US2618598A - High-temperature lubricating grease - Google Patents

Description

, acids.

Patented Na. 18, 1952 FMQE HIGH-TEMPERATURE LUBRICATKN GREASE Arnold .l.

Moi-way, mark Township,

Union iCounty, and Paul V. Smith, Jr., Westifield, N. 3., assignors to Standard Oil Development worm pany, a corporation of Delaware No Drawing. Application February 8, 195b, Serial No. 143,171

1 1'? Claims. l

The present invention relates tohigh temperature lubricating greases and, particularly, to greases which contain as thickeners the combined soaps oi. high molecular weight fatty acids and low molecular weight thio ether acids. The improved composition is particularly useful for the lubrication of antifriction bearings, especially where such bearings are to be operated at abnormally high temperatures.

It has been suggested in the prior art, that it is advantageous, in cases where improved high temperature performance is requisite, to combine with conventional metal soaps of long chain fatty acids the salts of certain low molecular weight Thus, the addition of such salts as metal acetates, acrylates, crotonates, furoates, and the like, has been found in the prior art to improve the high temperature stability of soda base greases, calcium base greases and certain other common grease compositions.

The particular reasons why the low molecular weight salts improve the high temperature performance of conventional greases are not entirely clear. It has been suggested that a complex of salt and soap is formed which has superior thickening effect in a given quantity of lubricating oil. Whatever may be the phenomena involved, the addition of low molecular weight salts is often advantageous, particularly in connection with alkali and alkaline earth metal greases. It does not'follow, however, that all low molecular weight acids are useful and, as a matter of fact, some have been found to be definitely objectionable.

According to the present invention, it is advantageous to use in combination with conventional fatty acid soaps, the metal salts of low molecular weight thio ether acids. The alkali metal salts of such acids are particularly useful, especially in combination with alkali metal soaps. However, certain other metal salts and soaps such as those of alkaline earth metals can be combined. Barium soaps and salts are very satisfactory. Also, alkali metal salts can be combined with alkaline earth metal soaps or vice versa. It is usually preferable to use the same metal base for forming both the salt and the soap. For

purposes of the present invention, the salts and thetic oils.

2 wherein R1 and R2 are each aliphatic hydrocarbon groups or radicals of l to 2 carbon atoms. In other words, the thio ether acid is a relatively short chain aliphatic acid having a thio ether linkage. The salts of such acids as ethyl thioglycolic acid, also known as ethyl mercapto acetic acid, are particularly preferred and the close homologs such as ethyl mercapto propionic acid salts appear to be equally useful, within the limits of the above formula. A lubricating grease of good properties is prepared by using about 2 to 10% by weight, based on the total composition, of the salt in combination with 5 to 35% of a conventional soap of the C12 to C24 fatty acids. The preferred proportions are about 3 to 6% of the salt and 15 to 25% of the soap. Any lubricating oil may be used, but the mineral base oils arepreferred because the soaps and the salts may be formed in situ therein without objectionable side reactions. Where synthetic oils are used, the soaps and salts should be formed under such conditions that there is no hydrolysis of the syn- In this case, as is now well understood in the art, the salts and/or soap may be preformed or may be prepared in a neutral diluent, such as mineral lubricating oil, to form a concentrate. This concentrate then may be ex tended by blending in the appropriate synthetic oil, such as an ester of dibasic acid, a polyglyccl or other suitable lubricating fluid.

The preferred process is carried out by first adding about 5 to 35 parts by weight of saponifiable fatty acids, preferably substantially saturated, of the C12 to C24 range, to about 25 parts of mineral base lubricating oil. The oil preferably has a viscosity between about 35 and S. S. U. at 210 F. This mixture is stirred and heated gently to melt the fatty acids, e. g. heated to about to F., and then the thioet-her acid is added. If another low molecular weight acid such as acetic acid is also to be added, this may also be stirred into the oil and fatty acid blend. Since the low molecular weight acids are quite insoluble, they should be continuously stirred while the saponification and neutralization step is being carried out.

The metal base, e. g. an aqueous solution or a ther heating and continued stirring. The grease is cooked to a final temperature between about 350 and 475 F., preferably about 400 to 450 F. Thereafter antioxidants and any other desired modifiers may be added and the product is packaged and cooled.

The invention will be more fully understood by reference to the following specific examples.

The fatty acids and of the mineral oil were charged to a fire heated grease kettle and warmed to 140 F. When all the acid was melted, the ethyl thioglycoiic acid was charged and the combined acids co-neutralized with a 33%% aqueous solution of sodium hydroxide. The combined soaps in mineral oil were then heated to 225 F. where they were dehydrated. When dry, the temperature was raised to 300 F. where /2 of the balance of the mineral oil was slowly added. The temperature was then raised to 425 F.; during this heating period the balance of the mineral oil was added. The grease was cooled to 400 F. and the phenyl alpha-naphthyl amin inhibitor added. The grease was then drawn into pans for cooling and the cold grease milled. The resulting product was smooth, of short fiber structure.

Properties Per cent free alkalinity as NaOH 0.16

Worked penetrationmm./ 330 stability to mechanical workingpenetration after 100,000 strokes in a mechanical grease worker, employing a 3251 hole worker platemm./10 335 Dropping point, F 386 As mentioned above, it has been considered desirable in the prior art to use the salts of certain low molecular weight carboxylic acids. Acetic acid has been considered particularly desirable for economic reasons. The acetic acid greases have shown good structural and oxidation stability, but in order to obtain satisfactory soap dispersions with the use of a minimum quantity of thickener for good structural stability it has been necessary to cook the acetic acid greases to very high temperatures, commonly in excess of 500 F. Cooking to such temperatures tends tov produce a grease of hard consistency which is difficult to dispense in commercial and industrial grease dispensing equipment. Such greases, furthermore, are often too hard for some important anti-friction bearing services.

A further aspect of the present invention is the discovery that a small amount of a low molecular weight sulfur-bearing aliphatic acid,

such as ethyl thioglycolic acid, may be combined with acetic acid, and with conventional soaps, to form a soft smooth and structurally stable grease which can be manufactured at considerably lower temperatures. This is illustrated in Example II and should be compared with the prior art product, shown in Example III, both of which appearbelow in the table.

TAIL] Formulation (per cent weight) Enfimle Oieic acid 20. 0 20. 0 Acetic acid 4. 0 4. 0 Ethyl thioglycolic acid. 0. 5 NaOH 6. 4 6. 4 Mineral oil 8. B. U. viscosity at 210 F 68. 1 68. 6 Phenyl aip a-naphthyi amine 1.0 1. 0 Maximum manufacturing temperature, F.... 410 610 Properties:

Per cent free alkalinity as NaOH 0. 58 0.78 Penetrations mm./l0:

Unworked 269 126 Worked strokes 291 146 Worked 100,000 strokes (325% e hole worker plate) 346 315 Dropping point Ft 460 482 Corrosion test: (In strip inserted in grease for 24 hours at 210 Norma Hoffman oxidation test: Hours to a 6 p. a. 1. drop in oxygen pressure 235 226 Dispensing test (hand gun) 0) 10,000 R. P. M. spindle test at 300 F. hours of operation 339 334 I No discoloration. I Easily dispensed.

' Too hard to feed into pump.

The greases of Examples II and III were prepared in exactly the same manner as that of Example I except that it was necessary to heat the grease of Example III to a considerably higher temperature, about 500 F., in order to obtain a satisfactory dispersion of the soap and the acetate. The greases of both Examples II and III were milled after manufacture. Example II gave a smooth product, while that of Procedure The Hydrofol acids 54 and one-third of the mineral oil were charged to a fired heated, grease kettle and warmed to 150 F. The ethyl thioglycolic acid and acetic acid were then added and the combined acids immediately neutralized with an aqueous solution of the barium hydroxide. The mass was heated to 225-230 F. and dehydrated at this temperature, whereupon the mass was further heated to 420 F. During this heating period the balance of the mineral oil was added. The phenyl alpha naphthylamine was incorporated into the grease, and the mass stirred while cooling, forming a smooth, soft short fibered product.

Evaluations Dropping point F 430 Penetrations mm./l0:

Unworked 340 Worked 60 strokes 345 Worked 60,000 strokes 311 Solubility in boiling water (10 grams of grease placed in boiling water for 30 minutes)insoluble with no disintegration of grease.

Procedure: Similar to that employed in Example II Dropping point F 47 Penetrations mm./

Unworked 300 Worked 60strokes 320 Worked 60,000 strokes 332 Corrosion test:

Cu strip inserted ingrease for 24 hours at 210 F --None (no discolorations).

Where the sulfur bearing acids are to be combined with a simple low molecular weight acid to form the low molecular weight salt, the proportions of sulfur bearing acids may be very small, for example from 0.1'to 1 or 2%. In such case, it is common to use about 4% by weight, based on the total composition, of the other low molecular weight salt but these proportions may be varied considerably, for example from 1 to about 10%.

It will be understood that other conventional additives such as antioxidants, tackiness agents, extreme pressure additives, metal deactivators, and the like, may be incorporated in usual proportions where desired without substantially modifying the properties of the grease composi I tions of this invention.

What is claimed is:

1. A lubricating grease composition comprising a lubricating oil thickened to a grease consistency with a salt-soap complex which comprises the reaction product of 0.1 to 10% by weight based on the total composition of a metal base with a low molecular weight acid of formula R1SR2COOH, wherein R1 and R2 are each aliphatic hydrocarbon groups of 1 to 2 carbon atoms, said thickener comprising also 5 to 35% by weight, based on the total composition of a soap of a long chain fatty acid having between 12 and 24 carbon atoms.

2. Composition according to claim 1 wherein the metal base is selected from the group consisting of alkali and alkaline earth metals.

3. Composition according to claim 1, wherein the low molecular weight acid comprises ethyl thioglycolic acid.

4. Composition according to claim 1, wherein the low molecular weight acid comprises ethyl mercapto propionic acid.

5. Composition according to claim 1, wherein the metal base is an alkali metal base.

6. Composition according to claim 1, wherein the metal base is a sodium base.

7. Composition according to claim 1, wherein the metal base is an alkaline earth metal base.

8. Composition according to claim 1, wherein the metal base is a barium base:

9. Composition according to claim 1, wherein the metal base is a mixed base selected from the metals or the group consisting of alkali and alkaline earth metals.

10. A lubricating grease composition comprising a lubricating oil thickened to a grease consistency with 2 to 10% by weight, based on the total composition, of a metal salt of an acid of general formula RlSRzCOOH, wherein R1 and R2 are each aliphatic hydrocarbon radicals of 1 to 2 carbon atoms, and 5 to 35% of a metal soap of fatty acid having 12 to 24 carbon atoms per molecule.

11. A lubricating grease composition consisting essentially of about 73 parts by weight of mineral base lubricating 011, about 8% soda salt of ethyl thioglycolic acid, about 17.5% of soda soap of substantially saturated C1: to C24 fatty acids, and about 1% antioxidant.

12. A composition according to claim 10, wherein the salt is present in proportions of 3 to 7% and the soap in proportions of 15 to 25%.

13. A lubricating grease composition comprising a mineral base lubricating oil thickened to a grease consistency with 0.1 to 2%, based on the total composition, of an alkali metal salt of an acid of formula RISRZCOOH, wherein R1 and R2 are each hydrocarbon radicals of 1 to 2 carbon atoms, 1 to 10% of another low molecular weight salt of low molecular weight organic acid, and 5 to 35% of a metal soap of fatty acid having between 12 and 24 carbon atoms per molecule.

14. Composition according to claim 13, wherein the low molecular weight salt is an acetate.

15. Composition according to claim 13, wherein the low molecular weight salt is sodium acetate.

16. Composition according to claim 13, wherein all salts and soap are of-sodium.

17. A lubricating grease composition consist- ;ing essentially of mineral base lubricating oil,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,182,137 Ricketts Dec. 5, 1939 2,197,263 Carmichael et al. Apr. 16, 1940 2,468,098 Morway et al Apr. 26, 1949 2,468,099 Morway Apr. 26, 1949 2,487,080 Swenson Nov. 8, 1949 2,513,680 Schott et a1. July 4, 1950 2,514,286 Morway July 4, 1950 2,516,136 Morway etal July 25, 1950

Claims (1)

1. A LUBRICATING GREASE COMPOSITION COMPRISING A LUBRICATING OIL THICKENED TO A GREASE CONSISTENCY WITH A SALT-SOAP COMPLEX WHICH COMPRISES THE REACTION PRODUCT OF 0.1 TO 10% BY WEIGHT BASED ON THE TOTAL COMPOSITION OF A METAL BASE WITH A LOW MOLECULAR WEIGHT ACID OF FORMULA R1SR2COOH, WHEREIN R1 AND R2 ARE EACH ALIPHATIC HYDROCARBON GROUPS OF 1 TO 2 CARBON ATOMS, SAID THICKENER COMPRISING ALSO 5 TO 35% BY WEIGHT, BASED ON THE TOTAL COMPOSITION OF A SOAP OF A LONG CHAIN FATTY ACID HAVING BETWEEN 12 AND 24 CARBON ATOMS.