Antiwear hydraulic oil

Abstract

An improved antiwear hydraulic oil comprises major amounts of a mineral lubricating oil (preferably a hydrocracked oil which has been solvent extracted to improve ultra-violet light stability) and minor amounts of a "secondary" zinc dialkyl dithiophosphate antiwear agent, chelating type and film forming type metal deactivators, a neutral barium salt of a petroleum sulfonate and a succinic acid based rust inhibitor. The hydraulic oil is especially useful in lubrication of high output (e.g., 100 gallons per minute) bronze-on-steel axial piston pumps.

Description

BACKGROUND OF THE INVENTION

Zinc dithiophosphates are widely used in lubricants as anti-wear agents. Although ashless anti-wear materials have been gaining prominence because of the absence of heavy metals, the zinc dithiophosphates still continue to provide one of the most economical sources of anti-wear protection. There are three general types of zinc dithiophosphates from which to select, depending on the specific application. The zincs are classified as either primary, secondary, or aryl, depending on the alcohols from which they are made, although the primary and secondary zincs are commonly referred to as alkyl. If the R-O- group in the structure for zinc dithiophosphate (shown below) is derived from a primary alcohol, then the zinc is referred to as primary; likewise, if it is derived from a secondary alcohol, it is referred to as secondary and, if derived from an alkylated phenol, it is referred to as aryl. ##EQU1## Each of these zincs usually displays a different combination of performance properties as summarized below:

Performance Type of Zinc Dithiophosphate Characteristic Primary Secondary Aryl ______________________________________ Wear Protection Average Best Poorest Oxidation Inhibition Average Best Poorest Thermal Stability Average Poorest Best Demulsibility Best Average Poorest Cost Lowest Average Highest ______________________________________

Based on their relative performance levels, zincs are selected for a particular application. For example, aryl zincs are used almost exclusively in diesel engine oils because of their excellent thermal stability. Primary zincs find a large application in both engine oils and hydraulic oils. Secondary zincs are used mostly in hydraulic oils, transmission and gear oils. Primary and secondary zincs have been selected for these applications because of their relatively good anti-wear performance, good anti-oxidant qualities and low cost. Where hydraulic oils are concerned, primary zincs have usually been preferred because they offered the best overall performance for the lowest cost.

However, problems have been encountered when primary zincs are used in certain axial in-line piston pumps. In these pumps, the bronze piston pads slide on a steel swash plate. With certain zinc-containing anti-wear hydraulic oils, a reaction occurred at the interface of the bronze piston pads and the steel swash plate. The reaction products raised the friction level between the sliding surfaces and eventually generated enough heat to crack the swash plate.

The present invention provides an anti-wear hydraulic oil containing a secondary zinc and which provides superior performance in vein pumps and piston pumps and especially with such "bronze-on-steel" pumps.

SUMMARY OF THE INVENTION

An improved anti-wear hydraulic oil comprises major amounts of a mineral lubricating oil (preferably a hydrocracked oil which has been solvent extracted to improve ultra-violet light stability) and minor amounts of a secondary zinc dialkyl dithiophosphate anti-wear agent, chelating type and film forming type metal deactivators, a neutral barium salt of a petroleum sulfonate and a succinic acid based rust inhibitor. The hydraulic oil is especially useful in lubrication of high output (e.g., 100 gallons per minute) bronze-on-steel axial piston pumps.

The preferred mineral oils consist mainly of oils termed "paraffinic" or "relatively paraffinic" by the viscosity gravity constant classification. Especially useful are the stabilized, hydrocracked oils described in copending U.S. Pat. applications Ser. No. 178,193 filed Sept. 7, 1971 and Ser. No. 298,126, filed Oct. 16, 1972 of Bryer et al. (the entire disclosure of which, and of Ser. No. 35,231 below is incorporated herein). Blends of such hydrocracked oils with a naphthenic acid-free naphthenic distillate can also be used on the present invention. The "polymer" and "soap" type antileak hydraulic oils shown in Ser. No. 35,231 of Griffith et al. (filed May 6, 1970 and now abandoned) can also be made containing the secondary zinc dialkyl dithiophosphates, for anti-wear, if the two types of metal deactivator, a neutral barium sulfonate and a succinic acid type rust inhibitor are included therewith.

The relative proportions of the essential ingredients are important. The weight ratio of the secondary zinc dialkyl dithiophosphate to the total weight of the deactivator compounds is generally no greater than about 15 to 1 (typically about 10 to 1).

The relative weight proportions of the succinic acid inhibitor and the neutral barium petroleum sulfonate are generally in the range of 3 to 1 to 1 to 1 (typically about 2 to 1). The relative proportion of the neutral barium petroleum sulfonate to the total metal deactivators is also important (and is best determined by experiment) since if the relative amount of the barium compound is too great, the hydrolytic stability of the lubricant will be poor and high metal losses will be encountered in use in the pump.

FURTHER DESCRIPTION

To predict which kinds of zinc dithiophosphates would cause swash plate cracking two test procedures are useful. One the beverage bottle hydrolytic stability test, measures the corrosive nature of the zinc-containing hydraulic oil in terms of metal loss and total acidity. This test, as described in the ASTM handbook, also calls for the amount of insolubles produced, the viscosity change of the oil, and the acid number of the oil. For this particular hydraulic oil problem, however, these data are not pertinent.

The other, the sludge and metal corrosion test, also measures corrosiveness in terms of metal loss, but measures sludge produced as well. The sludge and metal corrosion test is a combination oxidation and corrosion test. This test is run using the same conditions as the ASTM D 943 test. After a thousand hours, however, the test is terminated and the oil is analyzed for the total amount of sludge present, as well as the amounts of copper and iron present in the combined oil, water and sludge fractions.

Before the beverage bottle hydrolytic stability test and the sludge and metal corrosion tests were adopted to separate "good" and "bad" zinc-containing hydraulic oils, preliminary work was done using the low velocity friction apparatus to compare a secondary zinc formulation which performed satisfactorily in piston pump service with a primary zinc formulation which did not. This comparison gave the first indication that there might be a significant difference between primary and secondary zinc hydraulic oil formulations in lubrication of a bronze-steel piston pump.

The low velocity friction apparatus is an instrument which measures friction characteristics as a function of sliding speed and applied load. For most testing, a steel anulus is used which rotates on a steel plate. Both the anulus and plate are immersed in the test oil. To simulate the sliding conditions of the bronze-on-steel piston pump, however, a bronze anulus and a steel plate was used. In this case, testing was aimed at generating reaction products, rather than friction curves. At the end of the test the used oil was analyzed for copper content and also visually inspected. As shown by the results below, the primary zinc formulation showed a significant increase in copper content, indicating a substantial amount of reaction products. The secondary zinc formulation, however, showed little change. Even more dramatic was the difference in appearance of the two formulations at the end of the test. The primary zinc showed very severe accumulation of black reaction products; the secondary formulation remained clear.

Low Velocity Friction Apparatus Test ______________________________________ Oil Data Copper Content, ppm Primary Zinc Secondary Zinc Formulation (A).sup.(2) Formulation (D).sup.(2) New Oil 35 60 Used Oil 760 82 Appearance Heavy black Clear debris Conditions: Bronze-on steel specimens, 200F, 80 lbs. load, 8 ft/minutes sliding speed, 17 hours. ______________________________________ .sup.(a) These were fully formulated anti-wear hydraulic oils containing, in addition to zinc dithiophosphate, antioxidant, rust inhibitor and defoamer.

The beverage bottle hydrolytic stability test and the sludge and metal corrosion test have been adopted as part of the anti-wear hydraulic oil specification for the bronze-on-steel axial piston pumps by certain pump manufacturers and the Military under the MIL specification 24459. The hydrolytic stability test is an ASTM-established test and is found in the current ASTM handbook under ASTM D 2619-67. In the test, 75 grams of the anti-wear hydraulic oil are added to 25 grams of distilled water in a beverage bottle containing a copper strip. The bottle is capped and placed in an oven where it rotates end over end at 5 rpm for 48 hours at 200.degree.F. At the end of the test, the weight loss of the copper strip and the total acidity of the water layer are determined. They are considered a measure of the corrosiveness of the oil. Those anti-wear hydraulic oils which produce no more than 0.5 mg/cm.sup.2 of copper loss and no more than 6.0 mgKOH total acidity in the water portion are considered satisfactory for bronze-on-steel piston pump use, provided, of course, that they also satisfy the other requirement--the sludge and metal corrosion test. This test is a combination oxidation and corrosion test. It is run using the same conditions as the more familiar ASTM D 943 Turbine Oil Oxidation Test. At the end of a 1000 hours, however, the oxidation test is terminated and the oil is analyzed for total sludge produced, as well as the copper and iron content of the combined oil, water, and sludge portions. Maximum acceptable limits for the test are:

Total insoluble sludge, mg 400 Total Copper, mg 200 Total iron, mg 100

Complete description of the test is found under Federal Test Method 3,020.1.

With the results of the LVFA preliminary testing in mind, we evaluated the same primary zinc and secondary zinc formulations in the hydrolytic stability and sludge and metal corrosion tests. The results are shown in Table I. Note the converse relationship between the two zincs in the two tests. The primary zinc-containing formulations shows relatively poor hydrolytic stability primarily because of high metal loss which we believe is the more crucial part of this test. It does, however, perform well in the sludge and metal corrosion test. The secondary zinc-containing formulation, on the other hand, performed in the opposite fashion. It did relatively well in hydrolytic stability, but poorly in sludge and metal corrosion test.

The poor hydrolytic stability of this particular general-purpose primary zinc was not unique. The hydrolytic stability of two other similar general-purpose primary zincs was examined and relatively high metal loss was found. These are identified as B and C in Table II. Also shown in Table II is a secondary zinc, E, which shows the same degree of metal loss as the general-purpose primaries, indicating that the relatively low metal loss of the secondary reference zinc was not characteristic of all secondary zincs.

One feature which these two tests do have in common is that they both measure metal loss. Both the primary and secondary zinc were showing metal loss, although in different forms. However, we discovered that the combined use of two types of metal deactivators can minimize metal loss.

There are two common types of metal deactivators. One, the film-forming type, minimizes metal corrosion by plating out on the metal surface. In effect, this puts a protective barrier between the metal surface and the corrosive materials. The second type of deactivator reduces metal loss by chelating or tieing up the corrosive materials before they can catalyze further attack on the surfaces.

When the same primary and secondary zinc formulations as above are formulated using various types of metal deactivators, the results are shown in Table III. Table III shows that

1. None of the deactivators improved the performance of the general-purpose primary zinc dithiophosphates sufficiently to pass the hydrolytic stability test.

2. Both the chelating and combination type of metal deactivators were effective enough on the secondary zinc formulation for it to pass the hydrolytic stability test. The improvement in minimizing metal loss was substantial. Although the chelating metal deactivator was more effective than the combination type in improving hydrolytic stability, it had been linked to compatibility problems in earlier work. Therefore, the combination type was preferred because of its better compatibility. As shown in Table IV, this deactivator was also effective in dramatically reducing the sludge and metal corrosion of the secondary zinc formulation.

These results show that the "primary zinc" should not be used in formulations where hydrolytic stability was required. The secondary zinc formulation was clearly superior. However, this lubricant is still defective and requires for satisfactory performance the surface active component, namely, two specific types of rust inhibitors.

Although the use of the two combined metal deactivators represents a major means of improving the hydrolytic stability of the secondary zinc formulation, a far more successful lubricant is obtained by the proper selection of rust inhibitors. The effect of various types of rust inhibitors on the secondary zinc in the presence and absence of the combination type metal deactivator is shown in Table VI. Unlike the formulations shown in Table VI, these blends were not fully formulated, but contained only the components shown. Note that both the acidic and neutral type rust inhibitors which are surface active enough to provide adequate protection as measured by the ASTM D 665B test, also reacted with the zinc to promote severe metal attack in the hydrolytic stability test. The dibasic rust inhibitor which did not provide adequate rust protection, however, did not promote metal attack. The presence of the combination type metal deactivator did not substantially change these results. Where the deactivator did produce a significant change, however, was in the case of the mixed rust inhibitors which consisted of both acidic and neutral components used separately before. Without deactivator, metal attack occurred, but in the presence of deactivator, metal attack was reduced within the acceptable limits with no loss of rust protection. Obviously, the combination of the acidic and neutral components provides a balanced rust inhibitor which is surface active enough to protect against rust, but not active enough to overpower the metal deactivator.

With some commercially available secondary zinc dialkyl dithiophosphates, a precipitate or haze will form when an effective amount of the combination of the two types of metal deactivators is incorporated therein. For example, such a precipitate formed with E. This precipitate formation should be used as a screening test to determine the better "secondary zincs" for use in the present invention.

Based on the results discussed above, it can be seen that the reactivity of zinc dithiophosphates, particularly in combination with other components, has a significant effect on the bronze/steel metallurgy found in some piston pumps. Specifically, these results indicate that:

1. The secondary zinc reference formulation performed satisfactorily in the axial piston pump because it is less reactive than the general purpose primary zinc tested. These, being more reactive, are unsuited for use in bronze-on-steel axial piston pumps.

2. The film-forming, chelating, and combination types of deactivators were not effective in reducing metal loss in hydrolytic stability testing of the primary zinc examined. However, the chelating and combination type deactivators were effective in reducing metal loss of the secondary zinc formulation.

3. That rust inhibitors which are surface active enough to provide good rust protection can react with the secondary zinc to promote severe metal attack in the hydrolytic stability test. The presence of a combination type deactivator is not effective in these cases.

4. That the use of a mixed acidic-neutral type rust inhibitor with the combination type metal deactivator provides adequate rust protection without promoting metal attack.

Commercially available "primary" zinc dialkyl dithiophosphates are well-known and include "Amoco 5959", "Elco 103" and "Oronite 269N". Similarly, there are many commercially available secondary zinc dialkyl dithiophosphates, e.g., "Lubrizol 677A" (the "reference" or D of the present case), Lubrizol 1097, and Edwin Cooper "Hitec E653" (identified as E herein).

The commercially available "chelating type" metal deactivators include "Amoco 150" (an alkyl derivative of 2,5-di-mercapto-1,3,4-thiadiazole) and the related "compounds" in U.S. Pat. Nos. 2,719,125; 2,719,126 and 2,983,716.

The commercially available film-forming type metal deactivators include the benzotriazoles (e.g., Vanderbilt "BT Z" and U.S. Rubber Company "Cobrate 99"), and the Vanderbilt products "Cuvan 80" (N,N'-disalicylidene-1,2-propane-diamine, 80% in organic solvent), "Cuvan 7676" and "Cuvan XL".

The commercially available neutral barium petroleum sulfonates include NaSul BSN of R. T. Vanderbilt Co.

The commercially available acidic type rust inhibitors are primarily substituted-succinic anhydrides (e.g., "TPSA" or tetraphenyl succinic anhydride).

Accordingly, the following example is illustrative of lubricants which can be produced in accordance with the present invention.

ILLUSTRATIVE EXAMPLE

An additive mixture, for use in formulation of anti-wear hydraulic oils containing a secondary dialkyl dithiophosphate, was made by blending the following ingredients:

Weight % ditertiary butyl paracresol 20.0 naphthyl amine 20.0 zinc diamyldithiocarbamate 3.0 tetraphenyl succinic anhydride 2.2 neutral barium petroleum sulfonate 1.5 "Amoco 150" chelate-type deactivator 3.3 Cuvan 80 film-forming deactivator 6.7 diluent, paraffinic oil 43.3 100.0

The additive mixture was blended as indicated below to make an anti-wear hydraulic oil:

COMPOSITION, VOLUME % ______________________________________ UV stable hydrocracked oil 99.23 Secondary ZDP ("D") 0.40 Additive mixture 0.35 Silicone antifoam 0.02 ______________________________________

The hydrocracked oil had an SUS viscosity at 100.degree.F of 200, an ASTM VI of about 100 and was paraffinic by VGC class. The properties (and typical control limits) of the blend (in metric units) follow:

TYPICAL RANGE TESTS METHOD MIN. MAX. EXAM- PLE ______________________________________ # Viscosity, cSt/37.8C D445 42.9 46.2 44.6 Viscosity, cSt/40C D341 40.2 Viscosity, cSt/98.9C D445 6.50 Viscosity, cSt/100C D341 6.33 Viscosity Index D2270 100 106 Flash COC, C D92 204 235 # Pour, C D97 -18 -18 Color D1500 2.0 0.5 Density/15c, kg/m.sup.3 D1298 873 861 Total Acid No., mgKOH/g D664 1.0 Copper Strip, 3 hrs/100C D130 1 1 Sulfur, % D2622 0.14 Conradson Carbon, % D189 0.25 An line Point, C D611 112 # Demulsibility/54.4C D1401 Separation, minutes 30 25 # Foam, Tendency/Stability D892 Sequence I, cm.sup.3 50/0 25/0 Sequence II, cm.sup.3 50/0 25/0 Sequence III, cm.sup.3 50/0 25/0 # Rust, Syn. Sea Water D665B Pass Pass Oxidation Stability, hr. D943 2000 > 2000 Continental Oxid.,hr. 100 >100 4-Ball Wear Scar, mm 20 kg, 1800 rpm, 54.4C, 0.35 1hr # Appearance Visual Bright Bright # Zinc, wt.% .044 .054 .048 Phosphorous, wt.% D1091 .039 .051 .044 # DBPC, wt.% .070 .087 .077 ______________________________________

When non-hydrocracked solvent refined paraffinic oils are substituted for the hydrocracked oil, 0.50% of the mixture is required for equivalent performance.

Similarly, blends of hydrocracked and non-hydrocracked lubes can be used in the present example, as can unstabilized hydrocracked oils; however, in general the U.V. stabilized (by solvent extraction or hydrorefining) hydrocracked lube provides the best performance at lower additive levels.

Similarly, blends (as of 100 and 500 SUS, at 100.degree.F) of oils can be substituted for the 200 SUS base oil and higher or lower viscosity base oils (e.g., 80-2000 SUS) can be used, as in this example, to make hydraulic oils of varied viscosities.

In commercial additives, the type and amount of ZDP can vary from brand to brand of additive; however, in a given lubricant formulation, the amount of a given ZDP can be determined by calculation from the zinc content. As a rule of thumb, such substitutions are done by the zinc equivalent method. In the above example, the amount of additive should incorporated in the range of 0.044 to 0.054 Zn (typically 0.048 wt. %). In the work reported in the Tables, the ZDP additives were used at about the same Zn levels. The representative secondary ZDP, Lubrizol 677A (sometimes identified as D) analyzes 9.25 wt. % Zn and 8.5 wt. % P.

Compositions according to the present invention can be made wherein the viscosity of the base petroleum oil is in the range of 60-3,000 SUS at 100.degree.F. In general, for use as a hydraulic oil the typical base oil viscosity will be below 1,000 SUS at 100.degree.F.; however, lubricants consisting essentially of a 1,000- 3,000 SUS at 100.degree.F base oil are useful as gear lubricants (e.g., see Ser. No. 477,872, filed June 10, 1974, of Williams, Reiland and Griffity, the entire disclosure of which is incorporated herein).

The terms "compatible amount" and "mutually compatible amounts" as used herein mean that no precipitate is observed in the final lubricant when it is stored for 24 hours at about 65.degree.F.

Table I ______________________________________ COMPARISON OF PRIMARY AND SECONDARY ZDP* PERFORMANCE ______________________________________ Maximum Pri- Acceptable mary Secondary Test Limits ZDP ZDP ______________________________________ ASTM D 2619 Results Beverage Bottle Hydrolytic Stability Test -- Copper Wt. Loss, mg/cm.sup.2 0.5 3.5 0.5 -- Total Acidity of Water Layer, mgKOH 6.0 6.2 8.9 Federal 3020.1 Results Sludge & Metal Corrosion -- Insoluble Sludge, mg 400 198 921 -- Metals in Combined Oil Water & Sludge Copper, mg 200 76 306 Iron, mg 100 13 341 ______________________________________ *Zinc dialkyldithiophosphate?

The base oil, in all tables herein, was 200 SUS, at 100.degree.F, "U.V" stabilized (by solvent extraction) hydrocracked oil (ASTM VI about 100), available commercially as "Sunpar LW120" or "HPO 200", from the Sun Oil Company. The lubricant contained 0.5 vol. % of the ZDP, 0.07 wt. % ditertiary butyl paracresol, 0.07 wt. % naphthalamine, 0.006 vol. % NaSul BSN, 0.0088 vol. % TPSA, 0.012 % zinc Diamyldithiocarbamate (Vanlube AZ), and 2 ppm "active" silicon antifoam.

Table II __________________________________________________________________________ COMPARISON OF THE HYDROLYTIC STABILITY OF "ZDP" LUBRICANTS __________________________________________________________________________ Maximum Acceptable Primary Formulations Secondary Formulation Test Limits (A) (B) (C) (D) (E) __________________________________________________________________________ Beverage Bottle Hydrolytic Stability Test, ASTM D 2619 -- Copper Weight Loss, mg/cm.sup.2 0.5 3.5 1.5 2.4 0.5 2.09 -- Total Acidity of Water Layer, mgKOH 6.0 6.2 33.0 2.5 8.9 1.20 The lubricants of this Table (II) are fully formulated anti-wear hydraulic oils, similar to Table I, containing, in addition to ZDP (0.5 vol. %), antioxidant, rust inhibitor, and defoamer. __________________________________________________________________________

Table III __________________________________________________________________________ EFFECT OF METAL DEACTIVATORS IN HYDROLYTIC STABILITY OF ZDP __________________________________________________________________________ LUBRICANTS Combination of Maximum Film-Forming & Acceptable Film-Forming Type Chelating Type Chelating Types Test Limits Primary Secondary Primary Secondary Primary Secondary __________________________________________________________________________ Beverage Bottle Hydrolytic Stability Test (ASTM D 2619) Fail Fail Fail Pass Fail Pass -- Copper Weight Loss, mg/cm.sup.2 0.5 0.61 0.33 2.59 0.0 4.25 0.03 -- Total Acidity of Water Layer, mgKOH 6.0 10.0 17.0 6.21 1.7 1.6 3.1 Formulations were similar to those of Table I. __________________________________________________________________________

Table IV __________________________________________________________________________ EFFECT OF COMBINATION TYPE METAL DEACTIVATOR ON HYDROLYTIC STABILITY AND SLUDGE AND METAL CORROSION TESTS OF SECONDARY ZDP __________________________________________________________________________ (D) Maximum Acceptable Deactivator Deactivator Test Method Limits Absent Present __________________________________________________________________________ Beverage Bottle Hydrolytic ASTM Stability Test D 2619 -- Copper Wt. Loss, mg/cm.sup.2 0.5 0.5 0.03 -- Total Acidity of Water Layer, mgKOH 6.0 8.9 3.1 Sludge and Metal Corrosion Federal 3020.1 -- Insoluble Sludge, mg 400 921 288 -- Metals in Combined Oil, Water and Sludge Copper, mg 200 306 173 Iron, mg 100 341 57 Formulations similar to those of Table I. __________________________________________________________________________

Table V __________________________________________________________________________ EFFECT OF METAL DEACTIVATORS IN HYDROLYTIC STABILITY TESTING __________________________________________________________________________ (1) (2) (3) Film-Forming Type Chelating-Type Combination of (benzotriazole) (mercapto-thiodiazole) Film-Forming and Chelating Types Primary Secondary Primary Secondary Primary Secondary Metal Deactivator (A) (D) (A) (D) (A) (D) __________________________________________________________________________ Beverage Bottle Hydrolytic Stability Test (ASTM D 2619) Fail Fail Fail Pass Fail Pass -- Copper Weight Loss, mg/cm.sup.2 0.61 0.33 2.59 0.0 4.25 0.03 -- Total Acidity of Water Layer, mgKOH 10.0 17.0 6.2 1.7 1.6 5.6 __________________________________________________________________________ .sup.(1) R. T. Vanderbilt - "BTZ"? .sup.(2) "Amoco 150 .sup.(3) R. T. Vanderbilt - "OD 691 Formulations were similar to those of Table I

Table VI __________________________________________________________________________ EFFECT OF RUST INHIBITORS ON REFERENCE SECONDARY ZINC DITHIOPHOSPHATE* __________________________________________________________________________ Secondary Zinc Secondary Zinc Secondary Zinc Secondary Zinc Secondary Zinc without and "TPSA" and "Neutral Ba" and Dibasic Acid and Mixed** Rust Inhibitor Rust Inhibitor Rust Inhibitor Rust Inhibitor Rust Inhibitor Test Metal Deactivator Metal Deactivator Metal Deactivator Metal Deactivator Metal Deactivator __________________________________________________________________________ Hydrolytic Beverage Bottle Absent Present Absent Present Absent Present Absent Present Absent Present Stability Test (ASTM D 2619) -- Copper Weight Loss, mg/cm.sup.2 0.26 0.40 3.29 2.04 2.67 4.29 0.37 0.45 1.87 0.17 -- Total Acidity of Water Layer, mgKOH 2.86 1.80 11.78 14.0+ 1.68 0.56 1.18 1.40 2.24 3.37 Rust Protection, Synthetic Sea Water (ASTM D 665B) Fail Fail Pass Pass Pass Pass Fail Fail Pass Pass __________________________________________________________________________ *Basic Formulation 0.40 vol. % zinc dithiophosphate in 200 SUS/100 F paraffinic base oil (solvent-extracted after hydrocracking) rust inhibitors, 0.10 volume %. Combination of acid "TPSA" and neutral "Ba" (barium petroleum sulfonate) rust inhibitors.

Claims

The invention claimed is:

1. A composition, useful as an anti-wear hydraulic oil or as a gear lubricant, comprising major amounts of a mineral lubricating oil and minor, effective and mutually compatible amounts of a secondary zinc dialkyl dithiophosphate anti-wear agent, chelating type and film forming type metal deactivators, and, as rust inhibitors, a neutral barium salt of a petroleum sulfonate and an alkyl or aryl substituted succinic acid or acid anhydride.

2. The composition of claim 1, wherein said mineral lubricating oil consists essentially of oil having an SUS viscosity at 100.degree.F. in the range of 60-3,000 SUS and a viscosity-gravity constant in the range of 0.780-0.819.

3. The composition of claim 1, wherein said chelating type metal deactivator is an alkyl-substituted derivative of 2,5-di-mercapto-1,3,4-thiodiazole.

4. The composition of claim 1 wherein said film-forming type metal deactivator is N,N'-disalicylidene-1,2-propane-diamine.

5. The composition of claim 3 wherein said film-forming type metal deactivator is N,N'-disalicylidene-1,2-propane-diamine.

6. The composition of claim 1 wherein one said rust inhibitor is tetraphenyl succinic anhydride.

7. The composition of claim 5 and containing tetra phenyl succinic anhydride.

8. The composition of claim 7 wherein said lubricant is useful as a hydraulic oil and contains effective and compatible minor amounts of a naphthyl amine, zinc Dialkyldithiocarbamate and ditertiary butyl paracresol.

9. The composition of claim 8 wherein said base oil consists essentially of one or more hydrocracked oils having a viscosity gravity constant below about 0.80 and which have been stabilized against degradation by ultra violet light by extraction with an aromatic selective solvent.

10. The composition of claim 9 and containing an effective amount of an antifoaming agent.