US 3751010 A
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 axially extending blade members 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.
Claims available in
Description (OCR text may contain errors)
United States Patent. [1 1 Latinen, deceased Aug. 7, 1973 i 1 MIXER  Inventor: George A. Latinen, deceased, late of Springfield, Mass. by May V. Latinen, administratrix  Assignee:
Monsanto Company, St. Louis, Mo,
Aug. 16, 1971 (Under Rule 47)  Appl. No.: 172,059
 US Cl. 259/9, 23/252 R [5 ll Int. Cl. B0lf 7/04 [58 Field of Search 259/9, 10, 7, 8,
 References Cited UNITED STATES PATENTS 1,630,790 5/1927 Essick 259/178 3,0l7,l64 1/1962 Ayers 259,178 3,469,948 9/1969 Anderson 23/252 R 3,476,523 1l/l969 Leybournem. 259,110
Primary ExaminerRobert W. Jenkins Atl0rneyJohn W. Klooster et al.
57 ABSTRACT A housing and paddle assembly adapted for use in pro cessing 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 axially extending blade members 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.
14 Claims, 15 Drawing Figures PATENTEU M15 SHEET 2 0F 7 GEORGE A.
lllullnl'llll-Il PAIENIEDAU'E 1W 3.751010 SHEET 3 0F 7 FIG.5
GRAVITY FORCE FIG.4
GRAVITY FORCE FIG.3
GRAVITY FORCE INVENTOR GEORGE A. LATINEN ATTORNEY PAIENIEB AUG 71973 SHEET l 0F 7 INVENTOR GEORGE A. LATINEN ATTORNEY .YSLOIO PATENIEO AUG 7 I975 SHEEI 5 0f 7 FIG.9
INVENTOR GEORGE A. LATINEN ATTORNEY PATENTED Aug 7 3 7 51 .0 1 O sum 5 or 7 E COOLING WATER IN INVENTOR GEORGE A. LATINEN ATTORNEY PAIENTEU SHEEI'IN'I INVENTOR GEORGE A. LATINEN ATTORNEY MIXER BACKGROUND In processing fluids, especially viscous fluids having viscosities generally greater than, say, about 10,000 centipoises, it is often necessary to blend therewith additives. In mixing operations involving such viscous fluids, many problems are encountered, and specialized mixing apparatus is desirable and commonly necessary. Complex mechanical and fluid forces are 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 fluids, or to maintain such viscous fluids in, a substantially uniform or homogeneous condition in the most efficient manner possible. One problem with conventional mixing means has been the large amount of power required to drive an agitator placed in a highly viscous fluid. Another problem therewith has been the difficulty of mixing a liquid of low viscosity (for example, one having a viscosity of less than about centipoises) with one of high viscosity (for example, one having a viscosity of greater than about 10,000 centipoises). Still another problem has been the form and configuration of the agitator and of the mixer housing relative to the agitator.
One class of mixers recognized in the prior art characteristically has an agitator revolving generally (though not necessarily exactly) about a horizontal axis within a vessel or housing which is usually cylindrical. Such class of mixers is suitable (depending upon individual situations) for batch or continuous operation. There has now been discovered a new and improved mixer of this class wherein the mixing of highly viscous fluids (for example, of a low viscosity liquid into a high viscosity liquid) can proceed with unexpectedly low power and in a rapid and highly efficient manner. This mixer is especially well adapted for use conditions where the housing is only partially filled with a highly viscous fluid. The mixer is useful in a wide variety of end use applications involving mixing or agitation of fluids and produces a type of mixing action heretofore unknown.
SUMMARY The present invention is directed to a mixer which is especially well adapted for use in processing highly viscous fluids, but which is also suitable for mixing fluid or fluidizable materials generally. The mixer incorporates a housing which encloses an interior chamber with side and end walls. The chamber walls are generally radially symmetrical (e.g., cross-sectionally circular) with respect to a longitudinal axis extending therethrough. The housing is preferably adapted to be oriented during mixer operation so that the longitudinal axis extends generally horizontally. The housing preferably has an input port above the level of the axis and has an 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 paddle assembly which has a rotatably mounted shaft which extends generally longitudinally through said housing and generally parallel to said axis. From the shaft extends at least one pair of diametrically opposed blade members. Each blade member radially projects from the shaft preferably to near engagement with interior wall surfaces of the interior chamber of the housing. Each blade member generally axially extends continuously along the shaft. Each pair of diametrically opposed blades is slotted in the region of their respective diagonally opposite outside ends (or corners), with the effective total slot cross-sectional surface area in each blade ranging from about 3 to 50 percent of the total effective surface area of such blade (preferably ranging from about 4 to 20 percent thereof), though somewhat larger and smaller surface areas may be used without departing from the spirit and scope of the present invention, as those skilled in the art will appreciate. Preferably, the slots in each respective blade of such a pair of blades are substantially equally sized and similarly located at respective diagonally opposite outside ends. The diameter of each such pair of blade members in a paddle assembly in a mixer at any given location along the axis of the shaft except in slot locations is typically not less than about percent of the diameter of the interior chamber of the mixer taken at about the same location.
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 movements. Preferably, the shaft axis is coaxial with the housings 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 shaft and the housing are provided in an operating mixer, as those skilled in the art will readily appreciate.
The paddle assembly is in a mixer preferably adapted to rotate with substantially no contact betwen blade tips and chamber walls. For operation, a mixer is equipped with drive means for revolvably driving the paddle assembly shaft, including a power head and power transfer means. The paddle assembly when ro tating during mixer operation with fluid in the chamber of the mixer housing can produce :a simultaneous combination of cyclical vertical displacement, rolling action, horizontal displacement, and, even, fold over action. Preferably, the clearance between blade tips and housing wall ranges from about 0.01 to 1.5 inches, depending 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 0.01 to 0.0001. 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 view similar to FIG. 4, but using in place of the radially curved paddle blade configuration shown in FIG. 4, a radially flattened blade configuration operating in a fluid of differing viscosity from that shown in FIG. 4;
FIG. 8 is an end elevational view of another embodiment of a paddle assembly for use in a mixer of the present invention;
FIG. 9 is a view simlar to FIG. 2 but showing diagrammatically an alternative embodiment of a mixer of the present invention wherein two spray heads for feeding material(s) to a mixer are employed, two conduits for vapor removal are employed, and a four-bladed paddle assembly is employed;
FIG. 10 is a vertical, transverse sectional view through the embodiment of FIG. 9 showing the mixer filled to a maximum extent with a viscous fluid for preferred operation of a mixer in accordance with the teachings of the present invention;
FIG. 11 is an isometric view of a four-bladed paddle assembly of the type used in the embodiment of FIGS. 9 and 10;
FIG. 12 is a diagrammatic vertical, transverse sectional view through an embodiment of a mixer of this I invention equipped with a reflux condenser whereby such mixer may be used as a continuous reactor;
FIG. 13 is a side elevational view of one preferred embodiment of a paddle assembly;
FIG. 14 is a sectional view taken along the line 14-14 of FIG. 13; and
FIG. 15 is an enlarged, detailed vertical sectional view taken through the region 15-15 of FIG. 13.
FIGURE DESCRIPTION Referring to the drawings more particularly, there is seen in FIGS. 1 and 2 an embodiment ofa mixer of this invention which is herein designated in its entirety by the numeral 20. Mixer 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 embodi ment 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 a 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 outlet 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, meand 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 event 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. 12) 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 space 58 between walls 56 and 57 is conveniently maintained by such means as flanges 3i) and 31, conduits 35, 43, and 47, flange 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, 63, and 63A. Any conventional means for insulating housing 21 may be used for a mixer 20, if insulation is desired, as those skilled in the art will readily appreciate. Whether or not a mixer 21) needs insulation 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 211, 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. Any convenient sealing means between shaft and housing may obviously be employed. 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. 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 and straight in an axial direction substantially without spiralling along shaft 67 in chamber 22. The pair of blade members 83 and 84 are similarly slotted at their respective diagonally opposite outside ends (or corners) to form slots 85 and 86, respectively. Each slot 85 and 86 canrange from about 3 to percent of the total effective surface area of each blade 83 and 84, respectively, in general. The exact crosssectional size and location of the slot 85 or 86 in each blade can vary widely. Thus, a slot 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 ofa 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,v such as blade strength considerations, size, etc. I
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 thatthe ratio of the length of axis 69 in chamber 22 to the maximum diameter of chamber 22 range 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 90 with shaft 67. Any convenient means may be used to rotatably drive a paddle assemblyelectrical, magnetic, mechanical, or the like.
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 ofa paddle assembly 99 assure a good shear field (as in regions I011, 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 104 and 105) and foldover action (as in region 107).
FIG. 7 is a view similar to FIG. 4 but using, in place of the radially curved paddle blade configuration shown in FIG. 4, a flattened blade configuration and a fluid of differing viscosity from that shown in FIG. 4. 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 and 7, 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 1108 and 109 as paddle assembly 99 rotates on its axis in mixer 98 as diagrammed. The openings 1108 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 necessarily, a mixer 98 is not completely filled with fluid 97 in amixing operation. A generally constant large exposed surface area on fluid 97 in mixer 98, and a generally continuously fresh surface regenerationrate, 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 1111. In FIG. 6, the solid line configuration illustrates approximate fluid 97 surface position with the paddleassembly 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. 3-7, the paddle assembly 99 sweeps out substantially the entire mixer 98 interior volume with each revolution (except for slots 108 and 1109), 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 volume 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.
The cyclical vertical displacement occurs typically at a cycle rate in the range from about is to 60 times per minute. First, liquid in the mixer is subjected to a vertical lifting force (exerted by apaddle 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 application 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 1/10 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 produces 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 knift 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 ofa 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, though, for example, in FIG. 8, a relatively large clearance 116 for an embodiment of blade assembly 99 is shown in a mixer 98.
Turning to FIGS. 9 and 10, there is seen a diagrammatic view of another embodiment of the invention which is herein designated in its entirety by the numeral 119. Mixer 119 is similar to mixer 98 (see, for example, FIG. 6) but differs therefrom in that a pair of spray heads 120 and 121 are employed for feeding material into such mixer 119 instead of the single spray head 111 of the FIG. 6 embodiment. Each spray head 120 and 121 is mounted in a vent port 122 and 123, respectively; such a configuration is particularly advantageous where the input material can be used to condense materials in a vapor phase above a fluid in mixer 119, as when one is using a mixer of this invention in combination with a reflux condenser to conduct a polymerization reaction (see FIG. 12 below).
Observe that vents 122 and 123 in mixer 119 are an gularly displaced from the vertical so that a higher fill level can be achieved in a mixer 119 during operation thereof without plugging vents 122 and 123. Observe that, as the paddle assembly in mixer 119 normally operates, the fluid level tends to shift from a normal position to one where the fluid level is offset from the vertical and would, if vents 122 and 123 were not so offset, tend to plug such vents 122 and 123 at high fills.
Mixer 119 employs, instead of the two-bladed paddle assembly shown, for example, in FIGS. 1-8, a fourbladed paddle assembly which is herein designated in its entirety by the numeral 124. As isometric view of such a paddle assembly 124 is seen in FIG. 11, wherein, as a matter of convenience in drawing, the end edges of the paddle blades 125, 125, 126, and 126' are shown to be perpendicular to the shaft 127, though it will be appreciated that, in the embodiments shown in FIGS. 9 and 10, the corresponding blade end edges are curved so as to have a close tolerance with the inside walls of the housing 129 of mixer 119. Observe that paddle blades 125 and 125' and 126 and 126 are, respectively, generally diametrically opposed to one another on shaft 127; that such blades are slotted at their diagonally. opposite corners; and that such blades are diametrically opposed to one another on shaft 127. Slot patterns in pairs of radially adjacent blades are symmetrically located. Each paddle blade 125, 125, 126, and 126 is equipped with an adjustable knife 130 similar in construction details to the kinfe 113 described above in mixer 98.
In each of the mixers 98 and 119, an outlet port 131 and 132, respectively, is provided in order to permit material to be withdrawn from respective mixer 98 or II) in a continuous or discontinuous manner depending upon the mode of operation selected. Input to each of mixers 98 and 119, respectively, is had through respective inlet ports 133 and 134, respectively.
In FIG. 12 is shown a mixer which is herein designated in its entirety by the numeral 98' and which is simlar in constructional details to the embodiments shown in FIGS. 6 through 8. Mixer 98' employs a paddle assembly 135 having radially curved 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 copolymer. 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 I36, 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. i
In this descriptiomfor convenience, it will be appreciated that in afigure 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 element 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. 13 through 15, 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 I is seen to employ a shaft 151 whichhas affixed thereto, as by welding or the like, a pair of diametrically 0pposed blade members I52 and 153. Formed in paddle assembly 15 in diagonally opposite corner regions of respective paddle blades 152 and 153 are slots 154 and 155 which extend fromthe axial side edge of each such paddle blade 152 and-153 to shaft 151. The paddle assembly 150 has blade members 152 and 153 which are similarly both radially and convexly curved with respect to the direction of shaft rotation. To provide rigidity and support for blades 152 and 153, a plurality of axially spaced butradially extending gussets 156 are provided. Each gusset 156 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 and blade member 152 (or member 153, as the case may be) by means of welding or the like. The added rigidity provided by gussets 156 permits one to use thepaddle assembly 151 in a relatively largesized mixer and/or in one in which a relatively highly viscous fluid is to be mixed or agitated. Along the radially outwardly axially extending tip portions of each blade I52 and 153, respectively, there is mounted a knife or a doctor blade 156. Knife blade 156 is mounted, for example (see FIG. 15), through each paddle blade 152 and 153 by means of appropriate nut and bolt assemblies 157. A slot 160 is formed in doctor blade 159 for each nut and bolt assembly 157 to provide for adjustment in a radial direction of the blade. A slot 158 is formed in blade 152 and in blade 153 so that when paddle assembly 150 is mounted functionally in a mixer housing (not shown), a sensor, such as a pressure sensor or level sensor, can be inserted into the mixer from a side wall into the mixer interior without interferring with rotational movements of paddle as sembly 150.
It is preferred to use a paddle assembly, such as assembly 150, with solid blades (except in slot regions); however, small drain holes, or the like (not shown) for 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 small and the viscosity of the fluid being operated upon in the mixer is high.
It is preferred to use a paddle assembly, such as assembly 150, wherein the blades are radially curved because such a generally cross-sectionally S-shaped configuration in a paddle blade assembly tends to retain similar geometry at different mixer fillages.
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.
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.
What is claimed is:
l. 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:
l. a shaft rotatably mounted at its opposite end portions in said housing and extending generally longitudinally through said interior chamber parallelly to said axis, and I 2. at least one pair of diametrically opposed blade members, each blade member radially projecting from said shaft, each blade :member axially extending generally continuously along said shaft, each such pair of blade members being slotted in the region of their respective diagonally opposite outside corners, the effective total slot crosssectional surface area in each blade member ranging from about 3 to 50 percent of the total effective surface area of such blade member, the diameter of each such pair of blade members at any given location along said shaft except in slot locations being not less than about 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 2 wherein each of said blade members is substantially flat and planar.
4. The mixer of claim 2 wherein each of said blade members is similarly radially and convexly curved with respect to the direction of shaft rotation.
5. 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.
6. The mixer of claim 1 wherein said shaft is substantially coaxial with said axis.
7. 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 ranges from about 0.01 to 0.0001.
8. 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 diagonally opposite outside ends thereof.
9. The mixer of claim 1 further equipped with drive means for revolvably driving said shaft including a power head and power transfer means.
10. The mixer of claim 1 wherein there is an input port equipped with a spray head adapted to spray input materials delivered into said mixer.
11. 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 extending generally continuously along said shaft,
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 3 to 50 percent of the total effective surface area of such blade.
12. A paddle assembly of claim 11 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.
13. The paddle assembly of claim 11 wherein each of said blade members is substantially flat and planar.
14. The paddle assembly of claim 11 wherein each blade member is similarly radially and convexly curved with respect to the direction of shaft rotation between said shaft and said interior wall surfaces.