US2450222A - Shear-resistant greases - Google Patents

Description

Patented Sept. 28, 1948 SHEAR-RESISTANT GREASES Harry V. Ashburn, Glenham, Robert S. Barnett, Beacon, and Oney I. Puryear, Fishkill, N. Y., assignors to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing.

' This invention relates to improved lubricating grease compositions and particularly to texturestable lithium base grease compositions in which a synthetic oleaginous compound comprises part or all of the oil component.

This is a continuation-in-part of our copending application Serial No. 611,908, filed, August 21,

Recent developments in the production of lubricating greases and particularly those designed for specialty equipment employing sealed bearings and operating over wide temperature ranges,- have led to the use of a number of organic chemical compounds as substitutes for the conventional mineral lubricating oils, These oleaginous compounds offer a marked advantage over the mineral oils in that they possess a comparatively uniform viscosity over a wide temperature range and are not as susceptible to evaporation loss as a comparable viscosity mineral oil. These features are particularly desirable and have been used to advantage in the production of greases used in sealed life-time bearing installations and low temperature greases used in aircraft controls and the like. However, one undesirable characteristic of these so-called synthetic greases is their lack of resistance to shear. Under conditions of operation where high shearing stresses are involved, such as in ball and roller-bearing lubrication, the structure of these greases graduaily breaks down and their consistency falls off until they become liquid or semi-liquid. At this point the greases no longer adhere to the lubricating surfaces and bearing failures result.

In accordance with the present invention it has been found possible to produce a lithium base Application September 7, 1945, Serial No. 615,074

8 Claims. (Cl. 252--42.1)

grease compositions in which a synthetic oleaginous compound comprises part or all of the oil component. The term "synthetic oleaginous compound" as used herein embraces those organic compounds or mixtures thereof which possess lubricating qualities and may be substituted in whole or in part for the conventional mineral lubricating oils. The choice of v the particular compounds used in the preparation of the synthetic grease depends upon the type of lubricalion and the temperature range within which the grease is intended to be operated. In general, these compounds are adapted to specialized lubrication outside the conventional lubricating temsynthetic grease composition which possesses not only the desirable characteristics-imparted by the oleaginous compounds, but is also resistant to shear. The synthetic greases previously proposed and accepted by the industry have been prepared from the lithium soaps of the conventional fatty acid sources, such as stearic acid and other soapforming fatty acids or their glycerides. It has been discovered that the acid component of the lithium soap is an important factor in the production of synthetic greases and that synthetic greases produced from lithium soaps of soapforming hydroxy fatty acids or their glycerides possess exceptional texture-stability and maintain their structure with little change in consistency even after extensive working at either high or low temperatures.

This unusual characteristic of the lithium soaps of hydroxy fatty acids is applicable to those perature ranges, such as ultra-low temperature operation found in refrigeration systems and arctic service lubrication, or to general purpose lubrication over a wide lubricating temperature range which was previously unattainable through the use of a single mineral lubricating oil due to their high viscosity change over such wide temperature ranges.

As a general proposition, certain factors are prerequisite in the compounds falling within the category of synthetic oleaginous compounds. These compounds are necessarily chemically and physically stable liquids at the temperatures of operation and possess a minimum viscosity of 0.5 centistoke within the lubricating temperature range. Furthermore, the vapor pressure of these compounds in the lubricating temperature range is substantially negligible, although under conditions of flooded lubrication, where evaporation loss is not too critical, compounds of measureable vapor pressure may be used,

' Inasmuch as the primary requisites of the oleaginous compounds are physical in nature, they cannot be conclusively defined in terms of their chemical structure. However, the majority of these compounds are polar compounds with oxygen as the principal type of polar constituent. Another general observation is that, in the compounds of a given chemical classification, those of comparatively high molecular weight possess the least change in viscosity per change in temperature. The types of compounds which are recognized or have been proposed as synthetic oleaginous compounds include the aliphatic ethers, aromatic acid esters, aliphatic mono. and di-carboxylic acid esters, phosphorus acid esters,

and halogenated aromatic compounds. For the purposes of the present invention and as illustrative of the synthetic oleaginous compounds contemplated by the invention, those compounds falling within the category of aliphatic dicarboxylic acid esters are preferred. The compounds within this particular class are the esters of such acids as sebac c. adipic, pimelic, azelaic, alkenylsuccinic alkylma eic. etc, The esters thereof are preferably the aliphatic esters and particularly the branched chain aliphat cesters. Specific examples of the preferred oleaginous compounds are di-2-ethv hexyl sebacate. di-sec-amvl sebacate. di-2-ethylhexyl alkenylsuccinate. di-2-ethoxyethvl sebacate. di-2-(2'-methoxyethoxy) ethyl in the combination of mineral oil and oleaginous compound as the oil component of the finished "grease.

Furthermore, various addition agents may be incorporated with the oleacinous compounds to impart other desirable characteristics. Thus, an extreme pressure agent may be incorporated to improve the anti-wear characteristics of the compound or an anti-oxidant may be incorporatedto improve the anti-oxidant properties ofthe compound and/or the finished grease.

The lithium soaps which have been found to contribute to the desirable attributes of the s nthetic greases are those in which a, soap-forming hydroxy fatty acid constitutes at least part of the acid component. The soap-forming hydroxy fatty acids contemplated herein are those containing at least 12 carbon atoms in the molecule and one or more hydroxyl groups. as well as mixtures thereof. These hydroxy fattyacids may be obtained from natural sources, such as castor oil, or may be prepared by the classical synthetic methods, such as oxidation of unsaturated fatty acids or catalytic oxidation of petroleum oils and waxes with extraction and fractionation to the whether or not mineral oil is to be used as part of the oil component; The conventional method of preparing synthetic greases is the gelling method in which the preformed lithium soap and the cleagincus compound are heated to a homogeneous solution and rapidly cooled to form the grease gel. This method of preparation possesses certain disadvantages in that it requires a preformed lithium soap which in and of itself raises the cost of the grease because of the separate saponification step required and extensive milling equipment to work the grease gel to a homogeneous consistency. However, in preparing the greases of the invention other methods of manufacture, conventional to the grease industry, may be used. A particular'advantage in the use of lithium soaps of hydroxy fatty acids is the fact that the high temperatures required by the conventional gelling methods may be avoided and the preparation conducted at temperatures around 300 F. or at least those attained in a steam-heated kettle and the finished grease drawn from the kettle without redesired molecular range. In the practice of the invention, as descrimd herein, 12-hydroxy stearic acid and hydrogenated castor oil will be used as the representative types of hydroxy fatty acids and their glycerides. These acids are preferred because of their advantage of availability and cost which renders them competitive to the conventional fats and fatty acids.

The soap-forming hydroxy fatty acids may be used as the sole acidic component of the lithium soaps or they may be blended or combined with the conventional fats or fatty acids in such proportions that at least of the total acidic component is comprised of the hydroxy fatty acids. The choice of fats or fatty acids and the specific proportion thereof which may be blended or combined with the hydroxy fatty acids depends upon the particular metallic constituent and the type of service for which the synthetic grease is intended. In general. any of the recognized fatty acid materials normally used in grease manufacture may be used providing they are essentially saturated in character. These fats and fatty acids include mixtures of fatty acid glycerides found in naturally occurring fats and oils, together with fractionated components thereof. The fatty acids may be a mixture of acids split off from these fats or prepared from hydrogenaquiring homogenization. Furthermore, saponification in situ is possible either in the presence of mineral oil or a synthetic oleaginous compound which is inert to the saponification reaction.

The following examples are presented as illustrating the preparation of representative synthetic greases falling within the scope of the present invention. It is to be understood, however,

that these examples are merely illustrative and not definitive of the invention and as suchmay be modified within the scope of the invention as previously defined in accordance with the skill of the art.

Example I .hour and the kettle shut down over night. After standing over night stirring at 35 R. P. M. was begun and the saponification mixture dehydrated at 290-312" F. for four hours. At this point the soap had a very light tan color. The heat was then reduced and 12.2 pounds of mineral oil were added, The physical tests on th mineral oil and synthetic 'oleaginous compound are as-follows:

Di-2-Ethyl- Mineral hexyl Sebaofl cate Flash, 000 "F Fire, 000 F Viscosity Kinematic at F. m. Viscosity Kinematic at 210 F. cs. Viscosity Index At 236F. grams of triple-pressed stearic "acid were added to render the grease slightly acidic. 26 pounds of di-Z-ethylhexyl sebacate were then added slowly. At approximately 190 F. 36.60 pounds of additional di-2-ethylhexyl sebacate were added and during the addition of the ester 196.3 grams of phenyl alpha naphthylamine were added simultaneously. At this point the grease contained approximately 15% soap and possessed an A. S. T. M. penetration at 77 F. of 301-303 unworked and 317-324 worked. 5 pounds of a blend of 28% mineral oil and 72% sebacate ester and 23 grams of phenyl alpha naphthylamine were then added. The grease was finally drawn at a temperature of 166 F. and pumped through three 60 mesh screens. The product was a light cream-colored buttery grease having the following calculated composition: a

I Per cent Lithium soap (75% ydroxy stearic acid,

25% stearic acid) 13.6 Glycerlne 1.0 Mineral 011---; 23.8 Di-Z-ethylhexyl sebacate 60.9 Phenyl alpha naphthylamine 05. Free fatty acid 0.2

' The foregoing synthetic grease was subjected to a dynamic shear test which was conducted in an apparatus consisting of a perforated piston reciprocating within a, closed cylinder maintained at a constant temperature. In the test the grease Example I! 6 grease-breakdown machine wherein a No. 204 anti-friction bearing was packed with-the grease and mounted-on a motor-driven shaft operating at 3450 R. P. M. and surrounded by a heatingjacket.. The test was started atroom temperature and the bearing gradually .heated, while running at a constant speed, until the temperature reached-300 lubricating performance was noted. -At the conclusion of the test the grease was removed from tho bearin .'and examined as to change in texture and consistency. The results obtained on the subject grease indicated excellent lubrication, with no appreciable change in texture or consistency of the grease at the. conclusion of the test.

In comparison therewith a commercial dimethyl silicone grease was also tested and, although sup- A grease base consisting of the lithium soaps of the combination of 75% hydrogenated castor oil and 25% triple-pressed stearic acid and mineral oil was prepared in accordance with the procedure of Example I. This grea'se' base possessed the following calculated composition:

Per cent Lithium soap 47.2 Glycerine 3.5 Mineral oil 49.3

750 grams of the grease base were charged to a kettle and heated with stirringat 234.F. The heat was then reduced and 1020 grams of a dimethyl silicone polymer possessing a flash point above 600 F., with a kinematic viscosity of 82 cs. at 100 F. and 32 cs. at 210 F. were slowly added over a period of six and one-half hours. At this point the temperature was 147 F. and the A. S. T. M. control penetration at '77 was 203-210 unworked and 221223 worked. 1000 grams of additional dimethyl silicone polymer were then added slowly until a control worked penetration of 345 at 78 F. was obtained. The batch was then drawn at a temperature of 176F. The product was a smooth, light-colored, buttery grease having the following calculated composition:

Per cent Lithium soap 12.8 Glycerlne 0.9 Mineral oil 13.4 Dimethyl silicone polymer 72.9

The subject grease was tested in.a so-called plying excellent lubrication, the grease became semi-fluid toward the end of the test and drained from the bearing when the test was stopped.

Example III grams ,of lithium 12-hydroxy stearate and 900 grams of di-2-ethylhexyl sebacate were mixed I and heated with stirring. At 350 Fjt-he'soap began to dissolve in the ester and at 390" F. was completely in solution. The solution was heated to 400F. and poured in a thin layer on the bottom of a grease pan, taking care that no thick spots were formed. After cooling, a smooth, but- I ,tery gel was formed which showed no signs of separation. The A. S. T. M. control worked penetration of the grease gel was 240 at 77 F. The product possessed the following calculated composition:

, Per cent Lithium 12-hy-droxy stearate--- 10 Di-Z-ethylhexyl sebacate 90 This grease was tested in the dynamic shear test described in Example I in comparison witha 10% lithium stearate grease containing ell-2- ethylhexyl sebacate as the sole oil component and the results obtained are as follows:

, Lithium I Lithium- Miniature Penetration Hydroxy Stearate stearate Original .Q 126, 181. Final 268, 270 Semi-fluid.

Where the said application Serial No. 611,908 discloses and claims a lubricating grease composition of the synthetic ester type of'lubricating base, together witha metal soap of hydroxy fatty acids or hydroxy fatty acid glycerides, and specificallya sodium soap grease of this type, the present application is restricted to a lithium soap grease of this general type.

Obviously many modifications and variations to thicken said lubricant base, said soap-forming F. During the period of the test the e 7 fatty material consisting of more than 50% by weight of a hydroxy soap-forming-fatty material selected from the group consisting of hydroxy fatty acids and hydroxy fatty acid glycerides, said grease composition being texture-stable under high shearing stress.

2. A lubricating grease composition according to claim 1, wherein the said ester is a branched chain aliphatic diester of an aliphatic 'dicarboxylio acid.

3. A grease composition according to claim 2,

wherein the said ester is a branched chain aliphatic sebacate.

4. A lubricating grease composition according to claim 3, wherein the said diester is di-z-ethyl hexyl sebacate.

5. A lubricating grease composition comprising as the major portion of the composition a lubricant base consisting of a minor proportion of mineral lubricating oil and a major proportion of an oil-soluble high molecular weight high boilin liquid branched chain aliphatic dies'ter of an allphatic .dicarboxyiic acid, sufficient lithium soap of a soap-forming fatty material consisting of a major proportion of hydrogenated castor oil and a minor proportion of a saturated soap-forming fatty acid to thicken said lubricant base, glycerine resulting from the saponification of said hydrogenated castor oil, and a small proportion of an oxidation inhibitor, said grease composition being texture-stable under high shearing stress.

6. A lubricating grease composition according to claim 5, wherein said diester is di-2-ethy1 hexyl sebacate.

7. A lubricating grease composition comprising as the major portion of the composition a lubricant base consisting of a minor proportion of mineral lubricating oil and a major proportion of 8 an oil-soluble high molecular weight high boiling liquid branched chain aliphatic dies-ter of an aliphatic dicarboxylic acid, sufficient lithium soap of about a 3:1 mixture by weight of hydrogenated castor oil and stearic acid to thicken said lubri= cant base, glycerine, and a small proportion of an REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,993,738 Graves et al Mar. 12, 1935 2,049,072 Mikeska July 28, 1936 2,104,408 Wiezevich Jan. 4, 1938 2,303,256 'Camelford Nov. 24, 1942 2,334,274 Meadows Nov. 16, 1943 2,351,384 Woods et al June 13, 1944 2,376,312 Morgan May 15, 1945 2,379,850 Morgan July 3, 1945 2,380,960 Fraser Aug. 7, 1945 2,383,147 Morgan Aug. 21, 1945 2,390,450 Morgan Dec. 4, 1945 2,397,956 Fraser Apr. 9, 1946 FOREIGN PATENTS Number Country Date 406,136 Great Britain Feb. 22, 1934 157,953

Switzerland Jan. 2, 1933