Patent Publication Number: US-7896163-B2

Title: Sifter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Patent Application No. PCT/JP2007/000506, with an international filing date of May 10, 2007, designating the United States, now pending, which is based on Japanese Patent Application No. 2006-131904, filed May 10, 2006. The contents of these specifications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a sifter for sifting powder, e.g., a food article, a chemical, or a drug in a powder form. 
     2. Brief Description of Related Arts 
     In conventional chute sifters, powder commonly falls through a chute into a sieving chamber and is stirred by rotation of rotating blades attached to and arranged coaxially with a rotating shaft, which is located at the center of the sieving chamber and is rotated by means of a motor. Such conventional chute sifters are described, e.g., in Japanese Laid-Open Patent Nos. S63-69577, H03-131372, and H11-244784. A structurally similar pneumatic conveying in-line sifter with a rotating shaft and rotating blades is also known from Japanese Patent Publication No. 3492676. This sifter is effectively used for separation of a powdery substance from air in an air-powder mixture, classification of the separated powdery substance, and removal of foreign substances from the separated powdery substance. 
     However, in these conventional sifters, the rotating shaft located at the center of the sieving chamber has a fixed diameter that is smaller than the diameter of a sieve provided in the sieving chamber. The sieving chamber has a relatively wide space to enable a large flow of the powder or the air-powder mixture. Particularly as shown in  FIG. 19 , an excess load is applied to a partial area of a screen  170  in a sieve  107  corresponding to an angular range N from a 5 o&#39;clock angle to an 8 o&#39;clock angle. Namely, only the partial area of the screen  170  is effectively being used for sieving. The sieving chamber has too large of a space to sufficiently scoop up the powder by means of the rotating blades. The remaining area of the screen  170  other than the partial area corresponding to the angular range N is not effectively used for sieving. The powder is localized in the partial area of the angular range N. This undesirably accelerates deterioration of the screen and shortens the lifetime of the sieve, while limiting the sieving efficiency. 
     Conventional sifters also disadvantageously cause separation of powders in a powder mixture comprising various grain sizes, thus lowering the quality of the powder mixture. Conventional sifters also have problems of a large pressure loss and a relatively large amount of air used for sieving. 
     SUMMARY OF THE INVENTION 
     In order to eliminate the drawbacks explained above, the invention provides in one embodiment a sifter comprising: a receiver having a supply chamber for receiving material to be sifted from an upstream via an inlet; a sieve assembly having a sieving chamber coupled to and communicating with the supply chamber; a rotator having a rotating shaft laterally arranged to pass through the supply chamber and the sieving chamber; a drum having a circular cross-section and having a larger diameter than the diameter of the rotating shaft, the drum being extended in at least space of the sieving chamber and arranged coaxially with the sieve in an axial direction of the rotating shaft; a cylindrical sieve located inside the sieving chamber and arranged coaxially with the rotating shaft; a stirring rotor located in an inner area of the sieving chamber inside the sieve comprising a plurality of rotating blades attached to the rotating shaft to push the material to be sifted from the inner area to an outer area of the sieving chamber outside the sieve, the stirring rotor being attached to an outer circumferential face of the drum; an extraction member for enabling removal of oversize powder or foreign substances trapped by the sieve from the inner area; and an outlet for discharging powder passing through the sieve from the inner area to the outer area. 
     In the sifter according to this embodiment, the drum attached to the rotating shaft narrows the space of the sieving chamber to reduce the pressure loss and decrease the amount of gas (air) used for sieving. The narrowed space of the sieving chamber increases an effective area of a screen of the sieve and extends the life of the sieve. The powder is not localized in part (typically the center part) of the screen but is homogeneously dispersed to ensure stable sieving operation. This arrangement prevents the powder from being accumulated on the outer surface of the screen and reduces retention of the powder to shorten its floating time, thus enhancing the sieving yield and increasing the amount of sieved powder per unit time. In food industries, the sifter of this structure is effectively applied to reduce powder retention space inside the screen and thereby lower the potential for separation of powders in a powder mixture of various grain sizes. 
     In one class of this embodiment, the rotating blades protrude in a radial direction from the drum terminating close to an inner circumferential face of the sieve and extend in a direction parallel to or inclined with respect to the axial direction of the rotating shaft, and the rotating blades are arranged at even intervals around the circumference of the drum. This arrangement ensures homogeneous dispersion of the powder and enables uniform sieving. 
     In another class of this embodiment, the drum has a front end extending from the inner area of the sieving chamber inside the sieve to the supply chamber. The rotation of the drum ensures smooth introduction of the powder into the sieving chamber. 
     In another class of this embodiment, the drum has a conical front portion having a front end, and the front end is connected to the rotating shaft. This arrangement effectively reduces the loss of pressure. 
     In another class of this embodiment, the rotating shaft is cantilevered and comprises: a fixed end supported by a bearing in the receiver, and a free end where the drum is formed and which is arranged to pass through the drum. This arrangement desirably reduces the overall weight of the drum and simplifies the structure of the drum. 
     In another class of this embodiment, the rotating blade is supported by a support member protruding in the radial direction from the drum, and a clearance is formed between the drum and the rotating blade. This arrangement desirably reduces retention of the powder on the outer surface of the drum. 
     In another class of this embodiment, a partition plate is formed inside the drum in the radial direction to partition the inner area of the drum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described hereinbelow with reference to accompanying drawings, in which: 
         FIGS. 1(   a ) and  1 ( b ) are perspective views showing a rotating shaft, drum, and beaters of the sifter described in Example 1; 
         FIG. 2  is a longitudinal central cross-sectional view of the sifter described in Example 1; 
         FIG. 3  is a right side cross-sectional view of the sifter described in Example 1; 
         FIG. 4  is a front view showing a modified structure of the sifter described in Example 1; 
         FIG. 5  is a central cross-sectional view of the modified structure shown in  FIG. 5 ; 
         FIG. 6  is a longitudinal central cross-sectional view showing the sifter described in Example 2; 
         FIG. 7  is an elevational right side cross-sectional view of the sifter described in Example 2; 
         FIG. 8  is an elevational left side cross-sectional view of the sifter described in Example 2; 
         FIG. 9  is a partial cross-sectional front view of the sifter described in Example 2; 
         FIG. 10  is an elevational right side cross-sectional view showing a modified structure of the sifter described in Example 2 according; 
         FIG. 11  is an elevated left side cross-sectional view along a line in the vicinity of the receiver showing the sifter described in Example 3; 
         FIG. 12  is a partial cross-sectional front view showing the sifter described in Example 3; 
         FIGS. 13(   a ),  13 ( b ), and  13 ( c ) are side, front, and a plan views, respectively, showing a drum and an edge of a beater in the sifter described in Example 3; 
         FIG. 14  is a longitudinal central cross-sectional view showing the sifter described in Example 4; 
         FIG. 15  is a longitudinal central cross-sectional view showing the sifter described in Example 5; 
         FIG. 16  is a right side cross-sectional view showing the sifter described in Example 5; 
         FIG. 17  is a front view showing a rotating a shaft, a drum, and beaters in the showing the sifter described in Example 5; 
         FIG. 18  is a longitudinal central cross-sectional view showing the sifter described in Example 6; and 
         FIG. 19  is a perspective view showing a sifter according to prior art. 
     
    
    
     Legend:  1 —in-line sifter;  2 —receiver; L 1 —upstream line;  3 —inlet;  4 —sieve assembly;  5 —rotating shaft;  6 —drum;  7 —sieve;  8 —beater;  9 —inspection door; L 2 —downstream line;  10 —extraction member;  11 —motor;  12 —coupling mechanism;  20 —supply casing;  21 —supply chamber;  22 —bearing chamber;  23 —partition wall;  24 —shaft hall;  25 —first bearing;  26 —second bearing;  40 —sieve casing;  41 —sieving chamber;  42 —outlet;  43 —inner area;  44 —outer area;  45 —fixing element;  50 —shaft base;  51 —free end of the rotating shaft;  60 —conical body;  61 —cylindrical body;  62 —disk body;  63 —wheel;  64 —rib;  65 —rib;  66 —clearance;  70 —screen;  71 —screen fixing element;  201 —sifter;  208 —beater;  206 —drum;  208   a —beater;  208   b —beater;  209   a ,  209   b  and  209   c —inspection doors;  301 —sifter;  308 ,  308   a , and  308   b —beaters;  308   c —rib;  309   c —inspection door;  401 —sifter;  421 —supply chamber;  450 —shaft base;  408   a  and  408   b —paddles;  408 —beaters;  421 —supply chamber;  443 —inner area;  501 —sifter;  508   a  and  509   b —paddles;  508 —beater;  506 —drum;  568 —support member;  566 —clearance;  601 —sifter;  608   a  and  608   b —paddles;  608 —beater; and  606 —drum. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the invention are described below in Examples 1 to 6 with reference to the accompanied drawings. 
     EXAMPLE 1 
     With reference to  FIGS. 1-3 , a pneumatic in-line sifter  1  with a mount (not shown) having support legs (not shown) comprises a receiver  2  designed to receive an air-powder mixture (i.e., pneumatically-conveyed powder); an inlet  3  connected to the receiver  2  and configured to introduce the powder supplied from an upstream line L 1  via an upstream blower and an upstream rotary valve (not shown) to the receiver  2 ; a sieve assembly  4  coupled and communicating with the receiver  2  in a lateral direction; a rotating shaft  5  arranged in a horizontal direction to pass through the inside of the receiver  2  and the sieve assembly  4 ; a drum  6  attached to the rotating shaft  5 , formed across the area of the receiver  2  and the sieve assembly  4  to have a larger diameter than that of the rotating shaft  5 , and arranged in an axial direction of the rotating shaft  5  to be coaxial with a cylindrical sieve  7 ; and the cylindrical sieve  7  provided inside the sieve assembly  4 , arranged around the rotating shaft  5  and the drum  6  to be coaxial with the rotating shaft  5  and the drum  6 , and formed to have an inside communicating with the receiver  2 . 
     The in-line sifter  1  also comprises beaters  8  integrated with the rotating shaft  5  and attached to an outer circumferential face of the drum  6  to function as rotating blades of a stirring rotor provided in a rotatable manner inside the sieve  7 ; an inspection door  9  designed to enable access for inspection and cleaning of the inner area of the in-line sifter  1 ; an extraction member  10  designed to enable removal of oversize powder and/or foreign substances trapped by the sieve  7  from the inner area to the outside of the sieve  7 ; a motor  11  (not shown) driven to rotate the rotating shaft  5 , and a coupling mechanism  12  (not shown) constructed to link the rotating shaft  5  with the motor  11  by means of, for example, a pulley and a belt. 
     The structure of the in-line sifter  1  is described in detail hereinbelow. A filter unit and a relevant mechanism for removal of air from the sieve assembly  4  are neither specifically illustrated, nor explained herein. The details of the respective components of the in-line sifter  1  other than the rotating shaft  5 , the drum  6 , and the beaters  8 , are described, for example, in Japanese Patent Publication No. 3492676. The sieve  7  is described in Intl. Pat. Appl. Publ. No. WO2004/060584A1. 
     With reference to  FIG. 2 , the receiver  2  comprises a cylindrical supply casing  20 ; a cylindrical supply chamber  21  designed to communicate with the inlet  3  connected obliquely in a circumferential direction from an outer lower side face of the supply casing  20 ; a bearing chamber  22  designed to house bearings; and a partition wall  23  configured to separate the supply chamber  21  from the bearing chamber  22 . The receiver  2  also has a shaft hole  24  formed in the partition wall  23  to receive the rotating shaft  5  passing therethrough; a first bearing  25  attached to the shaft hole  24  to support the rotating shaft  5  in a rotatable manner; and a second bearing  26  formed on a front end (left in the drawing) of the receiver  2  to support the rotating shaft  5  in a rotatable manner at a position closer to the shaft end than to the first bearing  25 . 
     As further shown in  FIG. 2 , the sieve assembly  4  comprises a sieve casing  40  formed in a reverse U-shape from the side view to have a larger diameter than that of the receiver  2 ; a sieving chamber  41  provided inside the sieve casing  40  to communicate with the supply chamber  21 ; and a hopper-shaped outlet  42  located below the sieve casing  40 . The powder passes through the sieve  7  from the inner area to the outside and is discharged to a downstream line L 2  via the outlet  42  provided in a lower portion of the sieve assembly  4 . The cylindrical sieve  7  is located coaxially with the sieving chamber  41  to allow penetration of the rotating shaft  5  through the center thereof. An inner area  43  of the sieving chamber  41  inside the sieve  7  communicates with the supply chamber  21 . Namely the sieving chamber  41  has a substantially double-cylindrical structure and comprises the inner area  43  and an outer area  44  parted by the sieve  7 . The sieve casing  40  is equipped with a fixing element  45  for fixation of the sieve  7 . 
     As further shown in  FIG. 2 , the rotating shaft  5  is of a cantilevered structure and comprises a shaft base  50  and a free end  51  extended in the axial direction to be coaxially connected with the shaft base  50 . The free end  51  of the rotating shaft  5  is extended from a front end (left in the drawing) of the sieving chamber  41  to the proximity of the rear end (right in the drawing) of the sieve  7 . The shaft base  50  has one end supported by the bearings on the receiver  2  and the other end formed as the free end  51 . The preferable structural design extends the rotating shaft  5  to a rear end of the drum  6  as the rotating body to ensure center alignment. As long as the drum  6  has a sufficient strength, the rotating shaft  5  may alternatively be extended only to the area of the conical body  60 . 
     As further shown in  FIG. 2 , the drum  6  has a hollow shell to seal the inside. The drum  6  is connected coaxially with the rotating shaft  5  to allow penetration of the rotating shaft  5  through its inner axial center. The drum  6  comprises the conical body  60  extended forward from the sieve  7  and attached to the shaft base  50  to have a truncated head and a conical face linearly extended backward in the axial direction, a cylindrical body  61  connected with the conical body  60  and extended along the center axis of the drum  6 , and a disk body  62  fixed to the circumferential rear end of the cylindrical body  61 , arranged to fasten one end of the free end  51  passing therethrough in the axial direction, and bulged backward to have an arcuate shape. 
     The front end of the conical body  60  is extended from the inner area of the sieve  7  to the supply chamber  21  of the receiver  2  and is connected with the rotating shaft  5 . The tapered structure of the conical body  60  aims to lower the resistance to the inflow of the air-powder mixture, facilitate the cleaning of the innermost wall surface, and increase the structural strength. The cylindrical body  61  is formed coaxially with the free end  51  to surround the free end  51  and is extended to the middle of the sieve  7  (to the proximity of the end of the sieve  7 ). The arcuate shape of the disk body  62  increases the structural strength and facilitates cleaning. A disk-shaped wheel  63  is extended radially from a joint of the shaft base  50  with the free end  51  to be in contact with the inner circumferential face of the cylindrical body  61 . The wheel  63  has slits (not shown) formed in a radial direction in the outer circumferential face to hold the beaters  8  inserted therein. Ribs  64  and  65  protrude radially inward from the inner circumferential face of the cylindrical body  61  and are arranged along the circumferential direction. These ribs  64  and  65  are, however, not essential and may be omitted. The conical body  60  is not restricted to the conical shape but may be formed in any other suitable curved shape. 
     The distance D between the outer surface of the drum  6  and the inner surface of the sieve  7  is set to be neither excessively wide nor excessively narrow as described in detail below. To set the distance D adequately, the ratio of the (outer) diameter of the drum  6  to the (inner) diameter of the sieve  7  is particularly 40 to 85%, more particularly 45 to 85%, or most particularly 50 to 80%. The length of the drum  6  in the axial direction is set, for example, to be in a range of 50 to 100% of the axial length of the sieve  7 . 
     The sieve  7  comprises a screen  70  having an inner diameter substantially equal to the inner diameter of the supply casing  20 , and a screen fixing element  71  for fastening the screen  70  to the sieve assembly  40 . The length of the sieve  7  is practically similar to the length of the sieve casing  40 . In this example, the sieve  7  is fastened inside the sieve assembly  40  by means of the fixing element  45 , but may be also designed in a rotatable manner (see, e.g., WO 2005/102543 A1). The sieve  7  has a smaller mesh size (for example, 0.5 mm) than a conventional sieve. The sieve  7  is attached to the sieve casing  40  in a detachable manner by means of the fixing element  45 . 
     The beaters  8  are designed in a tornado type to form a swirling flow of the air-powder mixture. The beaters  8  are arranged along the outer circumferential face of the drum  6  and are located in the inner area  43  of the sieving chamber  41  inside the sieve  7 . The beaters  8  protrude radially from the drum  6  and extend in a direction parallel to the axial direction of the rotating shaft  5 . The radially-protruded ends of the beaters  8  are located close to the inner circumferential face of the sieve  7 . As shown in  FIG. 2 , the axial front ends of the beaters  8  are located at a position of approximately ½ of the length of the supply chamber  21 . The axial front ends of the beaters  8  particularly protrude to this ½ position or more forward. As shown in  FIG. 3 , the beaters  8  are of an even number and are arranged equally in a circumferential direction of the drum  6  to form an even number (for example, eight) of axially extending divisional spaces  47   a  to  47   h . The air-powder mixture flows in divided amounts into these spaces  47   a  to  47   h.    
     With the rotation of the drum  6 , the conical body  60  spirally introduces the air-powder mixture backward. The beaters  8  are formed radially and are extended in the axial direction from the middle of the conical body  60  to the disk body  62 . There are two different shapes of the beaters  8  one having a shorter front end and another having a longer front end. These two different shapes of the beaters  8  are arranged alternately around the drum  6 . The front ends of the beaters  8  are extended beyond the rear end of the conical body  60 , while the rear ends of the beaters  8  are extended to the periphery of the disk body  62 . The radially-protruded ends of the beaters  8  face the inner circumference of the sieve  7  across a certain gap to scrape out the air-powder mixture. The axial front ends of the beaters  8  are extended over the entire length of the supply chamber  21  to be rotated at a position very close to the inner circumferential face of the supply casing  20 . The axial faces of the front ends of the beaters  8  are rotated at a position very close to the inner face of the partition wall  23 . The beaters  8  are inserted into the outer circumferential face of the drum  6  and are fastened to the drum  6  by welding. The preset number (for example, eight) of the beaters  8  are arranged evenly at preset intervals (for example, every 45 degrees). 
     The position of the beaters  8  with respect to the drum  6  is determined by taking into account both the structural design and the manufacturing cost. Welding the beaters  8  after insertion into slits formed on the drum  6  is preferential for higher strength. However, perfect welding without insertion gives a practically sufficient strength. There are clearances  66  between the drum  6  and the beaters  8 . In the sifter of this example, the beaters  8  are welded to the drum  6  by tap welding. Formation of the clearances at non-welded portions facilitates cleaning. 
     The inspection door  9  is attached with multiple fixing knobs in a detachable manner and can be opened to enable visual inspection of the inside of the sieve assembly  4  and the receiver  2 . In the sifter of this example, only one inspection door  9  is formed along the upper curved face of the sieve casing  40  and extends in the axial direction to the middle of the sieve casing  40 . In a modified structure, two inspection doors  9   a  and  9   b  are provided at a preset interval in the circumferential direction as shown in  FIGS. 4 and 5 . In the modified structure, the inspection door  9  is not located on the top of the sieve assembly  40 . The advantage of the modified structure shown in  FIGS. 4 and 5  is in an easy access for internal cleaning. 
     The operation of the in-line sifter  1  is explained with reference to  FIGS. 1 to 3 . The in-line sifter  1  is a pneumatic conveying in-line sieve used with a pneumatic conveying supply system. An air-powder mixture supplied from the upstream line L 1  to the in-line sifter  1  by the pneumatic conveying supply system is subjected to sieving through the in-line sifter  1  in order to remove powder aggregates and foreign substances and to crush the powder aggregates, and is fed to the downstream line L 2 . The sieving operation of the powder inside the in-line sifter  1  is explained in detail below. 
     The inlet  3  is connected to the upstream line L 1 , and the outlet  42  is connected to the downstream line L 2 . The motor  11  (not shown) drives the rotating shaft  5 , the drum  6 , and the beaters  8 . The air-powder mixture is continuously supplied from the inlet  3  into the supply chamber  21  in the direction tangential to the cylindrical receiver  2  to form a swirling flow and to be forcibly flowed inside the sieving chamber  41 . The swirling flow of the air-powder mixture reaches the inner area  43  of the sieving chamber  41  inside the sieve  7  and is introduced by the rotating conical body  60  to dividedly enter cavities  47   a  through  47   h  defined by the outer circumference of the drum  6  and the beaters  8 . The swirling direction of the air-powder mixture is particularly identical with the rotating direction of the rotating shaft  5 . 
     With the rotation of the drum  6 , the beaters  8  are rotated at a high speed inside the sieve  7 . According to this rotation, the powder is introduced outward in the radial direction by the centrifugal force. The beaters  8  press the introduced powder against the inner face of the screen  70 . Thus, the powder aggregates and foreign substances are removed and the powder aggregates are crushed. 
     The drum  6  occupies the space around the axial center of the inner area  43  of the sieving chamber  41  and narrows the remaining space of the inner area  43  left for retention of the powder. This increases the effective area of the screen  70  and enables the whole area of the screen  70  to be fully used for sieving. This reduces also the pressure loss and decreases the amount of air used for sieving. The space formed between the outer circumference of the drum  6  and the inner circumference of the sieve  7  is divided by the beaters  8  to disperse the flow of the air-powder mixture and to reduce the load applied to the screen  70 . 
     As shown in  FIG. 3 , the beaters  8  divide the remaining space of the inner area  43  of the sieving chamber  41  around the drum  6  into multiple spaces  47   a  to  47   h  and are rotated with the drum  6  to sieve the powder. This disperses the load over the whole screen  70  and thereby practically equalizes the load applied to the screen  70 , so that the powder smoothly and substantially equally passes through the entire area of the screen  70 . This leads to a substantially-constant air flow, prevents retention of the powder in the screen bottom area N (see  FIG. 19 ), and increases the amount of powder sieved per unit time with a decrease in floating time of the powder. The sifter of this example ensures the stable sieving efficiency, while extending the life of the screen  70  to at least 4-fold according to the design specifications. 
     The front end of the drum  6  protrudes into the supply chamber  21 . The air-powder mixture flowing into the supply chamber  21  is thus introduced at a relatively early stage into the cavities  47   a  to  47   h  by the front end of the drum  6  and the front ends of the beaters  8 . This further reduces the load applied to the screen  70 . In the case of sieving a powder mixture including multiple different powders of various grain sizes, this structure lowers the potential for separation of the powders in the powder mixture and enhances the quality of the sieved powder mixture. 
     The air-powder mixture including powder of a grain size finer than the mesh of the screen  70  is fed to the outer area  44  of the sieving chamber  41  to reach the outlet  42  and to be discharged to the downstream line L 2 , while oversize powder of a grain size greater than the mesh of the screen  70  and the foreign substances remain in the inner area  43  of the sieving chamber  41 . 
     The oversize powder and the foreign substances gradually accumulate in the inner area  43  through the repeated sieving operations of the in-line sifter  1 . The accumulated oversize powder and foreign substances are discharged by opening the extraction member  10 . Removal of the remaining oversize powder and foreign substances from the sieving chamber  41  enables the inside of the sieve  7  to be restored to a clean condition. A used sieve  7  is taken out of the sieving chamber  41  from the extraction member  10  and replaced by a new sieve or may be cleaned and placed back to its original position. An operator visually checks the inner state of the in-line sifter  1  through the inspection door  9 , after stopping the operation of the in-line sifter  1 , and loosening the fixing knobs of the inspection door  9  to open the inspection door  9 . 
     The in-line sifter  1  of example 1 has the following features and advantages:
         (1) Attachment of the drum  6  to the rotating shaft  5  narrows the sieving space of the inner area  43  to reduce the pressure loss and to decrease the amount of air used for sieving. The narrowed space increases the effective area of the screen  70  and extends the life of the screen  70 . This structure prevents the powder from being accumulated on the bottom face of the screen  70  or on the outer surface of the screen  70  and ensures the stable sieving operation with homogeneous dispersion of the powder. The reduced retention of the powder shortens the floating time of the powder and increases the amount of sieved powder per unit time, thus enhancing the sieving yield. This structure also lowers the potential for separation of the powders in the powder mixture of various grain sizes.   (2) The beaters  8  are constructed by an even number of rotating blades which are arranged at equal intervals in the circumferential direction of the drum  6  to form multiple cavities of equal volume. This structure disperses the flow of the air-powder mixture equally and ensures uniform sieving.   (3) The conical body  60  of the drum  6  protrudes into the supply chamber  21  to enable smooth entry of the powder into the sieving chamber  41 .   (4) The conical body  60  has a conical face to ensure further reduction of the pressure loss.   (5) The drum  6  is attached to the free end  51  of the rotating shaft  5 . This arrangement desirably reduces the weight of the drum  6  and simplifies the overall structure.       

     EXAMPLE 2 
     As shown in  FIGS. 6 to 9 , a sifter  201  has a similar structure to that of the in-line sifter  1  in Example 1 except that beaters  208  have curved edges and that parts of the beaters  208  are inclined in an axial direction toward the drum  206 , as further explained below. Like constituents are expressed by corresponding numerals after adding  200  with respect to those in example 1. As shown in  FIG. 8 , each of the beaters  208  has one edge curved in a rotating direction of the drum  206  and inclined in the axial direction to the drum  206  to scrape out the air-powder mixture supplied from a powder inlet  203  along the circumferential direction of the drum  206 . The edges of all the beaters  208  are curved in the structure of this example, although only part of the beaters may have a curved edge. The beaters  208  include four beaters  208   a  arranged in parallel to the axial direction and four beaters  208   b  inclined to the axial direction. The beaters  208   a  have curved concave front edges and linear rear edges, whereas the beaters  208   b  have linear front edges and curved concave rear edges as shown in  FIGS. 7 and 8 . The beaters  208   a  with the curved front edges and the beaters  208   b  with the curved rear edges are alternately arranged along the outer circumference of the drum  206 . An inspection door  209   c  is provided at an outlet  242 . A modified structure shown in  FIG. 10  has two inspection doors  209   a  and  209   b  provided on the left and right sides of a sieve casing  240 , similar to the modified structure described in example 1 and shown in  FIGS. 4 and 5 . 
     EXAMPLE 3 
     With reference to  FIGS. 11 to 13 , a sifter  301  has a similar structure to that of the sifter  201  described in example 2, except that some beaters  308  have linear edges and some beaters  308  have reinforced curved edges as explained below. Like constituents are expressed by corresponding numerals after adding  300  with respect to those in example 1. The beaters  308  include four beaters  308   a  arranged in parallel to an axial direction and four beaters  308   b  inclined to the axial direction. The beaters  308   a  and the beaters  308   b  are alternately arranged along the outer circumference of a drum  306 . Among the four beaters  308   a , one pair of the beaters  308   a  opposed to each other have linear front edges, while the other pair of the beaters  308   a  opposed to each other have curved front edges. The curved front edges of the beaters  308   a  are reinforced by triangular ribs  308   c.    
     EXAMPLE 4 
     With reference to  FIG. 14 , a sifter  401  has a similar structure to that of the in-line sifter  1  described in example 1, except that paddles  408   a  and  408   b  are extended in the radial direction and are attached to the shaft base  450  in the supply chamber  421 . Beaters  408  do not protrude into the supply chamber  421  to avoid collision with paddles  408   a  and  408   b  but are limited to the inner area  443  of the sieving chamber  441 . Like constituents are expressed by corresponding numerals after adding  400  with respect to those in example 1. 
     EXAMPLE 5 
     With reference  FIGS. 15 to 17 , a sifter  501  has paddles  508   a  and  508   b , similar to the sifter  401  in example 4. Beaters  508  are fastened by support members  568  extended radially from the outer circumference of the drum  506 . The beaters  508  are set in the edges of the respective support members  568 . The beaters  508  are inclined to an axial direction of the drum  506  at a preset angle in the range of 3 to 7 degrees, and particularly, in this example at the angle of 5 degrees. There is a clearance  566  formed between the drum  506  and the beaters  508  to reduce retention of the powder on the outer surface of the drum  506 . Four beaters  508  are arranged at 90 degree intervals. In the sifter of this example, the beater  508  has a long rectangular shape as seen from the front view. 
     EXAMPLE 6 
     As shown in  FIG. 18 , in the chute sifter  601 , the powder falls from the inlet  603  open above a supply casing  620  into a supply chamber  621  by the gravity, is stirred with a pair of paddles  608   a  and  608   b , and is fed into the sieving chamber  641 . In other respects, the structure of the chute sifter  601  including the drum  606  is similar to that of the sifter  501  described in example 5. Like constituents are expressed by corresponding numerals after adding  600  with respect to those in example 1. The structures adopted in the in-line sifters described in examples 1 to 4 are also applicable to chute sifters. 
     The examples discussed above are to be considered in all aspects as illustrative and not restrictive. There may be many modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention. All changes within the meaning and range of equivalency of the claims are intended to be embraced therein. The characteristic of the invention is attainable by both in-line sifters and chute sifters with or without a screw feeder. In the sifters, a sieve  7  may be fixed or movable (see, e.g., WO 2005/102543 A1). The structure with paddles may also be adopted in both in-line sifters and chute sifters. 
     All publications and patent applications mentioned in this specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application mentioned in this specification was specifically and individually indicated to be incorporated by reference.