US2516136A - Lubricating grease compositions - Google Patents

Description

July 25, 1950 A. J. MoRwAY ETAL 2,516,136

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Patented vJuly 25, 1950 LUBRICATING GREASE COMPOSITIONS Arnold J. Morway, Clark, and David W. Young,

Roselle, N. J., assignors to Standard Oil Devel-g opment Company, a corporation of Delaware Application October 30, 1948, Serial No. 57,565

8 Claims. (Cl. 252-41) The present invention relates to lubricating grease compositions which aresuitable forhigh temperature use and particularly to lubricating greases which retain their `structure at high temperatures over extended yperiods of time. 'I

It has been suggested in the prior art that for some purposes it is advantageous to combine certain metal salts, particularly the metal salts of organic acids of low molecularweight, with the metal soaps which are ordinarily kemployed as thickeners for lubricating grease compositions. Various investigators have found that the addition of metal salts of the character referred to have utility for improving stability, high temperature properties, or the like. There appear to be several theories as to the operation of such metal salts in conjunction with the soaps. One such theory is that the addition of salts of low molecular weight acids to soaps of relatively high molecular Weight results inthe formationof a complex with superior grease thickening effect and of improved stability.

Whatever may be the phenomena involved, the addition of salts of low molecular Weight compounds appears to be particularly advantageous in connection with greases of alkali and alkaline earth metal soap bases. The low molecular weight salts appear in many cases at least to improve the physical structure of the grease and various investigators have found them particularly useful for stabilizing greases structurally at elevated temperature. Compositions of this character appear to be particularly receptive to the action of oxidation inhibitors and it is possible that the compositions themselves are more stable against oxidation than greases thickened with the simple soaps of high molecular weight carboxylic acids, for example.

Suggestions in the prior art have included the use of metal salts of low molecular weight carboxylic acids which'are saturated, such as acetic and propionic acids, and more recently it has been suggested that certain of the lower unsaturated acids, such as acrylic acid and crotonic acid,

and the like, may be used as modifiers. The lat-` ter acids, however, are relatively expensive andl one object of the present inventionis to replace them with a material which is abundantly avail'- able and relatively inexpensive.

According to the present invention, the salts of certain acids, particularly the salts of hetero-I cyclic acids, such as furoic acid, are highly useful as ingredients of lubricating greases. Furoic acid,v

for example, may be readily derived from furfural which is abundantly available at low `prim-2S 2 at this time. Thiofuroic-acid may be used. Other related compositions appear also to be similarly useful, for example, alkyl furoic acid, thiophene carboxylic acid, etc. `These compounds all have iive membered furan-type rings and are of low molecular weight;`

The use of the salts of acids of the type set forth'above, suchas furoic acid, is not to be confused with the use of relatedv esters ywhich have entirely different` purposes. been suggested in the prior art, Zimmer et al., Patent No. 2,113,754, datedApril '12, 1938, that certain furoic acid esters are useful as oiliness agents in various lubricating compositions. This reference suggests that such esters may be used either in lubricating oil or lubricating greases. The esters, however, are entirely different from the salts employed in the present instance and their function isnot related in any way to the function of the furoic acid salts and the equivalent compositions of low molecular weight heterocyclic acids.

In the present case, the low molecular weight salts are added to the grease for the purpose, as indicated above,l ofimproving high temperature stability of the grease and also to amplify the thickening elect of the soaps which are used. Hence, a further feature of the invention is the use of low molecular weight salts of the character referred to above to reduce the soap requirements for thickening lubricating oils to a given or required grease consistency.

In general, the metallic element of the salts as well as of the soaps may be any of the alkali or alkaline earth metals. Sodium and lithium are preferred of the alkali metals and calcium is the preferred alkaline earth metal partly because of its low cost. Salts of potassium, strontium, magnesium and barium may be used, however, as well as the soaps of any of these metals and mixtures of salts and/or soaps of any or all of the alkali and akaline earth metals also are contemplated.

`The relative proportions of the high molecular weight soaps and of the relatively low molecular weight salts may be varied rather widely. In molecular proportions, 1 to 3 parts of soap may be used with about 1 to 2 parts of the salt. In general, however, it is preferable that the molecular proportions be more nearly equal and proportions of l to 2 mols of soap with l to 1.5 mols of saltare usually more desirable. Specifically, molarproportionsof about 1 to 1 are generally the most satisfactory and appear preferable at this time.` The total quantity of the soap and Thus it `hasl salt ingredients to be used in a given grease composition vary with the type of grease whichis desired and also with the kind and viscosity of oil which is used as the liquid phase. For a stiff grease composition, the total quantities of soap and salt may approach 50% of the weight of the final composition. On the other hand, for a soft grease the total proportion of soaps and salts may be as low as about 5% based on the weight of the entire composition.

In general, the grease should consist of a lubri-l cating oil having a viscosity of about 35 to 200 S. S. U. at 210 F., containing about 3 to 30% by weight of the metal soap of C12 to Czz fatty acids or glycerides, along with 2 to 20% of the metal salt of the low molecular weight heterocyclic acid. In general, the carboxylic heterocyclic acids are preferred, furoic acid being particularly preferred because of its availablity and economy. It is, of course, possible to employ compounds which are converted to the heterocyclic acid during grease making, for example, esters and other derivatives of the acids.

For ordinary antifriction bearing greases, the sodium soaps and the sodium salt oi furoic acid are specifically preferred. There are instances where other metals of the alkali and/or alkaline earth groups may be preferred. The mixed base greases, such as calcium-sodium greases, sodabarium greases, and the like, are frequently highly satisfactory for some purposes.

For the liquid phase of the grease mineral base lubricating oils are preferred, but the invention is not necessarily limited to the mineral base oils. Various synthetic oils may also be used as is well known in the art of grease making. Certain synthetic esters, especially the dibasic acid esters, such as di-2-ethylhexyl sebacate and homologous and analogous esters, are preferred for certain purposes. The lithium soap greases of such compounds, modied with sodium or lithium Salts of furoic acid, and the like, are particularly useful for lubrication at very low temperatures. Other synthetic oil base greases, such as those employing the polyglycols, are also contemplated as being within the scope of the invention. The combined soaps and salts may be used to thicken mixtures of mineral oil and synthetic oil as ,well as being useful with either type of oil aloneil Example I A grease suitable for high temperature service in anti-friction bearings, and the like, was prepared with the following composition: by weight of hydrogenated sh oil acids (substantially saturated fatty acids of 14 to 22 carbon atoms sold under the trade name Hydrofol Acids 54) 6% furoic acid. 5% sodium hydroxide, 74%

- low cold test lubricating oil of 50 S. S. U. viscosity at 210 F.

In this example, furoic acid of commercial manufacture was used. The hydrogenated fish oil acids which have a fatty acid chain length averaging about 18 carbon atoms and the furoic acid of the formula Hc--CH o Il il Ho o-C\ o/ on were combined with about 5/3 of the mineral oil. These materials were charged into a fire-heated grease kettle and warmed to' a temperature of about 15G-160 F. The sodium hydroxide was then added in the form of a 30% aqueous solution to neutralize the acids. Thereafter, the temper- 4 ature was raised to about 220 F. to evaporate the water and dry out the soap mixed with salt of furoic acid. After drying was completed, the temperature was raised further to about 300 F.. stirring being continued while the remainder of the mineral oil was added in small proportions. After all the oil had been added, the temperature was raised further to 400 F. and part of the resulting grease was removed for test. The remainder was heated still further to about 480 F.

That part oi' the grease which was removed at 400 F. was worked while cooling and became a smooth composition of excellent appearance and structure. It had a penetration of 250 mm./l0 and a dropping point of 468 F. The other part of the grease which was heated to about 480 F. was cooled without stirring. Thereafter, it was homogenized and was found to have a penetration of 180 mm./l0 with a dropping point of 510 F.

The composition of the above example represents roughly a 1 to 1 molar ratio between the soap of higher fatty acid and salt of furoic acid. It appears that conventional oxidation inhibitors such as phenyl alpha naphthylamine, phenyl beta naphtnylamine, and the like, are useful to improve the oxidation resistance of these greases.

Example II Another composition was prepared in much the same manner as described above, having the following composition: hydrogenated fish oil acids, as in Example I, 12% by weight, furoic acid 4%, sodium hydroxide 4%, phenyl alpha naphthylamine 1%, naphthenic lubricating oil of 55 S. S. U. viscosity at 210 F. 78.2%.

The resulting composition was found to have excess alkalinity of 0.25% calculated as NaOH. The grease had a worked penetration of 210 mm./10 which increased to 240 mm./10 after working 100,000 strokes with the fine hole plate test apparatus. This grease had a dropping point above 500 F., showed a loss of only 5% when subjected to the standard water washing test, indicating good water resistance, and operated for 346 hours in the high speed spindle test at 10,000 R. P. M. under a temperature of 300 F.

When greases of this type were prepared with relatively large concentrations of soap (15% or more by weight, based on the total composition), the optimum ratio was 1 mol of furoic acid to l mol of hydrogenated fish oil acid. Other ratios gave a less satisfactory product.

Ercample III A series of lubricating greases was prepared using a mineral base lubricating oil having a viscosity of 55 S. S. U. at 210 F. Various quantities of commercial hydrogenated fish oil acids (sold under the trade name, Hydrofol 54, C12

When the soap content of the greases is lower than 15% by weight, it appears to be desirable to increase the molargproportlons' of fatty acid soap to concentrations of 1.2, 1.4, 1.6, or even 2 mols o1' soap to one mol of furoate, as shown'in Examples IV and V.

Example IV Using 7.5% by weight of substantially saturated hydrogenated fish oil acids of 12 to 22 carbon atoms, a grease based on the same mineral oil as that of Example III was prepared with a 1:1 molar ratio of furoic acid to fatty acid. A product of smooth texture and excellent grease structure was obtained.

Example V A product similar to that of Example IV was prepared. using 8.0% by weight, based on the total composition, of fatty acids of the same type (Hydrofol 54). A smaller quantity o-f furoic acid was employed, the molar ratio being 1.4 mols of fatty acid to 1 mol of furoic acid. The product had an excellent texture, being perfectly smooth, but of somewhat heavier' consistency at elevated temperatures.

. Molar Mineral Ratio Oil, Per- Fatty Furolc cant By NaOH Acid Acid Figl- Structure Weight Acid 87.0 2.6 7.5 2. 9 1:1 Excellent, smooth. 87.3 2. 4 8. 0 2. 3 1:1. 4 Excellent, smooth.

Heavier consistency at elevated temp., but no rubberiness.

Where high soap concentrations are employed, and the fatty acid to furoic acid ratio is increased much above l to 1, for example, to 2 to 1 the grease becomes quite rubbery in its texture at high temperature. This has no effect on the good properties of the grease at low or moderate temperatures, but it is undesirable in the lubrication of antifriction bearings in high temperature service since the lubricant may be pulled out of the bearings, leaving them unprotected. The rubbery structure becomes more pronounced in lubricants of higher soap content. It is less pronounced in greases of lower soap content.

On the other hand, the tendency of grease to become heavier (i. e., to increase in apparent viscosity) at higher temperatures, as in Example V, is desirable so long as the product does not become rubbery. Ordinary greases tend to thin out considerably at the temperatures attained in some antifriction bearings and may not remain in the bearings if they fluidize excessively.

Figure 1 of the drawings shows graphically the thickening at elevated temperatures of the last two compositions described in the table under Example III. Figure 2 showsasimilar graphical comparison between the compositions of Examples IV and V. A comparison of the two sets of curves illustrates the difference between greases containing over 15% of soap (Fig. 1) and those containing a lesser quantity (Fig. 2). The most important difference appears in the lower right corners of the respective figures where the pressureviscosity curve of the grease of high soap content goes up in one case and down in the other.

Example VI Wheel bearing lubrication tests employing the CRC laboratory wheel bearing tester also show that the greases prepared from 2.9% furoic acid and 7.5% Vfatty acids (Hydrotol acids 54) :become soft and tend to iiow outy of thelwheel hub, while greases prepared from 2.3% furoic acid and 8.0%,`

Example VII A soda base lubricating grease was prepared which contained 15.9% by weight of fatty (Hy drofol 54) acids, 5.7% of thiophene alphacarboxylic acid and 1.1% of phenyl alpha-naphthylamine in a mineral oil base of 55 S. S. U. viscosityat 210 F. This grease contained fatty acid and heterocyclic acid in a mol ratio of about 1 to 1. It was substantially neutral, did not stain copper on contact with it for 24 hours at 210 F., and had a dropping point above 500 F. It was an excellent, smooth, firm, yellow grease.

In the examples given above, sodium hydroxide was used as the saponifying agent, although the invention can be carried out with the other alkali and alkaline earth oxides or hydroxides. It is not necessary that the soap and the salt of the low molecular weight heterocyclic acid be formed of the same metal base. With respect to the acids or glycerides from which the soaps are formed, the saturated carboxylic aliphatic acids of l2 to 22 carbon atoms are usually preferred, although the unsaturated or hydroxy acids may also be used, for example, oleic acid or 12-hydroxy stearic acid. The salts of furoic acid and the like may also be combined with detergent materials such as sodium or other alkali or alkaline earth metal sulfonates. For example, sulfonates of C12 alkylated toluene may be used as a component or lubricating greases within the scope of the present invention. sulfonates or sulfates of various molecular weights derived from oils by treating with sulfuric acid, ranging from those which are water-soluble to those which are oilsoluble, may be used to some extent although generally the oil soluble sulfonates are preferred.

What is claimed is:

1. A lubricating grease composition consisting essentially of lubricating oil thickened to a grease consistency with 1 to 3 molecular proportions oi' metal soap of higher fatty acids and 1 to 2 molecular proportions of metal salt of a heterocyclic carboxylic acid, said heterocyclic acid being a low molecular weight acid having a tive-membered heterocyclic ring in which the hetero atom is selected from the group consisting of oxygen and sulfur.

2. A lubricating grease composition consisting essentially of lubricating oil thickened to a grease consistency with l to 3 molecular proportions of alkali metal soap of higher fatty acid combined with 1 to 2 molecular proportions of alkali metal salt of a heterocyclic carboxylic acid, said heterocyclic acid being a low molecular weight acid having a ve-membered heterocyclic ring in which the hetero atom is selected from the group consisting of oxygen and sulfur.

3. A lubricating grease composition according to claim 2 wherein said heterocyclic acid is furoic acid.

4. A lubricating grease composition according to claim 2 wherein the heterocyclic acid is thiophene alphacarboxylic acid.

5. A lubricating grease composition consisting essentially of mineral base lubricating oil thickened to a grease consistency with 3 to 20% by weight, based on the total composition of metal soap of C12 to C22 fatty acids and 2 to 15% of metal salt of furoic acid.

anarco 7 6. Composition as in claim 5 wherein said REFERENCES CITED metal soap is sodium soap and said metal It The following references are oi' record in the 1S Sodium Sm me or this patent:

7. A lubricating grease composition suitable for high temperature service, consisting essentially 5 UNITED STATES PATENTS of lubricating oil thickened to a grease consist- Number Name Date ency with substantially equimolar proportions of 2,113,754 Zimmer et al Apr. 12. 1938 metal salts of furoic acid and metal soaps oi' sub- 2,182,137 Ricketts Dec. 5, 1939 stantially saturated fatty acid within the range 2,441,720 Boehner et al May 18, 1948 of l2 to 22 carbon atoms. l0 2,448,567 Zisman et al Sept. 7, 1948 8. Composition according to claim 7 wherein said metal salts and soaps are oi' sodium.

ARNOLD J. MORWAY. DAVID W. YOUNG.

Claims (1)

1. A LUBRICATING GREASE COMPOSITION CONSISTING ESSENTIALLY OF LUBRICATING OIL THICKENED TO A GREASE CONSISTENCY WITH 1 TO 3 MOLECULAR PROPORTIONS OF METAL SOAP OF HIGHER FATTY ACIDS AND 1 TO 2 MOLECULAR PROPORTIONS OF METAL SALT OF A HETEROCYCLIC CARBOXYLIC ACID, SAID HETEROCYCLIC ACID BEING

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