Patent Publication Number: US-7914200-B1

Title: Mixing blade assembly with trailing scrapers and method

Description:
The present invention relates generally to apparatus and method for mixing liquids and, in particular, feedstock in the form of viscous liquids containing solid constituents, and pertains, more specifically, to directing the flow of such a feedstock to and from heat transfer surfaces within a vessel containing the feedstock in order to enhance heat transfer between the feedstock and the vessel, while attaining greater uniformity within a reduced mixing time. 
     Conventional mixing machines commonly employ mixing blades which confront and move across corresponding surfaces in a vessel within which a feedstock is contained while being mixed so as to facilitate the conduct of heat between the feedstock and these surfaces of the vessel. For example, in a typical mixing apparatus, a mixing blade constructed in the form of a helix is rotated within a vessel having a circular cylindrical side wall extending upwardly from a complementary circular bottom wall, the mixing blade being carried by a support structure having a horizontal support member which sweeps across the bottom wall and a vertical support member which sweeps across the side wall, while the feedstock is circulated within the vessel toward and away from the walls of the vessel by the helical mixing blade. The horizontal and vertical support members carry scrapers which engage corresponding walls of the vessel to scrape feedstock from the walls as the support members sweep past respective walls; however, the support members themselves play little or no part in moving the feedstock toward or away from the walls of the vessel to effect the desired heat transfer during a mixing operation. 
     The present invention provides a construction in which the support structure that carries the mixing blade works in concert with the mixing blade to attain better heat transfer between the feedstock and the walls of the vessel, with a concomitant increase in uniformity gained throughout the feedstock in less mixing time. As such, the present invention attains several objects and advantages, some of which are summarized as follows: Provides a mixing blade assembly in which a mixing blade support structure includes support members constructed to increase the effectiveness of the mixing blade assembly in mixing a batch of feedstock in a mixing vessel; facilitates heat transfer between a batch of feedstock and the walls of the vessel within which the feedstock is mixed, for attaining increased uniformity throughout the batch in less mixing time; reduces resistance to efficient circulation of feedstock within a batch of feedstock being mixed in a mixing vessel, with a concomitant reduction of energy needed to complete a mixing operation; provides a mixing blade assembly placed within a mixing vessel with an additional mixing mechanism, which mixing blade assembly is constructed to interact with the additional mixing mechanism to assist in circulating feedstock within the batch for increased effectiveness of both the mixing blade assembly and the additional mixing mechanism; attains a more uniform mixture within a batch of feedstock in less time and with the consumption of less energy; simplifies the maintenance of a mixing blade assembly for economical long-term operation; provides a rugged mixing blade assembly capable of exemplary performance over an extended service life. 
     The above objects and advantages, as well as further objects and advantages, are attained by the present invention which may be described briefly as a mixing apparatus for mixing constituents of a feedstock, the mixing apparatus comprising: a vessel including a heat transfer surface within the vessel for being engaged by the feedstock as the constituents of the feedstock are mixed within the vessel; a mixing blade assembly including a mixing blade and at least one mixing blade support member, the mixing blade assembly being adapted to move within the vessel to sweep the mixing blade and the mixing blade support member in a forward direction along a path of travel extending adjacent the heat transfer surface to circulate feedstock within the vessel; the mixing blade support member having a mixing surface confronting the heat transfer surface and spaced from the heat transfer surface to establish a passage between the mixing surface and the heat transfer surface, the mixing surface being configured to squeeze feedstock material passing through the passage, whereby the feedstock material squeezed within the passage will be subjected to mixing shear and to heat transfer between the squeezed feedstock and the heat transfer surface; and a scraper blade carried by the mixing blade support member in position to trail behind the mixing surface of the mixing blade support member and engage the heat transfer surface upon movement of the mixing blade support member along the path of travel so as to scrape from the heat transfer surface feedstock material squeezed between the mixing surface and the heat transfer surface and direct the squeezed feedstock material toward the mixing blade to be mixed with feedstock circulated by the mixing blade. 
     In addition, the invention includes a method for mixing feedstock within a vessel wherein the feedstock is moved along a heat transfer surface within the vessel as the feedstock is mixed within the vessel, the method comprising: providing a mixing blade assembly including a mixing blade and at least one mixing blade support member, the mixing blade support member having a mixing surface; confronting the mixing surface with the heat transfer surface and spacing the mixing surface from the heat transfer surface to establish a passage between the mixing surface and the heat transfer surface, the mixing surface being configured to squeeze feedstock material passed through the passage; moving the mixing blade assembly within the vessel to sweep the mixing blade and the mixing blade support member in a forward direction along a path of travel extending adjacent the heat transfer surface to circulate feedstock within the vessel and pass feedstock material through the passage to squeeze the feedstock material between the mixing surface and the heat transfer surface; placing a scraper blade on the mixing blade support member in position to trail behind the mixing surface of the mixing blade support member; and engaging the scraper blade with the heat transfer surface during movement of the mixing blade support member along the path of travel so as to scrape from the heat transfer surface feedstock material squeezed within the passage and direct the squeezed feedstock material toward the mixing blade, whereby feedstock material squeezed within the passage is subjected to mixing shear and heat transfer between the squeezed feedstock material and the heat transfer surface and then mixed with feedstock circulated by the mixing blade. 
    
    
     
       The invention will be understood more fully, while still further objects and advantages will become apparent, in the following detailed description of preferred embodiments of the invention illustrated in the accompanying drawing, in which: 
         FIG. 1  is a somewhat diagrammatic, vertical cross-sectional view of a mixing apparatus constructed in accordance with the prior art; 
         FIG. 2  is a somewhat diagrammatic, vertical cross-sectional view of the apparatus, taken in the direction of arrow  2  in  FIG. 1 ; 
         FIG. 3  is a somewhat diagrammatic, horizontal cross-sectional view of the apparatus, taken in the direction of arrow  3  in  FIG. 2 ; 
         FIG. 4  is an enlarged fragmentary cross-sectional view of a portion of  FIG. 2 ; 
         FIG. 5  is an enlarged fragmentary cross-sectional view of a portion of  FIG. 3 ; 
         FIG. 6  is a somewhat diagrammatic, vertical cross-sectional view of a mixing apparatus constructed in accordance with the present invention; 
         FIG. 7  is a somewhat diagrammatic, horizontal cross-sectional view of the apparatus of  FIG. 4 , taken in the direction of arrow  7  in  FIG. 4 ; 
         FIG. 8  is an enlarged fragmentary cross-sectional view of a portion of  FIG. 6 ; and 
         FIG. 9  is an enlarged fragmentary cross-sectional view of a portion of  FIG. 7 . 
     
    
    
     Referring now to the drawing, and especially to  FIGS. 1 through 3  thereof, a mixing apparatus constructed in accordance with the prior art is shown at  10  and is seen to include a vessel  12  having a circular cylindrical vertical side wall  14  extending upwardly from a circular horizontal bottom wall  16  to a top end  18 . A cylindrical jacket  20  surrounds the side wall  14  and includes vertically arranged chambers  22  for circulating a heat transfer fluid  24  in juxtaposition with vertical side wall  14  and heat transfer surface  25  provided by side wall  14 . A circular jacket  26  is juxtaposed with bottom wall  16  and includes horizontally arranged chambers  28  for circulating a heat transfer fluid  30  in juxtaposition with bottom wall  16  and heat transfer surface  29  provided by bottom wall  16 . 
     A mixing blade assembly  40  includes a helical mixing blade  42  and is mounted for rotation within vessel  12 , about a central axis of rotation  44 , to rotate mixing blade  42  in a direction R about the central axis of rotation  44  and effect mixing of a batch  46  of feedstock  48  placed within vessel  12 . Mixing blade  42  is juxtaposed with vertical side wall  14  and, upon rotation about axis of rotation  44 , in the direction R, effects mixing of the feedstock  48  while driving the feedstock  48  generally upwardly, in a direction from the bottom wall  16  toward the top end  18  of the side wall  14  to circulate the feedstock  48  within the vessel  12 . 
     Mixing blade  42  is carried by a support structure  50  of the mixing blade assembly  40 , the support structure  50  including a generally L-shaped frame  52  comprised of a vertical support member  54  and a horizontal support member  56 . The mixing blade  42  is affixed, adjacent upper end  58  of the mixing blade  42 , to the frame  52 , adjacent upper portion  60  of vertical support member  54 , and is affixed, adjacent lower end  62  of the mixing blade  42 , to the frame  52 , adjacent end  64  of horizontal support member  56 , as by welding the mixing blade  42  to the frame  52  at each end  58  and  62  of mixing blade  42 . The frame  52  is affixed, adjacent upper portion  60  of vertical support member  54 , to a drive member  70  which, in turn, is coupled to a drive motor  72  for effecting rotation of the frame  52 . An additional mixing mechanism is placed within vessel  12 , and is shown in the form of a submersible media mill  80  located coaxial with mixing blade assembly  40  and mixing blade  42 , the media mill  80  having an inlet at  82  and outlets at an apertured wall  84  and at an apertured bottom  86 , as is known in media mills. 
     In the operation of mixing apparatus  10 , mixing blade assembly  40  is rotated simultaneously with the operation of media mill  80 , and feedstock  48  is circulated within vessel  12 . Thus, feedstock  48  enters media mill  80  at inlet  82 , as indicated by arrows A, is processed by the media mill  80  and exits through apertured wall  84  and bottom  86 , directed generally toward the side wall  14 , as indicated by arrows B, and toward the bottom wall  16  of the vessel  12 , as indicated by arrows C. Helical mixing blade  42  moves the feedstock  48  upwardly, as indicated by arrows D, to once again enter the media mill  80  at inlet  82 , again as indicated by arrows A. 
     Usually, feedstock  48  consists of a viscous liquid which contains solid constituents and tends to accumulate along the side wall  14  and the bottom wall  16  of vessel  12 , at the respective heat transfer surfaces  25  and  29 . In order to facilitate the transfer of heat between the feedstock  48  and the heat transfer surfaces  25  and  29  of walls  14  and  16  of vessel  12 , mixing blade assembly  40  is provided with scrapers which engage the walls  14  and  16 , as the mixing blade assembly  40  is rotated, to scrape accumulated feedstock from the heat transfer surfaces  25  and  29  of the walls  14  and  16  and maintain contact between the circulating feedstock  48  and the heat transfer surfaces  25  and  29  of the walls  14  and  16 . Thus, as seen somewhat diagrammatically in  FIGS. 2 and 4 , horizontal support member  56  is spaced from bottom wall  16  by a space  88  and has a triangular cross-sectional configuration, and a bottom scraper blade  90  is carried by the horizontal support member  56 , mounted to a leading face  92  of the support member  56 , angled to engage the bottom wall  16  and scrape feedstock from the heat transfer surface  29  of the bottom wall  16 , and into circulation, as indicated by arrow F. The triangular cross-sectional configuration is oriented with a bottom face  94  of the support member  56  confronting the bottom wall  16 , substantially parallel to the bottom wall  16 , and following behind the scraper blade  90 , while a trailing face  96  of the support member  56  follows behind the leading face  92  and the scraper blade  90 . Scraped feedstock material S is a portion of feedstock  48  intercepted by scraper blade  90  ahead of support member  56  and is directed by scraper blade  90  to flow generally upwardly, away from bottom wall  16 , and over support member  56 , as indicated by arrows E. Thus, little or no feedstock flows through the space  88  between the support member  56  and bottom wall  16 . 
     In a like manner, as seen somewhat diagrammatically in  FIGS. 3 and 5 , vertical support member  54  has a triangular cross-sectional configuration spaced from side wall  14  by a space  98 . A side scraper blade  100  is carried by the vertical support member  54 , mounted to leading face  102  of the support member  54 , angled to engage the heat transfer surface  25  of the side wall  14  and scrape feedstock from the heat transfer surface  25  of side wall  14 , and into circulation, as indicated by arrow FF. The triangular cross-sectional configuration of the support member  54  is oriented so that a side face  104  of the support member  54  confronts the side wall  14 , is substantially parallel to the side wall  14 , and follows behind the scraper blade  100 , while a trailing face  106  of the support member  54  follows behind the leading face  102  and the scraper blade  100 . Scraped feedstock SS is that portion of feedstock  48  intercepted ahead of support member  54  and is directed by scraper blade  100  to flow generally sideways, away from side wall  14 , and over support member  54 , as indicated by arrows EE. Thus, little or no feedstock  48  flows through the space  98  between the support member  54  and side wall  14 . 
     Turning now to  FIGS. 6 through 9 , as well as with some reference to  FIGS. 1 through 5 , a mixing apparatus constructed in accordance with the present invention is shown at  110  and, as before, is seen to include a vessel  112  having a circular cylindrical vertical side wall  114  extending upwardly from a complementary end wall, shown in the form of a circular horizontal bottom wall  116 , to a top end  118 . A cylindrical jacket  120  surrounds the side wall  114  and includes vertically arranged chambers  122  for circulating a heat transfer fluid  124  in juxtaposition with side wall  114  and heat transfer surface  125  provided by side wall  114 . A circular jacket  126  is juxtaposed with bottom wall  116  and includes horizontally arranged chambers  128  for circulating a heat transfer fluid  130  in juxtaposition with bottom wall  116  and heat transfer surface  129  provided by bottom wall  116 . 
     A mixing blade assembly  140  includes a helical mixing blade  142  and is mounted for rotation within vessel  112 , about a central axis of rotation  144 , to rotate mixing blade  142  in a direction RR about the central axis of rotation  144  and effect mixing of a batch  146  of feedstock  148  placed within vessel  12 . Mixing blade  142  is juxtaposed with side wall  114  and, upon rotation about axis of rotation  144 , in the direction RR, effects mixing of the feedstock  148  while driving the feedstock  148  generally upwardly, in a direction from the bottom wall  116  toward the top end  118  of the side wall  114 , to circulate the feedstock  148  within the vessel  112 . 
     Mixing blade  142  is carried by a support structure  150  of the mixing blade assembly  140 , the support structure  150  including a generally L-shaped frame  152  comprised of a vertical support member  154  and a horizontal support member  156 . The mixing blade  142  is affixed, adjacent upper end  158  of the mixing blade  142 , to the frame  152 , adjacent upper portion  160  of vertical support member  154 , and is affixed, adjacent lower end  162  of the mixing blade  142 , to the frame  152 , adjacent end  164  of horizontal support member  156 , as by welding the mixing blade  142  to the frame  152  at each end  158  and  162  of mixing blade  142 . The frame  152  is rotated about axis of rotation  144  in a manner similar to that described above in connection with the rotation of frame  52  of mixing blade assembly  40 . As before, an additional mixing mechanism is placed within vessel  112 , and is shown in the form of a submersible media mill  180  located coaxial with mixing blade assembly  140  and mixing blade  142 , the media mill  180  having an inlet at  182  and outlets at an apertured wall  184  and at an apertured bottom  186 , as is known in media mills. 
     In the operation of mixing apparatus  110 , mixing blade assembly  140  is rotated simultaneously with the operation of media mill  180 , and feedstock  148  is circulated within vessel  112 . Thus, feedstock  148  enters media mill  180  at inlet  182 , as indicated by arrows AA, is processed by the media mill  180 , and exits through apertured wall  184 , directed generally toward the side wall  114 , as indicated by arrows BB, and exits through bottom  186 , directed toward the bottom wall  116  of the vessel  112 , as indicated by arrows CC. Helical mixing blade  142  moves the feedstock  148  generally upwardly, as indicated by arrows DD, to once again enter the media mill  180  at inlet  182 , again as indicated by arrows AA. 
     As set forth above, usually feedstock  148  consists of a viscous liquid which contains solid constituents and tends to accumulate along the side wall  114  and the bottom wall  116  of vessel  112 . As before, in order to assist in the transfer of heat between the feedstock  148  and the respective heat transfer surfaces  125  and  129  of walls  114  and  116  of vessel  112 , mixing blade assembly  140  is provided with scrapers which engage the heat transfer surfaces  125  and  129  of walls  114  and  116 , as the mixing blade assembly  140  is rotated, to scrape accumulated feedstock from the walls  114  and  116  and maintain contact between the circulating feedstock  148  and the heat transfer surfaces  125  and  129  of walls  114  and  116 . Thus, as seen somewhat diagrammatically in  FIGS. 6 and 8 , horizontal support member  156  has a polygonal cross-sectional configuration, shown in the form of a triangular cross-sectional configuration, and a bottom scraper blade  190  is carried by the horizontal support member  156 . However, in the improvement of the present invention, support member  156  includes a mixing surface  191  confronting the bottom wall  116  and spaced from heat transfer surface  129 , and mixing surface  191  is configured to squeeze feedstock between mixing surface  191  and heat transfer surface  129  as support member  156  is moved forward, in the direction RR, during rotation of frame  152  about axis of rotation  144 . To that end, the triangular cross-sectional configuration of support member  156  is oriented with an apex  5  of the triangular cross-sectional configuration confronting the bottom wall  116  so that support member  156  presents a leading face  192  which makes an angle α with the bottom wall  116 , and a trailing face  194  which makes an angle β with the bottom wall  116 . A passage  188  is established between horizontal support member  156  and bottom wall  116 . 
     Scraper blade  190  is mounted upon a bracket  196  carried by horizontal support member  156 , the bracket  196  extending rearwardly to space the scraper blade  190  from trailing face  194  in a rearward direction, relative to the direction of rotation RR of the mixing blade assembly  140 . With scraper blade  190  engaged with the heat transfer surface  129  of the bottom wall  116  at an angle θ, and apex δ of the horizontal support member  156  spaced a short distance from the bottom wall  116 , feedstock material M adjacent bottom wall  116  passes through an entrance portion  197  of passage  188  where the passage  188  contracts along leading face  192  and, by virtue of angle α, is urged into a narrow constriction, shown in the form of a throat T at an intermediate portion of passage  188  where the feedstock material M is squeezed between the apex δ and the bottom wall  116 , forcing the feedstock material M against the bottom wall  116 , thereby generating additional shear within the feedstock material M. 
     As the feedstock material M passes through throat T and then through an exit portion  198  of passage  188  where the passage  188  expands along the trailing face  194 , a pressure drop occurs within the feedstock material M, by virtue of angle β. Thus, the leading face  192  and the trailing face  194  establish portions  197  and  198  of passage  188  which, in combination with the intermediate portion of passage  188  at narrow throat T, act in concert to create additional shear in feedstock material M for enhanced mixing. At the same time, the trailing scraper blade  190 , spaced rearwardly from trailing face  194 , directs the flow of feedstock material M toward the helical mixing blade  142 , allowing the mixing blade  142  to pick up the feedstock material M and move mixed feedstock  148  toward the top end  118  of side wall  114 , enabling the scraped feedstock material M to be moved in an orderly and predictable manner, rendering the mixed feedstock  148  more uniform and enhancing heat transfer between the feedstock  148  and the heat transfer surface  129  provided by bottom wall  116 . 
     Further, whereas the flow pattern followed in mixing apparatus  10 , wherein the direction of flow of scraped feedstock material S, as indicated by arrow F in  FIGS. 2 and 4 , is counter to the direction of flow of feedstock  48  leaving the media mill  80  through the bottom  86  of the media mill  80 , as indicated by arrows C, and causes a disruption in the smooth circulation of feedstock  48  from the media mill  80  to the mixing blade  42 , the flow of scraped feedstock material M along the path of travel indicated by arrows P in mixing apparatus  110 , as illustrated in  FIG. 6 , is not counter to the flow of feedstock  148  out of the bottom  186  of the media mill  180 , in the direction indicated by arrows CC, thereby facilitating a smooth and uninterrupted circulation of feedstock  148  from the media mill  180  to the mixing blade  142 , with a concomitant enhancement of uniformity in the mixed batch of feedstock  148  and heat transfer. 
     In a like manner, as seen somewhat diagrammatically in  FIGS. 7 and 9 , vertical support member  154  has a polygonal cross-sectional configuration, shown in the form of a triangular cross-sectional configuration, and a side scraper blade  200  is carried by the vertical support member  154 . Support member  154  includes a mixing surface  201  confronting the side wall  114  and spaced from heat transfer surface  125 . Mixing surface  201  is configured to squeeze feedstock between mixing surface  201  and heat transfer surface  125  as support member  154  moves forward, in the direction RR, during rotation of frame  152  about axis of rotation  144 . To that end, the triangular cross-sectional configuration of support member  154  is oriented with an apex δδ of the triangular cross-sectional configuration confronting the side wall  114  so that support member  154  presents a leading face  202  which makes an angle αα with the side wall  114 , and a trailing face  204  which makes an angle ββ with the side wall  114 . A passage  205  is established between vertical support member  154  and side wall  114 . 
     Scraper blade  200  is mounted upon a bracket  206  carried by vertical support member  154 , the bracket  206  extending rearwardly to space the scraper blade  200  from trailing face  204  in a rearward direction, relative to the direction of rotation RR of the mixing blade assembly  140 . With scraper blade  200  engaged with heat transfer surface  125  of the side wall  114  at an angle θθ, and apex  66  of the vertical support member  154  spaced a short distance from the side wall  114 , feedstock material MM adjacent side wall  114  passes through an entrance portion  210  of passage  205  where the passage  205  contracts along leading face  202  and, by virtue of angle αα, is urged into a narrow constriction, shown in the form of a throat TT at an intermediate portion of passage  205  where the feedstock material MM is squeezed between the apex  66  and the side wall  114 , forcing the feedstock material MM against the side wall  114 , thereby generating additional shear within the feedstock material MM. 
     As the feedstock material MM passes out of throat TT and along an exit portion  212  of passage  205 , where the passage  205  expands along the trailing face  204 , a pressure drop occurs within the feedstock material MM, by virtue of angle ββ. Thus, the leading face  202  and the trailing face  204  establish portions  210  and  212  of passage  205  which, in combination with the intermediate portion of passage  205  at narrow throat TT, act in concert to create additional shear in feedstock material MM for enhanced mixing. At the same time, the trailing scraper blade  200 , spaced rearwardly from trailing face  204 , directs the feedstock material MM toward the helical mixing blade  142 , allowing the mixing blade  142  to pick up the feedstock material MM and move the feedstock material MM toward the top end  118  of side wall  114 , enabling the scraped feedstock material MM to be moved in an orderly and predictable manner, rendering the mixed feedstock  148  more uniform and enhancing heat transfer between the feedstock  148  and the heat transfer surface  125  provided by the side wall  114 . 
     Scraper blades  200  and  190  preferably are constructed of a flexible material enabling the scraper blades  200  and  190  to conform closely to the respective side and bottom walls  114  and  116  for effective scraping of feedstock material M and MM to accomplish the objectives of the present invention. 
     It will be seen that the present invention attains all of the objects and advantages summarized above, namely: Provides a mixing blade assembly in which a mixing blade support structure includes support members constructed to increase the effectiveness of the mixing blade assembly in mixing a batch of feedstock in a mixing vessel; facilitates heat transfer between a batch of feedstock and the walls of the vessel within which the feedstock is mixed, for attaining increased uniformity throughout the batch in less mixing time; reduces resistance to efficient circulation of feedstock within a batch of feedstock being mixed in a mixing vessel, with a concomitant reduction of energy needed to complete a mixing operation; provides a mixing blade assembly placed within a mixing vessel with an additional mixing mechanism, which mixing blade assembly is constructed to interact with the additional mixing mechanism to assist in circulating feedstock within the batch for increased effectiveness of both the mixing blade assembly and the additional mixing mechanism; attains a more uniform mixture within a batch of feedstock in less time and with the consumption of less energy; simplifies the maintenance of a mixing blade assembly for economical long-term operation; provides a rugged mixing blade assembly capable of exemplary performance over an extended service life. 
     It is to be understood that the above detailed description of preferred embodiments of the invention is provided by way of example only. Various details of design, construction and procedure may be modified without departing from the true spirit and scope of the invention, as set forth in the appended claims.