CA1057280A - Centrifugal-type liquid film-particulates mixer - Google Patents

Abstract

ABSTRACT OF DISCLOSURE

A mixing bowl having an outwardly flared inner surface is rotated around its axis at a speed which is great enough to cause a film of liquid within the bowl to be moved upwardly by centrifugal force to the rim of the bowl. A liquid is introduced into the bottom of the bowl at a rate that permits an unbroken film of liquid to form within the bowl and move from the bottom to the rim. Particulate material is uniformly distributed in a radial direction within the bowl to contact the liquid film and mix therewith. The rim of-the bowl is shaped to interact with an adjacent stationary surface to shear the liquid and particulate material mixture to increase the uniformity of the mixture. A basin is positioned around and under the rim of the mixing bowl to collect the mixture as it is thrown off the outer edge of the rim.

Description

~S7'Z1~30 B_ck$round of t~e`Invention This invention relates to apparatus for mixing piarticulate material '~
in a liquid. In the past, particulate material and liquids- were mixed to-gether in a common vessel by means of a mechanical agitator within the vessel which stirred the mixture until it reached the desired degree of uniformity, ~t which time the mixture was removed from the vessel and a new charge of liquid and particulate material were introduced therein. However, this pro-cedure is time consuming and has to be carried out in batches rather than ; continuously. Also~ some dry particulate materials are very difficult to wet. -~
The dry particles tend to agglomerate with each other, and the liquid con- ;~
tacts the outside of the agglomera~ion, but does not penetrate to wet the inner particles. When mixed in tanks br mechanical agitators, a long time is ; needed to break up these agglomerations and wet all particles.
Centrifugal mixers have been proposed in the past in which par-ticulate material falls upon a rotating cone and is flung by centrifugal force against a film of liquid that is moving downward under the force of ~ -gravity over a stationary cone that surrounds the rotating cone. The mixture - !
; of liquid and particulate material is then passed through a rotary mixing ~-disc halring intermeshed teeth which shear the mixture and increase its uni- ' 2Q formity as regards uniformity of mixture with particulate material that tends to agglomerate and has the additional drawback that the feed rate is deter-mined by a gravity feed of the liquid down a cone of fixed slope and thus the -- ''~
'j feed rate cannot be conveniently ad~usted without changing the thickness of ' the film. ~'~
Summary'of'thé'Invention ~
In accordance with this invention there is provided apparatus for -~ -mixing liquid and particulate matter comprising a mixing bowl having a verti-cal axis, means for rotating said bowl about its axis at a speed sufficient '~ ;~
to cause a liquid therein to be moved by centrifugal force up the inner 3~ surface of the bowl to the rim thereof, means for introducing a liquid into .' ' ; ' ~' ,.

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said bowl at a rate that permits an unbroken film of liquid to form on the lnner surface of the bowl~ means or introducing particulate material in a path having a component of radi.al motion into said film of liquid and abov~
the place where said liquid enters said bowl, and means for collecting the mixed liquid and particulate material at the rim of said ~owl.
In the preferred em60dimentl the inner surface of the bowl is para-bolic in shape in the zone where the dry particula~e material ~ ;

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is introduce~^~ into the liquid, and the rim of the bowl is shaped to form a sh~ar rLng which interacts wi-th an adjacent stationary shear ring to shear the mixed liquid and par-ticula-te material to increase the uniformity of the mixture.
5 DQS crip-tion of the Drawings Fig. 1 is a longitudinal sectional view of -the preferred ~
embodiment of the invention. r,Fig. 2 is a cross-sectional view taken on the line 2-2 of Fig. 1.
; 10Fig. ~ is a fragmentary cross-sec-tional view taken on the line 3-3 of Fig. 1.
Fig. 4 is a diagramatic longitudinal sectional view of a ~ -dry particulate material feed system for the embodimen-t of Fig. 1.
~, Fig. 5 is a diagramatic longitudinal sectional view of an 15 alterna-te dry particulate material feed system for the embodiment `
of ~ig. 1.
Fig~ 6 is a fragmentary plan view o~ the stationary shear ~ ring shown in Fig. 1.
; Figo 7 is a cross-sectional view taken on the line 7~7 of 20 ~?ig~ 6 Fig. 8 is a~fragmentary plan view of the rotatable shear ring ~`
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shown in Fig. 1.
Fig. 9 is a cross-sectional view taken on the line 9-9 of ` Fig. 8. ~ ~ .
25 Description of the Pref red Embodiment ~.,;

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Although the disclo3ure hereof is det;ailed and exac-t to enable those skilled -in the ~rt -to practice the invention, the physical embodiments herein disclosed merely exemplify the in-.vention which may be embodi.ed in other ~pec-Lfic structure. While the best kno~n embodiment has been described, the details may be changed without departing from the invention, wnich is defined by ths claims Referring to Figs. 1 and 2, a mixing bowl 10 which has an outwardly flared inner surface 12 is formed by a stainless steel body portion 14, a stainless steel bottom portion 16, and a stain-less steel rim portion 18 which are welded together to form a so1id stainless steel bowl struc-ture. The outward flara of inner surface ~-12 is pre~erable but not necessary since the invention will work Iwith a cylindrical inner surface or an i.n~ardly tapered surface. ~ -:l 15 ~ottom portion 16 has a central sleeve 20 which is splined to receive the splined portion 22 of a rotary drive shaft 24. Drive shaft 24 is rotatably mounted in a housi.ng 26 by conventional means including bearings 28 and is rotated by drive means 30.at a speed which is great enough t~ cause a li~uid film on the inner : 20 surface 12 of mixing bowl 10 -to be moved upwardly by centrifugal .
.Iforce along inner surface 12 to rim portion 18.
Liquid is introduced into mixing bowl 10 from an inlet port 32 which communicates into a c~lindrical chamber 34 formed by a :
hollow cylinder ~5 below bowl 10. Cylinder 35 is supported by ;~, 25 housing 26 and is sealed at its bottom by rotary seal 36 and at ':~
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its top rotary sQ~ 7. L,i.quid ~ravels up-.Ja ~ly from chamber ~4 -throu~h openings ~8 in the bot-tom portion 16 of mixi.ng bo~
10. The liquid i5 driven b~ a p~p 40 wh-ich pumps the liquid at ~n ~ a predetermined rate which permits ~ unbroken liquid ~ilm to form on the inner surface 12 of mixing bor~l 10 and to move from the . -~ :
bottom of bowl 10 to the rim 18 thereof. The rate at which liquid :~
is introduced may be vari.ed over a wide range depending on the desired effect. A disc 41 is clamped -to the top of sleeve 20 and extends almo3t to the inner surface 12 of mixing bowl 10 .
to cause the liquid to disperse itself as a film on the inner surface 12. ~:
Drive shaft 24 has an upwardly extending portion 42 above 51e eveS
splined portion 22 which supports three spacer ~he~ve 44 and 45 and 47, A slinger disc 46 is mountsd between sleeves 45 and 47.
Spacer sleeve 47 is rigidly a-t-tached to shaf-t 42.by a nut 48 and rotates with shaft 42, ~anes 50 are attached to sleeve 47 above slinger disc 46 and project radi~lly therefrom. A tube 52, which is supported on a bowl cover 54, surrounds vane~. 50 a~
bove slinger disc 46, ~anes 50 are not essential to the inventi~n . ..
~,.20 but are pre~erable because they help spread the particulate material on slinger disc 46. If desired, slinger disc 46 could .
be rotated independent of bo-~l 10 from ab~ve or thro~gh a concentric lower shaft. ~;
The length and number of sleeves 44 and 45 can be varied to adjust the position of slinger disc 46. Alternately9 other . :, ' ~,' '~
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~572~313 suitable a^ljustmen-t mean3 cfln be emplo~ed.
In ths opara-tio~ of thi.s embodimen-t, dry p~r-ticula-te material i.s fed do~n tube 52 and falls on slinger disc 46, . which throws it by centrifugal force o~-twardly in a path having a component of radial motion toward the inner surface 12 of mixing bowl 10. Ths par-ticulate material s-trikes the liquid film on inner bowl surface 12 and is entrained thereby and is carried up-~ardly in tha moving li~uid film.
In the general form of the invention, means is provided to collec-t the mixed liquid and partieulate material as it is thrown : -off the rim o-~ the rotating mixi.ng bowl 10 due to centrifugal .
~orce. In this partieular embodiment, the eollecting means eom-prises a basin 55 which includes a hollow cylinder 56 having a bottom 58 which is supported on housing 26 and having a eover 54 w'nich is removably supported on cylinder 55 by wing nuts 50.
i A tangential outlet port 62 is formed in the bottom 58 of basin In this embodiment, tha rim portion 18 of mixing bowl 10 ,.
has a shear ring 64 integrally ~ormed therewith whieh co~cts with ' 20 a stationary shear ring 66 on basin eover 54. Shear rings 64 l and 66 eaeh have a plurality of concentrie cireular teeth 68 , ;, whieh are radially separated by cireular grooves 70. Grooves 70 are wider than teeth 68 to permit shear rings 64 and 66 to be meshed with a small spaee between opposing teeth and grooves as shown ~i 25 in Fig. 1 with the teeth 68 of one shear ring extending into the ' .~ ~

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groov~s of` the other shear :ring.
An annular ~uard ri.ng 71 is pr~ferably ~ttached to ~asin ~ :
cover 54 to prevent mixed p~rticulate material and liquid fro~
dropping do-~n on top of slin~er disc 46.
~5 As mixing bowl lO rotates 3 the mixture of liquid and par-ticulate material is moved by centrifugal force up a ramp 72 on movin~ shear ring 64 and into the area where shear rings 64 and 66 are meshed. The separation between the meshed portions of shear rings 64 and 66 is small enough to cause shearing of the liquid and particulate material mixture therebet.ween which re- ~ -sults in increased mixing and uniformity of the mixture. The sheared liquid and particulate material mixture progresses out- ~`
waraly across the teeth and grooves of shear rings 6L~ and 66 due tp centrifugal force being continuously sheared as it moves, until it;is thrown off the outermost tooth 68 of rotating shear ring ~ ~?
64. Tha liquid and parti.culate matter mixture then strikes vertlcal ..
: surface 74 of basin 55 and drops down into the bottom 58 of basin .`55.. It will be understood that the final character of the mix- ~-, , .. ture depends upon the ingredients. It may be a solution, sus :
.20 pen3ion, colloid or the like.
, Tne baslc a.dvantage of this invention is that the particulates ,! are uniformly introduced into -the liquid. The particulates tend :~
to break up when they fall down on top of slinger disc 46 and ;~
are uniformly radially dispersed into ths.liquid film by centrifugal~
force. Each particle of dry material is separated from other -~ .

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particles, and each ls brolght into contact with a specific small quantity of liquid in the liquid film oppo3ite ~linger disc 46 The inner surface 12 of bowl 10 is preferably parabolic in shape in the zone opposite the edge of slinger disc l~6 where the particulats material is initially mixed with the liquid film.
This is due to the fact tha-t rotation of mixing bowl 10 ~auses the inner surface of the liquid film to tend to assume a parabolic form due to the forces of rotation and gravity and also tends to :
approximate the shape of the inner surrace 12 of bowl.l0. The ~-parabolic shape of inner surface 1~ iS7 however, an optional .
feature of the invention rather than an essential feature.
One particular advantage of the invention is that the liquid feed rate can be increased without increasing the thickness of ~15 the liquid film as was necessary in the prior art centrigugsl mixer discussed previously. Increasing the rotary speed of mixin~
bowl 10 tends to increase the upward velocity of the liquid ` ;~
film which makes possible a higher feed rate without an increase in liquid film thickness. This makes possible uniform introduction :20 of particulates at higher feed rates than has been hitherto possible. ~ -Some mixing takes place in the liquid film on theinnersurface 12 of bowl 10 due to turbulent shear in the film, and hence shear rings may not bs needed for some applications of th~
~ invention. Conversel~, the shear rings disclosed may not provide enough shear for other combinations, and additional shear teeth or - , : .'.. , ~.:;
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, area can be prQvicled. Tln~ gap between shear rings c~n also be varied to vary -the shearinr,. The speed of mixing bowl 10 and flow rates of the liquid and particulate material may be varied : to pe~mit better dry material control or better liqu-ld film ~ ;~
control.
The mixing ac-tion o~ shear rings 64 and 66 can be augmented by cuttin~ radial notches 76 and 78 in teeth 68 as shown in Figs.
6-9. Radial notches 76 and 78 each extend half way throug'n the corresponding teeth 68, as shown in Figs, 7 and 9, The lines '~ of notches 78 in stationary shear ring 66 extend radially with respect to the center C (Fig, 6) of shear ring 66, but the lines of notches 76 in rotating shear ring 64 are radially skewed at an angle A (Fig, 8) with respect to adjacen~ radii thereof to prevént material from passing directly through the lines of . .
,, notches 76 and 78 when they are substantially aligned with each other. Also, there is one less llne of notches 76 ~n there .
. are llnas of notches 78 to prevent all the lines of notches~from being aligned at the same time. rhus notches 76 and 78 agitate the mixture betwsen shear ~ngs 6L~ and 66 and increase the uniformi-ty of mixture without allowing the mixture to move ~ i directly along the radial lines formed by notches 78. However, although notches 76 and 78 are preferable in some applications of th3 inventi~n, it should be understood that they are not ..
essential.
: Fig. 4 shows one~suitable feed rarrangement for the dry j :25 particulate material in this embodiment of theinvention, The .:~ , ' ' '.. ~

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dry particulate mat~ri.al. is contained in a conventional hopper 80 (Fig. 4) which has a co~venti.onal feed screw ~2 in i-ts bottom that is rotatably ino~ted withirl a feed tube 8~. Feed screw 82 is rotated at a predetermined speed by a conventional motor and gear train which are not shown in the drawings. Feed tube 8~
is directly connected at its end to tube 52, and the d~ particu-late material which is formed by feed screw 82 out the end o~ feed tube 84 drops down tube 5'2 on-to slinger disc 46 Some mixtures -tend to allow air to be entrained in the fluid-particulate mîxture. To minimize this effect, all joints of the mixer are preferably sealed off to prevent entry of air.
However, in this case, the centrifugal action of mixing bowl 10 and shear rings 64 and 66 act as an air pump which tends to create a low pressure area in the center o~ bowl 10~ and this tends to pull dry particulate matter out of feed tube 84 faster than it is~ `.
required due to the fact that there is atmospheric pressure on the top of the dry particulate material in hopper 80. To circumvent this pumping action, a sealed top 86 (~ig. 5 ) can be mounted on top o~ hopper 80 and a sealed conduit 88 can be coupled ~rom the top of tube 52 to the top o~ hopper 80 above th~ level o~ ~he dry:
: 20 particulate material therein. This equalizes the pressure at the -;
-: top o~ the particulate material and in the center of mixing bowl 10 to prevent the pumping action for the dry particulate.material.
It should be understood,however7 that the sealed arrange~
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ment discussed above is not essential to the invention since the ~ :
problem of air entrainment doss not occur in all app1ications of "~ ` . . . .
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Claims (20)

I CLAIM:

1. Apparatus for mixing liquid and particulate matter comprising a mixing bowl having a vertical axis, means for rotating said bowl about its axis at a speed sufficient to cause a liquid therein to be moved by centrifugal force up -the inner surface of the bowl to the rim thereof, means for introducing a liquid into said bowl at a rate that permits an unbroken film of liquid to form on the inner surface of the bowl, means for introducing particulate material in a path having a component of radial motion into said film of liquid and above the place where said liquid enters said bowl, and means for collecting the mixed liquid and particulate material at the rim of said bowl.

2. The apparatus of claim 1 wherein the inner surface of said mixing bowl is approximately parabolic-in longitudinal sectional shape at the location where particulate material is introduced into said liquid.

3. The apparatus of claim 1 and further comprising a first shear ring on the rim of said mixing bowl and a coacting stationary shear ring opposite said first shear ring for shearing the mixed liquid and particulate matter to increase its uniformity.

4. The apparatus of claim 1 wherein said means for introducing a liquid into said bowl comprises means forming a chamber below said bowl, openings in the bottom portion of said bowl communicating into said chamber, and means for pumping said liquid into said chamber and through said openings into the bottom of said bowl

5. The apparatus of claim 4 and also comprising a disc supported within the bottom portion of said bowl in a position which allows the disc to assist liquid which is introduced into the bowl beneath the disc to form a film on the inner surface of the bowl above the disc.

6. The apparatus of claim 1 wherein said means for introducing particulate material into said film of liquid within said bowl com-prises a slinger means rotatably mounted within said bowl, means for rotating said slinger means, and means for dropping particulate material on said slinger means.

7. The apparatus of claim 6 wherein said slinger means is a slinger disc.

8. The apparatus of claim 1 wherein said means for collecting the mixed liquid and particulate material comprises a basin surrounding the rim of said bowl.

9. The apparatus of claim 1 wherein said means for rotating said bowl comprises a drive shaft attached to the bottom portion of said bowl and means for rotating the shaft and bowl.

10. The apparatus of claim 9 wherein said drive shaft extends within said bowl and wherein said means for introducing particulate material into said film of liquid within said bowl comprises slinger means connected to said shaft within said bowl, and means for dropping particulate material on said slinger means.

11. The apparatus of claim 10 wherein said means for dropping particulate material on said slinger disc comprises a sleeve mounted above said slinger disc and means for feeding particulate material into the sleeve.

12. The apparatus of claim 6 and further comprising means for adjusting the vertical position of said slinger means.

13. The apparatus of claim 3 and further comprising a stationary cover plate mounted over said mixing bowl, said stationary shear ring being on said cover plate.

14. The apparatus of claim 3 wherein each shear ring contains circular teeth which are separated by circular grooves.

15. The apparatus of claim 14 and further comprising circum-ferentially spaced radial notches in the teeth of both shear rings for increasing the mixing action of said shear rings.

16. The apparatus of claim 14 wherein said notches in the teeth of both shear rings are arranged in radially extending lines, the lines of notches on one shear plate being skewed with respect to the lines of notches on the other shear plate to prevent the fixed fluid and particulate material from flowing in a straight line down said lines of notches when they are substantially aligned.

17. The apparatus of claim 15 wherein there is at least one less line of notches on one shear plate than on the other to prevent all of the lines of notches from being simultaneously substantially aligned at the same time

18 The apparatus of claim 10 and also comprising a guard ring attached to said cover plate and extending downwardly therefrom over said slinger means to prevent mixed fluid and particulate material from dropping down on said slinger means.

19. The apparatus of claim 6 wherein said means for dropping said particulate material on said slinger means comprises a hopper for containing a supply of said particulate material, a feed tube extending from the bottom of said hopper to a position above said slinger means and a feed screw within a portion of said feed tube for moving said particulate material therethrough.

20. The apparatus of claim 19 wherein said mixing bowl is sealed to prevent entry of air therein, and wherein said hopper is sealed to prevent entry of air therein, and further comprising a sealed conduit coupled from the central portion of said bowl to said hopper at a point above the level of the particulate material therein to equalize the air pressure in the center of said bowl and the top of said hopper to pre-vent excess particulate material from being drawn into said bowl due to-low air pressure therein