US2478917A - Method and apparatus for making grease - Google Patents

Description

Aug. 16, 1949. I G. M. HAlN 2,478,917

METHOD AND APPARATUS FOR MAKING GREASE Filed Sept. 24, 1946 5 Sheets-Sheet l INVENTOR. G EORGE M. HAIN BY W ATTORNEY Au 16, 1949. G. M. HAlN 2,478,917

METHOD AND APPARATUS FOR MAKING GREASE Filed Sept. 24, 1946 3 Sheets-Sheet 5 INVENTOR. GEORGE M. HAIN ATTORNEY Patented Aug. 16, 1949 METHOD AND APPARATUS FOR MAKING GREASE George M. Hain, United States Navy Application September 24, 1946, Serial No. 699,068

6 Claims.

(Granted This invention relates to a method and apparatus for the manufacture of high quality greases by a continuous flow process.

The art of manufacturing high quality greases is recognized as a highly specialized phase of lubrication chemistry and is fraught with numerous difficulties. The control of sensitive variables must be closely maintained in order that operating conditions can be changed rapidly and accurately.

Continuous processes for grease manufacture generally include the successive steps of heating an intimately mixed slurry of prepared soap in a mineral oil or other base fluid medium to achieve complete solution of the soap therein, the sudden cooling of the solution thus obtained to form a gel, and the mechanical working of the gel to a grease consistency. Heretofore, both the apparatus and methods employed in such processes have in general proven unsatisfactory when applied to quality grease manufacture.

High-quality greases ar critical compositions comprising essentially loosely flocculated dispersions of tiny soap crystals in a fluid medium, the size and state of aggregation of the crystals having a pronounced effect on the physical properties of the finished grease. A microcrystalline soap structure of large inter-crystalline surface area is necessary in such a grease to hold the fluid phase in equilibrium and prevent its bleeding from the mass. However, none of the known continuous or semi-continuous processes for making greases are operative to produce the optimum microcrystalline dispersion of soap.

In the preparation of many greases having the desired microcrystalline soap structure, the transition from hot fluid to stable gel must be accomplished as quickly as possible, since slow cooling promotes crystal growth and therefore less interfacial area to hold the fluid. As an aid to the desirable rapid transition, the heating step should not be carried to a temperature materially beyond that needed to complete solution of the soap in the base fluid. Further, the cooling should proceed to equilibrium conditions at such a rate as to avoid the formation of coarse soap granules.

Accordingly, it is an object of my invention to provide a method and apparatus for the manufacture of high quality greases, such as lithium soap greases, by a continuous process which affords complete control of operating conditions at all stages.

Another object of my invention is to provide under the act of March 3, amended April 30, 1928; 370 '0. G.

a method and apparatus for the continuous manufacture of greases which method and apparatus create a condition whereby the grease is subjected to internal working in several successive stages. 7

It is another object of my invention to provide a continuous flow method and apparatus by which it is possible to convert a fluid grease formulation into a stable grease characterized by its stability and homogeneity,

Another object of my invention is to provide a simple apparatus for the continuous manufacture of high quality greases, which apparatus is characterized by its having a restricted cross section in its heating and cooling sections.

It is another object of my invention to provide an apparatus having heating and cooling sections wherein essentially film type heat transfer occurs and heating and cooling of the composition occurs at very rapid rates.

Further and more specific objects will in part be obvious and in part appear hereinafter.

My invention, accordingly, comprises the process of making high quality greases in continuous flow manner, which process includes the several steps and the relationship of one or more of such steps to each of the others, and the apparatus comprising successive mixing, heating, cooling, and working sections which possess the features of construction and combinations of elements exemplified in the following detailed disclosure. The scope of the invention will be indicated in the appended claims.

The process is carried out by preparing a fluid grease formulation which consists of the fluid base for the grease having suspended therein the soap thickener, a typical one of which is lithium stearate, and various balancing ingredients such as oiliness, oxidation inhibiting, rust inhibiting additives and the like as may be required in the final grease formulation. The fluid formulation is conducted through successive heating and cooling steps in a continuous flow method in essentially film form, so that the heating and cooling are characterized by being carried out as film heating and cooling heat transfer operations. Rather than heating and cooling a single large mass of fluid in a vat or conduit, a continuously flowing fluid having a cross section of the order of the thickness of a flowing film of the base fluid is subjected to the heating and cooling operations.

The apparatus in which the process is carried out is characterized by structure which maintains the flowing, fluid, grease formulation in the form of a fast moving film. It is further charcoil 38, water being introduced through the inlet acterized by being made up of small diameter 40, allowed to pass over and around the coil and thin-walled conduits in which the largest diam leave through the outlet 4 I. This discharge end ter is of the order of twice the thickness of a. of the cooling section is connected by a lead free flowing filmoi the base fluid, By employ- 5 througha alved; to a variable spe ear Dump ing sauch' restricted diameter throughout, and 43, Near this valve junction and alsoat the dismaintaining a high velocity of flow of the film charge (and 6f the 'pump 33 are connected other through the conduits, a precise control is main; sampling tubes 44 and 45, A pressure gage 57 i tained at a times Over the temperature of the 'aiso connected at the discharge end of this pump fluid, and in addition, the fiuid pagftj l la jb, i 10 which end is joined to the working section the the Cooling S a e Wh t is Converted to l; construction of which will be fully described hereis sub ec ed o internal shearing res whic inafter in connection with Figure 3. One end of imp t o t a Certain amellnt O'f Work during" a T junction 49 is connected to the discharge the thermal treatment qqitiQQfiHYe s i vi e oftheworking section, the other two ends ity of flow of the fluid through the heating e 15 being connected respectively through a valve cooling sections is matched to the heating 'cap'ac- 50 td a {iacuumizjng System 5 and through a ity and the cooling eapacityof h p atus, so i e 1- 52' to the-intake oi the gear pump as. lien is Closely Within few degrees of the 013171 valve 53 controls the flow of finished grease into t ct m v 20 the take-ofi tube 54 to th of e. Fiuie 2' 'th s n w l, 1 rent 6i [e the O QL l e le i disclosure when taken in conjunction with the aceomp n ng/ draw h i ,i a

Ffgufel. a c 'd "gram o'fan appa- 9 v diagram of a second 11 arac erlstic "Sft'he un ,7 A int .@ie 1ii iii 513. t. e em i the ho p WH m el WQ JIQF IFQ 'PL hi h r ei l e eaa i. vT o; heheatin ube described equivalent to t noeene i'ef ib fi u e. l. r u hfiaet aielt ilower el diiw t tafl maiyri pqrii ns g hi 1 1; as he. he t ng P SU-ISLPBQQ; 8 -.,.-Th tubes 68 are enclosed in a c insu ating material 68.v The tubes are elecifiurupQ ll. P? e Q eri 9 1 MW w I M t on 29. Jhaheat eaiin ffl i ubal-t IL-5 E unitislmas of; t

ap eiatee by o. q he ii e eetimi -s5. olui qe; is die-eh re s under. we eux fr m; heh a ine tui esnt aiheaiier .1 br uehlhi hit 1S @0 9 ed eano herh adsi p u a ty :.QQ mbes 1?. hav nethe, sameed mehs ou :aeth -h a ina tubes- Eac i fs he-p i ne be eie r asedm ialr r r ieual. Water-Jacket. lei-wh ch. sfitted; w h; a wa e ein et and azwat ncutlet 8L Jlfhewt in e me rom a condu t-. .i f out: lets 8i discharge into th epther conduit the w t m ly ystem. The, grea ecpmppsition d sch ed. f om; the Q o'f a bea. intoeth heaqe iilii n i ediu h arnum 5 and: edi e thee orkine; vic Bi vv Fi mers rti s 9i hafin shedi rea i mp t (m e ken fi een ian yo t9 thei e ntaelee h h-ea i e ballz hec valve"e ewhil ethe l r eor of anewlee. through the .ela b e 8$ to e ,ls rsiisfliimime i b cr y a 'B i the apparatus is placed in operatiom itiniaj lbe evac uated thro eh a valve e10 which connects to umpe l 1 t bi in 'thee qq ael ce ais, o he am? aresids I w larg'id ialn iie s meatoneenaatsioe cap 31 which hole through its; ce r 1ter, and atjheot plurality of small perforations over a central portionof a diameter matching the inlet is sandrwiched between the fiat surfaces of the flanges, gasketed, and secured firmly by the bolts 94 which pass through the plate and flanges and join the top and bottom sections. The fluid conduits of the apparatus may be used to connect the working means with the pump 43 shown in Figure 1.

With reference to Figure 1, in preparation for starting, the system is evacuated by means of any convenient pumping equipment 5i. When a substantial reduction of the air pressure in the system has been accomplished, valve 50 is closed and the cold slurry of soap and fluid, which has been maintained in a free-flowing state by means of the mechanical stirring apparatus, is pumped at a pressure of about 800 pounds per square inch into the narrow diameter tubing of the heating coil. Here, the accurate control afforded by the unique form of heating apparatus employed permits attainment of complete solution of the soap crystals in the base fluid medium just as the fluid is discharged from the heating coil. This hot solution enters the cooling coil under pressure where it is transformed quickly into a semi-rigid gel, which gel in its forced passage through the cooling coil is worked at least partially to a grease consistency by the severe shearing stresses set up in the narrow diameter tubing comprising the coil.

The rapid succession of heating and cooling steps occurring in the heating and cooling sections of the apparatus minimizes fire hazards and the possibility of oxidation of the hot fluid base and also avoids damage to the soap particles and additives in the composition. The rate of flow through the narrow diameter heating section is adjusted so that the total time of heating does not materially exceed about 15 seconds when a fluid is brought from an ambient temperature of about 70 F. to a maximum temperature of discharge from the heating section of about 480 or 500 F. The exact velocity of flow through the heating and cooling sections therefore will be fixed by the dimensions of the apparatus and the specific physical properties of the base fluid which fix those dimensions but will roughly approximate about 50 cubic centimeters per minute in a tube having a diameter of about one-quarter of an inch.

The cool, partially worked grease composition is picked up by the gear pump 43 shown in Figure 1 and pumped into the working section where it is worked to the consistency of a finished grease by being extruded through the finely perforated plate. The grease first passing the working section is recycled into the gear pump until the plumbing associated with this pump and the working means has been filled with grease and a head of grease has been built up sufficient to activate the preset ball back valve 53. Then, as grease continues to be forced out of the working means, which acts also as a reservoir for grease, a fixed minor portion is constantly taken off through the ball check valve as the finished product. The remaining rease is recycled into the pum and working section. By this method of constantly taking off only a small portion of finished grease and recycling the remaining portion, it will be apparent that each individual portion of finished grease has had at least several passes through the perforated plate of the working section.

During the process of manufacture, the occlusion of air to form detrimental pockets in the finished grease is substantially entirely prevented because of the high pressures employed, and the extensive working to which the grease is subjected.

Instead of employing the more or less conventional steam or water-jacketed pipe-still heating coils set in a furnace heated by coal, gas or oil fires, metal tubing, and preferably corrosion resistant stainless steel tubing, of very small diameter and wall thickness is employed and heated by an electric current. As seen from Figure l, the tubing is electrically connected across the secondary terminals of the power transformer 33. The current flowing through the tubing when the primary circuit of the transformer is energized produces heat at a steady even rate over the entire length of the coil. The rheostat 34 inserted in series with the primary windings of the transformer governs the amount of current flowing there and hence, :by normal transformer action, governs the amountof current induced in the secondary windings and flowing through the heating section. The rheostat thus serves as an effective and accurate temperature control of the heating means. Because the heat is generated directly and evenly in the tubing walls, and because the tubing is of such narrow diameter, substantially instantaneous heat transfer is obtained. Furthermore, local overheating or variations in rate of heating, both of which are detrimental to the attainment of good grease structure, can be avoided. Since any given slurry is flowing through the heating section at a rate fixed by the pumping means employed, it is practicable to regulate the heating so that the temperature needed for complete solution of the soap in the fluid medium may be reached close to the discharge end of the coil and not be exceeded to any appreciable degree. As stated above, this temperature may for certain soaps be as high as from about 480 F. to about 500 F.; but in general it will be slightly above 300 F.

Substantially instantaneous heat exchange is also afforded in the cooling section by virture of the employment of narrow diameter thin-wall tubing in its construction. It will be recognized by those skilled in the art that this point of control is very important with regard to the quality of grease produced. The solution must be cooled so rapidly that the fine soap crystals which precipitate and form the basis of a gel structure do not have time before equilibrium is reached to grow or agglomerate into the relatively large soap granules which permit the final grease composition to bleed. Furthermore, the solution must be cooled at the same rate throughout in order to produce a gel structure which is homogeneous D throughout.

My unique cooling means affords the operational control necessary to the accomplishment of these ends. In addition, it provides a means of at least partially working the semi-rigid gel to a proper grease consistency. As the gel is formed in the narrow diameter cooling section, it is forced rapidly through the tubing and tangentially against the inner walls thereof at high rates of shear. The gel structure is partially broken down to produce a composition which on leaving the cooling section has a grease texture. More extensive working of the grease takes place in the working section of the apparatus.

Because of the high operating pressures and the narrow diameter system employed in this continuous flow method of grease manufacture I have attained what is essentially a self working system which develops high rates of shear substantially throughout. In the working section the shearing stresses are magnified greatly as the grease compositions forced tlirou'ghthe tiiiyholes at the" perforated plate.-

- In describing the heating and'cooling sections of the apparatus, reference was" made to maintaihing a narrow diameter throughout these two sections preferably in the form of a narrow diameter tube which 'createda condition offiow-in the apparatus which-I" chose to calla forced-film new. The exact dimensions of the tube, that is, the tube diameter, are not critical but Shoilldbe of'the order of about two the free-flowing film of the base fluid and terraces greasefiuids this is less than one-half orthree eighths of an inch;

h To simplify a description of my apparatus and the operation thereof I have hitherto'spoken of a slurry as comprising merely a mixture of soap crystals ma base fluid medium It is to be understood that inaddition to the soap and base fluid constituents there may be present in the slurry any of the common balancing ingredients Suchas oxidation and corrosion inhibitors; oiliness and extreme pressure'additives, and polymer thickeners.

'Ihe-particular-soap and other additives are, in general, blended with the base fluid prior to its introduction into the apparatus. In other words, it is preferred that the compounding of the ingredients; including any necessary, chemical reactions, occurs outside the apparatus Using the apparatus described, and following the methods described, instrument greases of I high quality having various types of base fluids have been prepared by my continuous-process at a rate of about 120 pounds greases were all characterized by their being smooth homogeneous mixtures of abase fluid lubricant-with a'metallic soap and, when appro priate, various balancing ingredients. Various diesters and'othe'r synthetic fluids such as the silicones, hydrocarbon fluids and polyethylene'oxide fluids were used as base fluids; The dispersions of the-soap in the grease in all cases werenomm gene'cus and no objectionable base fluid sepaw tions occured even after months of standing in many'cases. Typical formulations which were prepared by the above methods and in the'above' d'escribed'apparatus are shown below in the't'abie.

times the thickness of per 8 hour day; The i terials thereby introducing a desirable factor of:

Aeration of the grease produced with the resale ant decrease in quality and'in'creasedtendency to bleed is'prcven'ted by using sures throughout the system;

' lit-will be apparent that manymodifications maybe made in my'invention Without departing from the scopethereoi= Accordingly, it'i's desired that the present disclosure be construed as illus--- trative tion. r r Y The'inven'tion described herein maybe manufactured and usedb'y or for the Government of of myinventio'n and not by way oilimitathe United States of'America for governmental- .p'unp'oses without the payment of any royalties thereon or therefor;

What is claimed is:

1; Apparatus for the continuous preparation of grease comprising a slurry mixing tank, a dis charge conduit from said tank, a-high pressure pump connected to said discharge conduit, a grease heating conduit connected to and electrically insulated from said high pressure pump,

an electrical heating circuit connected through said grease heating conduit, a heat insulating medium surrounding'said grease heating con duit, a grease cooling conduit connected to and electrically insulated from said grease'heating conduit, a cooling medium conducting jacket enveloping said grease cooling conduit, said heati {and said cooling conduits each being of a a; meter substantially twice the thickness of a free-flowing film or the base fluid of the slurry, asecond high pressure pump connected to the discharge side of said grease cooling conduit, a grease Working section connected to the discharge side of said second high pressure pump, said grease working section including a finely perforated membrane through which the grease is forced, and check valved means connected to said grease working section.

charge conduitfrom said tank, a high pressure Table V I Parts A.S.T.M. WgtPer No.- Components ,by; Pcnetra- 7 Cent Evan} Wgt. tion- Bleeding ration 2.. 4t cjrtiary-butyI-Q-Dhcnyl-phcnol 0.2 245 2 0.33'

(I -Z-ethylheXyl sebacat 34.8 di-Z-cthylhexyl adipate 52.0

. lithium stcaratefl nfl 14.0 I 4-tertiary-butyI-2-pllenyl-ph 0,2 7 v- H 3 sorbitan monoolcate 29 260 3.90 0.98

'polybutene (MW IZUOO). 1.0 did-ethylhexyl scbacateuens .i 82.8

My inventionlthuslprovidesza unique method and apparatus for the continuous manufacture of high quality" greases, whichzmethod ischar acterized by being: a continuous :process of forced-fi-lm-flow which works the grease-composition in all stages o'f-=its;rnanufacture.. The ap= paratus 'is correspondingly, a narrow diameter, self working', self =scraping system'inwhich high rates of shear within the composition are obtained. It alfordsi closecontrol of operational variables, and reduces the handling of raw mag pump connected to said discharge conduit,.a grease heating conduit connected. to and electrically insulated from said high pressure pump, an electrical heating circuit connected through said grease heating conduit, aheat insulating medium surrounding saidigre'ase heating con-- duit, a grease cooling conduit connectedto and electrically insulated from said grease heating conduit, a cooling medium conducting jacket enveloping said grease cooling conduit, said heat ing and said cooling conduits each being of a high Working pres grease discharge 2; Apparatus for the continuous preparation of grease comprising-a slurry mixing tank, a dis diameter substantially twice the thickness of a free-flowing film of the base fluid of the slurry, a second high pressure pump connected to the discharge side of said grease cooling conduit, a grease working section connected to the discharge side of said second high pressure pump, said grease working section including a finely perforated membrane through which the grease is forced, a recycling connection between the entrance and discharge sides of said grease work section, and check valved grease discharge means connected to said grease working section.

3. Apparatus for the continuous preparation of grease comprising a slurry mixing tank, a discharge conduit from said tank, a high pressure pump connected to said discharge conduit, a header connected to said high pressure pump, a second header, grease heating means connected between and electrically insulated from said headers, said grease heating means comprising a plurality of individual grease heating conduits and an insulating medium through which said grease heating conduits extend, an electrical heating circuit connected through each of said heating conduits in series, a conduit from said second header to a third header, a plurality of grease cooling conduits connecting said third header to a fourth header, individual cooling medium conducting jackets enveloping each of said grease cooling conduits, said heating and said cooling conduits each being of a diameter substantially twice the thickness of a free-flowing film of the base fluid of the slurry, a second high pressure pump connected to the discharge side of said fourth header, a grease working section connected to the discharge side of said second high pressure pump, said grease working section including a finely perforated medium through which the grease is forced, and check valved grease discharge means connected to said grease working section.

4. Apparatus for continuous preparation of grease comprising a slurry mixing tank, a discharge conduit from said tank, a high pressure pump connected to said discharge conduit, a header connected to said high pressure pump, a second header, grease heating means connected between and electrically insulated from said headers, said grease heating means comprising a plurality of individual grease heating conduits and an insulating medium through which said grease heating conduits extend, an electrical heating circuit connected through each of said heating conduits in series, a conduit from said second header to a third header, a plurality of grease cooling conduits connecting said third header to a fourth header, individual cooling medium conducting jackets enveloping each of said grease cooling conduits, said heating and said cooling conduits each being of a diameter substantially twice the thickness of a freeflowing film of the base fluid of the slurry, a second high pressure pump connected to the discharge side of said fourth header, a grease working section connected to the discharge side of said second high pressure pump, said grease working section including a finely perforated membrane through which the grease is forced, a recycling connection between the entrance and discharge sides of said grease work section, and check valved grease discharge means connected to said grease working section.

5. Apparatus for the continuous preparation of grease, comprising, a slurry mixing tank provided with a discharge conduit, a high pressure pump connected with said discharge conduit, a heating conduit connected to and electrically insulated from said high pressure pump, means for passing electric current through said heating conduit, a cooling conduit provided with a cooling medium conducting jacket and connected to said heating conduit and electrically insulated therefrom, said heating and cooling conduits being of a diameter not greater than approximately onehalf inch, a second high pressure pump connected to the discharge side of said grease cooling conduit, and a grease working section including a finely perforated membrane through which the grease is forced connected to the discharge side of said second pump.

6. Apparatus of the type defined in claim 5 wherein the worker section comprises two substantially symmetrical axially apertured flange members axially aligned with each other, a thin perforated metal plate positioned between the faces of said member in gasketed relation therewith and extending across said axial apertures, and bolt means holding said flange members in rigid, face-to-face relationship.

GEORGE M. HAIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,019,413 Batchelder Mar. 5, 1912 1,175,470 Perkins Mar. 14, 1915 2,257,945 Fraser Oct. 7, 1941 2,339,873 Morway et a1 Jan. 25, 1944 2,372,052 Beerbower et al Mar. 20, 1945 2,406,655 Bax et al Aug. 27, 1946 2,433,636 Thurman Dec. 30, 1947

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