US2760936A - Manufacture of lithium grease - Google Patents

Description

z- 8, 1956 P. J. BAKER 2,760,936

MANUFACTURE OF LITHIUM GREASE Filed May 20, 1952 2 Sheets-Sheet l r TO EVACUATION EQUIPME NT SOAP an. IE

STORAGE INVENTOR. PETE. R J. BAKE-R Aug. 28, 1956 P. J. BAKER MANUFACTURE OF LITHIUM GREASE Filed May 20, 1952 PENETRATION A.S.T.M. PENETRATION ASIM.

2 Sheets-Sheet 2 aeo'F z-Io'F aeov= a9o|= sooF 5\or= BLEND\NG TEMDERATURE FIE-7- 550 o 50 roo \50 200 50 500mm BLENDER SHAFT SPEED INVENTOR.

PETER J. BAKER United States Patent MANUFACTURE OF LITHIUM GREASE Peter J. Baker, Louisville, Ky., assignor, by mesne assignments, to National Cylinder Gas Company, Chicago, 11]., a corporation of Delaware Application May 20, 1952, Serial No. 288,854

3 Claims. (Cl. 252-41) This invention relates generally to the manufacture of grease compositions and more particularly to a novel continuous process for forming improved grease compositions of lithium soaps and oils.

It is well established that the quality of a grease varies substantially with the method of making it, and also that a satisfactory process for forming a grease of one metal soap and oil is not necessarily satisfactory, or even operative, for another metal soap even though the same oil be used. This is believed to be due to the fact that different types and lengths of fibers or micelle structures are formed by dilferent soaps, and by the same soap when different processes of forming the fibers are utilized. Moreover, the degree of orientation and twist of the fibers is a variable from grease to grease and affects the physical properties thereof.

Grease fiber or micelle formation is essentially a process of crystallization which is brought about by cooling a solution of soap from a relatively high temperature to a lower temperature at which the soap is insoluble in the oil. Various factors including rate of cooling and the degree of agitation during cooling through the critical crystallization range and thereafter affect the type of fibers which are formed. After the fibers have been formed the structure may be modified by milling which tends to minimize sineresis and improve the stability of the grease.

The heretofore prevalent process for manufacturing lithium grease involves the following steps: Initially a slurry of lithium soap in mineral oil is prepared in open kettles and heated to a temperature of about 400 F. to completely dissolve the soap. The soap may be prepared separately or in the slurry kettles from fats or fatty acids and lithium hydroxide in the presence of part or all of the oil. If only part of the oil is used to form the soap the remainder of the oil is added after saponification is completed and the slurry is heated to solution temperature. The solution of lithium soap in oil is then drawn from the kettle and allowed to cool statically, usually in open pans, until a gel is formed. The cooled gel is then subjected to a milling operation in which it is worked to form a homogeneous grease composition. This processhas a number of practical disadvantages. The high temperature heating in open kettles results in loss of more volatile components from the oil and creates a fire hazard. The process involves considerable manual handling of pans of gelled grease both in filling and feeding thegelled grease into the mill, which is time consuming and involves a danger of contamination. For these and other reasons, the process cannot be controlled to produce uniform greases from batch to batch, and, even more important, the yield of grease whish may be obtained from a given amount of soap is low. It is necessary to deaerate the grease during the milling operation. Furthermore from the standpoint of economy of operation, the power required to mill the cooled grease is quite high, and the .heat requirement to raise the slurry including Patented Aug. 28, 1956 the entire amount of oil in the grease to solution temperature is considerable.

I am aware that other processes have been proposed for the continuous manufacture of grease which in some respects more nearly resemble my new process than does the above described pan cooling method. Most of these other processes, however, are not specific to greases made from lithium soap and although they may work out satisfactorily for other metal soap greases they have not proved satisfactory for lithium greases, as evidenced by the continued use of the laborious pan cooling process by lithium grease producers.

I have provided an improved process for producing lithium grease which may be operated on a continuous or semi-continuous basis and which produces higher yields of grease from given amounts of soap (the most expensive constituent) and also produces grease of more uniform characteristics and superior quality. Moreover, my new process results in economics in labor, electric power and heat required.

One of the important features of my invention is the discovery that the above mentioned improvement may be obtained by blending a hot solution of the soap in part of the oil with additional oil having a substantially lower temperature, such blending being accomplished within a certain critical temperature range and under conditions of extremely mild agitation conducive to complete mixing with low shear. For practical purposes the critical temperature range lies between about 230 F. and 310 F. Following this rapid shock chilling by blending, the resultant greaseis additionally cooled under conditions of violent agitation to a temperature below a second critical temperature below which the soap micelle is stable and which I have found to be about 160 F. The grease may then be finished by milling in the conventional manner. In connection with the milling operation, I have found that considerably less power is required to mill the grease than in the case of pan cooled greases. this is not fully understood, but itis believed to be due to the fact that the rapid chilling without substantial agitation .during the blending step produces more soap micelle or fibers of the desired size and a lesser number of fibers of excessive length so that substantially all of the fibers are of the desired size and less milling power is required to break down overly long fibers.

This factor of proper fiber growth initially in the cooling stepis also believed to account for the higher yields experienced with my process since the fibers which are formed are utilized with greater effectiveness in the gel to produce adequate penetration values or stiffness in the finished grease even though the soap is present in smaller amount. Obviously if a pan .cooled grease must be worked to reduce extra. long fibers, that same working reduces the shorter fibers to less than optimum gel forming length.

Another particular advantage of my process is that virtually no gel forming time is involved. Gelation is completed by the time the grease is cooled below the second critical temperature, and consequently no holding vessels are required.

Other objects and advantages of the improved process of my invention will become apparent to those familiar with the art on reading the following specification in connection with the drawings and the appended claims. In the drawings:

Fig. 1 is a flow diagram showing a preferred system of apparatus for carrying out my novel process;

Fig. 2 is a longitudinal vertical section showing somewhat schematically the internal construction of a preferred form of heat exchange unit;

Fig. 3 is a transverse section of such unit, taken on line 3-3 of Fig. 2;

The reason for Fig. 4 's a longitudinal vertical section showing someschematically the internal construction of a preferred form of blender;

Fig. 5 is a transverse section of the blender taken on line 55 of Fig. 4;

Fig. 6 is a graph showing the effect of blending temperature on penetration; and

Fig. 7 is a graph showing the effect of blender shaft speed on penetration.

As previously indicated my improved process may be operated either continuously or semi-continuously. For continuous operation a pair of identical slurry tanks 10 are preferably employed. These tanks are provided with conventional agitators to keep the solids in suspension and are connected through a suitable line 11 to evacuating equipment (not shown) so that the slurry may be deaerated at this stage rather than in the finishing mill. Oil is supplied to the slurry tanks from the oil storage container 9 through conduit 12, either by gravity feed or a pump (not shown). prepared and added in solid form.

From the tanks 10, which are discharged alternately, the slurry is conducted by a valved conduit 13 to a slurry pump 14 which forces it through the heat exchange and blending apparatus described below. The outlet of the pump 14 is connected by a conduit 15 to the slurry heating unit 16 where the slurry is agitated and heated to a solution temperature within the range of about 375 F. to about 450 F., depending upon the particular soap used.

The construction of heating unit 16 is preferably identieal to that of the cooling unit 17, so that Figs. 2 and 3 are illustrative of either of these two heat exchangers. Each unit comprises a pair of generally circular end plates 20 and 21 recessed to receive the ends of the heat transfer tube 22. Ring members 23 are sleeved on the tube 22 adjacent to the end plates and support-a pair of cylindrical elements 24 and 25. Thus an annular space 26 is provided for heat transfer fluid around the tube 22. The space between the sleeves 24 and is preferably filled with insulation 27 to provide a heat insulating jacket.

The end plates 2i and 21 are provided with appropriate bearings and seals for journalling the agitator shaft 28 and sealing the point at which the shaft passes through the plate 21. The agitator shaft 28 fills a major portion of the space within the tube 22, and together with the tube forms a thin elongated annular passage 29 for the grease or slurry, as the case may be. The agitator shaft carries a plurality of blades or scrapers 30 which serve to prevent sticking of material to the inner surface of heat transfer tube 22 and to agitate the grease or slurry as the shaft rotates at relatively high speed, i. e. on the order of 500 R. P. M. A suitable drive mechanism (not shown) is provided to rotate the shaft at this speed.

In the case of the slurry being heated in the unit 16 the violent agitation aids in providing uniform heating and solution of the soap, while in the case of the grease being cooled in the cooling unit 17 the agitation serves to control micelle fiber growth and gel formation by promoting rapid controlled cooling from the critical blending temperature to the lower critical milling temperature.

The slurry or grease, as the case may he, enters the heat exchanger through an inlet conduit 31 at one end and leaves through an outlet conduit 32 at the opposite end. The heat transfer fluid is conducted to and from the annular space 26 by appropriate connections 33 and 34.

To those familiar with the art of heat transfer it will be readily apparent that the units 16 and 17 effect very rapid and efiicient heating andcooling of the slurry and grease under closely controlled conditions of temperature, pressure and degree of agitation. The heat transfer fluid in the case of the unit 16 is preferably a heating p medium having a boiling point at atmospheric pressure much higher than that of water, such as diphenyl or diphenyl oxide or a mixture of the two sold under the trade name Dowtherm. Cold water or brine may be .used in the cooling unit 17.

The soap is preferably previously Intermediate the two heat exchange units 16 and 17 a blender 35 is provided. A preferred form of blender is illustrated in Figs. 4 and 5. r This unit is similar in construction to the two heat exchange units in that an annular passage for the product is provided between a hollow cylinder 51 and a rotating shaft 52. The ends of the cylinder 51 are supported by end plates 53 and 54 which contain suitable bearings for the ends of the shaft 52. A seal 55 is provided in the plate 54 to prevent product leakage at the drive end of the shaft. Suitable means (not shown) are provided to drive the shaft at a slow speed to provide gentle agitation. Thorough mixing with low shear is accomplished by a series of pins 56 arranged in a helical pattern on the shaft 53 which cooperate with a row of similar stationary pins 57 mounted in the wall of the cylinder 51. The product enters and leaves the blender through inlet and outlet connections 58 and 59, respectively, provided in the end plates 53 and 54.

The purpose of the blender, as will be explained later in more detail, is to mix the hot solution emerging from heating unit 16 with relatively cold oil. The blender alternatively may be in the form of a length of pipe having several bends therein or of a chamber having circuitous passages therethrough. The use of a slowly driven mixing shaft in the blender is preferred, however, because it imposes less load on the pumps 14 and 37 than does a static system. In the illustrated embodiment the oil is pumped from the tank 9 through a conduit 36 by means of an oil pump 37. The oil pump and the slurry pump are preferably interconnected in any suitable manner to proportion the relative amounts of slurry and cold oil which are supplied to the blender. The ratio of oil in the slurry to cold oil is preferably about 1:1 although other ratios within the range of 3:1 and 1:3 have been tried and proved successful. In certain cases the oil from which the slurry is formed and the cold oil subsequently added may be of different types, in which cases separate oil storage tanks are used.

An oil heater 38 is shown in the drawing. This heater is not essential to the operation of the process, but its use is preferred for it provides a very simple arrangement for controlling the critical blending temperature. The heater 38 may be a conventional heat exchanger to which steam is supplied through a line 40. The steam line 40 is preferably rovided with an automatic control valve 42 which is connected as illustrated at 43 so as to be responsive to the temperature of the grease emerging from the blender 35 in the conduit 41 leading to the cooler 17. Thus the critical blending temperature is controlled by supplying more or less heat to the relative cold oil prior to its being mixed with the hot solution in the blender 35. The output temperature of the oil heater 38 is usually maintained within the range of F. to 180 F., but actually this temperature is dependent uponthe oil-slurry ratio and the blending and solution temperatures and may be varied considerably either above or below this range. For example, if a large proportion of the oil is initially incorporated in the slurry in slurry tank 10, it may be necessary to refrigerate the cold oil to reduce the slurry from solution temperature to the desired blending temperature. In this latter situation the apparatus 38 takes the form of a refrigerating device rather than a heater.

The critical blending temperature may also be controlled by varying the relative amounts of oil and slurry or by varying the temperature to which the slurry is heated. The control of relative rates of oil flow, however, has proved much more diflicult than the control of steam supplied to a heat exchanger such as indicated at 38.

From the blender 35 thegrease, at the critical blending temperature and in a gutty state indicating fiber or gel formation, is supplied to the cooling unit 17. in this unit its temperature is quickly lowered under controlled agitation in the thin annular space 29 to below the critical milling temperature of about F. At this temperature gel formation is believed to be complete and the grease is ready for milling and packaging. It is desirable not to exceed the critical milling temperature in the milling operation, and, if the type mill employed produces considerable temperature rise, it is preferred to chill the grease to a somewhat lower temperature in the unit 17. The milling operation, which may be performed in a suitable milling device indicated at 45, differs from the conventional procedure in that deaeration is not required and in that considerably less milling power is needed as described. Experiment has shown that suflicient power is saved in the mill to more than ofiset the mechanical power used in the two heat exchangeunits 16 and 17 and in the blender 35. Thus an overall economy in power is achieved by my process.

I have found that the blending temperature has very important bearing on final quality and characteristics of the grease, and that the blending temperature of each grease is quite critical. The effect'of the blending temperature upon the penetration is shown graphically in Fig. 4. Penetration is a measure of hardness of grease and indirectly a measure of the yield which may be obtained from a given soap content, the lower the penetration and the harder the grease and the better the yield. Curve X represents a grease formed of a lithium soap and a mineral oil having a viscosity index of 60. Curve Y represents a grease formed of a similar soap having a slightly lower softening point and a different oil, having a viscosity index of 41.8. In each case the soap content was 7%. As will be apparent from Fig. 4, the optimum blending temperature is about 270 F. in the first case and about 290 F. in the second. It has been found that different oils and soaps and percentages of soap produce similar curves but dilferent critical blending temperatures. Although the exact relationships are un predictable, nevertheless the critical temperatures may be readily determined by simple and conventional penetration test procedures. In general, however, the critical blending temperature has been found to be between about 230 F. and 310 F.

I also have found that the degree of agitation during blending is quite important. In Fig. 7 the relationship between agitation during blending and penetration is illustrated. In obtaining this curve a shaft type blender such as is illustrated in Figs. 4 and 5 was used and the speed of the shaft 52 was varied. The penetration of the greases corresponding to various shaft speeds was measured. The product cylinder 51 of the blender 35 used in this test had a diameter of three inches and'was 12 inches in length. The cylinder 51 has a single row of stationary pins 57 spaced an inch part. The shaft 52 was two inches in diameter and had a series of pins which extended through the shaft to protrude on each side. The shaft pins 53 were spaced about an inch apart along the shaft axis and were arranged in a helix. As will be seen from the curve of Fig. 7 the optimum shaft speed is about 60 R. P. M. in this blender 35. With this speed there is obtained a complete mixing of solution and cold oil and rapid cooling of the soap solution to critical blending temperature. The gentle agitation produces little shear and there are virtually no disruptive forces developed which might cause micelle fiber breakdown. For purposes of the process herein described, the extent of agitation employed at this point shouldbe a. minimum consistent with thorough mixing of the hot solution with the cold oil. Any greater degree of agitation involves excessive shear producing a softer grease and decreasing the possible yield. This explains the equivalency of a length 'of pipe or labyrinth to the blender 'unit 35.

A very important advantage of my process is the fact that the total heat requirement is substantially reduced since a large amount of the oil is not heated to solution temperature, as in the conventional process herein before referred to, but is introduced relatively cold. This is important from an operating as well as an initial equipment cost standpoint. For example, where about 50% of the oil is introduced cold the capacity of the heat. source supplying heating medium to the unit 16 need be only half as great as if all of the oil had to be heated as in the conventional process.

As stated previously it is preferred to use a ratio of 1:1 between cold oil and oil in the slurry. When this ratio is'maintained, it is possible to use heating and cooling units of the same size. The heating unit 16 handles only one-half the flow of the cooling unit 17 due to the fact that the cold oil does not pass through the heating unit. However, the temperature rise in the heating unit is about twice as much as the temperature drop in the cooling unit with the result that units having the same Example A Fourteen pounds of .prepared lithium stearate known as Witco #306, having a softening point 'of 210 C. and manufactured by the 'Witco Chemical Company, 295 Madison Avenue, New-York, New York, were mixed with eighty-six pounds of a naphthenic petroleum oil, having a pour'point of 15 F., a flash point of 410 F., a viscosity of 650 SSUat 100 F. and 60.6 SSU at 210 F., and a viscosity index'of 41.8, to form a'slurry containing 14% lithium soap. This slurry was then pumped through a heating unit similar to unit 16 shown in Figs. 1-3 at a rate of approximately pounds per hour. The shaft speed in the unit was 500 R. P. M., and the temperature of the slurry was raised to about 425 F. The resultant hot solution was blended with one hundred pounds of the same oil having a temperature of about 160 F. by pumping the oil and hot solution through a 10 foot length of /2 inch pipe having eight right angle bends to form grease at a temperature of approximately 290 F. The cold oil was supplied at a rate of about 75 pounds per hour so the combined flow through the pipe was about 150 pounds per hour. Pumping the hot solution and cold oil through the pipe produced a gentle agitation equivalent to that provided in the rotating shaft blender described. above when the shaft is rotated at very low speeds to provide rapid chilling of the hot solution with very low shear. Immediately after blending the grease was passed through an agitated cooling 'unit, similar to that hereinbefore described and having an agitator shaft speed of ,500 R. P. M.,

to lower its temperature to below 150 F. The rate of flow through the cooling unit was about 150 pounds per hour. Next the grease was worked in a Charlotte colloidv mill (Model W10).

. .The finished grease had a soap content of 7% and a penetration (ASTM) of 300 after 60 strokes in a conven-' tional grease worker. It exhibited no bleed upon standing and stood up well on additional working, showing a difference of penetration of only 33 after 10,000 strokes in the grease worker.

In order to determine the effect of blending temperature on the yield as measured by penetration, a series of greases was prepared by the procedure of the above example with all conditions maintained'the same except that the cold oil temperature was varied to give a series of blending temperatures from about 274 F. to about 307 F. The 60 stroke penetrations of the resultant greases were measured and the results when plotted gave the curve Y illustrated in Fig. 6. The grease having the lowest penetration value was obtained with a blending temperature of about 290 F.

Example B Fourteen pounds of a prepared lithium stearate known as Witco #305 and similar to the soap in Example A, but having a slightly lower softening point, namely 200 C., were added to eighty-six pounds of mineral oil having a flash point of 380 F., a pour point of 0 F., a viscosity of 567 SSU at F., and a viscosity index of 60. The oil and soap were mixed cold to form a slurry having 14% soap. A stream ofsuch slurry was continuously withdrawn and heated to 425 F. by the procedure of Example A to dissolve the soap. and then was blended with a stream of cold oil having various temperatures ranging from 120 F. to 160 F. in the blender 35 described in connection with Fig. 7. The two streams were supplied to the blender 35 at equivalent rates so that equal volumes of hot solution and cold oil were mixed. This produced blending temperatures ranging from 262 F. to 285 F. The blender shaft speed was about 60 R. P. M. The penetration values'of the resultant greases, which were cooled and finished as in Example A, were measured and plotted to produce curve X of Fig. 4. As shown by this curve the optimum blending temperature for maximum yield occurs in the range of 2681F. to 275 F. for the particular oil and soap utilized. All of the resultant greases had good texture and appearance and were not subject to sineresis.

Example C A slurry was prepared from the soap described in Example A and the oil referred to in Example B. This slurry contained 25% soap. Portions of this slurry were heated to approximately 425 F. and then were separately blended with sutficient cold oil inv the mixing blender described in connection with Fig. 7 to produce greases having soap contents of 7%, 9.5% and 11%, respectively. The blender shaft speed was 60 R. P. M., and the blending temperature. in each case was held at around 270 F. by adjusting the cold oil temperature which was varied between about 145 F. and about 210 F. Afterblending, the greases were cooled and milled as in Example A.

Although somewhat more viscous than the slurries of the preceding examples which had lower soap contents, the 25% slurry was easily pumped through the system by virtue of the fact that the rotary blenderwas employed. No significant diiferences in appearance, texture or stability between greases made by my process'from 14% slurries and from 25% slurries were noted, and all of the greases of this example were free from syneresis. The penetration values of the three greases of this example were as follows:

Penetration (ASTM) After Working in Grease Worker Example D Lithium hydroxide and stearic acid in combining proportions were mixed in a gas fired heating kettle with two thousand pounds of mineral oil to form a solution containing 14% soap after saponification was completed. The temperature of the mixture was raised to 400 F. to elfect saponification of the acid and hydroxide and complete solution of the soap produced. The mineral oil used had a viscosity of 500 SSU at 100 F, Two thousand pounds of cold oil having a temperature of about 140 F. were rapidly run into the kettle to lower the temperature of the batch to about 270 F. During the foregoing steps the batch was stirred gently by conventional paddle agitators rotating at 30 R. P. M.

The resulting grease was then run through a chilling unit similar to the unit 17 and its temperature was rapidly lowered to about 120 F. The throughput rate was approximately 1800 pounds per hour and the agitator shaft speed was 400 R. P. M. The cooled grease was milled in a centrifugal grease worker and packaged.

The resultant grease was free from syneresis and exhibited good stiffness both before and after additional working in a conventionalgrease worker. The 60 stroke penetration (ASTM) was 234 and the penetration after 5000 strokes was 275.

From the foregoing specific examples, which are included for purposes of illustration and not by way of limitation, it will be apparent that my process may be carried out with various different types of apparatus and may also be varied to utilize different oils, soaps and slurry compositions.

Various other changes and modifications, in addition to those set forth herein, may be made without departing from the spirit of my invention the scope of which is commensurate with the following claims.

What is claimed is:

l. The process of preparing lithium grease comprising forming aslurry of lithium stearate in a portion of the mineral oil desired in the finished grease, continuously passing a stream of said slurry through a heating zone and heating the slurry in said zone to a temperature at Which the lithium stearate is completely soluble in the oil and above about 400 F. while subjecting the slurry to violent agitation sufficient to produce a substantial shearing action, thereby to effect thorough and intimate mixing of the lithium stearate and oil and form a homogeneous solution of the lithium stearate in the oil free from undissolved lithium stearate particles, adding the remainder of the oil desired in the finished grease to the solution under conditions of substantially shear-free gentle agita tion, the added oil having a temperature selected with regard to the proportionate amount of the oil added in this step. to produce a resultant temperature of the mixed oil and solution of about 280 F., passing the resultant mixture through a cooling zone under conditions of violent agitation sufiicient to produce substantial shearing action-and rapidly cooling said mixture in said zone to a temperature below F., and finally milling the Cooled product for a sutficient time to eliminate syneresis and provide stabilityin the finished grease.

2. The process of preparing lithium grease comprising forming a slurry of lithium stearate and mineral oil containing substantially all the lithium stearate and approximately half the oil desired in the finished grease, raising the temperature of the slurry to a temperature consistent with complete solution of the lithium stearate in the oil and above about 400 F. to completely dissolve the lithium stearate in the oil and form a homogeneous solution free from undissolved lithium stearate particles by passing the slurry in a thin layer under agitation in contact with a heat transfer wall, continuously mixing the remainder of the oil desired in the finished grease with the hot solution under conditions conducive to mixing with a minimum of shear to provide intimate mixing without micelle disruption, the added oil having a temperature such as to produce a resultant temperature of the mixed oil and solution within the range from about 230 F. to 310 F., passing the resultant mixture through a cooling zone under conditions of agitation to reduce the temperature thereof below 160 F., and finally milling the product for a sulficient time at a temperature below 160 F. to eliminate syneresis and produce stability in the finished grease.

3. The process of preparing lithium grease comprising forming a slurry of lithium stearate and mineral oil containing substantially all the lithium stearate and a portion of the oil desired inthe finished grease, raising the temperature of the slurry to a temperature consistent with complete solution of the lithium stearate in the oil and above about400 F. to completely dissolve the lithium stearate in the oil, adding the remainder of the oil desired ill the finished grease under mild substantially shear-free agitation, the added oil having a temperature closer to room temperature than to the solution temperature and selected with regard to the proportionate amount of the oil added in this step to produce a resultant temperature of the mixed oil and slurry of between about 230 F. and 310 F., passing the resultant mixture through a cooling zone in contact with a heat transfer Wall under conditions of agitation to reduce the temperature thereof below 160 9 F., and finally milling the resultant grease at a temperature below 160 F. for suflicient time to eliminate syneresis.

References Cited in the file of this patent UNITED STATES PATENTS 2,363,013 Morway et a1 Nov. 21, 1944 2,397,956 Fraser Apr. 9, 1946 2,433,636 Thurman Dec. 30, 1947 10 Beerbower et a1. Ian. 13, 1948 Ashburn et a1. Sept. 28, 1948 Ashburn et a1 Sept. 28, 1928 Puryear et a1 Sept. 28, 1948 Puryear et a1 Sept. 28, 1948 Hetherington Feb. 8, 1949 McCarthy Jan. 1, 1952 Matthews et a1. Feb. 24, 1953 Jones et a1 Sept. 15, 1953

Claims (1)

1. 2. THE PROCESS OF PREPARING LITHIUM GREASE COMPRISING FORMING A SLURRY OF LITHIUM STEARATE AND MINERAL OIL CONTAINING SUBTANTIALLY ALL THE LITHIUM STEARATE AND APPROXIMATELY HALF THE OIL DESIRED IN THE FINISHED GREASE, RAISING THE TEMPERATURE OF THE SLURRY TO A TEMPERATURE CONSISTENT WITH COMPLETE SOLUTION OF THE LITHIUM STEARATE IN THE OIL AND ABOVE ABOUT 400* F. TO COMPLETELY DISSOLVE THE LITHIUM STEARATE IN THE OIL AND FORM A HOMOGENEOUS SOLUTION FREE FROM UNDISSOLVED LITHIUM STEARATE PARTICLES BY PASSING THE SLURRY IN A THIN LAYER UNDER AGITATION IN CONTACT WITH A HEAT TRANSFER WALL CONTINUOUSLY MIXING THE REMAINDER OF THE OIL DESIRED IN THE FINISHED GREASE WITH THE HOT SOLUTION UNDER CONDITIONS CONDUCTIVE TO MIXING WITH A MINIMUM OF SHEAR TO PROVIDE INTIMATE MIXING WITHOUT MICELLE DISRUPTION, THE ADDED OIL HAVING A TEMPERATURE SUCH AS TO PRODUCE A RESULTANT TEMPERATURE OF THE MIXED OIL AND

Images