Abstract:
An impact grinding apparatus for grains capable of obtaining ground product having a desired granularity without sifting the product after grinding or changing a screen cylinder as a whole. The impact grinding apparatus comprises an inlet for introducing material to be ground, a rotary disk arranged rotatably under the inlet and having a plurality of vanes arranged at a periphery thereof and directed in an approximately radial direction of the rotary disk, a screen cylinder stationary arranged outside the vanes of the rotary disk, an annular discharging path arranged outside the screen cylinder for discharging ground product. Each of the screen faces of the screen cylinder comprises a plurality of superposed screen plates arranged slidable with each other. The screen cylinder is constituted by a plurality of screen units stacked in the vertical direction.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an impact grinding apparatus for grinding granular material particularly such as grains by impact.  
           [0003]    2. Description of Related Art  
           [0004]    There is known an impact grinding apparatus for grinding grains by impact from U.S. Pat. No. 5,474,238, for example. In this impact grinding apparatus, a centrifugal wheel is fixed to an output shaft of a motor, and a supply pipe for supplying material to be ground is arranged above the centrifugal wheel. The centrifugal wheel comprises an upper stage and a lower state divided by a partition ring, and centrifugal passages are formed for guiding the material supplied from the supply pipe onto the respective stages of the centrifugal wheel. An annular impact ring is arranged outside a circumference of the centrifugal wheel, and a product discharging path is formed around the impact ring. In this impact grinding apparatus, the grains supplied on the respective stages of the centrifugal wheel through the centrifugal passages is threw towards the impact ring by centrifugal force produced by the rotation of the centrifugal wheel, to impact against the impact ring to be ground and the ground product is discharged from the product discharging path.  
           [0005]    The ground particles produced from grains is used as material of foods and is often required to have predetermined granularity. Thus, it is necessary to sift the ground product obtained by the above impact grinding apparatus by a sifting device. There is known a sample grinding device incorporated into a measuring apparatus for measuring and analyzing components contained in grains such as rice from Japanese Patent No. 2521475. This sample grinding device comprises a grinding disk connected to an output shaft of a motor, a supply hopper for supplying samples and a plurality of vanes arranged on a periphery of the grinding disk. A porous ring having predetermined mesh size which functions as a screen cylinder is arranged outside the periphery of the grinding disk with a small clearance therebetween, and a particle gathering path is provided outside the porous ring. In this sample grinding device, the grains supplied from the supply hopper onto the grinding disk are threw towards the porous ring by centrifugal force produced by the rotation of the grinding disk and thrust from the vanes, to be ground by impact against the porous ring. As the impact is repeated, the grains are ground to have sizes to pass through the meshes of the porous ring and the ground particles are discharged through the particle gathering path.  
           [0006]    In this sample grinding device, it is necessary to change the porous ring as a whole for altering mesh size of the porous ring so as to obtain ground particles having desired granularity.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides an impact grinding apparatus for grinding grains capable of obtaining ground product having a desired granularity without need of sifting the product after grinding or changing a screen cylinder as a whole.  
           [0008]    An impact grinding apparatus of the present invention comprises: an inlet for introducing material to be ground; a rotary disk arranged rotatably under the inlet, and having a plurality of vanes arranged at a periphery thereof and directed in an approximately radial direction; a screen cylinder stationarily arranged outside the plurality of vanes of the rotary disk and having screen faces constituted by a plurality of screen plates detachably mounted thereon; and an annular path arranged outside the screen cylinder for discharging ground product passed through the screen cylinder. Since the screen plates constituting the screen faces are detachable, the screen plates can be easily changed to ones having different mesh sizes and it is not necessary to replace the screen cylinder for changing the mesh size or to sift the ground product after the grinding.  
           [0009]    Each of the screen faces of the screen cylinder may comprise a plurality of superposed screen plates arranged slidable relative to each other. With this arrangement, the mesh size of the screen faces can be easily adjusted to be a desired size, and also strength and durability of the screen faces are enhanced by the superposed screen plates.  
           [0010]    The screen cylinder may be constituted by a plurality of screen units stacked in the vertical direction, to thus enable a desired combination of screen units having different shapes and mesh sizes.  
           [0011]    The screen units may include a round screen unit and a polygonal screen unit. The polygonal screen units allows the supplied material to be fed to comer portions formed between the vanes and the screen plates to increase capability of processing amount of material.  
           [0012]    Each of the screen plates may have a plurality of slits extending in the vertical direction. With this arrangement, the slits extend in the direction perpendicular to a rotating direction of the rotary disk, to effectively grind the material and to prevent passing of ground particle having diameter larger than widths of the slits.  
           [0013]    At least one of the screen plates is embossed on a side facing the rotary disk such that the material thrown from the rotary disk is impacted on bosses on the screen plates to enhance the efficiency of grinding. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a plan view of an impact grinding apparatus according to an embodiment of the present invention;  
         [0015]    [0015]FIG. 2 is a cross sectional view along a line II-II in FIG. 1;  
         [0016]    [0016]FIG. 3 is an exploded view of a rotary disk with vanes, a polygonal screen unit and a round screen unit;  
         [0017]    [0017]FIG. 4 is a cross sectional view along a line IV-IV in FIG. 2; and  
         [0018]    [0018]FIG. 5 is a cross sectional view along a line V-V in FIG. 2.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]    Referring to FIGS. 1 and 2, an impact grinding apparatus  1  comprises a spindle  4  rotatably supported vertically in a cylindrical pedestal  5  by a pair of bearings  2  and  3 . A lower end of the spindle  4  is operatively connected to an output shaft of a driving motor (not shown). A round base  6  is formed at an upper end of the cylindrical pedestal  5  integrally therewith. A rotary plate  7  is arranged above the round base  6  with an appropriate clearance therebetween to be out of contact with the round base  6 . The rotary plate  7  is fixed to an upper end of the spindle  4  to rotate therewith. A plurality of vanes  8  are arranged with appropriate gaps therebetween to extend approximately radially on an upper side of the rotary plate  7  along a circumference thereof. Each of the vanes  8  has a upright rectangular shape in side view as shown in FIG. 2 and an approximately rhomboidal shape in cross-section as clearly shown in FIGS. 4 and 5. Upper and lower protrusions  8   a  are formed at upper and lower ends respectively of each vane  8 , and each vane  8  is fixed to the rotary plate  5  with the lower protrusion  8   a  fitted into a concave formed in the rotary plate  7 , and fixed to a ring plate  9  with the upper protrusion  8   a  fitted into a concave formed in the ring plate  9  so that the ring plate  9  covers the upper ends of the vanes  8 . Each of the vanes  8  is arranged with the outer end thereof slightly inclined in a direction opposite to a rotating direction Y of the rotary disk  7  with respect to a radial direction of the rotary disk  7 , as shown in FIGS. 4 and 5. The ring plate  9  and the rotary disk  7  are connected with each other by bolts  9   a  as shown in FIG. 2.  
         [0020]    A screen cylinder  10  is arranged around the vanes of the rotary disk  7  with an appropriate clearance therebetween. The screen cylinder  10  comprises a polygonal screen unit  11  at an upper half portion and a round screen unit  12  at a lower half portion. An exploded view of the rotary disk  7  with the vanes  8  and the ring plate  9 , and the screen cylinder having the polygonal screen unit  11  and the round screen unit  12  is shown in FIG. 3. In FIG. 3, the vanes  8  arranged on the rotary disk  7  are depicted with the number thereof reduced and the shape thereof abbreviated. The polygonal screen unit  11  has an octagonal shape in this embodiment. A first grinding chamber F 1  is formed between the polygonal screen unit  11  and the vanes  8  as shown in FIG. 4, and a grinding chamber F 2  is formed between the round screen unit  12  and the vanes  8  as shown in FIG. 5. The first grinding chamber F 1  communicates with the second grinding chamber F 2  vertically.  
         [0021]    In this embodiment, the polygonal screen unit  11  has eight screen faces to form the octagonal shape. Each screen face comprises two screen plates  11   a . Each of the screen plates  11   a  has a plurality of longitudinal through holes (slits)  11   b  extending in the vertical direction and an oval through hole  11   c  elongated in the circumferential direction at both side ends thereof. The two screen plates  11   a  are superposed each other and attached to brackets  11   e  which are fixed to upper and lower ring plates  11   d  by welding, etc. Bolts  11   f  are provided at attachment faces of the brackets  11   e  for insertion into the oval through holes  11   c  of the screen plates  11   a , and each pair of the two screen plates  11   a  are detachably mounted on the attachment faces of the adjacent brackets  11   e  by the bolts  11   f  and the nut  11   g  screwed on the bolts  11   f . As shown in FIG. 4, a mesh size M of the superposed screen plates  11   a  is adjustable by sliding the screen plates  11   a  in the direction of elongated through holes  11   c  before fasten the nuts  11   g  on the bolt  11   f  to fix the screen plates  11   a . The other pairs of screen plates  11   a  are mounted on the brackets  11   e  in the same manner to form the eight screen faces of the polygonal screen unit  11 . It is preferable to set the shortest distance between the vanes  8  and the screen plate  11   a  to approximately 2 mm.  
         [0022]    The round screen unit  12  has a plurality of segmented screen faces in the circumferential direction thereof. Each of the segmented screen faces is constituted by superposing a pair of curved screen plates  12   a . Each screen plate  12   a  has a plurality of longitudinal through holes (slits)  12   b  extending in the vertical direction and an oval through hole  12   c  elongated in the circumferential direction at both side ends thereof. The pair of screen plates  12   a  are superposed each other and attached to brackets  12   e  which are fixed to upper and lower ring plates  12   d  by welding, etc. Bolts  12   f  are provided at attachment faces of the brackets  12   e  for insertion into the oval through holes  12   c  of the screen plates  12   a , and each pair of the two screen plates  12   a  are detachably mounted on the attachment faces of the adjacent brackets  12   e  by the bolts  12   f  and the nut  12   g  screwed on the bolts  12   f . As shown in FIG. 5, a mesh size N of the superposed screen plates  12   a  is adjustable by sliding the screen plates  12   a  in the direction of elongated through holes  12   c  before fasten the nuts  12   g  on the bolt  12   f  to fix the screen plates  12   a . The other pairs of screen plates  12   a  are mounted on the brackets  12   e  in the same manner to form the segmented eight screen faces of the round screen unit  12 . It is preferable to set the shortest distance between the vanes  8  and the screen plate  12   a  to approximately 2 mm.  
         [0023]    A ground product discharging path  13  for discharging the ground product passed through the mesh M of the polygonal screen unit  11  and the mesh N of the round screen unit  12  is formed annularly outside the screen cylinder  10 . The ground product discharging path  13  is formed by a peripheral portion  6   b  of the rotary base  6 , an upright wall  14  arranged at the periphery of the rotary base  6 , a top plate  15  covering an upper opening of the apparatus, and the screen cylinder  10 . An outlet  14   a  is formed on the upright wall  14  to which one end of a ground product conducting tube  16  is connected for conducting the ground product from the ground product discharging path  13 . The other end of the ground material conducting pipe  16  is connected with a suction fan (not shown). The upright wall  14  is divided into two parts which are connected together by bolts/nuts  14   b  to be detachable from the apparatus. An upper end of the upright wall  14  is attached to the top plate  15  by bolts  14   c  and an lower end of the upright wall  14  is attached to the peripheral portion  6   b  of the rotary base  6  by bolts  14   d  to be detachable therefrom.  
         [0024]    The polygonal screen unit  11  is placed on the ring plate  12   d  of the round screen unit  12  and fixed to the top plate  15 . Bolts  15   a  are inserted into the through hole formed on the top plate  15  and rotated to engage with the threaded holes  15   a  formed on the ring plate  11   d  at positions corresponding to the through holes on the top plate  15 , so that the polygonal screen unit  11  is fixed to the top plate  15 . The round screen unit  12  is fixed to the round base  6  by bolts  6   a  inserted into the through holes formed on the round base  6  and rotated to engage with the threaded holes  18  formed on the lower ring plate  12   d  at corresponding position to the through holes.  
         [0025]    An inlet  15   b  for introducing the material such as grains is formed at a center of the top plate  15  and a material supply pipe  19  for supplying the material is connected to the inlet  15   b  and fixed by bolts/nuts. An air supply pipe  20  for supplying air into the supply pipe  19  is connected to the supply pipe  19  in the vicinity of the inlet  15   b.    
         [0026]    Operation of the impact grinding apparatus  1  will be described. The spindle  4  is rotated by a rotating force transmitted from the driving motor to rotate the rotary disk  7 . It is preferable to set a rotational speed of the rotary disk  7  to approximate 3000 rpm. The vanes  8  on the rotary disk  7  move inside the inner circumference of the screen cylinder  10  at high speed. After starting an operation of the suction fan, the material to be ground and the air are supplied into the impact grinding apparatus  1  from the inlet  15   b  through the material supply pipe  19  and the air supply pipe  20 , respectively. The material supplied from the inlet  15   b  drops on the rotary disk  7  and is forced to leap in the radial direction by the centrifugal force produced by the rotation of the rotary disk  7  and the air suction of the suction fan to pass through the gaps of the vanes as being thrust thereby, and impacts against the polygonal screen unit  11  and the round screen unit  12  randomly.  
         [0027]    The material impacted on the polygonal screen unit  11  is ground, and the material not ground is thrust by the vanes  8  to be impacted against the polygonal screen unit  11  repeatedly. The ground material having particle diameters smaller than the mesh M of the polygonal screen unit  11  passes through the mesh M and discharged through the ground product discharging path  13  and the ground product conveying pipe  16 . The material which does not pass through the mesh M of the polygonal screen unit  11  and remains in the first grinding chamber F 1  drops into the second grinding chamber F 2  and is ground in the second chamber F 2 . Since the first grinding chamber F 1  is formed between the vanes  8  and the polygonal screen unit  11 , the supplied material is fed to corner portions K to increase capability of processing amount of material, as shown in FIG. 4.  
         [0028]    The material impacted on the round screen unit  12  is ground, and the material not ground is thrust by the vanes  8  to be impacted against the round screen unit  12  repeatedly. The ground material having particle diameters smaller than the mesh N of the round screen unit  12  passes through the mesh N and discharged through the ground product discharging path  13  and the ground product conveying pipe  16 . The material which has not ground in the first grinding chamber F 1  is completely ground in the second chamber F 2  by the repeated impact against the round screen unit  12  as being thrust by the vanes  8 .  
         [0029]    Since each of the screen faces of the polygonal screen unit  11  and the round screen unit  12  is formed by superposing two screen plates, strength and durability of the screen faces are enhanced. Further, in a state of one of the upright walls  14  removed, the mesh sizes can be adjusted easily by displacing the screen plates relative to each other after loosening the nuts  11   g  or the nuts  12   g  and thus it is not necessary to replace the screen cylinder for changing the mesh size. Further, since the screen cylinder  10  comprises two units of the polygonal screen unit  11  and the round screen unit  12 , different mesh sizes may be set to the polygonal screen unit  11  and the round screen unit  12 . Furthermore, since each of the screen faces of the polygonal screen unit  11  and the round screen unit  12  is constituted by the plurality of divided screen plates, it is possible to set different mesh sizes to the respective screen plates. By setting the different mesh sizes, ground product having different particle diameters can be obtained. Thus, it is not necessary to process the material by a plurality of grinding apparatuses having different mesh sizes.  
         [0030]    Various modifications of the impact grinding apparatus will be described. In the foregoing embodiment, the screen cylinder  10  is constituted by two units of the upper screen unit and the lower screen unit. The screen cylinder  10  may be constituted by more than two screen units to increase amount of material to be processed. In this case, various combinations may be adopted in selecting shapes of the respective screen units, e.g. a combination of the polygonal screen units and the round screen units alternately arranged or a combination of the round screen unit as the lowermost one and the polygonal screen units as the rest, and further, the polygonal screen units only or the round screen units only. Further, the screen cylinder  10  may be constituted by a single polygonal screen unit or round screen unit which has different mesh sizes in the divided screen faces.  
         [0031]    In the case where height of the screen cylinder  10  is considerably large, it is preferable to provide distribution paths under the inlet  15   b  so that the supplied material is guided to the grinding chambers uniformly. The height of the vanes  8  is set to corresponding to the height of the screen cylinder  10 . The screen plate may be embossed such that the material is impacted on bosses to enhance the efficiency of grinding. The longitudinal through holes (slits) of the screen plate extend in the vertical direction in the foregoing embodiment. However, the longitudinal through holes may be inclined from the vertical direction in view of the processing efficiency and granularity of product.