CA1079717A - Axial up and circumferentially downward circulating bladed mixer - Google Patents

Abstract

Abstract of the Disclosure Mixing apparatus which includes a housing having a central axis, a rotatable shaft disposed along said central axis and adopted to rotate in a predetermined direction; and a first and second group of interdigitated mem-bers each member having a leading and a trailing edge when said shaft rotates in said predetermined direction, a longitudinal axis and first and second ends each of said first group of members being attached at said first end to said rotatable shaft and extending outwardly from said rotatable sheet toward said housing and each of said second group of members being attached at said first end to said housing and extending inwardly from said housing toward said shaft and all of said members of both said first and said second groups of members comprising shaped members. Each of these shaped members includes first and second longitudinal portions adjacent to said first and second ends, respectively. The first portion has a first lateral axis passing through said longitudinal axis. The first lateral axis slopes downwardly from the leading edge to the trailing edge. The second portion has a second lateral axis passing through the longitudinal axis. The second lateral axis slopes downwardly from the leading edge to the trailing edge. The first and second lateral axes form an acute angle.

Description

79~7~7 Backclround In products comprising a nun~er of individual in-gredients i-t is frequcn-tly desirable -to premix these inyred-ients sufficiently ~o provide a uni~orm slurry which is suit-able ei-ther for immediate use or for further processing in other mixing apparatus. Premixing apparatus for this purpose may include a cylindrical housing with a centrally disposed rotatable shafk. A nur~ber of rotor blades are mounted on the central shaft so that they extend outwardly toward the sur-roundiny housing and a number of cooperatiny stator blades are mounted about the ou-ter wall of the cylindrical housing so that they extend inwarclly toward thc sha~t in~erdiyitat-incJ ~Jith thc~ rotors. :Cn opcratiorl the central shc~t rota~es causing the atkach~d rotor blades to pass between the stator blades thereby mixing and beating a mixture of ingredients introduced into the housing causing these ingredients to form a uniform slurry.
In prior art devices of this type the individual rotor and stator blades consisted oE elongated subskantially bar-like mer~bers oriented at a uniEorm ancJle to the horizontal plane such that when the shaft rotated the rotors impelled the ingredients to be miY~ed downwardly within the cylindrical housing. In such an appara-tus centrifugal force causes a vortex to form about the central shaft and the ingredients tends to ride up along the~outer wall of the housing where they are incomple-tely mixed~ If such apparatus is filled to ., ' ~

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capac~ y, mat~ricll carl spill ou~ oE thc housi.ng. With such priorart premiY.crs inyredicnts introduced i~ O the top of the housiny o:Eten failed to mi~ adequLItely within an accept-able period of mixiny ~cime because of the lack of circulation of the ingredients within -the housing.
In commercially useablc premixing apparatus of the t~pe described above, it is important to provide thorough mixing of a maximum quantity oE ingreclients in a minimum time without the incorporation of air into the mix-ture. Air should be excluded during this premixing st~p so that controll-ed amounts of air may be introduced into the mixture in later processincJ sl:eps. "
With pri.or art apparal:us tllo usor hacl t:o ~hoos~ be-tween two equally unCatis~actor~ alternatives. ~Ie could achieve adequate mixing in a relatively short time if the cylindrical - ;
housing was filled to only approximately 80% of its capacity or he could fill the housing to its capacity which would re-quire mixing times up to five times as lony. Since such lony mixing times were unacceptable most users chose to utilize only 80% o:E the rated capacity of their e~uipment. Because of the large vortex about the central shaEt and the tendency for material to clim~ up along the outer housing wall, such prior art apparatus also tended to introduce varying amounts of a ir lnto the s lurry .
~he above 6eiicie~ cies oi the prior art appara.-ls . .
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1~7~ L7 are overcome in the present apparatus by utilizing an improved configuration for the rotor and/or stator blades of the premixer. The use of rotor and/or stator blades of the inventive configuration results in better overall cir-culation of the ingredients introduced into the cylindrical housing and pro-vides more thorough mixing of a larger quantity of material within a far shorter time than prior art devices as described above while avoiding the introduction of air into the premixed slurry.
Summary of the Invention The invention provides mixing apparatus including a housing having a central axis, a rotatable shaft disposed along said central axis and adapted to rotate in a predetermLned direction; and a first and second group of interdigitated members each member having a leading and a trailing edge when sald shaft rotates ln sald predetermLned dlrectlon, a longltudlnal axls and Elrst flnd second ends, each of sald fLrst grouy oE members belng attached at sald flrst end to sald rotatable shaft and extendlng outwarclly from sald rotatable shaft toward said housing and each of said second group of members being attached at said first end to said housing and extending inwardly from said housing toward said shaft, and all of said members of both said ~irst and said second groups of members comprising shaped men~ers, each of said shaped members including first and second longitudinal portions ad~acent respectively to sald first and second ends, sa:Ld Elrst portlon having a first lateral axis passing through sald longltudinal axis, sald flrst :Lateral axls sloplng upwardly from sald leadlng to sald tralllng edge, and a second por-tion having a second lateral axis passing through said longitudinal axis, said second lateral axis sloping downwardly from said leading to said trail-ing edge, said first and second lateral axes forming an acute angle.

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Description of the Drawings Figure 1 is a partially sectional side elevational view of the premixer of this invention.
Figure 2 is an enlarged side elevation of a portion of Figure 1.
Figure 3 is a cross sectional view taken along plane 3-3 of Figure 1.
Figure 4 is a cross sectional view taken along plane 4-4 of Figure

2.
Description of the Invention Figure 1 shows a pre-mlxing apparatus utilizing the improved rotor and stator blades of the present invention. The apparatus 10 includes a substantially cylindrical housing 12 and a centrally mounted rotatable shaEt 14. Means, such as a motor and assocLated drLve train, which are not shown but are welL known ln the art n~ay be prov:Lded to turn the rotatabLe ~hclft L4.
A n~lmber oE ~tator blades :L6 are attactlcd to cyllndrlcal houslll~ 12 at a first end 16a by welding or other suitable means and extend inwardly in a substantially horizontal plane in the direction of shaft 14. The inner ends 16b of the stators 16 are positioned a short distance from the rotatable shaft 14. A number of rotors 18 are attached at a first end 18a to the rotating shaft 14. An aperture 11 having the same inside diameter as the outside diameter of ~7~37~7 shaft 1~ ma~ be fo.~ned in t}le end l~a oE each rotor 18 and the wall of thc aperture lL may be attaciled to shc~ft 14 b~
weldin~ or o-ther suitclble mcans. The rotors 18 extend out-t~ardly rrom the shaft 14 i.n a substantiall~ horizontal plane in the direction of thc housing 12. The outer ends 18b of rotors 18 are spaced a short clistance from the housing 12 to permit rotation.
- As can best be seen in Fiyures 2, 3 and 4 each of the stator blades 16 includes a first longi-tudinal portion 20 which is adjacent to housiny 12 and a second lonyitudinal portion 22 which is spaced from the housing 12. As best seen in Fiyure ~ the lateral axis 21 o~ t:he firc,t lonyitudinal portion 20 is or.i~ntccl at an ang:L~ with rQsp~ct: to a horiY,on~
tal plane 13 pa~s:incJ throucJh th~ stator 16. The :Lateral axis 23 of the second portion 22 of stator lG is oriented at an approximately equal and opposi-te angle wi-k~ respect to the horizontal plane 13. Within a central portion 25, the stator blacle 16 chanyes from the first to the second orientation with respect to the horizontal plane 13.
A st~tor blad~ 1~ as described abovQ may be ~ormed by bending a sinyle member o~ substantlaLly rect~ngular cross section about its longitudinal axis until the desired orientation of por-; tions 20 and 22 is achieved, by casting the member in -this shape or by fixedly attaching two separa-te parts constituting respectivel portions 20 and 22, Eor example, by t~elding these portions toge-ther , .

~0797~7 within th~ ccntral por-tion 25 to fo.~n a unitary rnel~er. In either case the la-teral aY~es 21 and 23 of portions 20 and 22 of the completed ~-kator 16 fo~n an acute angle which is pre-ferably bisected b~ the horizontal plane 13. It has been found that an angle o~ approxima-tely 40 between the lateral axes 21 and 23 WhiCIl iS bisected by the horizontal axis 13 so that axes 21 and 23 are each oriented at an angle of 20 with respect to the hori~ontal axis provides a-stator of superior mixing characteristics.
As can best be seen in Figures 3 and 4 individual skator blades 16 may be tapered from a maximurn width at the first end 16a ~hich ic: attached to the housinc~ wall 12 to a minim~n width at th~ sccond ~ncl 16b which is adjacent to thc rotatiny shaft 14. This taper provides a maxim~n widkh at the point of attachrnent to the housing 12 and provides a lesser width at the end 16b spaced froTn-khe housing. This taper results in a decrease in the vertical spacing between the rotors and stators, thus allowing more mixing elements in a given height of unit. This increases the mixing.capa-~0 city of the unit and at the same t.ime gives ma~irnum strength to the blades. It has been found that an angle o~ taper of approximately 2 along each of the longitudinal sides of the stator 16 provides a superior stator from the point of view of both strength and element spacing.
Fiuu~es ., 3 and 4 also sllow th~ rotor memb-r- 18 97~L7 in detail. The rotol- blade.-, :L~ includc a first end 18a having a groovc 11 :Eormed therein. The groove 11 has substantially the same insid~ ~iametcr as the ou~sicle diameter of cylindrical shaft 14 so that rotor member 18 may be fixedly attached to shaft 14 by weldi}lg or other suitable means along groove 11.
Rotors 18 exkend outwardly from the shaEt 14 in a subs-tantially horiæontal plane such as 31 in Figure 4 terminating in end 18b which is adjacent to, but spaced from, the housing 12 to permit rotation of the rotors 18 when shaft 14 is rotated.
The rotors 18 include a first lon~i-tudinal portion 30 which is adjacent to end 18a and a second longitudinal por-tion 32 adjac~nt to end 18b and located at the outcr cncl of the ro~or~ ~5 in the cca~c o~ stator 1~ the ~irs~ porti.on 30 is slanted so l-hat its lat~ra~ axis 34 orms an anc31e with the horizontal plane 31. The second por-tion 32 is slan;ted in a direction opposite to portion 30 with respect to the hori-zontal plane 31 so that its lateral axis 36 ~o.rms an anyle which is opposed to and preferably substantially equal to the angle formed by the lateral axis 34 of the ~irst portion 30.
It has been found t~lat providincJ an ancJle o:E approximately ~0 between the lateral axes 3~ and 36 which is approximately bi-sected by the horizontal plane 31 results in a ro-tor of superior mixing qualities.
As in the case oE stator 16, the rotor 18 further includes a central portion 28 in which the rotor lateral ~797~7 axis chancJes from ~he orierltcltion in the first portion 30 to that in the second po~tion 32. A'; in the case o~ stators 16, rotors 18 may he formed Frol~ a sinyle bar me~ber by bend-iny the mernber to provide the desired confiyuration by cast-ing a member in that confiyuration or by fixedly joining two separate mer~ers comprising rcspectively por-tions 30 and 32 in a manner known in the art, such as welding, within portion 28 to forrn a unitary member.
As can best be seen in Figur~s 3 and 4 the rotors 18 are tapered from a maximum wi.dth at end 18a where they are attached to shaft 14 to a minimurn width at their outer end 18b. As in the casc of stators 16 this res~lts in a rotor of sup~rior str~ngth whilc permi.ttlncJ a maxi.mum n~er oE
rotors and s~ators to be Inoulltecl with:in tlle ava:Llabl~ space in the premixer apparatus. As in the case of stators 16, the rotors 18 are tapered at an angle of approxirnately 2 along each longitudinal side oL the rotor to provide a superior rotor configuration haviny maxim~un width and therefore strength a-t their point of attachment to shaft 1~. rraperiny both the xotors and stators permits th~ :incl.usion of an oxtra set oE
blades and can provide up to 25% better rnixiny.
As can best be seen in Figure 2, the rotors 18 interdigitate with the s-tators 16 as they are rotated by .
sha-ft 14 so that the smaller second por-tion 32 of the rotor passes over the laryer first por-tion 20 of the stator. Por-tion 32 of each rotor 16 slants downwardly at a first anyle approximately equal and opposite -to the anyle ~t which the 2~ first portion 20 of the stator is orien-t~d upward with : _9_ ~6)7~7~7 respect to ~he horizontal axes passing t~oucJh them. The shaft 14 rotates in clockwise direction as sho~/n by arrow 50, Figure 3, so that the rnaterial -to be mixed tends to be im-pelled down~lardly by portion 32 of the rotor across the sloping surface of p~rtion 20 of thc adjacent stator in areas adjacent to housiny 12 yiviny rise to the downt1)ard circulation of ma-terial in this area shown by arrows 52.
The first portion 30 of rotor 18 passes over the second portion 22 of the stator. Portion 30 of the rotor, slants up~lardly at an approximately equal and opposite angle to the dowm~ard slope of stator port:ion 22 with respect to the ' horizontal axes passiny throucJh ~'hem. ~5 the shaft 14 rotates in a cloc~wis~ directlon a~ sho~ln 'by ~;'igur~, 3 the mat~rial to be mixed is impe~led upward aloncf shaft 1~ by rotatincJ rotor ' 15, portion 30 across the under surface of stator portion 22 giv-ing rise to an overall upward movernent of material along shaft 14 as shown by arrows 52. The combination of these two mo-tions provides an overall circulation of the material to be mixed as shown by a.rrows 52 and provides sup~rior mi~incJ capabllity without th~ incorporation o~ a:L.r into th~ slurry.
By crea-ting the circulation shown by arrows 52 the improved rotor and stator configuration offsets the tendency of the ma-terial being mixed to climb up -the housing wall~
. The upward force along -the shaft 1~ also minimizes the tend-ency of the material to form a vortex along the shaft 14.
By preven-ting' material from riding up -the housing wall and decreasing the vortex adjacent to the ,shaft 14 the improved !

' 1~797~7 apparatus cJreatl~ clccreases tl-le anlount o~ undcsil-clble ~ir wnich is in-troduccd in~o the ~ c;redicn~s during premixing.
By providing a ~encral ci.rculati.on of mcltcrial within housing 12 as illustrated by arro~s 52 of Figures 1 and 2 all in-gredients move throuyh the various levels within housing 12 and are thoroughly mixed off-settincJ -khe tcndency found in prior art apparatus ~or material to remain at the top of the housing and not be mixed with other inyredients.
Although the above preferrecl embodiment has been described as utili~ing both stators and rotors of applicant's improved configuration considerable improv~ment over prior art premixers can be achieved i~ either the .rotors or l-.he sta~ors u~ilize thc improved con:E.igurat:ion while the other members are made ln the prior art bar-like shape. A greater 1- 15 improvement is realized if the rotors alone are made in the improved configuration rather than the stators alone being made in this con~iguratior- but some improvement is realiæed in either case. If desired only some o~ ~le rotors and/or stators can be made in ~he -improved coniguration while others are made in accordance witll the prior art. This again will result in improvement ove.r prior art apparatus. .
In prior art premixers of the same size using con-ventional rotor and stator blades only 800 pounds of material to be mixed could be loaded into a mixer rated at 1,000 pound capacity if mixing was -to be completed witllin 2-1/2 minutes.

~ ~ 7~ ~ 7 If a full 1,000 pound~ wae placed in the housing 12 of the mixer a ~ubstantially longer period wa~ required to achleY0 adequate mixing in prior art mixer3~ By co~traet, the im~
proved premixQr of thi~ invantion utilizing applica~t~s im~
proved rotors and stators provide~ ~uperior mixing of loads of up to 1,000 pounds, or full rated capacity, ln ander 2 minut~
with no sub~tantial incorporation of air i:n the mixture.
The improved c~rculation provided by the conflguration and arrangement of rotor and ~ta~or blade~ in this premixer al~o prevent~ dry material~ from remaining at the top o~ th~ mix-ing conSainer and cause~ tham to m~x in with the remainder of the mixture.
Although the present in~ention has been descr:Lbed in oonjunct;Lon with preferred embodiments, lt i~ to b~
under~tood that modiflcations and variations may be r~sorted to wlthout departing from the spirik and scope of the ~nven-tion as those ~killed in the ark will readily under~tand.
Such modif~catione and variations ar~ considered to be within 19 the purview and scope of the inven~ion and appended claim~.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Mixing apparatus including a housing having a central axis; a rotatable shaft disposed along said central axis and adapted to rotate in a predetermined direction; and a first and second group of interdigitated members each member having a leading and a trailing edge when said shaft rotates in said predetermined direction, a longitudinal axis and first and second ends, each of said first group of members being attached at said first end to said rotatable shaft and extending outwardly from said rotatable shaft toward said housing and each of said second group of members being attached at said first end to said housing and extending inwardly from said housing toward said shaft, and all of said members of both said first and said second groups of members comprising shaped members, each of said shaped members including first and second longitudinal portions adjacent respective-ly to said first and second ends, said first portion having a first lateral axis passing through said longitudinal axis, said first lateral axis sloping upwardly from said leading to said trailing edge, and a second portion hav-ing a second lateral axis passing through said longitudinal axis, said second lateral axis sloping downwardly from said leading to said trailing edge, said first and second lateral axes forming an acute angle.

2. Mixing apparatus as claimed in claim 1 in which said longitudinal axes of said members are in planes substantially perpendicular to said central axis and in which said planes bisect the angle defined by said first and second lateral axes of said shaped members.

3. Mixing apparatus as claimed in claim 2 in which the angle between said plane and each of said first and second lateral axes of said shaped members is approximately 20°.

4. Mixing apparatus as claimed in claim 1 in which the acute angle formed by said first and said second lateral axes of said shaped members is approximately 40".

5. Mixing apparatus as claimed in claim 1 in which at least some of said members in at least one of said first and second groups of members are tapered from a maximum width at said first end to a minimum width at said second end.

6. Mixing apparatus as claimed in claim 5 in which the angle of said taper is approximately 2° along each lateral side of said member.

7. Mixing apparatus including: a housing having a central axis; a rotatable shaft disposed along said central axis and adapted to rotate in a predetermined circumferential direction;
and a plurality of stator members having first and second ends, and leading and trailing edges with respect to said predetermined circumferential direction each of said stator members being attached at said first end to said housing and extending inwardly in a substantially horizontal plane so that said second end is positioned adjacent to said rotatable shaft, each of said stators having a first portion adjacent to said first end, said first portion having a first transverse axis which slopes upwardly from said leading to said trailing edge to form a first acute angle with said horizontal plane and a second portion adjacent to said second end, said second portion having a second trans-verse axis which slopes downwardly from said leading to said trailing edge to form a second angle with said horizontal plane which second angle is substantially equal and opposite to said first angle; and a plurality of rotor members having a first and second end and leading and trailing edges when said shaft rotates in said predetermined circumferential direction inter-digitated with said stator members, each of said rotor members being attached at said first end to said rotatable shaft and extending outwardly from said shaft in a substantially horizontal plane so that said second end is positioned adjacent to said housing, each of said rotor members having a first portion ad-jacent to said first end, said first portion having a first transverse axis which slopes upwardly from said leading to said trailing edge to form a third acute angle with said horizontal plane and a second portion adjacent to said second end, said second portion having a transverse axis which slopes downwardly from said leading to said trailing edge to form a fourth acute angle with said horizontal plane, said third and fourth angles being substantially mutually equal and opposite.

8. Mixing apparatus as claimed in claim 7 in which said third angle is substantially equal and opposite to said second angle and said first angle is substantially equal and opposite to said fourth angle.

9. Mixing apparatus as claimed in claim 7 in which at least some of said rotor members are tapered from a maximum lateral width at said first end to a minimum lateral width at said second end.

10. Mixing apparatus as claimed in claim 7 in which at least some of said stator members are tapered from a maximum lateral width at said first end to a minimum lateral width at said second end.