US2491231A - Centrifugal homogenizer - Google Patents

Description

Dec. 13, 1949 P, M TRAvls ETAL 2,491,231

CENTRIFUGL HOMOGENI ZER Filed Feb. *10, 1947 1N NTORS PterceM.r vzs M Chael mellorl ATTORN EYS Patented Dec. 13, 1949 Tudor, Clifton, N. J., assignors to Travis Colloid lClifton, J., .a corpora- Bispersicn Co., Inc.,

:tion of New Jersey Application February 10, 1947, Serial No. '727,486 i 3 Claims.

This invention relates to mixers, particularly to homogenizers or :devices for mechanically producing emulsions from immiscibl-e liquids such as fats or oils in water and for .similarly producing fin-e suspensions from `mixtures of liquids and solids.

Homogenizers of the pressure type must w1thstand rpressures .of the order of from 13000 to 5000 pounds per square inch, and are therefore machines `of weight and cost out of all proportion to their output. Such machines are also costly in upkeep. since :they require regrinding of the rapidly wearing pressure valves .and periodic repacking of the pumps, especially when food products are treated, since harmful bacteria tend to propagate in the packing.

Homogenizers Lof the rotary type-that include two closely adjacent .plates or .nesting cylinders .or cones at least one .of which is a rotor, require a high speed of operation and a'large diameter of rotor so that the mixture 'which :must be subjected to treatment over 4a period .of time suflicient to obtain proper dispersion or emulsiiication, .does not traverse the course along the rotor too rapidly for the hydraulic shearing action required for thorough hornogenization. This `necessitates correspondingly high power consumption and heavier and more expensive parts to withstand :the stress and .strain of operation. Attempts to treat viscous substances `in this type of machine .may fail. due .to the/excessive frictional heat evolution and consequent injury to the material being treated.

The use .of an impeller in conjunction with a stator and a truncated conical rotor, to force the material against the .centrifugal force created by the rotor to give a longer period .of treatment and dispense with the need for increased speed and size of the rotor has the disadvantages of requiring an increase in power and more complicated construction.

In homogenizers of the rotary or centrifugal type, the liquid inthe feed bowl rotates and forms a vortex in the center thereof which sucks air into the mixture. This results in excessive foaming and forces the fat or .solids to the top of the mixture so that homogernzation is not complete. That difficulty is not completely overcome by attaching baffles to the side of the feed bowl, and such baffles moreover render difiicult the cleaning of the bowl.

It is among the objects .of this invention to provide a homogenizer or super-mixer of the rotary type that is relatively inexpensive, light in weight, compact, of relatively few parts and of rugged construction, simple to assemble Vand use, efficient in output on low power consumption, easy to clean and service and not likely to -get `out v'of order, that keeps the contents thereof from spilling over, and in which the same constant-speed 2 conventional drive motor may be utilized for direct drive of rotors for any of various viscositles of the material to be treated.

Amongv the features `of 'this invention isa feed bowl having -a baffle deflector screen at the bottom outlet thereof and aa substantially cylindrical frame afllxeol to the bottom of said bowl, said frame having an annular concave stator unitary therewith at the lower end thereof which encompasses and is uniformly spaced from a horizontal rotor rotatably mounted on lthe base of the device.

In a preferred construction the cylindrical fram-e has an annular flange extending radially outward at the bottom rim thereof, which is .affixed to the base Aof the device in such manner as to compress a gasket thereagainst and provide a liquid tight connection. In addition, the rotor and the base have on their adacent surfaces appropriate configurations encompassed by said gasket and which afford a centrifugal seal therebetween eective when the rotor is revolving. A collector duct is provided on the inner wall of the stator by means of which the treated liquid may be withdrawn from :the device.

In the accompanying drawings in which is shown'one or more of various possible embodiments of the several features -of the invention,

Fig. '1 is a longitudinal sectional view ofthe device,

Fig. 2 is a side elevation of the rotor,

Fig. 3 is a plan view of the baiiie deflector screen. Fig. 4 is a fragmentary view of another embodi ment of the lcentrifugal seal, and

Fig. 5 is a View, similar to Fig. `4, .of 'a third embodiment of the centrifugal seal.

Referring now to the drawings, the mixing machine preferably comprises a base I0 having an opening I I therethrough in which is journalled a vertical `drive shaft i2. A bearing I3 seated in a, cavity le beneath base I0 and coaxial with lopen-- ing I I, surrounds the shaft to afford almost frictionless rotation thereof. Drive shaft l2 has a frustro-.conical upper end I5 rising from base .YI-II over which is removably fitted the .conical bore 'H of a horizontal rotor I6. The rotor is retained in pla-ce by ascrew I8 which passes through washer Il?! into threaded opening 20 in `the shaft I2. Screw 1.8 lis threaded opposite to the direction of rotation of the shaft .so as not to become loose while the mixer is operating. Rotor IB is .so positioned on shaft i2 that its vis not in contactl with the base .I 0, thereby avoiding friction and wear of the parts.

Shaft I2 and rotor It thereon are preferably directly .driven by an eiectr'ic motor (not shown). In th-e .case of small rotors of i3 l/g :to 4" diameter at the base :and 13" .thickness Aor less, it has been found that BA H. P. motors .of the conventional universal .series wound type, and of `a speed of `rotation preferably from 10,000 to .14;000

3 R. P. M. are adequate for the purpose. A peripheral speed of approximately 9,000 feet per minute is thus effected at 10,000 R.. P. M. which is adequate for making fine emulsions.

In a preferred embodiment of the invention, the rotor comprises a horizontal member 2|, the bottom diameter of which is greater than the top diameter, as shown in Figs. 1 and 2. The periphery of the rotor is convex as at 22 and in axial section may be along any of a wide variety of curves. Desirably that curvature may be an arc of a conic section, usually of an ellipse, or of a parabola, or a circle or hyperbola. In the embodiment shown, the peripheral surface of the rotor is the segment of an ellipsoid of revolution, the minor axis C-D of which is two-thirds that of the major axis A-B.

In the preferred embodiment shown in Fig. 2, rotor 2| has on its undersurface near the periphery thereof and unitary therewith, an annular ridge 24. This ridge extends with clearance into a corresponding annular trough 25 in the base to form a centrifugal seal.

Other embodiments of this seal are shown in Figs. 4 and 5. In Fig. 4, base I0 has an upstanding annular ridge 2B which fits with clearance into an annular groove 21 on the undersurface of the rotor. In Fig. 5, base I has an annular groove 28 and an annular ridge 29 in juxtaposition to each other, which extend with clearance relative to complementary congurations on the undersurface of the rotor I6 to form the centrifugal seal.

The seal prevents liquid from passing under the rotor and coming in contact with shaft I2 or bearing I3 which are exposed to dirt and dust from the outside. With the use of the centrifugal seal the liquid treated only comes in contact with surfaces not exposed to contamination and which preferably are of stainless steel or Monel metal that are easy to clean and resistant to oxidation.

Base l0 has an annular iiange 30 extending radially outward therefrom to which is alxed by screws 3l the radially extending flange 32 of a substantially cylindrical frame 33. A rubber or plastic gasket 34 seated in annular grooves 35 and 36 in adjacent faces of flanges 3l] and 32 respectively, serves to make a liquid tight seal between the base and the frame.

Frame 33 has a concave annular stator portion 31 at its lower end extending upwardly from ange 32 and conforming in configuration to the convex periphery 22 of the rotor and equallyspaced therefrom with a clearance of from .002 to .008 of an inch.

To aid in the shearing action in the embodiment herein shown, the rotor preferably has a plurality of grooves 23 on its periphery inclined at an angle of about 15 degrees to the axial plane thereof, preferably not more than 3A; inch apart and not exceeding 1/8 inch in depth at the midpoints thereof and tapering off into the smooth top and bottom of the rotor, while the concave stator portion 31 of the frame 33 has a smooth face. However, the stator and rotor may be smooth or grooved or partly smooth and partly grooved depending upon the viscosity of the liquid being treated.

As the clearance 38 between the concave stator portion 31 of frame 33 and the convex periphery 22 of the rotor is extremely small, the liquid being treated will pass therethrough as a nlm. The globules or solid particles closest to the rotor will be hurled at a greater speed than those near the xed stator. Consequently the globules or particles will rub against each other and against the stator, causing a splitting or shearing action to take place.

As the liquid passes through the clearance or shearing nozzle 38, the centrifugal force of the rotor will hurl each globule or particle therein outward in a horizontal plane tangent to the periphery of the rotor. This horizontal force has a downward component tangential to the periphery of the rotor. As a consequence the course of the globules or particles will be in a long substantially helical path downward until the entire shearing nozzle 38 has been traversed.

By using a rotor the periphery of which is convex, the tangential component of force on and direction of movement of each particle will change in downward inclination as the particle progresses through the shearing nozzle 38. By reason of the progressive change in downward direction of motion of the particles (as contrasted with the action of a conical nozzle in which the inclination is constant and along the side of the cone), enhanced shearing action results and at the steeper portion of the convex periphery, near the lower edge of the rotor, as shown in Fig. 2, the pitch of the helix becomes quite low with consequent great increase in the length of the helical path through the shearing nozzle.

Thus the steeper the slope or curvature of the rotor periphery, the slower the traverse of a given material through the shearing nozzle at a given speed of rotor rotation. The embodiment of Fig. 2 would therefore be used for treatment of a material of relatively low viscosity, such as milk, to insure a suiciently long traverse thereof through the shearing nozzle. On the other hand, when a heavy or highly viscous material is to be treated, a rotor periphery of less steep slope or curvature would be used, as for instance the segment immediately above that shown at 23 in Fig. 2. For by reason of its high viscosity, the material would not be hurled through as quickly as more fluid material.

The processed liquid which is passed through the clearance or shearing nozzle 38 between the stator and rotor is collected in an annular collector duct 39 at the mouth of gap 38 on the inner side of the concave stator 31, and is discharged from the duct 39 through a laterial passageway 40 extending through a boss 4I unitary with the stator 31. A valve member 42.is threaded into said passageway 4B at the outer end thereof for controlling the flow of the processed mixture.

The substantially cylindrical frame 33 has, at its upper end, an outwardly turned peripheral ange 43 to which is aixed by means of screws 46, the outwardly turned ilange 45 on the bottom of the feed bowl 44 of substantially cylindrical form. Between ilanges 43 and 46 is clamped a rubber or plastic gasket 41, and seated in an annular groove 43 on the surface of flange 43 and encompassed by gasket 41, is a bale deflector screen 48. The deector comprises a circular plate 49 having a diametral vane 5I axed thereto on each side thereof, said varies being at right angles to each other and crossing at the center of the plate. Each vane is preferably an angle bar of length less than the bore of the frame, and the two vanes divide the screen into quadrants. Each quadrant preferably has a plurality of holes 50 therethrough which are from 1A; to 1A, inch in diameter depending upon'the viscosity of the liquid being treated.V With very viscous mixtures,

a baille plate having one or more of the quadrants removed, may be used.

Operation Starting out with the machine empty, the electric motor drive shaft l2 is started. With the rotor revolving, the mixture to be blended is poured into the bowl which is kept three-quai'- ters full during an entire run. The mixture passes through the openings 50 on the baiiie plate to drop upon the upper face of the rotor I6 and ll the cylindrical frame. As the rotor revolves at high speed, the liquid thereon will be hurled around. However, the baiiie plate and the varies 5| thereon will brake the whirl of the liquid in the bowl, preventing it from spilling over the sides thereof.

The liquid that has passed through the clearance or shearing nozzle 38 will pass into the annular collector duct 39 from which it is drawn off through passageway 40. The centrifugal seal 24, (Fig. 1) will prevent any of the liquid iiowing beneath the rotor from coming into contact with the rotor shaft I2 and its bearing I3, for as the rotor is revolving ai; high speed any liquid that comes into contact with annular ridge 24 would be thrown radially outward and back into the collector duct 39. It is important, however, that in the operation of the machine the bowl be empty until the rotor is operating at high speed in order that the centrifugal seal be fully operative, otherwise the liquid would flow through the clearance between the stator and the rotor and pass between the rotor and the base, thereby coming in contact with the drive shaft and the bearing.

The mixer is kept in operation until the run is completed, at which time, while the machine is still running, it is washed with water or suitable -cleaning fluid and then shut off. By operation in this manner the machine is thoroughly cleaned and ready for the next run. If desired, the machine may readily be taken apart in a few minutes for cleaning or inspection, by removal of flange screws 3| and 46.

The mixer described herein has an output; of 125 gallons of homogenized milk per hour, using a horsepower motor. This is to be contrasted with the output of an impeller type homogenizer which required from to 35 horsepower for an output of about 250 gallons of homogenized milk per hour.

As many changes could be made in the above construction, and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

l. A rotary mixing machine comprising a feed bowl having an outlet at the bottom thereof, a removable baffle deflector screen covering said outlet, a substantially cylindrical frame affixed to said bowl beneath said defiector screen, said frame including an annular stator at the lower end thereof, and a rotor encompassed by said stator, said stator having a concavity forming a portion of an elliptical -curve and said rotor having a convex periphery forming a corresponding portion of an elliptical curve, a tangent to the ellipse at the lower portion of the rotor being substantially vertical and a tangent to the ellipse at the upper portion of the rotor being at a substantial incline.

2. A mixing machine comprising a substantially circular base, a vertical drive shaft rotatably mounted on said base and extending therefrom on both sides thereof, a rotor having a convex periphery and aixed to said shaft on the upper end thereof, a frame including an annular concave stator at the lower end thereof in juxtaposition to the periphery of said rotor and uniformly spaced therefrom, said stator having a concavity forming a portion of an elliptical curve and said rotor having a convex periphery forming a corresponding portion of an elliptical curve, a tangent to the ellipse at the lower portion of the rotor being substantially vertical and a tangent to the ellipse at the upper portion of the rotor being at a substantial incline, said frame having an annular flange extending radially outward from the lower rim thereof and affixed to said base, said frame being substantially cylindrical above said stator, an annular iiange at the upper end of said frame, a feed bowl affixed to said annular flange, and a baille plate interposed between said frame and said feed bowl.

3. A mixing machine comprising a substantially circular base, a vertical shaft rotatably mounted in said base and extending therethrough on both sides thereof, a rotor having a convex periphery and aixed to said shaft at the upper end thereof, said rotor having a plurality of grooves on its periphery, said grooves being tilted slightly from the axial plane of said rotor, a substantially cylindrical frame including an annular concave stator at the lower end thereof in juxtaposition to the periphery of said rotor and uniformly spaced therefrom, said stator having a concavity forming a portion of an elliptical curve and said rotor having a convex periphery forming a corresponding portion of an elliptical curve, a tangent to the ellipse at the lower portion of the rotor being substantially vertical and a tangent to the ellipse at the upper portion of the rotor being at a substantial incline, and an annular flange extending radially outward from the lower rim of the frame and aflixed to said base, an annular duct on the inner side of said concave portion, a boss on the exterior of said concave portion having a lateral bore therethrough leading from said duct, an annular iiange at the upper end of said frame, a feed bowl aiiixed to said annular flange, and a baffle deiiector screen interposed between said frame and said feed bowl.

PIERCE M. TRAVIS. MICHAEL K. TUDOR.

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

UNITED STATES PATENTS Number Name Date 1,587,063 Austin June 1, 1926 1,626,297 Ramage Apr. 26, 1927 1,874,079 Black Aug. 30, 1932 2,083,171 Nester June 8, 1937 2,240,213 Fromm Apr. 29, 1941 2,424,932 Johasz July 29, 1947

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