Abstract:
A metering device for metering dry bulk material contained in a storage container has at least one metering element and a rotary drive connected to the at least one metering element. At least one outlet is provided, and the metering element feeds the dry bulk material to the outlet. The metering element transports the dry bulk material in a direction different from a horizontal direction and comprises at least one helical stay. The outlet has an outlet pipe that extends into the lower area of the storage container. The helical stay interacts with the outlet pipe for effecting transport of the dry bulk material.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention.  
           [0002]    The invention relates to a metering device for dry bulk material comprising at least one metering element driven by a rotary drive for feeding the bulk material from a storage container to at least one outlet.  
           [0003]    2. Description of the Related Art.  
           [0004]    Metering devices in the form of metering screws, metering transfer canals, or metering disks for dry bulk material are known. They have the disadvantage that they do not have absolutely linear metering properties. The metering transfer canal exhibits always pulsation as a result of the individual metering chambers. A metering disk also has a pulsing action because of its metering holes. The metering screw pulses according to a sine curve because of the drop of the dry bulk material at the exit of the screw. When positioning the metering screw at a slant, the sine-shaped pulsation during removal of the metered dry bulk material can be reduced but not prevented.  
           [0005]    In particular in discontinuously operating mixing devices, the irregular metering quantities have the disadvantage that, depending on the type of metering device, the concentration (proportion in percentage) of the individual components can exhibit short-term deviations as a result of pulsation. In connection with so-called batch mixing systems, the irregular metering action has the also the disadvantage that a defined weight or volume of dry bulk material cannot be metered with high precision. The imprecision of such systems results from the fact that, upon stopping the metering device, a chamber or a screw winding will not empty at all or will empty too much. The irregular metering quantities are particularly disadvantageous when small or even smallest quantities must be metered.  
         SUMMARY OF INVENTION  
         [0006]    It is an object of the present invention to configure the metering device of the aforementioned kind such that a uniform and precise metered flow is ensured.  
           [0007]    In accordance with the present invention, this is achieved in that the metering element transports the dry bulk material in a direction deviating from the horizontal direction and comprises at least one helical stay which during transport of the dry bulk material interacts with a pipe projecting into the lower area of the storage container.  
           [0008]    In the metering device according to the invention, the material to be metered is engaged by the helical stay and is uniformly fed to the outlet. Advantageously, the metering element extends vertically. The material is then transported by the helical stay in the upward direction. By means of the metering device according to the invention, even smallest amounts of material can be metered with high precision. Fluctuations in the metering action do not occur as a result of the embodiment according to the invention. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]    [0009]FIG. 1 is an axial section of a first embodiment of the metering device according to the invention.  
         [0010]    [0010]FIG. 2 shows a second embodiment of the metering device according to the invention in a representation corresponding to FIG. 1.  
         [0011]    [0011]FIG. 3 is an illustration corresponding to FIG. 1 of a third embodiment of the metering device according to the invention.  
         [0012]    [0012]FIG. 4 is an illustration corresponding to FIG. 1 of a fourth embodiment of the metering device according to the invention. 
     
    
     DETAILED DESCRIPTION  
       [0013]    The metering device serves for metering dry bulk material with high precision. The metering device according to FIG. 1 has a storage container  1  for bulk material  2  to be metered. The storage container  1  tapers at the lower end in a cone shape and has a bottom  3  through which an outlet pipe  4  projects into the storage container  1 . The outlet pipe  4  has a lower end that is provided with a radially outwardly extending flange  5  which rests against the underside of the bottom  3  of the storage container  1  and is fixedly connected to the bottom  3 .  
         [0014]    The outlet pipe  4  projects into the lower end of an inner pipe  6  which advantageously has a circular inner cross-section and is arranged centrally within the storage container  1 . The inner pipe  6  ends at a spacing from the bottom  3  of the storage container  1 . A drive  7  is provided In the inner pipe  6  and drives a metering element  8  in rotation.  
         [0015]    The metering element  8  is formed as a coil or helix which extends approximately from the bottom  3  of the storage container  1  upwardly into the inner pipe  6 . Here, the metering element  8  is connected fixedly to the drive shaft  9  of the drive  7 . The metering element  8  surrounds with a portion of its height the outlet pipe  4 .  
         [0016]    The metering element  8  has a helical stay  10  which is positioned at an acute angle relative to the axis of the outlet pipe  4  and the axis of the inner pipe  6 . The stay  10  approaches the outer peripheral surface of the outlet pipe  4  so closely that the bulk material transported by the metering element  8  cannot enter the space between the stay  10  and the peripheral surface of the outlet pipe  4 .  
         [0017]    The working diameter A of the metering element  8  and the inner diameter of the inner pipe  6  are adjusted to one another such that the bulk material particles cannot be jammed between the stay  10  of the metering element  8  and the inner wall of the inner pipe  6 . It is even possible, as illustrated in FIG. 1 in an exemplary fashion, to provide a sufficiently large spacing between the metering element  8  and the inner wall of the inner pipe  6 .  
         [0018]    The bulk material  2  is introduced into the storage container  1 . The dry bulk material  2  slides downwardly onto the bottom  3  along the conically tapering end  11  of the storage container  1 . Here, the dry bulk material  2  is engaged by the rotatably driven metering element  8 . The metering element  8  is rotated about its axis such that the dry bulk material on the stay  10  moves along the outer wall of the outlet pipe  4  upwardly until it reaches the upper end of the pipe  4 . Here, the dry bulk material drops into the outlet pipe  4  in which it falls downwardly to further processing stations. The dry bulk material flows in the area underneath the inner pipe  6  into the area of the rotating metering element  8  which is filled in accordance with-the repose angle of the bulk material  2  to be metered. By means of the metering element  8 , a uniform dry bulk material flow is transported upwardly. This dry bulk material flow drops downwardly in uniform flow about the circumference of the outlet outlet pipe  4 .  
         [0019]    By means of the helical metering element  8 , a uniform metering flow is transported upwardly with minimal force expenditure. A contributing factor is that the inner pipe  6  surrounds the metering element  8  at a distinct spacing so that the inner pipe  6  exerts no resistance on the transported bulk material  2  during its transport by the metering element. In this way, a uniform, linear, and precise metering flow can be generated. The described metering device is thus excellently suitable in so-called batch mixing systems because a defined weight or a defined volume of the bulk material can be metered with very high precision. Accordingly, the metering device is also excellently suitable for metering smallest quantities.  
         [0020]    During transport of the dry bulk material  2  by means of the metering element  8 , the dry bulk material particles are transported continuously in the upward direction in the area between the stay windings about the entire circumference of the outlet pipe  4 . Since the stay  10  extends at a slant downwardly in a direction toward the axis of the outlet pipe  4 , the dry bulk material during its transport along the outlet pipe  4  is entrained reliably by the helical stay  10  of the metering element  8 .  
         [0021]    In the embodiment according to FIG. 2, the metering element  8   a  has a horizontally arranged helical stay  10   a . In other respects, this metering device  8   a  according to FIG. 2 is embodied identical to the embodiment of FIG. 1. On the stay  10   a  extending perpendicularly to the axis of the outlet pipe  4 , the bulk material  2  is transported upwardly along the outer circumference of the outlet pipe  4  until it drops into the outlet pipe  4 .  
         [0022]    The metering device according to FIG. 3 has an inner pipe  6  which at its lower end passes into the outlet pipe  4 . The outlet pipe  4  projects seal-tightly through the wall of the cone-shaped end  11  of the storage container  1 . The bottom  3  of the storage container  1 , in contrast to the preceding embodiments, is closed. The outlet pipe  4  extends at an obtuse angle relative to the axis  12  of the inner pipe  6 . A pipe member  13  projects into the slantedly extending outlet pipe  4  whose axis  14  is aligned with the axis  12  of the inner pipe  6 . The pipe member  13  projects seal-tightly through the outlet pipe  4 , is spaced from the bottom  3 , and is fixedly connected to the bottom  3 . The metering element  8   b  extends through this pipe member  13  and has a helical stay  10   b  that, in contrast to the embodiment of FIG. 1, is positioned at an obtuse angle relative to the axis  12  of the inner pipe  6 . In this way, the stay  10   b  is positioned at a slant outwardly and downwardly. The stay  10   b  meets or extends up to the inner wall  15  of the pipe member  13 . In this way, the pipe member  13  assists the transport of the dry bulk material  2  on the stay  10   b  of the metering element  8   b.    
         [0023]    In accordance with the two preceding embodiments, the stay  8   b  extends to a location near the bottom  3  of the storage container  1 . In this way, it is ensured that the dry bulk material  2  within the storage container  1  is reliably engaged and transported upwardly by means of the helical stay  10   b . As soon as the upper end of the pipe member  13  is reached, the dry bulk material falls along the circumference of the pipe member  13  downwardly into the slantedly positioned outlet pipe  4 .  
         [0024]    In the embodiment according to FIG. 3, the stay can also be positioned, corresponding to the embodiment of FIG. 2, perpendicularly to the axis  12  of the inner pipe  6 . Since the stay is helical, in this case the dry bulk material  2  is also transported upwardly within the pipe member  13 .  
         [0025]    In the preceding embodiments, the helix of the metering element has a constant working diameter A across its length. In the embodiment according to FIG. 4, the working diameter A of the metering element  8   c  is smaller at the level of the lower end  16  of the pipe member  13  than in the other areas. In this way, the diameter of the stay  10   c  in this area is smaller than the inner diameter of the pipe member  13  so that there is no risk in regard to the dry bulk material particles becoming jammed between the pipe member  13  and the stay  10   c  when entering the pipe member  13 . At a short distance above the lower pipe member  16 , the stay  10   c  extends to the inner wall  15  of the pipe member  13  so that the dry bulk material can be reliably transported in the upward direction. In other respects, the metering device is identical to the embodiment of FIG. 3.  
         [0026]    In the embodiments of FIGS. 1 and 2, it is possible to connect the metering element fixedly to the outlet pipe. In this case, the outlet pipe rotates together with the metering element.  
         [0027]    In another embodiment (not illustrated), the metering element is fastened on the inner wall of the inner pipe  6 . In this case, the inner pipe  6  extends to the bottom  3  of the storage container  1 . The helical stay extends to the periphery of the outlet pipe. In this case, by means of the drive  7 , the inner pipe  6  is driven in rotation about its axis  12  so that the metering element can also be rotated accordingly. The dry bulk material, as explained with the aid of FIGS. 1 through 4, is transported by means of the helical stay upwardly to such an extent until the dry bulk material can fall into the outlet pipe.  
         [0028]    While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.