ALUMINUM STEARATE
GREASES FIGURE 1. ANCIENTCHARIOTFOUND WITH FATTY MATTER OK
ITS AXLE
FRANCIS J. LICATA Metasap ChemicaI Company, Harrison,
N. J.
An attempt is made t o show that aluminum stearate greases are in line with the requirements of mechanical and lubricating development. In some cases, because of their customer appeal, heat resistance, and stability, aluminum stearate greases are the only ones that can be used. Data are presented t o show that the grease maker can modify the properties of aluminum stearate greases by control over (a) viscosity and type of oil, (b) rate of cooling, (c) time of compounding and moisture content, and ( d ) use of fluxes. With fluxes it is often advisable t o use ready-made bases which are designed t o give definite desirable results.
F
ROM the earliest times man has been concerned with the problem of lubrication. As civilization progressed, this problem became more complex. It is likely that, for transportation, the use of the sledge and the use of lubricants antedate the discovery of the wheel and axle. Carvings on the Egyptian tomb of Ra-Em-Ka, 2700-2600 B. c., show a sledge being used to transport a stonemonument. A man is shown pouring a liquid, possibly oil, to lubricate the runners of the sledge (6). Therefore, when the wheel and axle made their appearance, lubricants were already in existence, and such developments as wagons, chariots, etc., were made possible.
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FIGURE 2. EARLYMACHINERY Robert Fulton’s Clermont, the first steamboat, 1810, is shown a t the t o p (from a lithograph in the New York Public Library). The type of covered wagon shown i n the center (developed about 1750) and the replica of Stephenson’s Rocket (1829) are reproduced through the courtesy of the New York Museum of Science and Industry.
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Fatty matter was actually found on the axle of a chariot (6) buried in the tomb of Yuaa and Thuiu about 1400 B. c. (Figure 1). Pliny records that the ancients, before his time, used hog fat to lubricate the wheels of their vehicles (7). The development of lubricants was retarded by the slow mechanical development preceding the nineteenth century. Up to that time the available supply of oils, fats, and unctuous minerals was sufficient to meet the few requirements of the then existing machinery and transportation (Figure 2). The nineteenth century was a period of great mechanical achievement. By this time the steam engine had been perfected as a source of power. It was made to take the place of animal, wind, and water power. The problem of lubrication assumed greater proportions. New and cheaper lubricants found a market as soon as they were produced. I n 1831 Booth introduced his patented lubricant which consisted of tallow, palm oil, sodium carbonate, and water. The partial saponification of fatty matter by sodium carbonate allowed the incorporation of variable quantities of water. The railroads, which were expanding rapidly and buying on a price basis, used large quantities. At the middle of the century the search for larger and more economical supplies of lubricants brought in cottonseed, whale, and rosin oils with a miscellaneous collection of other materials. About this time a large number of secret and patented lubricants became available.
Modern Lubrication Soon it was possible to compound petroleum oils with all of the previously used lubricants. This gave rise to a whole new large class of lubricating compounds, many of which are still in use. It may be said that there was more advancement along mechanical and lubricating lines during the nineteenth century than in all the combined centuries which preceded it. Similarly, a review of the first thirty-five years of the twentieth century shows an even greater acceleration of mechanical progress. The development of lubricants has been equally accelerated. I n addition to the demand for larger quantities of lubricants for a larger number of machines, we now have a demand for a large number of highly specialized lubricants, each to serve a specific purpose. To meet these requirements, research has been directed into new channels. Metallic soaps, naphthenic acids, and extreme pressure lubricant bases have received special attention.
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With a few exceptions, and then only after being pressed by their own sales departments, grease makers have been reluctant to produce greases from this material. This attitude is not surprising. Investigators were hampered by the total nonexistence of published data. I n 1931 Zublin announced that aluminum soap greases were desirable for rocker arm lubrication (IO). This was followed in 1932 by Kopp’s directions for the manufacture of lucid compounds (3). A year later the present writer (4) called attention to the fact that the consistency of aluminum stearate greases depends on (a) quantity and quality of the stearate, (6) viscosity of the petroleum oil used, and (c) rate of cooling of the hot grease discharged from the kettle. The use of aluminum soaps has grown tremendously. I n addition, words of encouragement are beginning to find their way into the literature. Garlick (1) stated in a paper on lubricating greases : “As ingredients in grease manufacture, aluminum soaps are gaining in popularity now that intensive study has revealed the best means of their utilization. One of the main objects in the renewed study of aluminum soap products has been the desire for an all-purpose automotive grease.” Wilch (9) said that .f‘aluminum soap greases compare closely in structure and lubricating adaptability to calcium soap greases.’’ It was soon realized that the quality of the aluminum stearate used had a great effect on the consistency of grease made from it. Consequently, the writer’s company has standardized the manufacture of three types of stearate as the V, R, and GM grades. Recently another firm has designated three similar types as aluminum mono-, di-, and tristearates. The work in this investigation was done with the R type, which corresponds to the distearate. Because of the lack of sufficient data, each investigator has had to develop his own technic which would apply to the inherent conditions of his manufacturing equipment. Whenever possible, the stearate manufacturers have co-
Aluminum Stearate Type of Grease One of the chief items which has demanded the attention of grease makers has been the production of aluminum stearate greases. This type of grease has the advantage of crystal transparency and customer appeal, relatively high temperahre resistance, stability, waterproofness, and the possibility of wide application in a variety of lubrication problems. The original introduction of aluminum soaps for lubricants seems to have been lost in the dark past of the grease maker’s art. They were mentioned by Redwood (8) as early as 1898, when their reputation was as bad as that of petroleum oils a half century earlier. However, when their value in nonchatter oils was proved, grease makers again took up the study of this material. As a result of a campaign by metallic soap manufacturers, aluminum stearate began to be used as a base for cup greases. This led to a variety of results, each representing the resources and ingenuity of the investigators. I n 1927 Klemgard (2) described a test for aluminum stearate to determine its value as a grease base.
FIGURE3. ASSEMBLEDAPPARATUSWITH STIRRER RAISED
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drying oven at 105" C., and the current was then shut off t o give a constant rate of cooling. Unworked and worked consistencies were determined according to the A. s. T. M. procedure. Variations in the procedure to bring about a special effect will be described later, whenever they occur.
Effect of Petroleum Oil
I
250
0 UNWORKEP A.s.T.M.
300
I
350
WORKED PENETRATIONS
GREASE
OIL ON GREASECONFIGURE4. EFFECTOF PETROLEUM SISTENCY
operated with the grease maker to the end that the sales of both aluminum soaps and greases made from them have shown a healthy growth. It is believed that enough experience has been obtained to set down certain general rules to serve as adequate guides to those who still have difficulty in the manufacture of this type of grease These general rules may also serve as a basis for discussion and the foundation for future development. For this purpose greases were prepared from the same lot of aluminum stearate and oils from various sources and different viscosities to show the effect of the petroleum oil on the consistency. Then, assuming that an asphalt oil with a viscosity of 300 a t 100" F. was most desirable economically, several series of grease were prepared to show the effect of (a) the rate of cooling, ( b ) moisture and time of compounding, and (c) repeated working of this type of grease.
I n order to compare the effect of paraffin, naphthenic, and asphalt oils on grease consistency, four oils1 were obtained from each group, having approximately similar viscosities a t 100" F. (37.8' C.) Samples of grease weremade from each oil according to the general procedure, and A. S.T. M. penetrations were determined several days after reaching room temperature. One determination was made in the tin cans for the unworked penetration, and an average of two or three observations was taken for the worked consistency. Most samples showed check determinations within four points. Table I and Figure 4 show the data obtained. Greases made from paraffin or Pennsylvania oils show greater penetration or softness as the viscosity of the oil rises. On the other hand, the penetration readings indicate very little change in the greases made from various asphalt oils. The graphs giving the penetration in greases made from naphthenic oils show an anomalous behavior. Up to the 1000-viscosity oil, the greases seem to behave similarly to the paraffin oils in that they become softer as the viscosity rises, However, the penetration of the grease made from the 2000-viscosity oil was almost as low as that from the 100-
General Procedure Fifty grams of aluminum stearate were thoroughly mixed with 450 grams of oil, while cold, in a liter Monel metal beaker. The mixture was placed in a pot containing oil to serve as an oil bath. Heat was applied by means of a small electric hot plate, and agitation was furnished mechanically by a stirrer attached t o a small drill press driven at 120 r. p. m. The whole assembly, with the stirrer raised, is shown in Figure 3. When the temperature reached 150" C., the grease was transferred into one-pound tin cans, which were 3 inches (7.6 cm.) in diameter and 4.5 inches (11.4 cm.) high; the cans were immediately placed in a Freas
FIGURE 5.
COOLING RATE CURVEOF ALUMINUMSTEARATE GREASES
viscosity oil. This observation led to the discovery of the fact that the presence of moisture and the time of compounding also affect the consistency of aluminum stearate greases. This will be discussed later in greater detail under "Effect of Moisture and Time of Compounding."
Effect of Cooling Rate TABLEI. EFFECTOF Sample
OIL O N
Oil Viscosity Unworked a t loOD F. Penetratlon
A. 8. T. M. GREASE CONSISTENCY Worked Penetration
A B C
D
153 310 1050 2300
Paraffin Oil 166 256 178 287 193 340 192 370
E F G H
100 320 1040 2000
Naphthenic 152 155 169 120
rJ
100 310 1040 2000
153 145 144
K
L
170
Remarks Smooth, no bleeding Same Same Same
Oil 223 246 276 230
Firm, slight bleeding Smooth, no bleeding Same Same
dsphalt Oil 234 23 1 234 248
Granular, bleeding Smooth, no bleeding Same Same
One of the chief sources of variation in grease consistency is the rate of cooling. This is easily realized when, by the use of the same formula, a small laboratory batch of a few ounces will cool in a short time to a hard, brittle, granular mass, not a t all like a grease; on the other hand, a large batch made in the factory will cool very slowly to a soft, smooth, unctuous, and somewhat adhesive grease. To show the relatively large effect of the rate of cooling, samples similar to J were prepared by heating to 150" and cooling to room temperature (25" C.) a t various rates (Figure 5 ) . Sample M was cooled within 3 hours by passing cold water around the tin container. Sample N was cooled within 12 hours in the oven as described in the general procedure. Samples 0 and P were made to cool within 18 and 25 hours, 1
Obtained through Fiske Brothers Refining Company.
INDUSTRIAL AND ENGINEERING CHEMISTRY
MAY, 1938
respectively, by various thicknesses of asbestos insulation. Table 11 and Figure 6 show the data and graphs of the results obtained.
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the moisture contents decreased. The ’data are recorded in Table 111and Figure 7.
Miscellaneous Properties of Aluminum Stearate Greases
ASXM. WORKED PENETRATIONS
FIGURE 6. EFFECTOF COOLING
RATE
It is clear that by using the same formula, the rate of cooling will change the worked A. S. T. M. penetrations from 193 to 267, a difference of 74 points. Moreover, the whole general appearance of the greases was different. Sample M showed excessive bleeding or oil separation. With slight pressure i t crumbled between the fingers into a coarse, dry powder. Subsequent samples showed increasing softness, smoothness, and a degree of unctuousness as the grease was made to cool more slowly. TABLE11. EFFECTOF COOLING RATE ON GREASES Sample
Hours of Cooling
M N 0
2 12 18 25
P
Worked Penetrations 193 225 238 267
Remarks Granular, excess bleeding Smooth, no bleeding Same Same
Effect of Moisture and Time of Compounding The anomalous behavior of sample H , made from the 2000viscosity naphthenic oil, led to the discovery of the fact that this sample had been held a t 150” C. several hours longer than others. During this period there was the possibility of finer stearate dispersion into the oil and the loss of moisture held captive in the grease. Moisture determination on samples G and H revealed 1.2 and 0.7 per cent, respectively. It is common knowledge that even in this type of grease the presence of moisture affects the consistency. Hence it seemed desirable to make several observations on this phase of grease making.
Greases of this type are ordinarily regarded CONSISTENCY. with apprehension because of their reputed great changes in consistency. This fear is based on the fact that the stearate type of grease is sold on an unworked basis, whereas the consumer is interested in its worked consistency. All greases become softer on working. Therefore, a large percentage of complaints will be eliminated as soon as aluminum stearate greases are sold on a worked basis. It may be of interest to record that sample J , with a worked penetration of 231, changed to only 250 with sixty additional strokes of the grease worker and seemed to reach a maximum of 255 with sixty more strokes, bringing the total up to one hundred eighty. WATERPROOFNESS. Another wrong notion about aluminum stearate greases is that they hydrolyze in the presence of water. An easy way to show that water has no effect is to boil some aluminum stearate grease in water. When the excess is poured off and the remaining water is boiled out, the grease is still as solid and transparent as before the test. WIDEAPPLICABILITY.With proper modification, aluminum stearate greases may be compounded to obtain an infinite variety of p r o d u c t s . The aluminum stearate can itself be changed to have a low 0 J or high bodying effect on the Y 3 oils used. Various grades are v) sold under trade names for that purpose. Fluxes can be added to the stearate and oil so that the resulting products may be a thickened oil, a s t r i n g y a d h e s i v e semifluid grease, or a high-melting solid WORKED PENETRATIONS lubricant. I n this connection it is well FIGURE7. EFFECTOF to state that as little as 5 per MOISTURE AND TIMEOF COMPOUNDING cent sodium base or lime grease will liquefy on alumiGum stearate grease. Therefore, the need for absolute cleanliness is imperative.
OF MOISTURE AND TIMEOF COMPOUNDINQ TABLE 111. EFFECT
Sample
Q
R
s T
Hours Held a t 150’ C. 0 1 3 6
Worked Penetration 275 240 225 222
r0Moisture in Grease 0.15 0.12 0.10 0.05
A series of greases were made similar to sample J with 10 per cent aluminum stearate in the 310 asphalt oil, and were heated to 150’ C. However, the general procedure described above was modified so that the samples were mixed a t 150” C. from 0, 1, 3, and 6 hours and then placed in the oven t o cool as usual. The penetrations on the resulting greases showed an increasing hardness as the time of compounding increased and
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Acknowledgment The writer is greatly indebted to Joseph Nothum for the preparation of the samples and to G. E. Merkle, of the Fiske Brothers Refining Company, for valuable advice.
Literature Cited (1) Garlick, H. S., J. Inst. Petroleum Tech., 20, 860 (Sept., 1934).
(2) Klemgard, E. N., “Lubricating Greases,” New York, Chemical Catalog Co., 1927. (3) Kopp, C. H., Petroleum Eng., 3, 84 (Oct., 1932). (4) Licata, F. L., Natl. Petroleum News, 25, 23 (June 7, 1933). (6) Lucas, “Ancient Egyptian Materials,” 1926. (6) Metropolitan Museum Art Bull., 3, No. 12, 221 (1908). (7) Pllny, “Natural History,” Book XXVIII, Chap. 37. (8) Redwood, I. I., “Lubricants, Oils and Greases,” Spon and Chamberlain, 1898. (9) Wilch, C. C., Natl. Petroleum News, 26, 28 (Sept. 5, 1934). (10) Zublin, E. W., Ibid.,23, 33 (Sept. 9, 1931). RECEIVEDDecember 31, 1937. Based on a paper entitled “Metallic Soaps in Grease Manufacture,” which was presented by the author before the Oklahoma Local Section of the American Chemical Society. Ponca City, Okla., December 7. 1935.
