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Vol. 17, No. 10
Control of Consistency in Manufacture of Cup Grease’ By David R. Merrill UNIONOIL COMPANY OF CALIFORNIA, OLEUM,CALIF.
U P grease, which is the most common type of lubricating grease, consists of a mineral lubricating oil thickened with a calcium soap, or occasionally with a sodium soap or a mixture of the two. The data in the present paper, however, apply to greases made from calcium soap exclusively. From the standpoint of the user the consistency is perhaps the most important property, since because of the consistency he is willing to pay a higher price than for lubricating oil. Moreover, even small differences in consistency are important, especially in industrial lubrication, because they affect the rate of feed of the grease to the machine, and hence the consumption of the lubricant. The user is not unreasonable, therefore, in insisting upon a high degree of uniformity of consistency throughout the container and in succeeding purchases. The manufacture of cup grease of uniform consistency is not easy, however, because the consistency depends upon a colloidal gel structure and this structure, in turn, is subject to great variation with changes in composition and in conditions of manufacture. General M e t h o d of M a n u f a c t u r e The fats commonly used in the manufacture of cup grease are tallow, horse oil, cottonseed oil, and fish oil, but other fats and mixtures can also be used, and even fatty acids, with proper modification of the conditions of saponification to avoid lumping. The relative proportions of solid and liquid fatty acids affect the properties of the finished grease, and the data given later concerning the effect of temperature on consistency apply particularly to greases made from tallow. Considerable variation is possible in the details of the manufacture of cup grease, depending upon the kind and acidity of the fat used, the design of the mechanical equipment, and the personal preferences of the greasemaker. A typical method of procedure for calcium cup grease is as follows:
C
The fat, of which tallow may be taken as an example, is weighed or measured into a steam-jacketed kettle equipped with a mechanical agitator of the paddle type, and a portion of the mineral oil, equal to about half the volume of the fat, is added to prevent the formation of lumps of soap during the saponification. A slight excess of hydrated lime in the form of a thin paste is then added and the mixture cooked, with agitation, until saponification is complete, which usually requires several hours. At times the mixture may boil up rather high in the kettle, and in such cases a small amount of mineral oil may be added each time to cause the foaming to subside. Completeness of saponification is judged by the texture of the soap, which, with the proportions of mineral oil mentioned above, should be firm and brittle when cold. A soft, pasty consistency indicates incomplete saponification or a n excessive water content, whereas a stringy consistency indicates excessive evaporation of water, in which case additional water must be added. Mineral oil is then added slowly, t o avoid chilling the grease with formation of lumps, until the consistency is reduced to the desired extent. The grease may then be drawn into packages, but preferably is first strained by pumping through some type of strainer t o remove any lumps of soap or of hard grease.
For a No. 3 cup grease, which is the standard grade for use in compression grease cups for general lubrication, the final composition is usually about 18 per cent calcium soap, 1 Received July 23, 1925. Presented bpfore t h e Division of Petroleum Chemistry a t the 70th Meeting of the American Chemical Society, L o s Angeles, Calif., August 3 t o 8, 1925.
1 to 3 per cent water, 1.8 per cent glycerol (if a fat, rather than fatty acid, was used) and the remainder, a mineral oil with a viscosity of about 100 to 150 seconds Saybolt at 100’ F. (37.8’ C.). The glycerol apparently has little effect upon the properties of the grease beyond influencing the general appearance and transparency, but the water is a very important ingredient. The chief disadvantage of excessive amounts of water is the undesirable color and opacity produced, but with insufficient amounts of water th6 consistency of the grease is affected. If the water content is somewhat below 1 per cent, for a grease of medium grade like No. 3, the gel structure is very pronounced but is easily broken down by mechanical working to give a mixture of comparatively low viscosity, and with still smaller amounts of water the gel may refuse to form and the grease have very little body. The probable reason for these phenomena is that in the presence of water the calcium soap is more or less hydrated and insoluble in the mineral oil, but in the unhydrated form tends to go into true solution in the mineral oil, or at least to form a colloidal solution rather than a gel. Under certain conditions-as, for example, through addition of water in the course of the reduction, with insufficient cooking to cause it to be taken up by the soap-it is possible to have the phenomena usually accompanying excessivelylow water contents, even though the water content as determined by analysis may be normal. This, of course, is due to an excessive proportion of water being present in the free condition merely as an emulsion in the grease rather than in combination with the soap. M e t h o d s for D e t e r m i n a t i o n of Consistency
Except for the determination of consistency by feeling the grease in the container with the finger, probably the most common method has been to use some form of penetrometer, generally an asphalt penetrometer, such as the Dow or New York Testing Laboratory instrument, with special conical or cylindrical plungers or “needles” to adapt the machine to the testing of grease. Another instrument, designed originally for the testing of asphalt, which can be used for testing greaseJ2is the Abraham con~istometer.~The present work has been done principally with this instrument, and a brief description of it will therefore be given. The Consistometer
The Abraham consistometer is an instrument by means of which a plunger with a flat circular head and shank of reduced cross section can be forced into the sample a t a uniform velocity. The force required to cause penetration is applied by means of a hand wheel and screw and is transmitted to the plunger through a spiral spring. The elongation of this spring is indicated by a pointer on a scale and gives the force directly in grams or kilograms. The rate of penetration is indicated by a hand which makes one revolution for 1 em. of travel, and hence, to cause the plunger to penetrate a t the standard rate of 1 cm. per minute, the force is applied a t such a rate that the hand turns at, the same speed as the second hand of a watch. Plungers are provided having 2 8
As suggested in Battle, “Industrial Oil Engineering,” 1920, p. 218. Abraham, “Asphalts and Allied Substances,” 1918, p. 498.
I X D U S T R I A L A N D ENGINEERING CHEMISTRY
October, 1925
areas of 0.01, 0.1, 1, and 10 sq. cm., and also two springs, in order to adapt the instrument to the testing of substances throughout a wide range of consistency. The pressure applied to the sample is calculated by dividing the force in grams by the mea of the head of the plunger in square centimeters, and for convenience, to avoid excessively large numbers, the cube roots of the pressures are taken as the Abraham hardness numbers or the Abraham consistencies. The Abraham consistometer, rather than a penetrometer, was used in this work, primarily because of its adaptability to the testing of grease in comparatively small containers. It may be of interest, however, to discuss briefly the relative advantages and disadvantages of the two methods. Among the advantages of the consistometer is its adaptability to the testing of grease of all the usual grades from transmission grease to railroad greases, with results expressed on a single scale of numbers of convenient size and with larger numbers representing harder greases. With the consistometer it is also possible to note and allow for the presence of soft spots, cracks, and air pockets in the grease. Among the disadvantages of the consistometer are the somewhat higher cost of the instrument, the greater skill required in its operation, and the inapplicability, as a t present designed, to the testing of grease in large containers. A disadvantage of the penetrometer a t present is the lack of an established standard for the needle or cone, but this will probably be remedied in due c o u r ~ e . ~ Cup grease, particularly in the unworked condition-that is, with the structure not disturbed by mechanical working-is a plastic solid, and hence the readings, both of the consistometer and of the penetrometer, depend upon both the yield point and the mobility. I n a worked grease the effect of yield point is, of course, reduced, but it is found that a curve expressing the relationship between Abraham consistencies and penetrations with a 45degree cone, for unworked grease, also holds fairly satisfactorily for worked greases. Standard Consistencies for Cup Grease To permit those not familiar with the consistometer to follow the subsequent data given in terms of Abraham consistencies, the consistencies and soap contents considered approximately normal for the usual commercial grades of calcium cup grease are given in Table I. These consistencies are determined a t 77" F. (25' C . ) , since this is a convenient temperature and is standard for penetration of asphalt. For accurate work, it is desirable that the sample be brought to within about 1' F. of the standard temperature. Some work on the effect of the temperature of testing has shown that, for No. 3 to No. 6 cup grease, the normal temperature coefficient of change in consistency in the vicinity of 77" F. is around 0.02 to 0.03 point hardness, respectively, on the Abraham scale per degree Fahrenheit (0.036 to 0.054 per degree Centigrade), with the hardness decreasing, of course, as thg temperature rises. These figures apply particularly to normal samples of calcium soap cup grease made from tallow, and some variation may be expected in batches having abnormal consistencies for the soap content. Table I-Approximate Normal Consistencies a n d S o a p C o n t e n t s f o r C o m m e r c i a l Grades of C a l c i u m C u p Grease Approx. normal Approx. normal consistency soap content Grade (unworked) at 77' F. Per cent b y wt. 10.5 11.5 14.5 4.5 17.5 6.5 8.6 20 22.5 11.0 29 16.5
3
'
4 The American Society for Testing Materials. Committee D-2, Subcommittee on Grease, is working on the standardization of a penetrometer cone for testing grease.
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In current work5 on standardization of methods for determining the consistency of cup grease, consideration is being given to the advisability of using the consistency of the worked grease as a standard, rather than of the unworked grease. The worked consistency is determined upon a sample which has been worked mechanically, with care to avoid inclusion of air, until the consistency is substantially constant. The use of worked consistency has the great advantage, from the standpoint of inspection of purchases, that it permits testing of samples which have been transferred from one container to another. Also, the worked consistency may give an indication of the way in which the grease may function in a bearing or gear case, and the rate a t which it will leak out. With the harder grades, however, and especially in use in compression grease cups or open boxes, the working in transferring the grease from the container to the cup or box is not sufficient to break down the structure completely to the worked consistency, and hence the unworked consistency will have some effect on the rate of feed of the grease to the bearing. From the standpoint of the manufacturer, the unworked consistency is of primary importance because of the prevalence of the custom of testing the consistency with the finger, and the certainty, under present conditions, that a grease which had an abnormally low unworked consistency, because of being drawn from the kettle a t too low a temperature, would be considered too soft by the average customer, even though the worked consistency were normal. With standardized procedure and proper control of manufacture so that the product is uniform in quality, there need be no fear that the worked consistency of individual batches will be excessively low. On typical samples of No. 5 to KO.2 calcium cup grease made entirely, or predominantly, from tallow, the ratio of the worked to the unworked consistency varied from about 50 to 70 per cent, with the greater drop in consistency usually taking place in the case of the harder greases. This is equivalent roughly to a drop of one or two commercial gradesthat is, from a No. 5 to a No. 3 or a No. 3 to a soft No. 2. In appearance, however, a worked No. 5 cup grease is quite different from an unworked No. 3, since it is usually rather dull and pasty, even though care has been taken to avoid inclusion of air. Quick Consistency Test for Grease in the Kettle
The chief difficulty in the control of consistency in the manufacture of cup grease lies in the fact that considerable time is required for the grease to attain its final set, and hence its final consistency, when a sample of the melted grease is drawn from the kettle and allowed to cool in the air. When drawn into 1-pound (0.5-kg.) cans, the final consistency is attained in about 3 days, whereas in wooden barrels about 5 days are required because of the slow cooling, particularly in the centers. A fairly close approximation to the final consistency can be obtained, however, by drawing a sample in a 1-pound can and allowing it to stand overnight before testing. This method of control is frequently used, but is not very convenient, particularly if the batch requires further reduction with oil. An attempt was made, therefore, to develop a more rapid method of testing, based upon the principle that by means of a low temperature of testing it is possible to compensate more or less perfectly for the incomplete setting in the limited time of cooling. In preliminary work, the samples were taken in 1-pound slip-top cans 4 inches in diameter by 2'/2 inches high (10.2 cm. by 6.3 cm.) and cooled in crushed ice and water. It was found that approximately 3 hours were required for the grease to reach a fairly uniform'temperature of about 35' F. A. S. T. M. Committee D-2, Subcommittee on Grease.
.
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I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
(17” C.), and that when the consistency was determined immediately after the cooling period the results gave a fairly satisfactory indication of the ultimate consistency of a sample cooled naturally. This period of cooling was considered excessive for a control test, however, and attempts were made to shorten it by the use of smaller cans. After rather unsatisfactory results with small cylindrical cans, because of formation of shrink holes and circular cracks, rectangular cans were tried with greater success. The final procedure developed has now been in use for over two years, and has been a great improvement over previous methods. For taking the samples, spice cans of stock design are used. These are rectangular cans with slip tops and are 11/4 inches wide, 2l/4 inches long, and 3l/8 inches high (3.1 X 5.7 X 7.9 cm.). To reduce the trouble from cracks, the cans of grease are precooled in air for 15 minutes before being placed in the bath of crushed ice and water. They are left in the bath for one hour and then removed one a t a time and tested immediately with the consistometer, two tests being made on each can. On the harder greases it is advisable to separate the grease from the sides of the can, after precooling, by running a spatula down next to the tin. This reduces trouble from cracks, but on No. 5 and No. 6 cup greases it is usually necessary to use special cans of the same size, but with removable bottoms, and to test the grease in an inverted position. It is also advisable to fill four to six cans each time, so that at least four consistency determinations can be made and averaged.
Vol. 17, No. 10
the batch have been drawn, but the drawing is not delayed pending receipt of the results. Control of Consistency during Drawing
After the batch of grease has been brought to the correct consistency for the grade, subsequent operations must be carried on in such a way as to avoid further changes. This involves, in particular, careful control of temperature until the grease is in the containers in which it will cool and set, since the temperature from which the grease cools without being disturbed has an important bearing on its final consistency. I n general, if the grease is drawn a t too low a temperature, particularly when a pump is used in the discharge line, the structure will be broken down to some extent by mechanical working in the kettle and in passing through the pump and lines, and the consistency will be lower than if the same grease were drawn a t the proper temperature. This effect on the consistency is more marked in the quick test than in the standard test, however, and under such conditions the final consistency is likely to be higher than anticipated from the results of the quick test. At excessively low temperatures the mechanical working may be sufficient to give the grease an undesirable dull appearance or poor luster. If, on the other hand, the grease is drawn a t too high a temperature, the consistency will be increased, but a so-called “false body” will be obtained. In such cases the gel structure is particularly marked and the difference b e tween the unworked and worked consistency is abnormally large. For a No. 3 calcium cup grease made from tallow, Application of Control Test for Consistency the increase in consistency is about 0.15 point hardness on I n the manufacture of cup grease the consistency is de- the Abraham scale per degree Fahrenheit (0.27 per degree pendent to such an extent upon the colloidal condition of Centigrade), within a short range above the normal drawing the soap that the production of grease of standard consistency temperature, which is considered to be about 195” F. (91’ C.) by making the batch according to a definite formula is very I n drawing grease into large containers, such as barrels difficult, although a fair approximation can be obtained in and half-barrels, temperatures much above the normal a large proportion of the batches by careful standardization drawing temperature are particularly to be avoided, because and control of all conditions of manufacture. Even with of the tendency for formation of soft centers under such such careful control, however, a consistency test on the grease conditions. Apparently, in the slow cooling from the high in the kettle before it is drawn into packages is very desirable temperatures, changes take place in the colloidal condition in order to avoid the necessity of condemning or rebranding of the soap so that the usual gel structure is not properly an occasional batch. I n the application of the quick test formed. I n consequence, the grease in the centers of the just described, the grease in the kettle is first reduced with large packages, instead of having an abnormally high consistoil to give approximately the normal yield for the particular ency, or “false body,” has an abnormally low consistency for grade and is brought to the correct temperature for drawing. the soap content, more like that of a worked grease. Under During this reduction the grease-maker keeps a rough check extreme conditions this loss of consistency in the centers on the consistency by feeling samples removed from the of large packages may be more than two commercial grades. kettle from time to time and cooled in the air. These samples From the foregoing it is apparent that the establishment may be obtained either by dipping a wooden paddle into the of correct drawing temperatures is very important in avoidgrease several times to build up a coating, or by pouring a ing “false body” and soft centers in large packages on the small amount into a can cover. one hand, and loss of consistency by mechanical working When the batch is reduced to a point slightly on the hard on the other. These temperatures will vary both with the side of the desired grade, samples are taken in spice cans and grade of the grease and the character of the soap, since lower two samples are also taken in 1-pound cans. These latter temperatures can be used with the softer grades and with samples are tested a t 77” F., after standing for a t least 3 greases made from fats containing large proportions of liquid days, and give a basis for determining the correspondence fatty acids. In applying the correct drawing temperatures, between the two tests under the current conditions, and also when determined, it is important not only to have the grease serve to reveal any serious errors in procedure. After the in the kettle a t the proper temperature throughout the drawresults of the quick test are reported to the grease-maker, ing, but also to have the grease as it enters the containers the consistency of the grease in the kettle is adjusted, if a t substantially the same temperature. This necessitates necessary, by further addition of oil, and a second test is the avoidance of poorly lagged lines, high steam pressure in made. When a satisfactory result is obtained, the grease steam-jacketed lines, or generation of a large amount of is again brought to the correct temperature for drawing frictional heat in the pump. Aeration, from leaks in the and drawn into packages. The drawing of a batch of about suction line or excessive agitation in the kettle, is also to 12,000 pounds (5500 kg.), particularly into small cans, re- be avoided. With proper attention to these points, differquires considerable time, and care must be taken to prevent ences between the consistency of the grease in the kettle, further changes in consistency during this period. As a as shown by the 3-day test, and the final consistency of the control on these operations, samples for quick tests and stand- grease in packages may be kept down to very moderate ard 3-day tests are taken when one-third and two-thirds of proportions.
IIC'DCSTRIAL AND ENGINEERIXG CHEMIXTR Y
October, 1925
I n t e r p r e t a t i o n of R e s u l t s of Quick T e s t
As previously mentioned, the correspondence between the 1-hour quick test and the 3-day standard test is influenced somewhat by the temperature of the grease in the kettle when the samples are taken. Another cause of poor correspondence between the tests is reduction of the grease in the kettle with oil, without allowing sufficient time for the oil to enter into the proper combination with the soap. Under such conditions the quick test may show a greater reduction in consistency, from the addition of oil, than will be subsequently found in the standard test or in tests on the grease in packages. With standardization of the drawing temperature and of the procedure of taking the samples and of making the quick test, the relationship between the consistency determined by the quick test and the standard test should be satisfactorily constant. For greases made exclusively from tallow, this relationship is sufficiently close to equality to permit the
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quick results to be taken as a direct indication of the final consistency, but for greases made from fats containing greater proportions of liquid fatty acids, the quick results are usually somewhat low, especially for the harder grades of grease. For such greases, therefore, the relationship between the two tests is best expressed by means of a curve, and this curve then used to find the true consistency corresponding with the apparent consistency given by the quick test. This curve can be developed easily from the results of quick tests and 3-day tests on samples taken from the kettle a t the same time, either while bringing the grease to grade or during drawing. Acknowledgment
Acknowledgment is due H. R. Linhoff and P. 8. Clarke for assistance in developing the details of the quick test and applying it to large-scale operations.
Manufacture of Hydrochloric Acid from Chlorine' By Wilhelm Hirschkind GREATWESTEKK ELECTRO-CHEMICAL C o . , PITTSBURG, CALIF.
HE conversion of chlorine into hydrochloric acid, a reversal of processes marking the accomplishments of a Weldon and Deacon several decades ago has not only become an economic necessity due to the world-wide over-production of electrolytic chlorine, but for some time an accomplished fact. The combination of hydrogen and chlorine is carried out today in large installations at several plants, and has been described in detail by H. K. Moore and others. This phase of hydrochloric acid production will not be considered here. The other reaction capable of converting chlorine into hydrochloric acid is the reversal of the Deacon process.
T
Cl?
+ H20 = 2 HC1 +
'/s
equals its affinity to oxygen. At higher temperature the affinity to chlorine, a t low temperature to oxygen, predominates. Therefore, for production of hydrochloric acid by the reversed Deacon process only high temperatures are in question. The process has no technical interest, however, because the temperature a t which the equilibrium is completely on the hydrochloric acid side becomes very high. The reaction between chlorine and water-i. e., the reversed Deacon reaction assumes a new aspect if a reducing agent such as carbon is used to combine with the oxygen liberated by the reaction. History of Method
Oe
Lorens6 as early as 1895 clearly foresaw the trend of the A study of the equilibrium of this reaction shows that a t chlorine and hydrochloric acid industries toward a manufacture lower temperature chlorine and a t higher temperature hydro- of hydrochloric acid from chlorine. His paper contains scant chloric acid is favored. The old Deacon process was therefore experimental material, but he concludes that the reaction between carried out at asjow a temperature as the rate of reaction chlorine, steam, and carbon a t dull red heat proceeds according to the following equation: aided by a catalyst in form of cupric chloride would permitC Cls H20 2 HCl f CO (1) between 480" and 500" C. Two years later Nauman and Mudford6 published a comThe Deacon chlorine process was one of the earlier exprehensive experimental investigation of the reaction between amples of accurate equilibrium measurements carried out chlorine, steam, and carbon. Chlorine and steam were passed principally by Lunge and MarmierJ2 von F a l k e n ~ t e i n , ~through a tube filled with carbon and heated to a definite temperand Lewis.4 Von Falkenstein studied the reaction from both ature measured by a thermocouple which was inserted into the sides using a continuous flow method, whereas Lewis used a tube. The influence of variations in temperature, length of the layer of carbon, and excess water vapor was determined and the static method. With copper chloride as catalyst the lowest following conclusions were reached: temperature a t which equilibrium can be reached is 430" C. ( 1 ) T h e reaction within t h e temperature interval of 400' t o 850' C. Above 500" C. copper chloride melts and naturally becomes proceeds according t o t h e equation impossible. Between 600" and 700" C. platinum chloride C f 2 Clz f 2Hz0 = 4 HC1 + COz (2) becomes a good catalyst, and between 900" and 1000" C. no contrary t o t h e assertion of Lorens. (2) T h e presence of carbon monoxide in t h e exit gas is due t o a secondary catalyst is necessary. of the carbon dioxide on carbon. At 577" C. the equilibrium constant of the Deacon process reaction (3) Excess water vapor results in t h e presence of water gas-i. e., a is one. Since the reaction is one of hydrogen with oxygen on mixture of hydrogen and carbon monoxide in the exit gas. one side and with chlorine on the other, this means that a t If a rational discussion of this comprehensive experimental this temperature the affinity of hydrogen to chlorine material had been attempted by the authors, i t would probably
+
1 Received July 24, 1925. Presented a s a p a r t of t h e symposium, Chemical Industries of t h e West, before t h e Joint Meeting of t h e Divisions of Industrial a n d Engineering Chemistry, Paint and Varnish Chemistry, a n d Cellulose Chemistry a t t h e 70th Meeting of t h e American Chemical Society, Los Angeles, Calif., August 3 t o 8, 1925. 2 Z . angew. Chem., 105 (1897). a Z . physik. Chem., 69, 313 (1907). 4 J. A m . Chem. S O L .28, , 1380 (1906).
+
have had some effect on the subsequent developments of the process. However, the later patents hardly took notice of this investigation. Nagel' in 1912 described a practical gas generator in which 6
6
7
Z . anorg. Chem., 10, 74 (1895). Ber., 80, 347 (1897). Chem. Z l g . , 86, 54 (1912).
