Abstract:
A metering apparatus includes a roller charging device having an encircling groove which allows an accurate metering in minimum quantities, using the respective angle of slope of a pourable loose material.

Description:
This is a continuation of application Ser. No. 556,523, filed 11/30/83, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a metering apparatus, in particular for fine metering, for slope-forming loose materials, consisting of a housing provided with a charge and discharge opening, in which housing a rotor with a groove is positioned. 
     In various chemical processes, pourable materials often have to be added continuously. In such an operation, particular difficulties are presented by minimal quantities, as they have to be supplied, for example, in laboratory experiments. 
     A roller metering hopper is known, in which the material being conveyed is drawn off from the feed funnel in grooves which are arranged parallel to the axis, in order to then freely fall out below after being conveyed along the housing wall. 
     The disadvantage of this apparatus is that a continuous discharge is impossible, because at the moment when the groove leaves the surrounded housing, this groove immediately runs completely empty. An evening-out of the metering operation may indeed be achieved by increasing the throughput, which is then generally no longer suitable for laboratory experiments because of the quantity. Moreover, a forced cleaning of the grooves is difficult technically, so that the roller metering hopper is of hardly any use for products which adhere thereto. Furthermore, the parallel edges of the grooves and opening produce an undesirable abrasion, and one can usually count on a blockage of the metering apparatus as a result of the product becoming wedged in. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a product-sparing metering apparatus which allows a continuous addition of loose materials with a high metering accuracy, in particular in the case of minimal quantities. 
     This object is achieved according to the present invention in that at least one groove is positioned along the circumference of the rotor. 
     As a result of the groove in accordance with the present invention, the cross-sectinal dimensions of which amount to at least one times the maximum particle diameter, it is possible to continuously add a pourable loose material in a pre-determined quantity, and the rotating rotor ensures that no blockages occur, and thus no irregularities take place in the supply. Moreover, the conveyance may be influenced, depending on the position of additionally corresponding frictional forces due to corresponding direction pre-settings of the encircling groove to the vertical plane. The apparatus has a simple, compact construction which facilitates maintenance and a change of conveyed material. 
     In one specific embodiment, there is provided on the metering path a corresponding fictitious tangent between the edge directly opposite the groove in the region of inlet or outlet of the loose material in the housing, and a lowest point of the cross section of the groove at an angle to the horizontal which is smaller than the angle of repose of slope (natural) from respective loose material. 
     If the acute angle of the line, which lies in the plane through the circumference of the groove foot on the rotor and the inside edge of the housing opening, is smaller than the slope or flow angle of the loose material inside the groove to be metered, said groove may indeed be filled, but a shooting-through action of the loose material is no longer possible. In this case, the desired metering quantity still only depends on the groove volume and on the speed of the rotor. Consequently, the metering error, in particular during the addition of minimal quantities, is very small. At the same time, the loose material is treated sparingly. 
     In one particular embodiment, the product-charged construction parts have varying coefficients of friction. 
     On account of, for example rough entraining surfaces in the groove and smooth sliding surfaces in the housing, the loose material is passed to the discharge point without a substantial change to the structure, as a result of which, the metering accuracy is increased and abrasion on the housing is reduced. 
     In another embodiment, the groove cross section has a predetermined shape. 
     Due to the shape of the groove, the conveyed volume may be predetermined while simultaneously changing the entraining surface. For example, a triangular groove is suitable for small quantities, and a rectangular groove is suitable for larger quantities. In the case of an irregular grain diameter of the loose material, a groove which has a semicircular cross section is to be preferred. 
     In another embodiment, a metering device is positioned upstream of the groove. 
     With a metering device which may consist of, for example a loosener (stirring apparatus) or a condenser (roller wheel), it is possible to avoid a bridge formation, and to introduce the loose material into a groove with a regular density, so that the metering accuracy is increased even further. 
     In one embodiment, a stripping device is positioned at the discharge point. 
     By means of the stripper, it is possible to clean the groove thoroughly during each rotation, even in the case of loose material which sticks on, so that a high metering accuracy is achieved. 
     One example of the present invention is shown in the drawings and will now be described in the following. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross section through a roller, and 
     FIG. 2 shows a longitudinal section through the roller. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2 show a metering apparatus 1, in which a feed funnel 2 is positioned with its charging opening 3 over a rotor 5 which rotates about an axis 4. The rotor 5 has a groove 6 and is positioned in a housing 7. Furthermore, the section shows part of a cover 8 and a stripper 9 in a discharge opening 10. A stirrer as a metering device 11, and a partition 12 are also shown in the funnel 2. The rotor 5 and the metering device 11 are driven by motors which are not shown. 
     Loose material is charged into feed funnel 2. This material then trickles automatically through the charging opening 3 along an encircling groove of the rotor 5, with the formation of a constant slope, possibly with an evening-out of the supply by a metering device 11. The geometric dimensions are calculated such that the outflow of the material terminates upstream of the point in the groove 6 from where the material would overcome the frictional forces as a result of gravity due to a standing-back incline. During the continued transport, the loose material is then continuously entrained due to rotation of the rotor 5, and an accurately metered quantity is conveyed as a result of the speed and the filling of the groove 6 until this quantity finally falls downwards automatically through the discharge opening 10. Any residues which remain are removed from the groove 6 by a stripper 9. 
     The metering apparatus is appropriately constructed using those materials which have the necessary hardness and corrosion resistance with respect to the loose material to be conveyed. It may be judicious to produce the rotor or the product-charged parts thereof from a different material to that of the housing, or of the product-charged parts thereof. 
     EXAMPLES 
     Three metering apparatus having the following dimensions were produced according to FIGS. 1 and 2: 
     
         __________________________________________________________________________           RotorMeteringHousing    Outside    GrooveapparatusMaterial     Material           diameter                Shape Width  Depth__________________________________________________________________________No. 11.4571     PTFE/GF           40 mm                Triangle                      2 mm   1 mmNo. 21.4571     PTFE/GP           60 mm                Triangle                      6 mm   3 mmNo. 31.4571     1.4571           60 mm                Trapezium                      above 20 mm                             4.8 mm                      below 15 mm__________________________________________________________________________ 
    
     The following products were metered using these three metering apparatus: 
     
         __________________________________________________________________________           Apparent                Grain                     Roller                         Metered                              VolumeMetering   density                diameter                     speed                         quantity                              efficiencyExampleapparatus     Product           g/cm.sup.3                mm   1/min.                         g/h  C__________________________________________________________________________1    No. 1     sodium           1.4  &lt;0.20                     0.7   3  0.40     sulphate     anhydrous2    No. 2     Oxalic           0.69 &lt;1   32   1670                              0.78     acid3    No. 3     Sodium           1.09 &lt;0.25                     17  14580                              0.90     hexameta-     phosphate__________________________________________________________________________