comprising an effective amount of

(1 ) a random or block copolymer polyalkylene glycol based on ethylene oxide and propylene oxide, wherein at least 30 percent by weight of the polyalkylene glycol is ethylene oxide units;

(2) a polyol ester;

(3) N-phenyl-1 ,1 ,3,3-tetramethylbutylnaphthalen-1 -amine, as a first antioxidant;

(4) an alkylated diphenylamine formed from the reaction product of N-phenyl- benzenamine and 2,4,4-trimethylpentene, or a mixed octylated and butylated diphenylamine, as a second antioxidant;

(5) a phosphorus-based extreme pressure additive;

(6) a yellow metal passivator; and

(7) at least one corrosion inhibitor selected from the group consisting of (a) an amine salt of an aliphatic phosphoric acid ester; (b) an alkenyl succinic acid half ester in mineral oil; (c) an amine salt of an alkyl phosphoric acid combined with a dithiophosphoric acid derivative; (d) a combination of barium dinonylnaphthalene sulfonate and dinonylnaphthalene carboxylate in a hydrotreated naphthenic oil; and (e) combinations thereof.

2. The lubricant composition of claim 1 wherein the random or block copolymer polyalkylene glycol contains from 50 weight percent to 85 weight percent ethylene oxide units, the remainder being propylene oxide units.

3. The lubricant composition of claim 1 wherein the polyol ester is a pentaerythritol ester of an alkanoic acid.

4. The lubricant composition of claim 1 wherein the phosphorus-based extreme pressure additive is selected from a group consisting of isopropylated triaryl phosphates; amine-phosphates; phosphor-thionates; acid phosphates; alkyl phosphates; and combinations thereof.

5. The lubricant composition of claim 1 wherein the yellow metal passivator is selected from a group consisting of benzotriazole, tolyltriazole, tolutriazole, mixtures of sodium tolyltriazole and sodium tolutriazole, and combinations thereof.

6. The lubricant composition of claim 1 wherein the composition passes ASTM D665B for at least 168 hours after initiation.

7. The lubricant composition of any of Claims 1 -6, wherein the composition passes SKF-Emcor Test Method DIN 51802: 1990 (ISO 1 1 007) with distilled water and with salt water (0.5 weight percent sodium chloride, based upon total weight of the salt water) with a rating of zero.

8. A lubricant composition comprising

(1 ) 80 percent by weight of a random or block copolymer polyalkylene glycol based on ethylene oxide and propylene oxide, wherein 60 percent by weight is ethylene oxide units and 40 percent by weight is propylene oxide units, having an ISO viscosity grade of 460;

(2) 15 weight percent of a pentaerythritol ester of an alkanoic acid;

(3) 1 weight percent of N-phenyl-1 ,1 ,3,3-tetramethylbutylnaphthalen-1 -amine, as a first antioxidant;

(4) 1 .3 weight percent of an alkylated diphenylamine formed from the reaction product of N-phenyl-benzenamine and 2,4,4-trimethylpentene, as a second antioxidant;

(5) 1 .5 weight percent of an isopropylated triaryl phosphate combined with dodecyl phosphate and triphenyl phosphate as an extreme pressure additive;

(6) 0.1 weight percent of tolyltriazole as a yellow metal passivator; and

(7) 0.6 weight percent of at least one amine salt of an aliphatic phosphoric acid ester as a corrosion inhibitor.