Abstract:
A bottom element for a device for treating particulate has a two-dimensional body having numerous apertures. Means for imposing to a treatment medium passing said bottom are provided. Said bottom being designed as blade-shaped body, said apertures being designed as slots, said slots being generated by a removal of material from said plate-shaped body. Said slots having side walls sloping towards a plane of said body. For facilitating a cleaning of said bottom said side walls of said slots further consecutively tapers to a direction of a side of said bottom a particulate material rests.

Description:
CROSSREFERENCE OF PENDING APPLICATION 
     This application is a continuation of pending international application PCT/EP01/03379 filed Mar. 24, 2001 and which designates the U.S. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a bottom element for a device for treating particulate material, having a two-dimensional bottom, in which are provided numerous apertures, via which a treatment medium can be passed through the bottom, and having means that impose a motion component in the direction of the plane of the bottom on the treatment medium flowing through the bottom. 
     A device with a bottom element of this kind is known from EP 0 370 167 A1. 
     The device described in this document is used to dry, granulate or coat a particulate material. 
     In this case, a gaseous medium, referred to as process air, is, for example, introduced into a process chamber via the bottom, passing approximately horizontally and in the circumferential direction into the process chamber through the numerous apertures in the bottom. 
     In this device, the bottom comprises a ring of baffle plates, which extend radially and overlap one another circumferentially. Via the apertures formed in the overlapping region between the overlapping baffle plates, the treatment medium passes through the bottom and into the process chamber. The mutually overlapping baffle plates are set approximately horizontally or slightly obliquely and, as a result, impose a motion component in the direction of the plane of the bottom on the treatment medium flowing between the overlapping plates. Depending on the alignment of these baffle plates, the process air enters the process chamber more or less horizontally and in a circumferential direction. Owing to the initially horizontally directed component of the process air, the particulate material to be treated flows in the form of a rotating band of material on a kind of cushion of process air. Nozzles can be arranged in the bottom, between the baffle plates, in order to spray a liquid treatment medium on the particulate material to be treated. 
     The disadvantage with a bottom element of this kind constructed from overlapping baffle plates is that it is very expensive to manufacture. First of all, the approximately trapezoidal individual plates must be produced and assembled in the overlapping arrangement to give a ring. 
     The number of apertures for the passage of the treatment medium is thus determined by the number of plates. In the case of bottom elements with large diameters, there is the problem that the trapezoidal plates are very wide in the circumferential direction in the radially outer region. Since the treatment air or process air emerging from the apertures between the plates must accelerate the particles of material treated in the process chamber, a particle of material moving at a position disposed very radially outward is moved again in front of an aperture from which process air is emerging only after traveling a relatively long distance. A particle which is moving circumferentially more radially inwards, on the other hand, meets an aperture again after a much shorter distance of travel. Precautions therefore have to be taken to compensate for this. This was carried out in such a way, for example, that the height of the aperture between two overlapping baffle plates was made larger in the radially outward direction, e.g. by raising the overlapping baffle plate obliquely as seen in the radially outward direction. This then enabled more process air to emerge in radially outer regions in order to achieve acceleration motion components in the region of two successive apertures that were as similar as possible. 
     However, this had the effect that, in the case of bottom elements of large diameter, the radially outer plates are raised, thus presenting mechanical resistance surfaces to the material to be treated. Since such devices are used especially in the pharmaceutical sector, there was therefore the risk, when coating tablets for example, that there would be spalling on the tablets owing to collisions with these raised radially outer regions of the baffle plates. The distribution of the treatment medium, whether a gaseous or liquid medium or one containing solids, or a mixture of these, is thus not optimal. The relatively large apertures between the plates entail the risk that the material will fall through the bottom. 
     It is therefore the object of the present invention to provide a remedy here and to provide a bottom element of the type stated at the preamble which can be produced in a simple manner in terms of manufacturing technology and allows optimum guidance of the treatment medium. 
     SUMMARY OF THE INVENTION 
     According to the invention, the object is achieved by virtue of the fact that the bottom is designed as a plate-shaped body, said apertures are designed as slots, said slots have been generated by a removal of material from said plate-shaped body, and wherein said slots have side walls sloping towards the plane of the bottom, thereby imposing to the treatment medium said motion component when passing said slots. For facilitating a cleaning of said bottom, said side walls further consecutively taper to a side of the bottom the particulate material rests. 
     In terms of manufacturing technology, these measures have the advantage that it is now no longer necessary to produce individual baffle-plate elements, which then have to be assembled in an involved process to form a bottom, but that only a two-dimensional bottom has to be provided, from the material of which the numerous slots are then formed by removal of material. This makes it possible to select the number, shape, length, width, angle of inclination and pattern of the slots as a function of the treatment process and of the product to be treated. The motion component in the direction of the plane of the bottom is produced by virtue of the fact that the aperture cross sections of the slots slope in an appropriate manner. 
     This now allows significantly greater variation as regards the guidance of the process air. Thus, it is possible, for example, for a large number of relatively narrow slots to be provided, through which the process air can then be uniformly distributed and motion component aligned at the appropriate angle of inclination or in the direction of the plane of the bottom. The numerous relatively narrow slots prevent the material from falling through the bottom down to a size of material corresponding to the width of the slots. In the case of a circular or annular bottom, an appropriate number of slots can then be made in the radially outer regions in order thereby to compensate for the longer circumferential path in radially outer regions. 
     In terms of manufacturing technology, such removal of material can be carried out rapidly, easily and with high precision, e.g. by laser cutting, water-jet cutting, by combinations of these methods, by erosive methods or even by milling. 
     This simple structure also allows the possibility of providing different bottom elements for one apparatus, allowing optimum treatment of the particulate material depending on its size, whether it is, for example, fine powder or oblong tablets in the centimeter range. Rapid exchange of the bottom element is easily possible by virtue of the simplicity of the design. 
     The necessary cleaning too, which must meet high standards especially in pharmaceutical technology, is made considerably easier since there is not a large number of individual parts assembled to form an overlapping ring but a single plate-shaped body, in which corresponding slots have been made. 
     Due to the consecutively tapering of the side walls of the slots in a direction to that side of the bottom, the particulate material rests, no particles can enter into a slot and obstruct it. 
     If a particle having a size smaller than the width of the slot enters the slot at the side the particles are present, this particle will fall through the slot downwards but does not obstruct it, since in the downwards direction the side walls diverge. 
     In a further embodiment of the invention, the slots run in a straight line. 
     Slots of this kind are particularly simple to make in terms of manufacturing technology, and the straight-line geometry of the slots allows regular slot patterns, in particular slot patterns aligned in parallel. 
     In further embodiments, the slots are curved. 
     This measure has the advantage that longer slots can be made on a surface element through the curvature than with just a straight-line slot, making this measure particularly advantageous when as large as possible an exit area for certain predetermined parameters, e.g. slot width, is to be achieved per surface element. 
     In a further embodiment of the invention, the slots extend toward a central center of the bottom. 
     This alignment then allows guidance of the air in a circle on the bottom, possibly with the formation of a toroidally rotating band, a geometry which has proven particularly favorable for the treatment of particulate material. 
     In a further embodiment of the invention, in the case of a circular bottom, the slots extend radially. 
     This slot pattern is particularly favorable to the formation mentioned above of a circular, toroidally rotating band of material. 
     In a further embodiment, the further the slots are from the center, the more of them there are in the circumferential direction. 
     This measure has the advantage that the provision of an increasing number of slots compensates for the differences in distance traveled between particles of material circulating more radially inwards and particles of material circulating more radially outwards. In other words, a particle of material circulating radially outwards crosses a slot approximately after the same distance as a particle circulating radially inwards, and the particles can thus be accelerated uniformly. This leads to uniform treatment of the material, irrespective of whether a particle of material is being moved radially further toward the inside or radially further toward the outside. 
     In a further embodiment, there is a row of slots lying close together in the outer circumferential region. 
     This measure has the advantage that the critical transitional zone between the outer circumferential edge of the bottom and the housing accommodating the latter is virtually blown free by virtue of the large number of slots, excluding the possibility that material will gradually accumulate in this angular zone. 
     In a further embodiment of the invention, there are openings in the bottom to accommodate spray nozzles. 
     This measure then allows additional treatment of the material with a liquid sprayed medium, directly in the region of the bottom, when coating for example. 
     In a further embodiment of the invention, there are slots in the bottom that at least partially surround the openings in the region of these openings. 
     This measure has the advantage that optimum flow conditions around the nozzles can be created in a specifically intended manner by the provision of slots in the area surrounding these openings for the nozzles, thus preventing the accumulation of material in the reduced-pressure region surrounding the nozzles, the surrounding area thus being kept free by the provision of these additional slots. This is in fact possible because these additional slots can be made very easily in terms of manufacturing technology. 
     In a further embodiment of the invention, the bottom is flat. 
     This measure has the advantage that there is a particularly homogeneous surface without mechanical obstructions for the product. 
     In a further embodiment of the invention, the bottom is contoured. 
     This measure is advantageous if undulating movements are desired, or unwanted undulating movements can be compensated for by appropriately contoured bottoms. 
     In a further embodiment of the invention, the bottom is rotatable. 
     This measure has the advantage that the rotary motion provides an additional variation parameter for moving the material. Rotation of such a simple component as the bottom element is considerably easier to accomplish than assembly of different baffle plates. 
     In a further embodiment of the invention, a longitudinal center line of the aperture cross section is at an acute angle to the plane of the bottom, preferably in the region of 5° to 85°, most preferably in a range of 30° to 60°. 
     In these annular ranges, optimum treatment results can be achieved for a large range of material to be treated. 
     In a further embodiment of the invention, a plurality of slots, which are separated from one another by bridges of material, are arranged in series as seen in the direction of extension of the slots. 
     This measure has the advantage that, although a multiplicity of slots can be provided, the bottom still has adequate mechanical stability thanks to the bridges of material between the slots. 
     In a further embodiment of the invention, the bottom is annular and a cone is provided centrally on the side of the outflowing treatment medium. 
     This assembly allows the formation of the toroidally rotating band on an annular bottom in a particularly favorable manner. This compact construction element can also be used, for example, to convert existing systems operating on this principle. 
     It is self-evident that the features mentioned above and those that will be explained below can be used not only in the combination indicated but also in other combinations or alone without exceeding the scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described and explained in greater detail below in conjunction with the attached drawings with reference to a number of selected exemplary embodiments. In the drawings: 
     FIG. 1 shows a plan view of a bottom element according to the invention, 
     FIG. 1 a  shows an enlarged plan view in the region bounded by a circle in FIG. 1, 
     FIG. 1 b  shows an enlarged fragmentary plan view in the ring segment region defined in FIG. 1, 
     FIG. 2 shows a section along the line II—II in FIG. 1, 
     FIG. 3 shows a sectional representation, comparable to the sectional representation in FIG. 2, of another exemplary embodiment with a contoured bottom, 
     FIG. 4 shows an illustration, comparable to the sectional representation in FIG. 2, of another configuration of a bottom element with a waved bottom, 
     FIG. 5 shows a plan view of a disk segment of another exemplary embodiment of a bottom according to the invention with various slot geometries, 
     FIG. 6 shows a fragmentary sectional representation on a greatly enlarged scale corresponding to FIG. 2, an aperture cross section with parallel side walls being illustrated on the left-hand side, and an aperture cross section with tapering side walls being illustrated on the right-hand side, and 
     FIG. 7 shows, in a highly schematized form, a perspective view of a device for treating particulate material, in which a bottom element according to the invention is fitted. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A bottom element illustrated in FIGS. 1 and 2 is denoted overall by the reference numeral  10 . 
     The bottom element  10  comprises a two-dimensional bottom  12 , which has a body  13  in the form of a disk  14 . A large number of apertures shaped as slots  16 , whose configuration, geometry, arrangement and the like are described in greater detail below, are made in the body  13 , which is composed of metal, by means of a method involving the removal of material. 
     A circular central hole  18  is provided in the body  13 . 
     Three elliptical openings  20 ,  21 ,  22  are furthermore arranged uniformly in the circumferential direction halfway along the radius, allowing nozzles to be pushed through them, as will be described later. 
     FIG. 1 a  shows that the slots, which are represented here by slot  23 , end just before the corresponding openings, in this case opening  22 . The slot pattern in the disk  14  will be described in greater detail with reference to the ring segment, which is defined in FIG.  1  and illustrated on a larger scale in FIG. 1 b.    
     Three rectilinear slots  24 ,  25  and  26  extend along a radius from a central center of the disk  14  (not denoted specifically here). 
     Slots  24  and  25  are separated from one another by a web  38  of material, i.e. there is not one completely continuous slot in the radial direction but a plurality of slots in series. 
     This serves to maintain adequate mechanical stability of the disk  14 . 
     A circumferential row  28  of relatively short slots is made in the outer circumferential end region, these slots ending a short distance from the circular outer circumferential edge of the disk  14 . A row of two slots  32  and  33  arranged in series is provided in a position circumferentially adjacent to the row of three slots  24 ,  25  and  26 . These slots  32  and  33  likewise extend along a radius and are separated from one another by a bridge of material (not denoted specifically here). The arrangement and longitudinal extent is such that slot  32  extends across the bridge of material between adjacent slots  25  and  26 . 
     The radially outer end region of slot  33  fits into the circumferential row  28  of short slots. 
     Adjacent to the row of slots  32  and  33  there is then once again a row of three slots  34 ,  35  and  36  arranged in series along a radius. This slot pattern is then continued circumferentially. In the exemplary embodiment illustrated, the disk has a diameter of about 30 cm, while the width of the slots is 0.2 mm and the length of the slots is in a range of from about 32 mm to 10 mm in the case of the circumferential row  28  of short slots. The slots are each offset from one another by about 1° of the total circumferential angle of 360°, i.e. the outer circumferential row comprises 360 slots. Each of the slots ends about 2.5 mm from the outer circumferential edge and from the central aperture  18  and from the other openings  20 ,  21  and  22 . 
     The cross-sectional view in FIG. 2 shows that the slots, represented by slot  16 , are cut into the body  13  of the disk  14  in such a way that their aperture cross section  46  slopes relative to the plane  40  of the bottom. In the exemplary embodiment illustrated in FIG. 2, the aperture cross section  46 , denoted by its longitudinal center line  42 , is at an angle  44  of about 45° to the plane  40  of the bottom. 
     This situation is illustrated again on an enlarged scale on the left-hand side of FIG. 6, that is to say therefore that the aperture cross section  46 , which has the form of a parallelogram, has correspondingly sloping parallel side walls  47 ,  47 ′. 
     The aperture cross section tapers, in particular tapers conically, in one direction, as illustrated by the aperture cross section  48  in FIG.  6 . The aperture cross section  48  is such that there are conical side walls  49 ,  49 ′. In FIG. 6, the cone is illustrated as a broken line. The axis of the cone then once again extends along the longitudinal center line  42  and is likewise at an angle of 45° to the plane  40  of the bottom. A particle having a size greater than the distance between the walls  49 ,  49 ′ at the upper side cannot enter the cross section  48 . A particle having a size approximately the distance of the walls  49 ,  49 ′ at the upper side can enter but does not obstruct the cross section  48  since the cone widens to the lower side of the bottom  12 . A cleaning liquid pushes out the particle assisted by the downwardly diverging cone. 
     If the flow through the bottom element  10  is from the bottom up, as illustrated in FIG. 2, the sloping aperture cross sections impose a motion component in the direction of the plane  40  of the bottom on the medium. 
     In other words, the medium does not flow from the bottom upward at a right angle to the plane  40  of the bottom but slopes in accordance with the slope of the aperture cross section. 
     There is thus the possibility of setting correspondingly desired flow conditions of the treatment medium passing through the bottom element  10  by means of the angle of inclination of the aperture cross section  46 . Depending on the area of application, this treatment medium can be gaseous, liquid, pulverulent or a mixture of these. 
     The slots can be produced with a precise geometry and precise dimensions by laser cutting, but other methods, e.g. water-jet cutting or, in the case of an appropriately large slot width, milling, can also be employed. 
     The bottom element  10  described above comprised a flat disk. 
     FIGS. 3 and 4 illustrate the fact that the bottom can also be contoured to a certain extent. 
     Thus, the bottom  50  illustrated in FIG. 3, for example, comprises a number of sloping sections  52 , which slope relative to the plane  51  of the bottom and are connected to one another by vertical sections  54 . This bottom contour can be formed by embossing the bottom  50  with an embossing tool from an originally flat plate, for example. 
     Depending on requirements, the slots can then be provided in the sloping sections  52 , as illustrated by slot  56  for example, or can be provided in the vertical sections  54 , as represented by slot  58 . 
     Here too, the aperture cross section is such that the latter slopes relative to the plane  51  of the bottom, with the result that a motion component in the direction of the plane  51  of the bottom is imposed on a treatment medium passing through the slots  56  and  58  in this case too, as indicated by the flow arrows. 
     In the case of the bottom  60  illustrated in FIG. 4, the latter is of waved construction, i.e. wave tips and troughs project above and below the plane  61  of the bottom. Here too, there are once again corresponding slots, it being possible for them to be provided in a wave trough, as illustrated by slot  62 , in the transitional zone, as illustrated by slot  63 , or in a wave tip, as illustrated by slot  64 . 
     Here too, the aperture cross section is again such that this slopes relative to the plane  61  of the bottom, with the result that, here too, a motion component in the direction of the plane  61  of the bottom is again imposed on the treatment medium flowing through the slots  62 ,  63 ,  64 , as indicated by the flow arrows. 
     The slots illustrated in this exemplary embodiment can also be made by laser cutting or the like. It is also possible to punch out these slots already during the forming of the bottoms, if the material and size permits. 
     FIG. 5 shows a circular segment of a disk-shaped bottom  70 , which is likewise of flat design. 
     The slots extending toward the central center, not denoted specifically here, are designed as wavy slots  72 , the waviness of which increases from the center to the radially outer end. This increase in waviness makes it possible to compensate for the ever-increasing circumferential propagation path in the radially outward direction. 
     FIG. 5 furthermore illustrates a circumferential row of short slots  74 , which is situated a relatively long way out, which are curved approximately in the form of a circular arc. This curvature is advantageous if as large as possible an area of passage per element of area in combination with a relatively narrow slot is desired. This is the case, for example, if a very fine-grained product is being treated, in which case the slots should therefore be made as narrow as possible, in particular to avoid a situation where the product falls through the slots. The area of passage through a curved slot  74  is larger than the area of passage through a corresponding rectilinear slot connecting the two outer ends of the curvature in a straight line, for example. 
     An opening  76 , through which a nozzle can be pushed, is made in the circular segment illustrated in FIG.  5 . 
     In practice, it has been found that a certain vacuum is formed around the nozzles owing to the high exit velocity of the media sprayed, drawing in material, especially in the case of products in the form of fine dust, with the result that this proximate zone around the nozzle often becomes encrusted. To prevent this, a row of slots  78 ,  79  is provided around the opening  76 , partially surrounding it in the direction of spraying and “blowing free” this critical zone. This demonstrates in a particularly impressive way the great variability and flexibility of the design configuration of the invention, i.e. appropriate additional slots can be provided to prevent accumulation of material precisely in the critical zones. 
     This is also the reason for providing the circumferential row  28  of small slots illustrated in FIG.  1 . 
     The disk  14  is installed in a housing that extends approximately perpendicularly to the disk  14  and is connected to its circumferential edge. Product sometimes tends to adhere and become encrusted in this angle region, this now being eliminated by the circumferential row  28 , i.e. this angle is continuously blown free by the medium passing through the circumferential row  28 . 
     FIG. 7 illustrates, in a highly schematized form, a device  80  in which a bottom element  90  according to the invention, the slot pattern  99  of which corresponds approximately to the slot pattern of the bottom element  10 , is installed. 
     The device  80  has a lower inflow chamber  82 , into which a treatment medium  84 , e.g. warm process air, is introduced. 
     An upper end of the inflow chamber  82  forms the bottom element  90  with the slot pattern  99 . A cone  92  is inserted into the central hole, more specifically on the side of the bottom element  90  on which the treatment medium  84  emerges. 
     Two diametrically opposite nozzles  94  and  95  are provided, purely by way of example, being pushed into the openings described above. The angle of inclination of the aperture cross sections of the slot pattern  99  is such that an annular motion component in the clockwise direction is imposed on the treatment medium  84  flowing through the bottom element  90 . Above the bottom element  90  there is a treatment chamber  96 , in which the material to be treated is accommodated. From the upper end of the treatment chamber, the process air is then discharged as exhaust air  98  after the treatment of the material. The filters and the like that are customary in such apparatuses have not been shown, for the sake of clarity. 
     If the device is operated, for example, for the purpose of granulating a fine powder, this powder is introduced into the treatment chamber  96  and initially rests on the upper side of bottom element  90 . The narrowness of the slots prevents the product from falling through the slots into the inflow chamber  82 . If the bottom element  90  is supplied with treatment medium  84 , e.g. hot process air, this air passes through the bottom element  90 , being directed circumferentially with a horizontal component by the slot pattern  99  with the innumerable slots, and produces a floating and toroidally rotating band of material above the top side of the bottom element  90 , as indicated by the arrows  100 . A liquid medium with adhesive properties is then sprayed through the nozzles  94  and  95 , as a result of which the fine powder coagulates into granules.