Abstract:
A rotor-stator assembly includes a rotor and a stator, each of which includes at least one surface having a plurality of grooves defining a plurality of ridges and valleys. The grooves are located so that material in the rotor grooves is caused to collide with material in the stator grooves or vice versa. Ideally, the grooves have a curved cross section so that material is caused to spin in the grooves. Material spinning in a stator groove is caused to collide with material spinning in a rotor groove and vice versa. The number of times that particles are caused to collide depends on the number and length of the grooves in relation to the depth of the grooves. Shear zones are located between the grooves on the stator and the grooves on the rotor.

Description:
BACKGROUND OF THE INVENTION 
     1.Field of the Invention 
     The invention relates to mixers and emulsifiers used in industrial applications. More particularly, the invention relates to rotors and stators which are used in industrial mixers and emulsifiers. 
     2.State of the Art 
     Industrial mixers and emulsifiers are used to blend various materials such as adhesives, coatings, cosmetics, foods, pharmaceuticals, plastics, etc. Depending on the processing requirements, mixers/emulsifiers may be arranged as a “batch” mixer or an “in-line” mixer. In either case, high speed mechanical and hydraulic shearing forces are created by rotating a rotor relative to a stator such that material is drawn axially into the rotor-stator assembly and dispersed radially outward from the rotor-stator assembly. Prior art FIG. 1 shows a schematic representation of a typical rotor-stator assembly  10 . The rotor  12  is a stainless steel disk  14  with a number of teeth or vanes  16  and the stator  18  is a stainless steel cylinder having radial openings  20 . The rotor  12  is mounted coaxially within the stator  18  and is rotated at a typical speed of 3600 rpm. A close clearance between the rotor and the stator generates a shearing action. Many different rotor and stator designs are in use today. Prior art FIG. 2 shows another type of rotor-stator assembly  22  shown in schematic form. Here the rotor  24  and the stator  26  are substantially similar stainless steel cylinders each having a plurality of teeth or blades  28 ,  30  which define a plurality of radial openings  32 ,  34  in the cylinder. The rotor  24  has a slightly smaller diameter than the stator  26  and generates a shearing action between the openings  32 ,  34  as it rotates relative to the stator  26 . Prior art FIG. 3 shows a “multi-rowed” rotor-stator assembly  36 . The multi-rowed rotor  38  and the multi-rowed stator  40  are similar cylindrical members each having arrays of teeth  42 ,  44  arranged in concentric circles. The rotor  38  and the stator  40  are dimensioned so that the rotor  38  fits inside the stator  40  with the rotor teeth  42  and the stator teeth  44  interleaved. Rotor-stator assemblies are available in a variety of sizes, ranging in diameter from two to thirteen inches. The teeth or vanes on a rotor-stator typically have a height which is approximately one tenth to one fifth the diameter of the rotor-stator. 
     Co-owned U.S. Pat. No. 5,632,596 discloses a rotor-stator assembly having vanes with slots as shown in prior art FIGS. 4-8. The stator  100  is a stainless steel disk having a central fluid opening  102  and a pair of diametrically opposed mounting holes  104 ,  106 . One surface of the stator  100  is provided with seven concentric vanes  108 ,  110 ,  112 ,  114 ,  116 ,  118 ,  120  which define six concentric wells  109 ,  111 ,  113 ,  115 ,  117 ,  119 . Forty-four radial slots, e.g.  122 , are arranged at intervals of 8°, thereby defining forty-four teeth, e.g.  124 , in each vane. The rotor  150  is a stainless steel disk having a central keyed mounting hole  152 . One surface of the rotor  150  is provided with seven concentric vanes  158 ,  160 ,  162 ,  164 ,  166 ,  168 ,  170  which define six concentric wells  159 ,  161 ,  163 ,  165 ,  167 ,  169 . Forty-four radial slots, e.g.  172 , are arranged at intervals of 8°, thereby defining forty-four teeth, e.g.  174 , in each vane. The rotor  150  is dimensioned to match the stator  100 . The vanes in the rotor are placed so that they fit into the wells in the stator. The overall heights of the rotor  150  and the stator  100  are dimensioned to provide proper clearance between the rotor and the stator as shown in FIG.  8 . 
     The rotor-stator of the &#39;596 patent achieved a higher amount of shear than the prior art rotor-stators which preceded it. However, there is a limit to the amount of shear which can be achieved with this design. In particular, it has been discovered that the slots in the vanes can allow some material to pass through without being sheared very much. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide rotor-stator assemblies which can develop a very high amount of shear. 
     It is also an object of the invention to provide rotor-stator assemblies which can handle a large throughput with consistent shearing. 
     It is another object of the invention to provide rotor-stator assemblies which do not permit any material to pass through without being sheared very much. 
     It is still another object of the invention to provide rotor-stator assemblies which can process materials which could not be processed by prior-art rotor-stator assemblies. 
     It is a further object of the invention to provide rotor-stator assemblies which can be used in liquid/liquid emulsions, liquid/solid particle dispersions, liquid/solid particle deaglomeration, liquid/solid particle size reduction, liquid/gas dispersion, and solid/gas particle size reduction. 
     In accord with these objects which will be discussed in detail below, the rotor-stator assembly of the present invention includes a rotor and a stator, each of which includes at least one surface having a plurality of grooves defining a plurality of ridges and valleys. The grooves are located so that material in the rotor grooves is caused to collide with material in the stator grooves or vice versa. Ideally, the grooves have a curved cross section so that material is caused to spin in the grooves. Material spinning in a stator groove is caused to collide with material spinning in a rotor groove and vice versa. The number of times that particles are caused to collide depends on the number and length of the grooves in relation to the depth of the grooves. Shear zones are located between the grooves on the stator and the grooves on the rotor. When the rotor spins, all the material is forced through the entire shear zone or zones. 
     Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1-3 are exploded schematic perspective views of prior art rotor-stator assemblies; 
     FIGS. 4-8 are plan and sectional views of a rotor and stator according to co-owned U.S. Pat. No. 5,632,596; 
     FIG. 9 is a perspective view of a rotor according to a first embodiment of the invention; 
     FIG. 10 is a perspective view of a stator according to the first embodiment of the invention; 
     FIG. 11 is an enlarged perspective view of a portion of the rotor of FIG. 9; 
     FIG. 12 is an enlarged perspective view of a portion of the stator of FIG. 10; 
     FIG. 13 is a schematic sectional view of the rotor and stator of the first embodiment illustrating the locations of two shear zones; 
     FIG. 14 is a sectional view of the rotor of the first embodiment illustrating the keyed mounting hole; 
     FIG. 15 is a sectional view of the stator of the first embodiment illustrating the central fluid entry port and mounting holes; 
     FIG. 16 is a schematic view of the grooves of the rotor and the stator of the first embodiment; 
     FIGS. 17-19 are views similar to FIG. 16 showing alternate geometries for the grooves; 
     FIG. 20 is a schematic sectional view of a second embodiment of the invention having a single shear zone on the outer surface of the stator; 
     FIG. 21 is a schematic sectional view of a third embodiment of the invention having a single shear zone on the inner surface of the stator; 
     FIG. 22 is a schematic sectional view of a fourth embodiment of the invention having four shear zones; 
     FIG. 23 is a schematic sectional view of a fifth embodiment of the invention having five shear zones with progressively smaller grooves in each zone; 
     FIG. 24 is a schematic sectional view of a sixth embodiment of the invention having five shear zones, all with the same size grooves; 
     FIG. 25 is a schematic sectional view of a seventh embodiment of the invention having a single shear zone made up of grooves which are long relative to their depth; 
     FIG. 26 is a schematic sectional view of a eighth embodiment of the invention similar to the seventh embodiment but with a non-tapered shear zone; 
     FIG. 27 is a schematic sectional view of an ninth embodiment of the invention having radial shear zones; 
     FIG. 28 is a schematic sectional view of a tenth embodiment of the invention having a low profile and fifteen shear zones; and 
     FIG. 29 is an enlarged detail of the tenth embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIGS. 9 through 16, the first embodiment of the invention includes a rotor  200  and a stator  202 . The rotor  200  has a central keyed hole  204  and a circular well  206  which defines an outer surface  208  and an inner surface  210  each of which are provided with a plurality of parallel grooves  211 ,  213  (seen best in FIG.  11 ). The stator  202  has a central fluid entry port  212 , a plurality of mounting holes  214  arranged around the entry port  212 , an upstanding circular flange  216  defining an outer surface  218  and an inner surface  220 , each of which are provided with a plurality of parallel grooves  219 ,  221  (seen best in FIG.  12 ). 
     According to the first embodiment, the diameter of the rotor  200  is approximately 12.00″ and the depth of the well  206  is approximately 1.25″. As seen best in FIGS. 11 and 16, the grooves  211 ,  213  in the surfaces of the well are substantially circular in section. According to this embodiment, the grooves are approximately 75% circular and have a diameter of approximately 0.25″ giving them a depth of approximately 0.1875″. The center to center spacing of the grooves is approximately 0.310″ and the ratio of groove spacing to groove depth is approximately 1.6:1. According to the invention, this ratio should be small and should not exceed 10:1. The stator is similarly dimensioned so that the upstanding flange  216  fits inside the well  206  as shown in FIG.  13 . Moreover, the flange and the well are tapered approximately 7° so that the clearance between them may be adjusted. Tests performed with this embodiment were performed with a clearance of approximately 0.005″. 
     As shown best in FIGS. 13-15, this embodiment presents two shear zones, one between the surfaces  210  and  220  and the other between the surfaces  208  and  218 . In operation, material flows into the inlet port  212 , is drawn into the first shear zone  210 - 220  and forced out to the second shear zone  208 - 218  and is forced out of the assembly through the peripheral space between the rotor  200  and the stator  202 . As the material passes up the first shear zone and down the second shear zone, high velocity streams traveling in the stator grooves interact with high velocity streams traveling in the rotor grooves. In particular, material traveling in the respective streams collide a number of times. 
     As mentioned above, the grooves define ridges and valleys. As shown in FIG. 16, the grooves  211  define ridges  211   a  and valleys  211   b  and the grooves  219  define ridges  219   a  and valleys  219   b . The ridges  211   a  interact with the valleys  219   b  and the ridges  219   a  interact with the valleys  211   b  causing the material in the grooves to spin. It is for this reason that the grooves are preferably curved in cross section. According to the first embodiment, the grooves are 75% circular in section and it is preferred that they are no less than 50% circular. As shown in FIGS. 17-19, the grooves  211 ′,  219 ′,  211 ″,  219 ″,  211 ′ ″,  219 ′ ″ may have other curved sections which are not strictly circular but which nevertheless define ridges and curved valleys. 
     FIG. 20 shows a second embodiment of the invention where rotor  300  is provided with a well  306  which defines only a single inner surface  308  for grooves. The stator  302  similarly has an upstanding member  316  which defines only a single outer surface  318  for grooves. These surfaces and their grooves form a single shear zone. Material flows downward through the single shear zone. 
     FIG. 21 shows a third embodiment of the invention where rotor  400  is provided with a frustrum  406  which defines only a single outer surface  410  for grooves. The stator  402  has an upstanding member  416  which defines only a single inner surface  420  for grooves. These surfaces and their grooves form a single shear zone. Material flows upward through the single shear zone. 
     FIG. 22 shows a fourth embodiment similar to the first embodiment except that the rotor  500  has two concentric wells  506 ,  506 ′ and the stator  502  has two concentric upstanding circular flanges  516 ,  516 ′. Both of the wells and both of the flanges are provided with grooves and the resulting assembly has four shear zones. 
     FIGS. 23 and 24 show fifth and sixth embodiments of the invention which are similar and where similar reference numerals refer to similar parts. According to these embodiments, the rotor  600  ( 700 ) has two concentric upstanding members  605 ,  605 ′ ( 705 ,  705 ′) defining five surfaces  630 ,  632 ,  634 ,  636 ,  638  ( 730 ,  732 ,  734 ,  736 ,  738 ). The stator  602  ( 702 ) has three concentric upstanding members  616 ,  616 ′,  616 ″ ( 716 ,  716 ′,  716 ″) defining surfaces so that the rotor stator has five shear zones  640 ,  642 ,  644 ,  646 ,  648  ( 740 ,  742 ,  744 ,  746 ,  748 ). None of the upstanding members are tapered. In the sixth embodiment all of the shear zones have the same sized grooves. In the fifth embodiment, the shear zone  640  has larger grooves than the grooves in the shear zone  642 ; the shear zone  642  has larger grooves than the grooves in the shear zone  644 ; the shear zone  644  has larger grooves than the grooves in the shear zone  646 ; and the shear zone  646  has larger grooves than the grooves in the shear zone  648 . 
     The seventh embodiment shown in FIG. 25 is substantially the same as the third embodiment shown in FIG. 21 except that the rotor  800  and stator  802  have a much taller profile. 
     The eighth embodiment shown in FIG. 26 is substantially the same as the seventh embodiment shown in FIG. 25 except that the rotor  900  and stator  902  are not tapered. 
     FIG. 27 shows a low profile rotor  1000  and stator  1002  having radial grooves  1011 ,  1019 . The grooves are curved in cross section and define a plurality of ridges and valleys. When in operation all of the ridges on the rotor pass over all of the ridges on the stator. 
     FIGS. 28 and 29 illustrate a low profile tenth embodiment of the invention where the rotor  1100  and the stator  1102  are similar in some respects to the rotor and stator of the &#39;596 patent. Here, however, each of the concentric vanes  1116  on the stator is provided with a plurality of parallel grooves  1119  which extend toward the rotor. Further, each of the concentric wells  1106  on the rotor is provided with a plurality of parallel grooves  1111  which interact with the grooves on the stator as described above. 
     For comparative purposes, two illustrative examples of the effectiveness of the present invention is provided below in tabular form. The tests compare the prior art rotor-stator designs illustrated in FIG. 1, FIG. 3, FIGS. 4-8, to the FIGS. 9-15 embodiment of the present invention. The prior art rotor/stator dimensions are the same as set forth in U.S. Pat. No. 5,632,596, the subject matter of which is incorporated by reference herein. The FIGS. 9-15 embodiment of the mounting employed a 12 inch rotor and 12 inch stator of the type and dimensions described above. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 MEDIAN DROPLET SIZE IN MICRONS 5% OIL IN WATER 
               
               
                 EMULSION 
               
             
          
           
               
                 # OF PASSES 
                 FIG. 1 
                 FIG. 3 
                 FIGS. 4-8 
                 FIGS. 9-15 
               
               
                   
               
             
          
           
               
                 Start 
                 41.21 
                 41.21 
                 41.21 
                 41.21 
               
               
                 1 
                 10.49 
                 3.95 
                 2.79 
                 1.34 
               
               
                 2 
                 6.82 
                 3.38 
                 2.48 
                 0.96 
               
               
                 3 
                 6.15 
                 2.98 
                 2.15 
                 0.85 
               
               
                 4 
                 5.58 
                 2.52 
                 1.91 
                 0.79 
               
               
                 5 
                 5.20 
                 2.35 
                 1.66 
                 0.75 
               
               
                   
               
             
          
         
       
     
     The above results were obtained by recirculating through each device a 5% oil in water emulsion having an initial median droplet size of 41.21 microns. The number of passes were determined by taking the flow rate for each device and the batch size into account to determine the correct sampling time intervals. As can be seen, the above table represents the relative drop or decrease in median droplet size in microns of the 5% oil in water emulsion after five passes through each device. As can be seen, after five passes, the present invention of FIGS. 9-15 produced a median droplet size of 0.75 microns which was more than 50% less than the closest prior art design, thus representing a dramatic improvement in rotor-stator performance over the prior art designs. 
     
       
         
               
             
               
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 NUMBER OF PASSES REQUIRED TO REACH TARGET MEDIAN 
               
               
                 DROPLET SIZE OF 0.13 MICRONS FROM STARTING MEDIAN 
               
               
                 DROPLET SIZE OF 10.87 MICRONS USING A MICRO-EMULSION 
               
               
                 CONSISTING OF 15% OIL, 80% WATER AND 5% SURFACTANT 
               
             
          
           
               
                   
                   
                 FIG. 1 
                 FIG. 3 
                 FIGS. 4-8 
                 FIGS. 9-15 
               
               
                   
                   
               
               
                   
                 # of Passes 
                 1148 
                 87 
                 46 
                 32 
               
               
                   
                   
               
             
          
         
       
     
     In the second test as shown above in tabular form, the prior art rotor-stator designs illustrated in FIGS. 1, FIGS. 3, and FIGS. 4-8 were again compared to the present invention as shown in FIGS. 9-15. A micro-emulsion consisting of 15% oil, 80% water, and 5% surfactant having a starting median droplet size of 10.87 microns was recirculated through each device until a target droplet size of 0.13 microns was reached. The total number of passes required for each device to reach this target median droplet size was recorded and, once again, the number of passes to reach the target median droplet size was determined by taking the flow rate for each device and the batch size into account. As can be seen, the present invention had the lowest number of passes, namely 32, as compared to Applicant&#39;s prior invention of FIGS. 4-8 which took 46 passes to reach the target size. Thus, there was an approximately 30% reduction in the number of passes (and time), further representing a dramatic improvement in rotor-stator performance over the prior art designs. 
     Finally, it should be noted that, although the rotor and stator grooves are shown in the various embodiments as being parallel, they may advantageously be tilted or angled up to about 10 degrees with respect to the vertical, in the same or opposite direction. 
     There have been described and illustrated herein several embodiments of a high shear rotor and stator. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as so claimed.