US2450219A - Texture-stable lithium base grease - Google Patents

Description

Patented Sept. 28, 1948 TEXTURE-STABLE LITHIUM BASE GREASE Harry V. Ashburn, Glenham, and Oney P. Pur- N. Y., assignors to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing. Application April 10, 1945, Serial N0. 587,622

1 This invention relates to an improved lubricating grease composition and particularly to a texture-stable lithium base grease and methods of P paring the same.

In general, lithium basegreases, prepared from saturated fats or fatty acids, possess a high dropping point and are water-resistant. These properties are particularly desirable in that they permit lubrication over a wide temperature range and minimize the solubilizing or leaching effect of water and moisture condensation on the grease. However, there are certain difficulties associated with the production of these greases, together with certain undesirable performance characteristics, which prevent any large scale acceptance thereof as a commercial lubricating grease.

In the preparation of the conventional lithium base grease, a slurry of a lithium soap, such as the stearate, which is either preformed or pre- .pared in situ, and a mineral oil, are heated to temperatures of around 360-500 F. until a homogeneous solution is obtained. This solution of lithium soap in oil is then drawn from the kettle and allowed to cool statically until a gel structure is set up The cooled gel is then subjected to a milling operation where it is homogenized to a homogeneous grease composition. It becomes quite apparent that the efiiciency and economies of such a method are quite poor, due to the high temperature operation, special equipment required, and the lack of control over the consistency and yield of the finalproduct.

One of the most important drawbacks ofthe conventional lithium base greases is, however, the

inability of these greases to maintain their struc-' ture and lubricating qualities under conditions of operation where shearing stresses are involved, such as in ball and roller bearing lubrication, and particularly at temperatures above atmospheric. In such installations the greases gradually lose their onsistency until they become liquid and no longer adhere to the lubricating surfaces, thereby causing bearing failures. Attempts have been made to correct this deficiency by the in- 3 Claims. (Cl. 252-41) yield of product, and may be carried out at temperatures attainable in a steam-jacketed kettle.

In its broadest aspect, the invention contemplates the use of a blend of a soap-forming hydroxy fatty acid glyceride and a soap-forming fat or fatty acid as the acidic component .in the preparation of a lithium base grease composition. While it has been found that a lithium soap grease prepared from a hydroxy fatty acid glyceride possesses exceptional texture stability even after extensive working at either high or low temperatures, these greases possess a peculiar characteristic in that their consistency tends to harden after being subjected to high shearing stresses. utilizing a blend of the hydroxy fatty acid glycerides with the conventional saturated fats and fatty acids in such proportion that the hydroxy fatty acid glyceride predominates, the hardening characteristics of the hydroxy fatty acid glycerides may be overcome and a lithium base grease prepared which maintains an approximately constant consistency even after being subjected to high shearing stresses. An added advantage in the use of a predominant amount, e. g., greater than 50%, of hydroxy fatty acid glycerides in the aforementioned blend, is the fact that the presence of the hydroxy fatty acid glyceride permits the use of a simple low temperature method of preparation as distinguished from the high temperature complex method required by the use of predominant amounts of the conventional fats and fatty acids.

The hydroxy fatty acid glycerides contemplated by the invention are the glycerides of hydroxy fatty acids containing twelve or more carbon atoms and one or more hydroxyl radicals separated from the carboxyl roup by at least one carbon atom. In the following description of the preferred form of the invention, hydrogenated castor oil is used as the representative soap-forming hydroxy fatty acid glyceride. For practical application at the present time, hydrogenated castor oil possesses the advantage of availability and cost over the other sources of hydroxy fatty However, it has been found that by 3 with the conventional saturated fats and fatty acids in such proportions that the hydroxy fatty acid giycerides predominate. The specific ratio which is to be used in the preparation of the grease composition depends largely upon the type of service for which the resulting grease composition is intended. In the production of a low temperature lithium base grease employed in the lubrication of bearings and the like at temperatures below 60 F., it has been found preferable to utilize a blend in which the hydroxy fatty acid glycerides are present in amounts exceeding 70% of the total acidic component.

Furthermore, the type of service for which the grease is intended also has a bearing upon the choice of the fat or fatty M ld to be blended with the hydroxy fatty acid glyceride. In general, the

invention contemplates any of the recognized fatty acid materials, which include the fats or fatty acids normally used in grease manufacture provided they are essentially saturated in character. These fats or fatty acids include mixtures of fatty acid glycerides found in naturallyoccurring 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 hydrogenation of fish oils, etc., or the individual acids themselves. In the preparation of the low temperature lithium grease referred to above, it has been found preferable to utilize the fatty acids rather than the glycerides and, in particular, stearic acid.

The oil component of the subject grease composition may be broadly described as an oleaginous vehicle, which would include the conventional mineral lubricating oils, the synthetic lubricating oils prepared by cracking and polymerizing products of the Fischer-Tropsch process and the like, or a synthetic oleaginous compound within the lubricating oil viscosity range. The synthetic oleaginous compounds are those organic compounds which possess lubricating characteristics and may be substituted inwhole or in part for the conventional mineral lubricating oils.

Examples of these compounds are the aliphatic.

dlcarboxylic acid esters, such as the alkyl esters of sebacic acid, the high molecular weight aliphatic ethers, such as normal hexyl ether, and the aromatic acid esters, such as the alkyl esters of benzoic or phthalic acids. The choice of the oil component bears directly upon the type of lubrication required of the finished product. For example, in a low temperature lithium base grease, a mineral lubricating oil within the viscosity range of 40-70 S. U. S. at 100 F., a low our point, and a viscosity index of 30 or more is preferred.

Where a high degree of oxidation stability is required an oxidation inh bitor is preferably incorporated. For these lithium base greases the aromatic amine type of inhibitor has been found particularly effective. of this class of inhibitors the poly-nuclear aromatic amines, such as tetramethyl diamino diphenyl methane, diphenyl amine, and phenyl alpha naphthylamine' are preferred. I

The preparation of these greases is carried out by saponifying a blend of the soap-forming hydroxy fatty acid glyceride and saturated fat or fatty acid with a basic lithium compound. The acidic components may be saponii'ied separately in situ. The saponification product is then dehydrated and the oil component is added until the desired consistency is reached. The total operation is easily conducted in a steam-jacketed 4 open kettle and the resulting finished lithium base grease requires no homogenization or further treatment prior-to actual use.

It has been found particularly desirable to avoid a high free neutral fat content and/or free fatty acid content in the greases due to the excessive setting up of the grease during storage. It is preferred to maintain the free fatty acid content within the range of 0.05-0.30% and the free neutral fat content below 1.0%. The measurements of free fatty acid and free alkali, as

used in the description of the invention, follow the test methods set forth in The Institute Spokesman, National Lubricating Grease Institute, January 1944. "Test Methods for Determining Free Acid and Free Alkali in Greases." Also, it has been found desirable to effect the dehydration of the saponified product at temperatures above 270 F. At temperatures of around 270 F. it is necessary to heat for several hours in order to cause the soap mass to become translucent and lose its cloudy-white appearance, whereas at temperatures of around 300 F. a shorter dehydration time may be used. At lower temperatures the yields of the product fall off materially.

The procedure involved in the preparation of the lithium base greases of the invention, as exemplified by the preparation of a low temperature lithium base grease using a blend of 75% hydrogenated ca-stor oil and 25% stearic acid, may be obtained from the following example:

A steam-jacketed open kettle was charged with 2.40 pounds of 53.6% lithium hydroxide in the form of the mono-hydrate and 16 pounds of water, and heated with stirring at 160-180" F. until all the lithium hydroxide was dissolved.

Twelve pounds of hydrogenated castor oil (saponification No.=181, iodine No.=8, hydroxyl No.=148, titer=72.5 C.) and 12 pounds of a mildly-refined mineral oil having a S.'U.' V. of 57 at. 100 F., were then added. Stirring was continued for 3-5 hours at 170-200 F., and 4 pounds of stearic acid (saponifioation No.=210) were then added and the mixture stirred at 1.70-200 F. for an additional hour. The saponificatlon product was t en dehydrated by heating to 280-300 F. until the base was translucent. The heat was then reduced and the oil addition started. When the temperature of the kettle reached approximately 200 F., 0.35 pound of stearic acid and 0.35 p und of phenyl alpha naphthylamine were add d. Add tion of the oil was then continued until the desired consistency was obtained, wh ch, in this case. was a worked penetration of 336 at 79- F. The grease was then drawn and pumped through a 60 mesh screen. The resulting grease composition was a glossy. buttery grease possessing a light buff color. The tests obtained thereon are as follows:

Lithium soap, 14.6 Free alkali (LiOH), 1 0.08 Free fatty acid (oleic), 1 0.14; Free neutral fat, 0.75 Phenyl alpha naphthylamine (calc.), 0.5 Penetration (ASTM) at 77 F. worked...-- 320 Dropping point, F. (ASTM) 357 Navy Water absorption, 3 5 Norma-Hoffman oxidation hrs. at 210 F.), pounds pressure drop-..) 4.6

The Institute Spokesman," National Lubricating Test Methods for Detel-mining Free Acid and Free Alkali in Greases."

AN-G-{ia-March 6, 1943.

are presented. This test was conducted in an' apparatus consisting of a perforated pistonreciprocating within a closed cylinder maintained at. a constant temperature. In this test the grease was charged to the cylinder maintained at a temperature of 225 F. and the piston then reciprocated at 49 strokes per ,minute for a period of eight hours. At the conclusion of the test the grease was removed and miniature penetra-' tions taken. This miniature penetration was then compared with theminiature pentration of the grease taken before the test to determine the effect of the shearing action upon the grease structure. The results obtained on a lithium base grease prepared from a blend of 75% hydrogenated castor oil and 25% of stearic acid, designated as "grease A," are as follows:

Shear test Minis Penetra t l After Before GreaseA I Miniature Penetmmeter for Determining the Consistency of Lubricating Greases," nd. Eng. Chem., analytical edition, vol. 11, page 108, February 15, 1939.

As may be seen from the results obtained, the lithium base grease of the invention possesses excellent texture-stability and resistance to shear and, even under the severe conditions of the test, maintains practically constant consistency. This fact distinguishes from the greases prepared solely from the hydroxy fatty acid glycerides, such as hydrogenated castor oil, which normally harden after being subjected to shearing stresses.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may

'after being subjected to said high shearing stresses, which comprises saponlfying with a basiclithiumcompound at a temperature of about Mil-200 F. of a blend of a major proportion of a soap-forming essentially saturated hydroxy fatty acid glyceride and a minor but substantial proportion of a soap-forming saturated fatty acid. the latter being sufficient in 6 amount to prevent any material increase in consistency due to high shearing stress of the final grease product referred to hereinbelow, as determined by a decrease of not more than a few points in the miniature pentration values obtained before and after-subjecting the said grease to the described dynamic shear test, then heating the resulting saponified reaction product above about 270 F. but not substantially above 300 F. for a period of time to dehydrate the product and render the same translucent, then reducing the heat and adding an oleaginous vehicle to the dehydrated product as the latter cools to at least about 200 F. and the desired consistency is obtained, and finally drawing the resultant mix to obtain a glossy buttery homogeneous gel-type grease as a finalproduct.

2. The methbd according to claim 1, wherein, the essentially saturated hydroxy fatty acid glyceride is hydrogenated castor oil.

3. A method of preparing at temperatures attainable in. a steam-jacketed kettle a texturestable gel-type grease consisting of lithium soap as the entire soap content thereof, said lithium base grease being resistant to substantial lowering in consistency when subjected to high shearing stresses of the character herein described, as;

well as being resistant to substantial hardening after being subjected to said high shearing stresses. which comprises saponifying with a basic lithium compound at a temperature of about -200 F. of a blendof hydrogenated castor oil and stearic acid in a weight ratio of about 3:1, then heating the resulting saponifle'd reaction product above about 270 F. but not sub-L stantially above 300 F. for a period of time to dehydrate the product and render the same REFERENCES CITED The following references are of record in the file of this patent: I

UNITED s'ra'rss ra'rsn'rs Name Date Earle Mar. 3, 19 42 Earle Aug. 18, 1942 Camelford Nov. 24, 1942 Number Woods et a1. June 13, 1944 Morgan Nov. 14, 1

Morgan Dec. 28, 1944 Fraser Apr. 9, 1946 roman ra'rrm'rs Country Date gwitaerland Jan. 2, 1983 Number I Fraser Jan. 19, 1943