Abstract:
An agitator assembly, in particular for mixing, granulating and drying solid matter, includes a vessel; and an agitator received in the vessel and having at least one sweep blade, with the sweep blade ascending from an inner zone of the vessel to an outer zone thereof at an angle of inclination ranging from about 15° to 60° with respect to the horizontal.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application Serial No. 100 06 253.9, filed Feb. 11, 2000 the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates, in general, to agitator assemblies, and more particularly to an agitator assembly of a type having one or more sweep blades mounted at a motor driven shaft and operating in an agitation vessel. 
     Agitator assemblies of this type are typically used for mixing, granulating and drying solid matter. In this case, it is desirable to avoid inadequate or insufficient mixing during agitation. Furthermore, if agitation is carried out for drying solid matter, agitation should not only provide proper mixing of the solid matter but, in addition, should also provide a high degree of heat transfer during the process of agitation. Thus, it is desirable that agitation performing a high degree of mixing the solid matter is provided and that also a high degree of heat transfer within the agitated material is realized. 
     Apart from heating or cooling solid matter, such an agitator assembly may also be useful for carrying out chemical reactions, for volatilizing solvents, and for crystallization through evaporation or cooling. 
     It would be desirable and advantageous to provide an improved agitator assembly for agitation of solid matter in an agitation vessel such as to provide a high degree of mixing and a high degree of internal heat transfer. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, an agitator assembly is provided which includes a vessel; and an agitator received in the vessel and having at least one sweep blade, with the sweep blade ascending from an inner zone of the vessel to an outer zone thereof at an angle of inclination ranging from about 15° to 60° with respect to a horizontal. 
     Suitably, the inner and outer peripheral edges of the sweep blade is configured in an elliptical shape. The sweep blade may have a minimum width at its lower end and a maximum width at the upper end. 
     In a configuration of the agitator assembly with more than one sweep blades, at least one of the sweep blades may be provided with a bottom blade mounted at the lower end of the sweep blade and serving as a bottom clearer of the agitation vessel. The bottom blade may be attached with its upper end to the lower end of the sweep blade and is suitably so configured that its maximum width is at the upper end and its minimum width is at its lower end. Advantageously, the bottom blade may be formed in a helical shape and mounted relative to the horizontal at an angle in a range from 5° to about 55° and increasing from the lower end to the upper end. 
     According to another feature of the present invention, the sweep blade is provided at its upper end with a side blade, which is suitably of flat configuration and attached to the sweep blade at an angle of inclination from about 1° to about 30° relative to the vertical. The side blade may also be attached to the sweep blade at a clearance angle of about 1° to about 30° with respect to the inner wall of the agitation vessel. 
     The side blade may have a leading edge which is positioned at a substantially constant distance from the cylindrical inner wall of the agitation vessel, with the distance ranging approximately from 5 mm to 10 mm. Suitably, the leading edge of the side blade has an elliptical shape. 
     According to a further feature of the present invention, a baffle may be arranged above the sweep blade, with the baffle having a lower edge extending relative to the horizontal at an angle from about 15° to 60°. The baffle is suitably oriented relative at an angle from about 0° to about 75° to a radial line which extends through a center axis of the baffle and through a center axis of a driveshaft by which the agitator is driven. Suitably, the driveshaft is installed in overhead configuration so that no bearings or seals are required in the product zone. 
     According to a further feature of the present invention, at least one motor-driven crusher may be mounted above the sweep blade, with the crusher having one end carrying a plurality of knives. The circumferential speed of the crusher is suitably in the range of about 15 m/sec. 
     According to a further feature of the present invention, the agitation vessel is configured with an upper cylindrical portion and a lower conical bottom portion connected to the upper portion and having a cone angle in the range of about 60° to about 120°, preferably a cone angle of 90°. Suitably, the sweep blades are disposed in the conical bottom portion of the agitation vessel. The upper cylindrical portion and the lower bottom portion have heights at a ratio of about 1:1 to about 2:1. 
     With the agitator assembly according to the invention, a complete circulation of product material is realized, resulting in a high degree of product mixing. A high degree of product mixing provides a high rate of heat transfer and an even temperature level among the product, thus leading to an extensive product surface regeneration and accomplishing good discharge of the product without leaving recondensation on the cooler product. In turn, the high heat transfer surface leads to shorter drying and cooling sessions. In conjunction with the baffles and the crushers, the sweep blades of the agitator assembly according to the present invention, bring about a good coarse comminution and a rapid and easier break up of clumps and lumps. 
     An agitator assembly according to the present invention is thus capable to also disperse agglomerates or to produce granulates, and to agitate doughy or waxy masses. It is therefore not only suitable for flowable products but also for use with those materials that have a doughy consistency and with those that form clumps at drying, as oftentimes encountered in the pharmaceutical industry. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other objects, features and advantages of the present invention will be more readily apparent upon reading the following description of preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
     FIG. 1 is a simplified schematic view of one embodiment of an agitator assembly according to the present invention; 
     FIG. 2 is a top view of the agitator assembly shown in FIG. 1; 
     FIG. 3 is a simplified schematic view of another embodiment of an agitator assembly according to the present invention; 
     FIG. 4 is a top view of the agitator assembly shown in FIG. 3; 
     FIG. 5 is a schematic view of yet another embodiment of an agitator assembly according to the present invention; and 
     FIG. 6 is a cutaway view of a sweep blade provided with a side blade for use in an agitator assembly according to the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. 
     Turning now to the drawing, and in particular to FIG. 1, there is shown a simplified, schematic view of an agitator assembly according to the present invention, generally designated by reference numeral  10  and including an agitation vessel  12  whose outline is shown here only by way of a dash-dot line. The agitation vessel  12  has an upper open-topped cylindrical portion  14  and a conical lower portion  16  which is connected to the upper cylindrical portion  12  and has a cone angle in the range of about 60° to about 120°, preferably about 90°. 
     The open top of the upper portion  14  of the agitation vessel  12  can be closed by an arched lid  18 , and the lower portion  16  has with an outlet  20 . 
     A driveshaft  22  extends from above through the lid  18  into the interior of agitator vessel  12  for attachment of an agitator and rotation of the agitator in a rotation direction, as indicated in FIG. 2 by arrow D. The driveshaft  22  has a lower end which carries two struts  24  in opposite disposition for attachment to two sweep blades  26  which form part of the agitator and are thus located substantially in the lower portion  16  of the agitation vessel  12 . Persons skilled in the art will understand that the arrangement of two sweep blades is done by way of example only, Of course, the agitator may certainly have more or less than two such sweep blades and agitators of such configuration should also be considered within the scope of the present invention. 
     As shown in FIG. 1, the sweep blades  26  are arranged in slanting disposition within the agitation vessel  12  such as to extend from a lower inner zone to an outer upper zone relative to the horizontal at an angle α ranging from about 15° to about 60°. 
     In the following description, the term “horizontal” will denote any direction that is perpendicular to a center axis of the driveshaft  22 , while the term “vertical” will denote the same direction as the center axis of the driveshaft  22 . 
     At least one of the sweep blades  26  (here the sweep blade  26  on the left side of FIG. 1) is provided with a bottom blade  28  that is designed for use as a bottom clearer. The bottom blade  28  has an upper end  48 , which is securely mounted to a lower end  44  of the sweep blade  26  (cf. FIG.  3 ), and a lower end  50  which extends into the outlet  20 . The bottom blade  28  is twisted into a helical shape and is disposed downwards relative to the rotation plane and the horizontal at an angle δ which ascends from top to bottom and ranges from about 5° to about 50°. 
     Each sweep blade  26  is defined by an inner peripheral edge  40  and an outer peripheral edge  42 , whereby the geometry of the sweep blades  26  is generated by an oblique cut through a cone so that the inner peripheral edge  40  and the outer peripheral edge  42  of the sweep blade  30  have an elliptic configuration whereas the sweep blades  26  remain flat. The width of the sweep blades  26  increases from a minimum width at the lower end  44  to a maximum width at the upper end  46  of the sweep blades  26 . On the other hand, the width of the bottom blade  28  decreases from top to bottom such that a maximum width is at the upper end  48  and a minimum width is at the lower end  50 . 
     A side blade  30  is securely fixed to the upper, outer end  46  of each of the sweep blades  26 . The side blade  30  is flat and its geometry is generated by an oblique cut through a cylinder, whereby the leading edge or leading rim  52  of the side blade  30  has an elliptic configuration. The side blades  30  are mounted to the sweep blades  26  at an angle γ of about 1° to about 30° relative to the vertical. 
     As shown in FIG. 4, the side blades  30  are oriented relative to the side wall of the agitation vessel  12  with a clearance angle β ranging from about 1° to about 30°. The clearance angle β is determined as follows: A line  64  is drawn between the center point M of the driveshaft  22  and the intersection point P between the side blade  30  and the sweep blade  26 . A vertical  66  upon the line  64  at intersection point P represents the reference line for angle β which is defined between the vertical  66  and the intersection line  68  between the sweep blade  26  and side blade  30 , wherein the intersection point P designates the leading end of the intersection line  68  in rotation direction D of the agitator assembly. 
     As shown in particular in FIG. 6, the leading edge  52  of each of the side blades  30  is spaced from the cylindrical inner wall  56  of the agitator vessel  12  at a substantially constant distance of about 5 mm to 10 mm. 
     FIGS. 3 and 4 show a modification of an agitator assembly according to the present invention which is provided with auxiliary devices, for example a baffle  32  and/or a crusher  34  which are mounted from above into the agitation vessel  12 . Although FIGS. 3 and 4 show the installation of both, baffle  32  and crusher  34  in the agitation vessel  12 , persons skilled in the art will understand that this is done by way of example only, as the agitation assembly  10  may be configured also in such a manner as to include only one of these components. 
     The baffle  32  may be formed as a flat plate of substantially V-shaped configuration and is installed into the agitation vessel  12  from above, whereby a lower edge  60  of the baffle  32  defines relative to the horizontal an angle ε of about 15° to about 60°, and extends from an inner lower zone to an upper outer zone of the vessel  12 . As shown in FIG. 4, the baffle  32  is disposed in the rotation direction D at an angle ψ of about 0° to about 75° relative to a radial line  62 , whereby the radial line  62  runs through the center axis of the driveshaft  22  and through the center axis of the baffle  32 . 
     As shown in FIG. 3, the crusher  34  is inserted likewise from above through the lid  18  into the agitation vessel  12  and dips in the agitation product in a same way as the baffle  32 . The crusher  34  includes a motor-driven shaft  36  having a lower end which carries a plurality of knives or similar cutting tools for comminuting possible clumps in the agitation product. The drive (not shown here) for the crusher  34  is mounted onto the lid  18 , with the shaft  36  extending eccentrically between the shaft  22  and the sweep blades  26 . 
     The circumferential speed of the crusher  34  is preferably above 15 m/sec so that locally high shear forces can be introduced into the product, particularly heavy clumps and lumps within the agitation product can be comminuted. As described above, the cutting knives  34  may be replaced by other tools to apply more or less of shear forces in the product depending on the product properties. 
     The baffle  32  reduces the rotational motion in the agitation product and is capable to move larger clumps that may have been formed during drying of the product, in the direction of the sweep blades  26  for subsequent comminution. 
     As shown in FIGS. 1 and 3, the struts  24  mounted at the lower end of the shaft  22  are disposed in the lower half of the conical bottom portion  16  of the agitation vessel  12 , thereby leaving as much space as possible for mounting auxiliary devices such as the baffle  32  or the crusher  34 . If desired, an additional pair of struts  54  for attachment of further sweeping blades  26 , as shown in FIG. 5, may be mounted to the driveshaft  22  above the first pair of struts  24 . 
     The agitator assembly according to the present invention operates as follows: 
     When rotating the sweep blades  26  in rotation direction D, the product is first transported along the wall of the agitation vessel  12  along a slanted path and then axially upwards and ultimately by the side blades  30  in the region of the surface level of the product towards the center of the agitation vessel  12 . In the center region, the product is being drawn downwards as a consequence of the mass flow, thereby generating a spatially expansive mixing motion that leaves the agitated material essentially free of dead space, and thus ensures short mixing periods and high heat transfer. The circumferential speed of the driveshaft  22  is high enough so that easily disintegrateable clumps and lumps can be broken up by the shearing forces generated by sweep blades  26 . Clumps that are more difficult to break up can be disintegrated by one or more baffles  32 , while clumps that are difficult to break up can be crushed by employing the eccentric crusher  34  mounted from above. 
     By means of the bottom blade  28  which is configured as a bottom clearer, a product mixture that is free of dead space is realized in the lower region of the conical bottom portion  16  and above the outlet valve (not shown here). The afore-described downwardly increasing angle δ of the bottom blade  28  maintains throughout the product a good mixing action which, if that angle were constant, would deteriorate, as the circumferential speed at the bottom blade  28  would progressively decrease toward the outlet valve. The increasing angle δ compensates this effect and realizes a product mixture free of dead space throughout the entire agitation vessel  12 . 
     The afore-described close proximity of the side blades  30  to the inner wall of the agitation vessel  12  avoids, at least substantially, wall deposits and crust formation and ensures good heat transfer coefficients. 
     Because of the cantilevered mount of shaft  22  which projects into the agitation bearings or gaskets need not be mounted within the area of the agitation material. 
     While the invention has been illustrated and described as embodied in an agitation assembly, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.