US3747899A

US3747899A - Mixer

Info

Publication number: US3747899A
Application number: US00172107A
Authority: US
Inventors: G Latinen; M Latinen; L Carter
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1971-08-16
Filing date: 1971-08-16
Publication date: 1973-07-24
Anticipated expiration: 1990-07-24

Abstract

A housing and paddle assembly adapted for use in processing and mixing highly viscous fluids is provided. The mixer employs a paddle assembly which rotates about a horizontal axis and which has at least one pair of diametrically opposed blade members which helically extend along the shaft in an axial direction and which are slotted at diagonally opposite outside ends. In operation, the paddle assembly can sweep out substantially all of the housing interior and produce simultaneously in a fluid cyclical vertical displacement, rolling action, horizontal displacement, and, even, fold over action.

Description

United States Patent 1 Latinen, deceasedet a1.

[11] 3,747,89 [451 July 24, 1973 MIXER [75] Inventors: George A. Latinen, deceased, late of Springfield, Mass. by-May V.

Latinen, administratrix; Leo F. Carter, wilbraham, Mass.

[73] Assignee: Monsanto Company, St. Louis, Mo.

[22] Filed: Aug. 16, 1971 [21] Appl. No; 172,107

[52] us. Cl. 259/9 51 1nt.Cl 301:.1/04 [58] Field of Search 259/9, 10, 7, s, 259/5, 6, 109, no, 21, 22, 23, 24, 2s, 26, 43, I a 44, 4s, 46

[56] mum Cited UNITED STATES PATENTS 2,576,995 12/1951 Carve] 259/109 3,469,948 9/1969 Anderson 23/252 3,476,523 11/1969 Leybourne 259/10 3,524,730 8/1970 Yokouchi 23/252 3,591,344

7/1971 Schnock 23/252 Primary Examiner-Robert W. Jenkins Attorney-John W. Klooster et al.

[57] ABSTRACT A housing and paddle assembly adapted for use in processing and mixing highly viscous fluids is provided. The mixer employs a paddle assembly which rotates about a horizontal axis and which has at least one pair of diametrically opposed blade members which helically extend along the shaft in an axial direction and which are slotted at diagonally opposite outside ends.

in operation, the paddle assembly can sweep out substantially all of the housing interior and produce simultaneously in a fluid cyclical vertical displacement, rolling action, horizontal displacement, and, even, fold over action.

11 Claims, 13 Drawing Figures PATENIEBJULZMSIS SHEET 2 [IF 8 INVENTORS George A. Lat/nan Leo E Car/er ATTORNEY PAIENIEDJuL24ms SHEET 3 [IF 8 PATENIED 24 3.747. 899

saw u 0F 8 INVENTORS George A. Laf/nen Leo E Carter ATTORNEY PATENTEB SHEET 5 BF 8 COOLING WATER IN m vw FIG. 6

INVENTORS George A. Lo/inen Leo E Cor/er BY M W 2?%%EY PAIENTEB JUL 2 4 7 SHEET 6 OF 8 George A. Lat/nan INVENTORS Leo Carfer ATTORNEY PATENIEUJUIZWH 3.147. 899

SHEET 7 0f 8 IN-VENTORS George A. Lat/nan Leo F Car/er BYiwyowwaw ATTORNEY PMENIEB M24575 SHEET 8 UF 8 INVENTORS GEORGE A.LATINEN BY LEO F. CARTER ATTORNEY MIXER BACKGROUND In processing fluids, especially viscous fluids having I viscosities generally greater than, say, about 10,000 centipoises, it is often necessary to blend therewith'additives. In mixing operations involving'such'viscous flu ids, many problems are encountered, and specialized mixing apparatus'is desirable and commonly necessary.

Complex mechanical andfluid forcesare involved. The

art has long sought new and improved mixing: means adapted for use with highly viscous fluids, the. end result generally'desired being to achieve in'such viscous highly viscous-fluid: Another problem therewithghas been the difficulty of mixing afluid of low viscosity( for example, one having a viscosity of 'less than about'zl0 centipoises) with one of high viscosity. (for example,

one having a viscosity'ofgreater-than about 10,000 centipoises). Still another problemv has-been :theform' and configurationof the agitator and of the m-ixerh'ous ing relative .to the agitator.

One class of mixers'recognized within a'vessel or housing-which is usually cylindrical.

least one pair of generally opposed blade members. Each individual blade member projects generally radially from the shaft. Each blade member also axially extends generally-continuously except that such pair of blade members is slotted in the region of one pair of their respective diagonally opposite outsidecorners. Thus, the effective total slot cross-sectional area in each blade member of such pair ranges from about 3 to 50 percent of the total effective surface area of such blade member. I

The unslot'ted corner portion of each blade member is circumferentially disposed angularly. from the soslotted corner thereof. Both blade members of such pair have a similar angular disposition which extends generally in the same direction relative to the shaft, the angular displacement for each blade ranging from about 0 to 90 in opposite respective directions.

I v inithepriorart' characteristically has an agitator revolving-, general;ly (though not necessarily exactly) about a horizontal axis Such class ofmixers is suitable(dependingiuponindi vidual situations) for batch or continuousoperation.

There has now been discoveredanew. and improved mixer of this class wherein the mixing of=highlyviscous fluids (for example, of a low viscosity-liquid into a high viscosity liquid) can proceed with unexpectedly. lowpower and in a rapid and highly 'efficientmanner. This mixer is especiallywell'adapted for use conditions where the housingis only partially v filled 'fwitha-highly viscous fluid. The mixer is useful in a wide variety of end use applications involving mixingor-agitation of highlyviscous fluids and produces a typeof mixing action heretofore unknown.

SUMMARY housing is preferably adaptedto be oriented. during mixer operation so that the longitudinal axis extends I generally horizontally. The housing preferably has an input port above the level of the, axis and hasa'n' output;

port preferably below the level of the axis, although a housing with only a single "port may be used, if desired, as when: an auxiliary fluid pump is used and the mixer is not used in a continuous operation; The housing can be formed of any convenient construction material, though steel-is presently preferred.

The mixer employs a paddleassemblywhich hasarotatably mounted shaft'inthehousing'and.which extends generally longitudinally through said housing-and gen erally parallel to said axis. From the shaft extends at Theradially outer tip portion of each blade member at any given location axially along the shaft, together with the adjacent wall of the housing of the mixer at about the same location, together define a gap which is not more than about 5. percent'of the diameter of the interior chamber of the housing measured at about the same location. k j

' The shaft of the paddle assembly is journaled at its opposite end regions in fixed relationship to the housing to adapt the shaft for rotational m0vements. Preferably, the shaft axis is coaxial with the housing s longitudinal'axis. The paddle assembly can be formed of any convenient material of construction, though metals such 'as steel are presently preferred. Sealing means to prevent fluid leakage between the paddle assembly shaftand the housing are provided inv an operating mixer, as those skilled in the art will readily appreciate.

The effectivetotal'slot'cross sectionalarea in each blade ranges from about i to 50 per cent of the total effective surface area thereof and preferably from about 4 to 20 per cent; Preferably also, the slot in each respective blade of a pair of blades is substantially equally sized compared to the other blade of such pair. Preferably, the slots in each pair of blades are similarly located at respective diagonally opposite outside corner edges.

The, angular displacement preferably ranges from about 10 to 45 in each blade and the angular displacement in each diametrically opposite corner of a pair of blades in the same angular direction and of similar but not necessarily identical magnitude. Preferably, each blade is both axially curved generally continuousy and radially curved generally continuously, though those skilled :in the art will appreciate that the angular displacement of the unslotted corner portion of each blade can be achieved by one or more creases, folds, or the like, in the body of the blade rather than by a continuous curving of the blade body. f

The paddle assembly is in a mixer preferably adapted "to rotate with substantially no contact between blade tips and chamber walls. .For operation, amixer is equipped with drive means for revolvablyJdriving the paddleassembly shaft, including apower head and power transfer means. The paddle assembly when rotating' during mixer operation with fluid in-the chamber of the mixer housing'can produce a simultaneous combination of cyclical vertical displacement, rolling action, horizontaldisplacement, and even, fold-over ac- .tion". Preferably, the clearance between blade tips and housing wall ranges from about 0.01 to 1.5 inches, de-

pending on mixer size, though preferably, in a mixer of this invention, the ratio of the clearance between the blade tips and the adjacent chamber walls to the chamber diameter measured at about the same location at substantially all locations in the chamber along the longitudinal chamber axis except opposite slot locations ranges from about 0.1 to 0.0001 (preferably 0.01 to 0.001). Preferably, in a mixer, the paddle assembly is operated so as to produce during operation uniform rotational movements of the paddle assembly shaft.

The invention is further directed to the paddle assembly itself which is employed in a mixer of this invention.

DRAWINGS Turning to the attached drawings, there are seen various illustrations intended to provide a better understanding of the present invention, as follows:

FIG. 1 is a side elevational view of one embodiment of a mixer of the present invention;

FIG. 2 is a vertical, longitudinal sectional view taken through the mixing chamber of the embodiment shown in FIG. 1;

FIGS. 3, 4, and 5 are diagrammatic representations of the fluid mixing mechanics in one embodiment of an operating mixer of the present invention, as seen in cross-section;

FIG. 6 is a diagrammatic representation of the fluid mixing mechanics in the operating mixer of FIGS. 3 through 5, but as seen in a vertical, longitudinal section;

FIG. 7 is a perspective view of an embodiment of a paddle assembly for use in a mixer of the present invention;

FIG. 8 is a diagrammatic vertical, transverse sectional view through an embodiment of a mixer of this invention equipped with a reflux condenser whereby such mixer may be used as a continuous reactor;

FIGS. 9, 10, and 11 illustrate one preferred embodiment of a paddle assembly; FIG. 9 being a side elevational view; FIG. 10 being a sectional view taken along the line 10-10 of FIG. 9; and FIG. 11 being an enlarged detailed vertical sectional view taken along the line 1111 of FIG. 9.

FIG. 12 is a view similar to FIG. 10 but showing an alternative embodiment of the paddle assembly of FIG. 9 which is adapted to rotate in a reverse direction.

FIG. 13 is a side elevational view of another preferred embodiment of a paddle assembly.

FIGURE DESCRIPTION Referring to the drawings more particularly, there is seen in FIGS. 1 and 2 an embodiment of a mixer of this invention which is herein designated in its entirety by the numeral 20. Mixer 20 has a housing designated herein in its entirety by the numeral 21 formed of steel or the like which encloses an interior chamber 22 (see FIG. 2). Housing 21 is formed by a central cylindrical portion 23 to which are secured at opposite ends thereof heads 24 and 25, respectively. In the embodiment depicted, head 24 is secured to one end of cylindrical portion 23 by welding along flange 27, while head 25 is secured to the opposite end of cylindrical portion 23 by a series of bolts 28 with mating nuts 29 extending through adjoining

flanges

30 and 31 on cylindrical portion 23 and head 25, respectively.

Housing 21 has formed therein an,input port 33 located in the top mid-region of cylindrical portion 23.

An appropriately flanged conduit 35 connects port 33 to feed dome 34, conduit 35 and dome 34 being secured together by bolts 36 which extend through the flange of feed dome 34 into threaded rolls in the flange of head 35. Through dome 34 extend

feed pipes

37 and 38. Pipe 37 terminates within dome 34 in a spray head 40 so located as to be adapted to spray material into a wide area of chamber 22 according to a preselected pattern, while pipe 38 terminates within dome 34 in a conventional orifice (not detailed) which delivers material into chamber 22 as a stream.

Housing 21 also has formed therein an output port 41. An appropriately flanged conduit 42 connects port 41 to pipe 43, pipe 43 and conduit 42 being similarly secured together by bolts 44. Pump means (not shown) may be provided to deliver material to, or to take material from, chamber 22, via feed pipe 37 and/or 38, or via pipe 43, respectively. Additional input and output ports on a mixer 20 may be employed, of course, as desired.

Housing 21 further has formed therein a vent port 46 in the top mid-region of cylindrical portion 23. An appropriately flanged conduit 47 connects port 46 to pipe 48, head 47 and pipe 48 being similarly secured together by bolts 49. During a mixing operation, port 46 may serve as a safety valve permitting escape of pressurized gases from chamber 22 in the vent of excessive pressure build-up in housing 21,as through rupture of a rupture disc 50. To isolate the interior of chamber 22 from the atmosphere and prevent during operation of mixer 20 leakage of fluid therefrom appropriate seals 51 (for head 25 and cylindrical portion 23), seal 52 (for conduit 35 and dome 34), seal 53 (for conduit 42 and pipe 43), and seal 54 (for conduit 47 and pipe 48) are provided. Vent 46 is also useful when mixer 20 is to be employed as a reactor wherein mixing of viscous fluids takes place, and wherein a reflux condenser (not shown in FIGS. 1 and 2; but see FIG. 8) is connected with vent 46.

Housing 21 in mixer 20 is effectively formed by two walls, an inner wall 56 and an outer wall 57 with a space 58 thus being defined therebetween. This apace 58 between walls 56 and 57 is conveniently maintained by such means as

flanges

30 and 31,

conduits

35, 42, and 47, flanges 27, and the like, with appropriate welds (not shown). Space 58 provides a cooling, or heating jacket for delivering heat to, or removing heat from, chamber 22, as desired, or necessary during operation of mixer 20 by circulating a fluid coolant, such as water, or a heated fluid, such as hot oil, hot water, steam, or the like, in space 58, such a cooled or heated fluid (not shown) being fed to space 58 through

input ports

59 and 60, and being removed from space 58 through

output ports

61, 62 and 63. Any conventional means for jacketing housing 21 may be used for a mixer 20, if jacketing is desired, as those skilled in the art will readily appreciate. Whether or not a mixer 20 needs a jacket depends, of course, on the particular end use to which such is intended to be put in accordance with individual wishes.

Positioned and contained within chamber 22 of housing 21 is a paddle assembly designated herein in its entirety by the numeral 66. Paddle assembly 66 serves as an agitator in mixer 20 and revolves on a shaft 67. Shaft 67 in mixer 20 is generally coaxial with the longitudinal, horizontally extending axis 69 of housing 21, and extends through respective housing 21 heads 24 and 25 into

conventional bearing assemblies

70 and 71, respectively. Any convenient bearing means may obviously be employed. Bearing assembly 70 is supported by and secured to, as by welding, bearing support spars 72 which, in turn, are similarly secured at their respective bases to head 24, while bearing assembly 71 is supported by and secured to, as by welding, bearing support spars 73 which, in turn, are similarly secured at their respective bases to head 25. In order to make shaft 67 be in sealing engagement with housing 21, and thereby prevent fluid leakage from housing 21 around shaft 67 during operation of mixer 20, a pair of

conventional packing glands

74 and 75 are provided, one each in, respectively, head 24 and head 25, circumferentially about shaft 67. Pressure upon packing 76 and 77 in

respective glands

74 and 75 is adjustable and is maintained at a predetermined value by means of tensioning nuts 78 on bolts 79 and nuts 80 on bolts 81, respectively. Any convenient sealing means between shaft and housing may obviously be employed. Thus, shaft 67 is mounted for sealed, rotational movements within housing 21.

A pair of diametrically

opposed blade members

83 and 84 are each secured, as by welding, to shaft 67. Each

blade member

83 or 84 radially projects from shaft 67 to near (but not actual engagement with) interior wall surfaces of chamber 22. Each blade member extends continuously in an axial direction and simultaneously spirals along shaft 67 in chamber 22, the angle formed by the blade with theaxis of shaft 67 ranging from 0 to about 90, and preferably from 3 to 35.

The pair of blade members 83 and 84are similarly slotted-attheir respective diagonally opposite outside ends to form

slots

85 and 86, respectively. Each

slot

85 and 86 can range from about 3 to percent of the total effective surface area of each

blade

83 and 84, respectively, in general. The exact cross-sectional size and location of the

slot

85 or 86 in each blade can vary widely. Thus, aslot 85 or 86 may be open (not joined to, or circumscribed by) on one or two sides in a

blade

83 or 84. In general, a

slot

85 or 86 does not extend longitudinally beyond the mid-line of a blade, such as mid-line 87 of

blades

83 and 84. Further, a

slot

85 or 86 may extend down radially to the shaft 67 in a

blade

83 or 84. A pair of blade members such as 83 and 84 is preferably mathematically symmetrical as respects location and size of

slots

83 or 84. A

single slot

85 or 86 may be comprised of more than one individual aperture in a

blade

83 or 84, depending on circumstances, such as blade strength considerations, size, etc. Observe that paddle assembly 66 can rotate in chamber 22 either clockwise or counterclockwise. In general, it is presently preferred to operate the paddle assembly 66 so that, as assembly 66 rotates, the unslotted corner of each blade member first throws the liquid in a partially filled chamber 22.

A mixer 20 is adapted to achieve and maintain substantial homogeneity and uniformity in a liquid agitated by paddle assembly 66. Preferably, a mixer 20 has a chamber 22 whose dimensions such that the ratio of the length of axis 69 in chamber 22 to the maximum diameter of chamber 22 ranges about 0.5 to 3.5, and more preferably, from about 1.5 to 2.5.

To rotatably drive the shaft 67, an electric motor 88 is provided which interconnects with shaft 67 through a transmission 89 and a drive shaft 90. Transmission 89 is equipped with a safety clutch 91 to prevent overloads. Clutch 91 can be considered to interconnect drive shaft with shaft 67.

Conveniently, mixer 20 has a base 93 wherein a pedestal 94 supports the drive assembly (motor 88, shaft 90, transmission 89 and clutch 91) while

leg assemblies

95 and 96 together support housing 21, paddle assembly 66, and their associated elements.

FIGS. 3-7 illustrate bulk mixing principles for a highly viscous fluid 97 in a mixer 98 of this invention, the level of such fluid 97 in mixer 98 being such as to only partially fill mixer 98. In the vertical transverse views of FIGS. 3, 4, and 5, the broad surfaces of a paddle assembly 99 assure a good shear field (as in

regions

101, 102 and 103). As paddle assembly 99 rotates, gravitational forces cooperate to produce effective fluid randomization (as in region 106) via fluid extension (as in regions 104i and 105) and fold-over action (as in region 107). Blades of a paddle assembly may be radially curved. If radially curved, the curvature may be convex or concave with respect to the direction of paddle assembly 99 rotation.

Concurrently with the type of mixing activity illustrated in FIGS. 3-5, fluid 97 is being mixed through axial recirculation in mixer 98 by means of the

slot openings

108 and 109 in paddle assembly 99 (see FIG. 6). Fluid 97 flows through

slot openings

108 and 109 as paddle assembly 99 rotates on its axis in mixer 98 as diagrammed. The

openings

108 and 109 give rise to equal and opposite mass gradients and paddle nip pressures which function to produce remarkably rapid axial recirculation.

Preferably, though not necesarily, a mixer 98 is not completely filled with a fluid 97 in a mixing operation. A generally constant large exposed surface area on fluid 97 in mixer 98, and a generally continuously fresh surface regeneration rate, provide a maximum initial distribution of a material 110 being fed into mixer 98 for mixing with fluid 97, especially when such an input material 110 is fed into mixer 98 in a spray form, as from a spray head 1 11. In FIG. 6, the solid line configuration illustrates approximate fluid 97 surface position with the paddle assembly 99 in the vertical position shown and the spirally looped arrow indicates generally the pattern of axial fluid flow. The dotted line and dotted arrow illustrate approximate fluid 97 surface position and flow pattern when the paddle assembly 99 has subsequently revolved through As shown, for example, in FIGS. 3-6, the paddle assembly 99 sweeps out substantially the entire mixer 98 interior volume with each revolution (except for slots 108 and 109), thereby eliminating the possibility of low turnover stagnation regions in a mixer 98, and assuring a good cross-sectional shear field throughout fluid 97. It will be appreciated by those familiar with fluid mechanics that in, for example, a mixer 98 of this invention, which is filled to about 10 to 90 percent by volumn with a fluid or liquid during revolutions of a paddle assembly 99 therein, three distinct types of mixing (agitation, or flow patterns) may be discerned occurring simultaneously. One type may be termed cyclical vertical displacement; another, rolling action; and the third, horizontal displacement. 1

The cyclical vertical displacement occurs typically at a cycle rate in the range from about one-half to 60 times per minute. First, liquid in the mixer is subjected to a vertical lifting force (exerted by a paddle blade in a paddle assembly) which force is greater than that exerted downwardly by gravity, yet is at least sufficient to move vertically a portion of the total volume of liquid in the mixer from a gravitationally lower region to a gravitationally higher region in the mixer. Secondly, such so displaced liquid is subjected to a gravitational falling force by effective removal of such lifting force therefrom (as the paddle blade continues to rotate). The total gravitational falling force applied to the liquid is at least sufficient to return substantially all of such so displaced liquid to the gravitationally lower region before a vertical displacement cycle is repeated on such so displaced liquid.

The rolling action occurs in a generally peripherally located and generally horizontally extending region which extends generally circumferentially about the entire internal periphery of the mixer. This region is continuously moving in a direction which is generally normal to the horizontal. This rolling action is produced by a similarly so moving band of pressure (created by the paddle blades in a paddle assembly) which is located adjacent to but following behind said region. The region of rolling action may be considered to be discontinuous in slot regions, depending upon the slot design in any given mixer. The paddle blades create a zone of pressure which exerts a force on the liquid in this region of rolling action at least sufficient to cause movement of a portion of such liquid in such region along (or in) a roughly cross-sectionally circular path. This path moves (or extends) normally away from the adjacent internal periphery of the mixer housing adjacent to such band of pressure (e.g., adjacent to a paddle blade) towards the interior of the mixer a distance which is generally less than the internal diameter across the mixer housing at a given peripheral position, then back towards such internal periphery forwardly of said band of pressure, and then towards the band of pressure adjacent such internal periphery. Between the blade tips and the mixer housing wall at and in the zone of pressure, there generally exists a shear rate of at least about 2,000'", the exact value of this shear rate depending on this clearance and the blade tip speed in any given mixer. This shear rate can be as great as 10,000, or even greater if desired, but it is presently preferred that such rate be lower than 10,000"" to avoid applications of excessive force to a given liquid which could deteriorate same.

The horizontal displacement occurs in a longitudinal, circulatory manner in a mixer at a cycle rate such that the actual volume of the liquid moved from one end region of the mixer to the opposite end region thereof within one minute is equivalent to from about onetenth to 30 times the total volume of the liquid in the mixer. Such equivalent volume, and the horizontal circulation rate for such liquid so moved, respectively, are each approximately proportional to said cyclical vertical displacement cycle rate in any given instance. Such horizontal displacement is produced by the slots in the blades of the paddle assembly.

The cyclical vertical displacement, the rolling action, and the horizontal displacement take place while continuously maintaining substantially the total volume of the liquid in the mixer under laminar flow conditions. Preferably, the cyclical vertical displacement in combination with the rolling action produce fold-over action in the liquid in the mixer.

FIGS. 3-6 illustrate a type of preferred paddle blade construction wherein the radially outermost, axially extending edge portions of each paddle blade are equipped with an adjustable, radially extensible or retractable knife member 113. Such adjustability is achieved by bolting knife 113 to each adjoining paddle by nut and bolt assemblies 114 which fit through slots 115 in each knife 113 and extend through mating holes (not shown) in each paddle. By means of a knife member 113, the distance between the tip of each paddle blade and the interior wall surface of a mixer may be conveniently adjusted, and in addition, the total effective land area in a given paddle assembly may be adjusted as desired. For present purposes, the land area of an individual paddle blade may be considered to refer to that part of a paddle blade edge which lies on the radially outermost peripheral outside longitudinally axially extending edge portion thereof and is thus approximately adjacent to mixer interior side wall surfaces.

It is preferred that a paddle blade not actually engage or scrape the interior wall surfaces of a mixer 98 during rotation of a paddle assembly 99 therein, and that there be a relatively small finite clearance between blade tips and interior wall surfaces of a mixer, as indicated above, which clearance is generally too small to show in, for example, FIGS. 3-7.

In mixer 98, an outlet port 131 is provided in order to permit material to be withdrawn from mixer 98 in a continuous or discontinuous manner depending upon the mode of operation selected. Input to mixer 98 is had through inlet port 133.

In FIG. 8 is shown a mixer which is herein designated in its entirety by the numeral 98 and which is similar in constructional details to the embodiments shown in FIGS. 6 through 8. Mixer 98' employs a paddle assembly 135 having radially curved and axially spiralled blades (pair), and is equipped with a reflux condenser 136. Mixer 98 with reflux condenser 136 is suitable for operation as a reactor in the manufacture, as by continuous mass polymerization of such polymers as, for examples, homopolystyrene or styrene acrylonitrile copolymers. The interior mixing action achieved in a mixer 98 with a paddle assembly 135 can maintain a viscous polymer melt therein in a substantially isothermal condition. Appropriate jacketing (not shown) on mixer 98' helps avoid heat losses. Monomer vapors evolved from the polymer melt (not shown in FIG. 12) pass upwardly through a vapor space maintained over the viscous fluid melt within the lower part of mixer 98 past spray head 137 into a vent port 139 through which the vapors are fed to the reflux condenser 136. In condenser 136, the vapors are condensed and then are allowed to be fed back to the interior of mixer 98, as through a suitable piping and pump arrangement herein designated in its entirety by the numeral 138. In the case of, for example, homopolystyrene manufacture, the vapors evolved from a mixer 98 during continuous mass polymerization operation comprise styrene monomer for the most part.

In this description, for convenience, it will be appreciated that in a figure wherein there is used a numeral with one or two prime marks thereafter, such so primed numeral designates a second or a third embodiment of this invention, respectively, wherein the part or ele-' ment so designated is like or similar to a corresponding part or element identically numbered, but without prime marks in the embodiment of FIGS. 1 and 2.

Referring to FIGS. 9 through 11, there is seen an illustration of one preferred paddle assembly embodiment of the present invention herein designated in its entirety by the numeral 150. Paddle assembly 150 is seen to employ a shaft 151 which has affixed thereto by welding or the like a pair of diametrically opposed blade members l52and 153. Formed in paddle assembly 150 in diagonally opposite corner regions of

respective paddle blades

152 and 153 are slots 15.4, and 155 which extend from the axially side edge of each

paddle blade

152 and 153 to shaft 15.1. The unslotted corner portion 156 and157 of each

respective blademember

152 and 153 is circumferentially disposedv angularly from the so slotted

corner

154 and 155, respectively. Each of blade members 152 and 153.has asimilar angular disposition which extends generally in the same direction relative to.shaft 151, The angular displacement can range from. greater than to about 90. To provide rigidity and support for

blades

152 and 153, a plurality of axially spaced but radially extending gussets 158 are provided. Each gusset 158-extends from shaft 151 radially outwardly along the concave surface of each

blade member

152 and 153, respectively, and is conveniently secured to the adjoining shaft 151 andblade member 152 (or member 153, as the case may be) by means of welding or the like. The added rigidity provided by gussets 158 permits one to use the paddle assembly in a relatively large size mixer and/or in one in whicha relatively highly viscous fluid is to be mixed or agitated. Along the radially outwardly axially extended tip portionof each

blade

152 and 153, respectively, there'is mounted aknife or doctor blade 159; Knife blade 159 is mounted by means of appropriate nutand bolt assemblies .160 to each paddle blade 152 .and*153. Slots 162 are provided in blades 159 so that theblades may be adjusted.

Observe that the paddle assembly 1- 0is ada pted to rotate'in a directionwhereeach slot 154and 155 enters a fluid in a mixer of this invention before the other. end

156 or 157, respectively, does.

A paddle assembly of this invention may alsooperate in a reverse direction in which event'the blade configuration may be of the same as respects axial and radial bers 152' and 153" are reinforced with rib members 167 mounted analogously to gussets 158 in paddle assembly 150 but on the convex surfaceportions of the respective blades 152' and 153'.

It is preferred to use a paddle assembly, suchas as:

, sembly 150, with solid blades (except in slot regions);

however, small drain holes, orthe like (not shown) for In operating a mixer of this invention using a highly viscous fluid, it is preferred to employ rotational speeds for the paddle assembly therein which produce laminar flow in such viscous fluid.

Referring to FIG. 13, there is seen another preferred embodiment of a paddle assembly of this invention which embodimentis designated in its entirety by the numeral 170. Paddle assembly 170 has doctor blades 171- mounted on the radially outside edges but on reverse respective faces of

blade members

172 and 173, respectively. The blades 170 and 171 are secured to their respective paddles 171 and 173 by nut and bolt assemblies 174. As in the case of the paddle assembly of FIGS. 9'through 11, rigidity is given to the paddle assembly 170 by means of rib members 175. Observe that the rib members 175 are intended to be on the trailing faces of the

paddles

172 and 173 as the assembly 170 rotates about shaft 176 during operation in a mixer. The paddle assembly 170, as those skilled in the art will appreciate, can operate in a reverse direction, but in such an event it is preferred to employ braces (not shown) on the reverse faces, respectively, of each of

paddles

172 and 173.

Observe that while in the case of the paddle assembly, for example, of FIGS. 9 through 11, the mixing characteristics are such that material will tend to move to one end region or the other of a mixer because of the screw like configuration employed for the blades 153 I and 154. In the case of the paddle assembly 170, no end build up of material in a mixer will occur since with each revolution of the assembly 170, the action of the

paddle

172 and 173 is such that material in a mixer is continuously and regularly moved from one end region to the other. The paddle assembly of FIGS. 9 through 1.1 is advantageously employed in a mixer where it is desired to concentrate materialmore at one end of a mixer relativeto the axis thereof than at the other end opposite and opposite end thereof. Such asymetrical mixing (with respect to the axis of a mixer) is particularly desirable when a mixer of this invention is being used to mix reactants and it is desired to keep a liquid draining fluid from a paddle assembly when it stops rotating'may be provided, if desired, without adversely affecting this invention, particularly when the holes are smaller and the viscosity of the fluid being operated or afluid mixture separate from a vapor phase. Such separation is accomplished by connecting appropriate pipes to one end region or the otherof a mixer, depending upon whether one desires the pipe to face into a vapor phase or a fluid phase, predominantly. On the other hand, the paddle assembly is adapted for use in a mixer whereina uniform distribution of material in a mixer during mixer operation relative to the axis thereof is desired.

It will be appreciated that, while the embodiments of the present invention as shown and described herein are necessarily limited to a few forms of the present invention, many variations and modifications thereof are feasible and practical without departing from the spirit and scope of the present invention disclosed and claimed herein. 7

What is claimed is:

' 1. A mixer adapted for use in processing highly viscous fluids comprising:

A. a housing enclosing an interior chamber whose walls are generally radially symmetrical with respect to a longitudinal axis extending therethrough, said'housing having defined therein port means adapted for input and output of material into and from said chamber,

B. a paddle assembly positioned generally within said housing and comprising:

1. a shaft rotatably mounted at its opposite end portions in said housing and extending generally longitudinally through said interior chamber and parallelly to said axis, and

2. at least one pair of generally opposed blade members, each blade member projecting generally radially from said shaft, each blade member axially extending generally continuously, except that such pair of blade members is slotted in the region of one pair of their respective diagonally opposite outside corners so that the effective total slot cross-sectional area in each blade member of such pair ranges from about 1 to 50 percent of the total effective surface area of such blade member, the unslotted corner portion of each blade member being circumferentially disposed angularly from the so-slotted corner thereof, both blade members of said pair having a similar angular disposition which extends generally in the same direction relative to said shaft, the angular displacement ranging from to about 90, the radially outer tip region of each blade member at any given location axially along said shaft together with the adjacent wall of said housing at about the same location forming a gap which is not more than about 5 percent of the diameter of said interior chamber measured at about the same location,

C. bearing means functionally located between said housing and said shaft and adapting said shaft for rotational movements, and

D. sealing means for said shaft adapted to prevent fluid leakage between said shaft and said housing.

2. The mixer of claim 1 wherein said paddle assembly has one pair of said blade members with generally equally sized slots in each individual blade.

3. The mixer of claim 1 wherein each of said blade members is similarly radially and convexly curved with respect to the direction of shaft rotation.

4. The mixer of claim 1 wherein said chamber has dimensions such that the ratio of the length of said chamber along said axis to the maximum diameter of said chamber ranges from about 0.5 to 3.5.

5. The mixer of claim 1 wherein said shaft is substantially coaxial with said axis.

6. The mixer of claim 1 wherein the ratio of the clearance between blade tips and said chamber walls at substantially all locations in said chamber along said axis except opposite slot locations to the inside diameter of said chamber ranges from about 0.1 to 0.0001.

7. The mixer of claim 1 wherein the effective total slot cross-sectional surface area in each blade ranges from about 4 to 20 percent of the total effective surface area thereof, and wherein the slot in each respective blade of such a pair of blades is substantially equally sized and similarly located at respective diametrically opposed outside ends thereof.

8. The mixer of claim 1 further equipped with drive means for revolvably driving said shaft including a power head and power transfer means.

9. The mixer of claim 1 wherein there is an inlet port equipped with a spray head adapted to spray input materials delivered into said mixer.

10. A paddle assembly adapted for use in a mixer chamber whose walls are generally radially symmetrical with respect to a longitudinal axis extending therethrough, said paddle assembly comprising:

A. a shaft, and

B. at least one pair of diametrically opposed blade members,

C. each blade member radially projecting from said shaft to near engagement with interior wall surfaces of said chamber,

D. each blade member axially and spirally extending generally continuously along said shaft, the angle of spiral measured between the axis of said shaft and each such blade member ranges from 0 to about E. each such pair of blade members having its individual blade members slotted in the region of their respective diametrically opposite outside ends, the effective total slot cross-sectional surface area in each blade ranging from about 1 to 50 percent of the total effective surface area of such blade.

1 1. A paddle assembly of claim 10 wherein the effective total cross-sectional surface area in each blade ranges from about 4 to 20 percent of the total effective surface area thereof, and wherein the slot in each respective blade of such a pair of blades is substantially equally sized and similarly located at respective diametrically opposed outside ends thereof.

Claims

1. A mixer adapted for use in processing highly viscous fluids comprising: A. a housing enclosing an interior chamber whose walls are generally radially symmetrical with respect to a longitudinal axis extending therethrough, said housing having defined therein port means adapted for input and output of material into and from said chamber, B. a paddle assembly positioned geNerally within said housing and comprising: 1. a shaft rotatably mounted at its opposite end portions in said housing and extending generally longitudinally through said interior chamber and parallelly to said axis, and 2. at least one pair of generally opposed blade members, each blade member projecting generally radially from said shaft, each blade member axially extending generally continuously, except that such pair of blade members is slotted in the region of one pair of their respective diagonally opposite outside corners so that the effective total slot crosssectional area in each blade member of such pair ranges from about 1 to 50 percent of the total effective surface area of such blade member, the unslotted corner portion of each blade member being circumferentially disposed angularly from the soslotted corner thereof, both blade members of said pair having a similar angular disposition which extends generally in the same direction relative to said shaft, the angular displacement ranging from 0* to about 90*, the radially outer tip region of each blade member at any given location axially along said shaft together with the adjacent wall of said housing at about the same location forming a gap which is not more than about 5 percent of the diameter of said interior chamber measured at about the same location, C. bearing means functionally located between said housing and said shaft and adapting said shaft for rotational movements, and D. sealing means for said shaft adapted to prevent fluid leakage between said shaft and said housing.

2. at least one pair of generally opposed blade members, each blade member projecting generally radially from said shaft, each blade member axially extending generally continuously, except that such pair of blade members is slotted in the region of one pair of their respective diagonally opposite outside corners so that the effective total slot cross-sectional area in each blade member of such pair ranges from about 1 to 50 percent of the total effective surface area of such blade member, the unslotted corner portion of each blade member being circumferentially disposed angularly from the so-slotted corner thereof, both blade members of said pair having a similar angular disposition which extends generally in the same direction relative to said shaft, the angular displacement ranging from 0* to about 90*, the radially outer tip region of each blade member at any given location axially along said shaft together with the adjacent wall of said housing at about the same location forming a gap which is not more than about 5 percent of the diameter of said interior chamber measured at about the same location, C. bearing means functionally located between said housing and said shaft and adapting said shaft for rotational movements, and D. sealing means for said shaft adapted to prevent fluid leakage between said shaft and said housing.

10. A paddle assembly adapted for use in a mixer chamber whose walls are generally radially symmetrical with respect to a longitudinal axis extending therethrough, said paddle assembly comprising: A. a shaft, and B. at least one pair of diametrically opposed blade members, C. each blade member radially projecting from said shaft to near engagement with interior wall surfaces of said chamber, D. each blade member axially and spirally extending generally continuously along said shaft, the angle of spiral measured between the axis of said shaft and each such blade member ranges from 0* to about 90*, E. each such pair of blade members having its individual blade members slotted in the region of their respective diametrically opposite outside ends, the effective total slot cross-sectional surface arEa in each blade ranging from about 1 to 50 percent of the total effective surface area of such blade.

11. A paddle assembly of claim 10 wherein the effective total cross-sectional surface area in each blade ranges from about 4 to 20 percent of the total effective surface area thereof, and wherein the slot in each respective blade of such a pair of blades is substantially equally sized and similarly located at respective diametrically opposed outside ends thereof.